bluuebunny/crossref_metadata_2025 huggingface dataset:
Erythroid cell differentiation in unincubated chick blastoderm in culture
Authors: Zagris Nikolas
Published: April 2021

Morphologically distinct erythroid cell types characteristic of the primitive and the definitive erythroid cell lines, and embryonic and adult haemoglobins are produced when the unincubated chick blastoderm is cultured ventral side down on a filter raft to inhibit morphogenetic movements and subsequent primitive-streak formation mechanically in serum-free minimal essential medium. The primitive and definitive erythroid cell populations appear consecutively in culture even though there is no axis formation nor apparent morphogenesis. The information to produce both the early and late haemoglobins and erythroid cell types is independent of axis formation and of specific extra-embryonic influences, such as progressive induction exerted by the yolk mass.
Actin synthesis during the early development of Xenopus laevis
Authors: Sturgess E. A. , Ballantine J. E. M. , Woodland H. R. , Mohun P. R. , Lane C. D. , Dimitriadis G. J.
Published: April 2021

Cytoskeletal β and γ-actin are amongst the most rapidly made proteins of oocytes, blastulae and later embryonic stages of Xenopus laevis but, relative to other proteins, the rate of synthesis is low in the egg or cleaving embryo, although the messenger RNA is present in comparable amounts at the different stages. Actin synthesis therefore involves post-transcriptional regulation, α-actin, the actin class characteristic of striated muscle cells, is first detectable in late gastrulae and it is an abundant newly synthesized protein from the neurula stage onwards. mRNA template activity for this protein is not detectable before the gastrula stage. Thus a-actin synthesis probably reflects new gene action, confined to part of the embryo, for α-actin only appears in the section which includes presumptive skeletal muscle cells. It therefore constitutes the earliest cyto-specific protein so far demonstrated in Amphibia. When tadpole tail poly(A)-containing mRNA is injected into oocytes and eggs α-actin synthesis is seen in both cases. Extensive evidence for the identification of the actins is presented. This is based on location of synthesis, DNase-I binding and partial peptide mapping.
Cellular morphology in haploid amphibian embryos
Authors: Ellinger Mark S. , Murphy Judith A.
Published: April 2021

External surfaces of haploid and diploid embryos of Bombina orientalis were examined with the scanning electron microscope to determine the possible contribution of cellular morphology to the amphibian haploid syndrome. Cellular anomalies were prevalent in all surface areas of haploid embryos. The epithelium appeared uneven due to the displacement of ciliated cells and the rounded apical surfaces of the non-ciliated cells. The ratio of ciliated to non-ciliated cells was altered in comparison to diploid embryos. Cells of the gill filaments and adhesive organs were abnormal in morphology, and the adhesive organs themselves were fused into a single large rudiment in haploid embryos. Uniformity of cell size was markedly reduced in head regions of haploid embryos with severe microcephaly. Haploid and diploid embryos elaborated mucoid matrices over the surface cells when removed from the fertilization envelope.

It is apparent that aberrant cellular morphologies are widespread in haploid embryos, and it is likely that these defects are major contributors to the gross morphological anomalies of the haploid syndrome.
Positional information around the segments of the cockroach leg
Authors: French Vernon
Published: April 2021

Epidermal cells from different circumferential positions around the femur of Blabera craniifer can interact to form an intercalary regenerate consisting of that section of the circumference normally separating graft and host positions, by the shorter route. This result is extended to other leg segments; the tibia and coxa (TT and CC Grafts). Grafting strips of integument from the tibia (TF Grafts) or the coxa (CF Grafts) to a corresponding position on the host femur results in simple healing. Grafting to a non-corresponding position leads to intercalation of the shorter intermediate arc of circumference, composed partly of graftsegment and partly of host-segment structures. These results show that the same continuous sequence of positional values is distributed around the circumferences of the coxa, femur and tibia. Cellular interactions along the edges of strip-grafts obey the Shortest Intercalation Rule.

At the ends of strip-grafts intercalation usually restores continuity of positional values where possible but, when a complete circumference is generated, a supernumerary distal regenerate is usually formed. This is in general agreement with the Complete Circle Rule and the exceptions are discussed.

In intercalary regeneration following the intersegmental strip-grafts, the host femur cells seem unable to intercalate beyond two positions (posterior/internal and posterior/external). These lineage restrictions operating during regeneration indicate that the cockroach leg, like the Drosophila leg disc, may consist of an anterior and a (smaller) posterior ‘compartment’.
Cell membrane regions in preimplantation mouse embryos
Authors: Izquierdo L. , López T. , Marticorena P.
Published: April 2021

Cell membrane regions characterized by alkaline phosphatase activity are described in cleaving mouse embryos and early blastocysts. Enzyme activity is demonstrated by light and electron microscopy, from the late 4-cell stage onwards, on the cell surfaces between blastomeres but not on the outer surface of the embryo. Experiments with dissociated morulae show that this is probably not an artifact due to the retention of the enzyme reaction product between the blastomeres. With the electron microscope the activity is also demonstrated in crystalloid bodies within the cytoplasm. The localization and growth during cleavage of cell membrane regions with enzyme activity is interpreted as the result of new cell membrane formation and/or as a relation of the crystalloid bodies with the cell membrane through the cortical system of microtubules and filaments.
The Forces Producing Neural Closure in Amphibia
Authors: Selman G. G.
Published: April 2021

It has been shown by Smith (1946), working with trout eggs, that when an embryo develops the heat lost to the surroundings is balanced by the loss in the calorific value of its energy-rich storage substances. Other workers (e.g. Shearer, 1922) have shown that the heat lost by eggs and developing embryos is approximately equal to the available energy deduced from the observed respiration. It would seem, therefore, that only a very small fraction of the energy known to be available to the embryo from its aerobic metabolism can be stored as potential energy in the visible pattern of tissue structures which the embryo progressively develops. It has sometimes been concluded from this that little energy can be required for morphogenesis. This conclusion is doubtless true, but the argument is unsound, because no knowledge of the energy balance between the total energy being released by the embryo and the energy being lost to the surroundings can tell us anything about the work which may be required to overcome a potential energy barrier. For instance, consider this example which is used here as a simple illustration of the argument rather than as a model of what actually happens. It is conceivable that when a newt embryo gastrulates, considerable work must be done in so deforming the cells against their own elasticity that the blastula tissue may pass through the narrow blastopore opening. To perform such work energy is required from the chemical energy source; it will be stored as potential energy by deformed cells as they pass through the blastopore; yet when the constriction is passed, the cells relax to their equilibrium shapes once more and the energy is dissipated as heat. In such a case a knowledge of the energy-balance could tell us nothing about the work done in gastrulation. On the other hand, if we knew about the forces required to deform the cells we should be able to estimate the work required for gastrulation, using this particu-lar model for the process.
A definite number of aphidicolin-sensitive cell-cyclic events are required for acetylcholinesterase development in the presumptive muscle cells of the ascidian embryos
Authors: Satoh Noriyuki , Ikegami Susumu
Published: April 2021

In order to determine whether or not a crucial number of DNA replications are prerequisite for cellular differentiation, we have studied development of a tissue-specific enzyme, muscle acetylcholinesterase (AChE) in the presumptive muscle cells of cleavage-arrested ascidian embryos. Embryos were cleavage-arrested with cytochalasin B (an inhibitor of cytokinesis) and aphidicolin (an inhibitor of DNA synthesis). The 64-ceIl-stage embryos which had been permanently cleavage-arrested with cytochalasin B developed AChE in all the eight presumptive muscle cells, but the same stage embryos which had been prevented from undergoing further divisions by simultaneous treatment with aphidicolin and cytochalasin did not produce AChE at all. Cytochalasin-arrested 76-cell-stage embryos were able to differentiate AChE in the ten presumptive muscle cells, while aphidicolin-cytochalasin-arrested 76-cell stages in as many as four cells. The early gastrulae which had been arrested with cytochalasin B produced AChE in all the sixteen presumptive muscle cells, while the same stage embryos arrested with aphidicolin and cytochalasin in as many as twelve cells. Cytochalasin-arrested late gastrulae developed AChE in twenty blastomeres, while aphidicolin-cytochalasin-arrested late gastrulae in eighteen cells.

The presumptive muscle cells at these four stages consist of those of three different (seventh, eighth, and ninth) generations, and the relative positions of the blastomeres in the cleavage-arrested embryos remained fixed. Judging from the relative positions of the blastomeres, the AChE-producing cells in aphidicolin-cytochalasin-arrested embryos were always at eighth or ninth generation, while those with no AChE activity were certainly at seventh generation. Based on these findings it was supposed that aphidicolin-sensitive cell-cyclic events, presumably DNA replication, are closely associated with AChE development and that the eighth cleavage cycle may be ‘quantal’ for the histospecific enzyme development.
Morphologic aspects of adhesion and spreading behavior of amphibian blastula and gastrula cells
Authors: LeBlanc Jacqueline , Brick Irving
Published: April 2021

By means of SEM we have examined spreading and adhesive behavior of cells isolated from superficial and deep regions of germ layers from blastula to late gastrula in Rana pipiens embryos. Each of the cell populations sampled show adhesive and spreading characteristics distinctive for each region and stage which we interpret as demonstrating the following:

From blastula through late gastrula, cells from each region have already acquired the ability to express surface morphologic and adhesive features independently of their association with their neighbors, i.e. autonomously. The distinctive spreading and adhesive characteristics for each tissue sub-population suggest kinetic properties seemingly related to their in vivo morphogenetic movements, epiboly or invagination. The appearance within germ layers of two subpopulations between blastula to mid-gastrula, suggests early intratissue inductive interactions. The outermost, superficial cells from each germ layer show proximal and distal surface differences which may reflect adhesive differentials as postulated by Steinberg (1970) for presumptive ectoderm cells. With the exception of superficial cell proximal and distal differentiation, freshly disaggregated cells do not show morphologic characteristics seen in corresponding cells spreading for one hour.
Abnormal overgrowth of chick embryos treated withp-nitrophenylβ-D-xyloside at early stages of development
Authors: Oohira Atsuhiko , Nogami Hiroshi , Nakanishi Yasuo
Published: April 2021

The effect of p-nitrophenyl β-D-xyloside, an inhibitor of proteoglycan biosynthesis, on the growth of chick embryos was studied by injection of the single dose of 1.0mg/egg into fertile eggs on day 3. Embryos examined on day 10 had systemic edema, and were increased not only in wet weight (142% of the non-treated embryos) but also in dry weight (125%). No skeletal malformations were observed in the treated embryos. The glycosaminoglycan content in the treated embryos began to increase 6 h after treatment and reached the maximum level (174% of the non-treated) after 3 days, while the DNA and protein content began to increase 12 h after treatment and reached the maximum level (about 140%) within 3 days. p-Nitrophenyl α-D-xyloside, p-nitrophenyl β-D-galactoside, and a mixture of p-nitrophenol and D-xylose produced neither the abnormal overgrowth nor the edematous change of chick embryos.

When fertile eggs were treated with 1·0 mg/egg of p-nitrophenyl β-D-xyloside on day 6, the increase in wet and dry weights was also observed in all surviving embryos. On the contrary, treatment on day 9 resulted in the slight reduction of embryonic growth in addition to the systemic edema. Both embryos treated on day 3 and on day 6 contained glycosaminoglycans rich in chondroitin 6-sulfate, whereas the embryos treated on day 9 contained glycosaminoglycans rich in undersulfated chondroitin sulfates. These findings seem to support the view that glycosaminoglycans play an important role in the regulation of embryonic growth.
Presence of multipotential hemopoietic cells in teratocarcinoma cultures
Authors: Cudennec Claude A. , Johnson Gregory R.
Published: April 2021

Previous investigations have shown that the teratocarcinoma line PCC3/A/1 is able to differentiate in vitro to produce red blood cells of the primitive hemopoietic cell population of the mouse embryo. The present paper demonstrates the presence in the same cultures of multipotential cells capable of giving rise to colonies containing erythrocytes, macrophages, and megakaryocytes when stimulated by pokeweed-mitogen spleen-cell conditioned medium.
Erythropoiesis and haemoglobin ontogeny in the turtle Emys orbicularis L
Authors: Vasse J. , Beaupain D.
Published: April 2021

The erythropoietic sites and developmental patterns of haemoglobins have been investigated during ontogeny of Emys orbicularis. The yolk-sac blood islands seem to be the unique erythropoietic site during most of embryonic life. Bone marrow haemopoiesis is first observed in young turtles aged one year. The cortical haemopoietic layer of the liver appears involved mainly in granulopoiesis. There is no morphologically well-defined series of primitive or definitive erythrocytes. Rather there is a gradual shift in size from a mean length of 17·4μm in embryos to 19·9μm in the adult. However the size of erythrocytes is highly variable at all stages. Three haemoglobins of adult type and three haemoglobins of embryonic type have been identified by electrophoretic separation. It seems that one haemoglobin is synthesized during the whole life. Embryonic haemoglobins persist for more than a year after hatching while the typically adult haemoglobins appear shortly before hatching.
Enzymo- and immunocytochemical analyses of the differentiation of liver cells in the prenatal mouse
Authors: Shiojiri Nobuyoshi
Published: April 2021

Differentiation of the endodermal cells of the mouse liver was studied enzymo- and immunocytochemically by analyzing the cellular localization of alphafoeto protein (AFP), glycogen, and alkaline phosphatase (ALP) and 5’-nucleotidase (5′-Nase) activities.

In 8-5-day foetuses, AFP appears in some endodermal cells of the anterior intestinal portal region. The cells of the cranial diverticulum contain much AFP at 9-5 days, while those of the caudal diverticulum contain less AFP. In 9·5- to 15·5-day foetuses, hepatocytes are intensely fluorescent for AFP. After 16·5 days less-positive hepatocytes increase in number. AFP is still present in a few hepatocytes of 14-day-old postnatal mice. ALP and 5′-Nase activities appear in a small proportion of hepatocytes at 13·5 and 14·5 days of embryonal life, respectively. At 15-5 days, many hepatocytes possess these enzyme activities, and initiate accumulation of glycogen. AFP-containing hepatocytes type I (gestation day 9·5–16·5) successively acquire ALP and 5′-Nase activities and accumulate glycogen, and then differentiate into hepatocytes type II after gestation day 17·5. Endodermal cells constituting lumen structures in the liver trabeculae are the precursor of the intrahepatic bile duct cells. They possess much AFP, but no glycogen and no ALP activity, and are similar to hepatocytes type I. Since immature hepatic duct cells also possess much AFP, but no glycogen, and no ALP and 5′-Nase activities, they are similar to endodermal cells of the lumen structures. Therefore, that the endodermal cells of the lumen structures are the intermediate cells between hepatocytes type I and hepatic duct cells may be conceivable.
Cell interactions and endoderm differentiation in cultured mouse embryos
Authors: Hogan Brigid L. M. , Tilly Rita
Published: April 2021

Morphological and biochemical evidence is presented that the visceral extraembryonic endoderm of the 6·5-day mouse embryo will differentiate into parietal endoderm when cultured in contact with extraembryonic ectoderm undergoing transition into trophoblast giant cells. Egg cylinders from 6·5-day embryos were dissected into embryonic and extraembryonic halves and cultured in suspension in vitro for up to 7 days. After 4 days, the endoderm cells of the extraembryonic fragments morphologically resemble parietal endoderm, are associated with a thick basement membrane and synthesize large amounts of the matrix proteins laminin and Type IV procollagen. A similar transition in phenotype is not seen in the endoderm of embryonic fragments, nor in visceral extraembryonic endoderm cells cultured in isolation. In another series of experiments, complete egg cylinders were dissected free of visceral endoderm ovei lying the extraembryonic ectoderm and then cultured in vitro. The visceral endoderm cells which recolonize the surface of the extraembryonic ectoderm develop a parietal endoderm phenotype and lay down a thick basement membrane. These results suggest that the differentiation of the extraembryonic endoderm of the early mouse embryo into visceral and parietal phenotypes can be influenced by local cell-cell or cell-substrate interactions, and is not determined solely by cell lineage.
Proteoglycan synthesis by sternal chondrocytes perturbed with vitamin A
Authors: Vasan N. S.
Published: April 2021

Proteoglycan synthesis by sternal chondrocytes was studied in the presence of excess vitamin A (10 i.u./ml). Proteoglycans synthesized by the treated cells were smaller, and had larger amounts of chondroitinase ABC-resistant materials than control cells. Vitamin A-pretreated cells, when provided with normal feeding medium, failed to revert back to normal morphology and synthetic processes. Chrondrocyte cultures prelabelled with [35S]- sulphate, when maintained in the presence of excess of vitamin A, showed: (1) increased release of labelled proteoglycans into the medium, and (2) increased (19%) degradation of the proteoglycans. The proteoglycans synthesized by the vitamin A-treated chondrocytes are also incapable of binding with exogenous large molecular weight hyaluronic acid. Thus, high levels of vitamin A modulate the differentiation of chondrocytes by altering cellular synthetic processes.
The bursa of Fabricius of the chicken embryo: localization and ontogenic evolution of sex-steroid target cells
Authors: Gasc Jean-Marie , Stumpf Walter E.
Published: April 2021

Androgenic hormones induce inhibition or regression of the bursa of Fabricius in the chick embryo. The high doses of hormones necessary to this involution raises the question of the processes involved and their putative role in the normal development of the bursa. If androgens play a role it is mediated by receptor sites in target cells. Using an autoradiographic technique, receptor sites for androgenic hormones were localized in mesenchymal cells of the bursa from the primordium (7-day embryo) up to the fully differentiated immune organ (15-day embryo). No target cells containing receptor sites in their nuclei were observed in the endodermic epithelium or the follicles. Oestrogen target cells in very small number are found in the mesenchyme of the bursa, in 15-day embryos. The early presence of receptor sites for steroid hormones in the bursa of Fabricius shows that the normal development may be influenced by androgens, but the actual effects are yet to be demonstrated.
An ultrastructural study of the maternal-effect embryos of the ac/ac mutant of Pleurodeles waltl showing a gastrulation defect
Authors: Bluemink John G. , Beetschen Jean-Claude
Published: April 2021

Embryos of the ac/ac maternal-effect mutant in Pleurodeles waltl show disturbed epibolic movement during gastrulation. At the early gastrula stage, ectoderm cells begin to sink in at random sites in the animal half of the embryo. At the advanced gastrula stage the ectodermal pits develop into grooves. Electron microscopical analysis shows that many cells in the bottom of the pits and grooves have narrowed apices and bear many microvilli, while the cortical cytoplasm is dense, filamentous and underlain by a stratum of vesicles. These findings are interpreted as indicating that ectoderm cells contract rather than expand leading to disturbed epibolic movement.
Presence of serotonin in the palate just prior to shelf elevation
Authors: Zimmerman Ernest F. , Wee Elizabeth L. , Phillips Nancy , Roberts Nancy
Published: April 2021

Since serotonin and its antagonists affect shelf rotation in mouse embryo culture, experiments were carried out to determine whether a serotonergic system is present in the palate. Employing [3H]5-HT, day-14·5 embryos incorporated the monoamine into palates. Active uptake of [3H]5-HT was shown since excised palates incorporated 9-fold more radioactivity at 37°C than at 4°C. Synthesis of palatal serotonin was measured. Embryos were cultured in the presence of the serotonin precursor, [3H]5-HTP, and radioactive 5-HT was monitored in the palate by thin-layer chromatography. Furthermore, excised palates were incubated with [3H]5-HTP and radioactive 5-HT was measured. Incorporation was linear for about 6 h. In addition, another radioactive compound was detected which had the same Rf as the methylated derivative, 5-methoxytryptamine. Synthesis of this compound was appreciable, about 30% of that of serotonin. Levels of serotonin in the palate were measured by high pressure liquid chromatography. Palates at day 14·5 of gestation contained 0·40 ng serotonin/ mg protein, which was greater than that of tongue (0·33), body (0·14) but less than that of brain (3 09). Serotonin in palate and other embryonic tissues increased with time of development. Dopamine levels in the palate and other tissues were also determined. The distribution of serotonin in the palate was analyzed by culturing day-14-5 embryos in the presence of [3H]5-HTP, and after aldehyde fixation, paraffin embedment and sectioning, autoradiography was performed. Grains were observed throughout the palate in cells of regions 2 and 3, internal mesenchyme, tooth germ, and epithelium. Surprisingly, the pterygopalatine nerve, maxillary nerve and pterygopalatine ganglion contained an appreciable concentration of grains. Thus, the presence of serotonin in the palate is consistent with the neurotransmitter playing a role in shelf elevation.
Random X-chromosome inactivation in female primordial germ cells in the mouse
Authors: McMahon Andy , Fosten Mandy , Monk Marilyn
Published: April 2021

The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from -day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle’s translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chromosome is expressed. This confirms Johnston’s evidence (1979,1981) that Pgk-1 expression reflects a single active X chromosome at this time. Extracts of -day germ cells from heterozygous females carrying two normal X chromosomes show both the A and the B forms of PGK; since only one X chromosome in each cell is active, different alleles must be expressed in different cells, suggesting that X-chromosome inactivation is normally random in the germ line. This result makes it unlikely that germ cells are derived from the yolk-sac endoderm where the paternally derived X chromosome is preferentially inactivated. In their pattern of X-chromosome inactivation, germ cells evidently resemble other tissues derived from the epiblast.
The formation of somites and early myotomal myogenesis in Xenopus laevis, Bombina variegata and Pelobates fuscus*
Authors: Kiełbówna Leokadia
Published: April 2021

Myogenesis in Xenopus laevis and in Bombina variegata is similar despite differences in the structure of the nonsegmented mesoderm and in the formation of the myotomes. In X. laevis the nonsegmented mesoderm consists of two cell layers with the premyocoel between them. During somitogenesis the premyoblasts rotate covering subsequently the whole myotome length. In B. variegata the premyocoel is absent. The myotomal cells change their shape and elongate, attaining ultimately the whole myotome length. The morphologically mature mononuclear muscle cells in both species result from myogenesis beginning in similarly arranged myoblasts. The multinuclear myotubes arise in the swimming tadpole (stage 45).

The structure of the nonsegmented mesoderm and of the newly formed myotomes in Pelobates fuscus is similar to that of B. variegata, while the process of myogenesis is different. It begins in the multinuclear myotubes. The stage of morphologically mature mononuclear muscle cells was not observed in the light microscope.

The results suggest that myotomal myogenesis is related neither to any particular type of nonsegmented mesoderm structure nor to any specific mode of myotome formation.
Positioning of inner cell mass determines the development of mouse blastocysts in vitro
Authors: Wu Tsung-Chieh , Wan Yu-Jui , Damjanov Ivan
Published: April 2021

We have explanted mouse blastocysts into culture dishes and studied the positioning of the inner cell mass (ICM) at the time of attachment in order to establish what effect the location of the inner cell mass has on the subsequent development of embryos in vitro. We show that blastocysts may attach to the substrate with any portion of the trophectoderm. The location of ICM within the attaching blastocysts is unpredictable. The directions of egg-cylinder development may be either upward or downward. The axis assumed by a developing egg cylinder in vitro depends to a large extent on the initial positioning of the ICM at the time of attachment. Egg cylinders grown from blastocysts that have the ICM in the lower position (close to the plastic dish) reach advanced stages of development in greater numbers than egg cylinders grown from blastocyst with their ICM’s in the upper lateral or upper position. Only upward-growing egg cylinders can develop further into somitic stage (which is equivalent to 8i-or 9-day in vivo embryos). In contrast, downward growing egg cylinders become thwarted in their further development by the surrounding trophectoderm. If the downward growing egg cylinders are freed of trophectoderm and repositioned to face upwards they will develop in a manner similar to the originally upward growing egg cylinders. These findings indicate that the initial positioning of the ICM at the time of attachment is an important factor in governing the development of blastocysts to somite stage in vitro.
Ectoderm-mesoderm interactions in relation to limb-bud chondrogenesis in the chick embryo: transfilter cultures and ultrastructural studies
Authors: Gumpel-Pinot Madeleine
Published: April 2021

Limb ectoderm induces cartilage differentiation in mesoderm from chick embryo limb buds. Transfilter cultures have shown that this interaction requires ‘contact’ conditions and cannot take place at a distance. In vivo, a basement membrane is always present between ectoderm and mesoderm.

The present paper demonstrates that the relationship between ectoderm and mesoderm is similar in vivo and in transfilter cultures. In culture conditions, the filter appears to be infiltrated by mesodermal cell outgrowths which form a continuous mesodermal cover on the filter. A basement membrane is always present between the mat of mesodermal cell processes and the ectoderm.

Mesodermal cell processes are able to cross the Nuclepore filters (pore size 0-6-0-8 μm) within 15 min. After 2 h in culture, the surface of the filter opposite to the mesodermal explant is completely covered with mesodermal outgrowths.

The extracellular material accumulating at the ectoderm-mesoderm interface appears to be mainly of mesodermal origin.
Regeneration from duplicating fragments of theDrosophilawing disc
Authors: Karlsson Jane , Smith R. J.
Published: April 2021

It is a general rule that of two complementary Drosophila imaginal disc fragments, one regenerates and the other duplicates. This paper reports an investigation of an exception to this rule. Duplicating fragments from the periphery of the wing disc which lacked presumptive notum were found to regenerate notum structures during and after duplication. The propensity for this was greatest in fragments lying close to the presumptive notum, with the exception of a fragment confined to the posterior compartment, which did not regenerate notum. Structures were added sequentially, and regeneration stopped once most of the notum was present.

These results are not easily explained by the polar coordinate model, which states that regeneration cannot occur from duplicating fragments. Since compartments appear to be involved in this type of regeneration as in others, it is suggested that a new type of model is required, one which permits simultaneous regeneration and duplication, and assigns a major role to compartments.
The distribution of ingested horseradish peroxidase in the 16-cell mouse embryo
Authors: Reeve W. J. D.
Published: April 2021

Cells of the 16-cell mouse embryo endocytose horseradish peroxidase (HRP) which becomes localized in most cases to a juxtanuclear position. Cells that have ingested HRP in intact embryos, and cells dissociated from embryos prior to culture in HRP, showed similar patterns of cytoplasmic distribution of the ingested enzyme. Cells in the embryo in situ were incubated in HRP, and then labelled with fluorescent antibody either before (to label the outside surface of the embryo) or after (to reveal populations of outer polar and inner apolar cells) their disaggregation into single cells. The population of polar outside cells from the morula includes more cells with a highly restricted localization of HRP-containing vesicles than does the population of inside cells, and this restricted localization underlies the exposed surface or pole of the cell. A 2/16 couplet formed by division in vitro of a 1/8 cell is comparable to the pairs of cells dissociated from 16-cell embryos; most couplets from either source consisted of a larger cell that showed polarized surface binding of fluorescent ligand (fluorescent pole) and a smaller cell with a uniform distribution of bound ligand. The incidence of restricted patterns of HRP staining was highest among populations of both larger and polar cells. When 1 /8 cells labelled with HRP are observed during division to 2/16, the previously clustered vesicles of ingested HRP become more dispersed throughout the cytoplasm and, although the two cells of some couplets can stain differently very soon after their formation, the patterns of distribution of HRP take about 1 h after division to stabilize. These observations are consistent with cells of the 16-cell embryo inheriting different features of cytoplasmic organization.
Differentiation of the optic cups from an anophthalmic murine strain, in culture and in intrafoetal grafts
Authors: Salaün Josselyne
Published: April 2021

The optic anlage of the anophthalmic murine strain ZRDCT/an has been studied. In this strain, 70% of the adults are anophthalmic, 30% are one-eyed. The eye primordium appears and starts to differentiate at day 9 of gestation, then it degenerates. At 13 days of gestation, it has practically disappeared.

When isolated and cultured in vitro, the 10-day anophthalmic anlage develops in the same way as a control optic-cup culture from a Swiss or C57B16 mouse.

When grafted in the back of a 15 –17 day Swiss foetus, this 10-day anophthalmic anlage also develops: retina and lens differentiate, the structures which grow are very similar to those obtained when C57B16 optic cups are grafted in the same conditions.

It appears from these results that the eye regression of the mutant in situ is not a process intrinsic to the anlage. If withdrawn from its local environmental influences, the eye primordium is able to express its aptitude for differentiation.
The proximodistal determination of skeletal parts in the developing chick leg
Authors: Rowe Donene A. , Fallon John F.
Published: April 2021

Currently the chick leg bud or its components are being used extensively to study questions in development. Although fate maps of the leg, similar to that developed by Saunders (1948) for the wing, have been available (Hampé, 1957 a, 1959), no study of the proximodistal sequence of the specification of leg structures exists. Such a sequence developed for the wing by removal of the apical ectodermal ridge at successive stages (Saunders, 1948 ; Summerbell, 1974), has proven useful to the study of wing development. In this paper, we present a similar proximodistal sequence for the chick leg including the same developmental stage range as that of the wing sequence.
Distribution of osteo- and chondrogenic neural crest-derived cells and of osteogenically inductive epithelia in mandibular arches of embryonic chicks
Authors: Hall Brian K.
Published: April 2021

Mandibular arches of H.H. stage-22 embryonic chicks were divided into halves (lateral/ medial; cephalad/caudal; or proximal/distal) and grafted to the chorioallantoic membranes of host embryos. All six halves formed both cartilage and membrane bone. Epithelial-mesenchymal recombinations performed between half mandibles showed (a), that the cephalad half of the mandible contained more chondrogenic cells than did the caudal half, (b), that the proximocaudal quarter of the mandible contained more osteogenic cells than the remainder of the mandible, and, (c), that the epithelium of the caudal half was more osteogenically inductive than was the cephalad epithelium. Differential distribution of mesenchymal cells and differentially inductively active epithelia are both components of this epithelial-mesenchymal interaction.
Functional differentiation of chick gonads following depletion of primordial germ cells
Authors: McCarrey John R. , Abbott Ursula K.
Published: April 2021

The endocrine capacity of embryonic chick gonads depleted in germ cells was compared to that of controls to determine whether the somatic elements of germ-cell-depleted gonads will undergo normal functional sex differentiation. Primordial germ cells were removed from early embryos, Hamburger and Hamilton stages 7 – 11, by excision of the anterior germinal crescent. Embryos were sacrificed at 14 days of incubation, and their gonads were analysed for functional differentiation by: (1) electron microscopy to detect ultrastructural cellular morphology characteristic of steroid-secreting cells; (2) growth in cell culture to detect development of characteristic cell morphologies ; (3) radioimmunoassay of cell-culture media to detect androgens and oestrogens (androstenedione and oestradiol 17 β) secreted by gonadal cells; and (4) measurement of steroid levels produced by cultures treated with human chorionic gonadotropin (hCG) to detect the ability of gonadal cells to increase steroid production in response to gonadotropin stimulation. As a bioassay of gonadal endocrine activity, a gross morphological analysis was performed on the genital ducts, the development of which is ovary-dependent in females and testis-dependent in males.

This study demonstrated that both male and female embryonic gonads exhibit normal functional differentiation following a significant reduction in the number of primordial germ cells. These results confirm and extend our previous finding that morphological differentiation of sterile embryonic gonads is normal (McCarrey & Abbott, 1978). It is concluded frofn the present study that a normal complement of germ cells is not essential to either morphological or functional sex differentiation of the somatic elements of the embryonic ovary or testis, thus arguing against any inductive role for the germ cells in this process.
The innervation of a virgin tectum by a double-temporal or a double-nasal eye in Xenopus
Authors: Straznicky C. , Gaze R. M.
Published: April 2021

In Xenopus embryos at stage 32/33 one eye anlage was removed and the other made into a compound double-nasal or double-temporal eye. At metamorphosis the optic nerve was cut and the compound eye was permitted to regenerate fibres both to its own contralateral tectum and to the ipsilateral ‘virgin’ tectum. One month later the projection from the compound eye to the virgin tectum was assessed autoradiographically by use of tritiated proline. Projections from double-temporal eyes were found to be restricted to rostrolateral tectum, whereas projections from double-nasal eyes covered the entire tectal surface. It was concluded that the results did not suggest that positional markers existed on the tectum before the arrival of the optic fibres.
Organization of actin filaments in early chick embryo ectoderm: an ultrastructural and immunocytochemical study
Authors: Wakely J. , Badley R. A.
Published: April 2021

By combining transmission electron microscopy (TEM), scanning electron microscopy (SEM) and immunocytochemistry at both light and TEM levels the organization of actin in early chick ectoderm has been demonstrated. Every cell is encircled by a ring of actin filaments which are associated with apically situated intercellular junctions. In this way the actin ring of each individual cell is connected to that of surrounding cells and a continuous network is formed. As clearly shown by immunofluorescence and SEM studies on intact and Triton X-100 treated whole-mount preparations this network extends throughout the entire layer, interrupted only at the blastoderm margins and the primitive streak. A more diffuse arrangement was sometimes seen at cell bases. It is suggested that the network extending throughout the ectoderm gives it stability and cohesion and is important in gross morphogenetic movements involving the entire layer. The less-organized arrangement at cell bases is associated more with movements of individual cells.
Neurotrophic control of events in injured forelimbs of larval urodeles
Authors: Mescher Anthony L.
Published: April 2021

Denervated forelimbs and contralateral innervated forelimbs of Ambystoma larvae were injured internally distal to the elbow by compression with watchmaker’s forceps. Innervated controls completely repaired the crush injury within one week; denervated limbs failed to repair the injury and exhibited varying degrees of limb regression. Histological examination revealed that the process of tissue dedifferentiation initiated by injury was more extensive in denervated, regressing limbs than in controls. In innervated limbs, both the DNA labelling index and the mitotic index peaked approximately 4-6 days after the injury and returned to baseline levels by 10 days. In denervated limbs, the DNA labelling index also increased and remained at an elevated level for at least 2 weeks after the injury, but significant mitotic activity was not observed. The data indicate that intact nerves are not needed for cellular dedifferentiation, cell cycle re-entry, and DNA synthesis in injured limbs, but are required for the cells to proliferate and repair the injury. These results are discussed together with those of similar experiments on the role of nerves during the initiation of epimorphic regeneration in amputated limbs.
Studies in Embryonic and Larval Development in Amphibia: II. The Spinal Motor-Root
Authors: Hughes Arthur
Published: April 2021

The development of the spinal motor-roots is described in the Anurans Xenopus and Eleutherodactylus, together with observations on the embryonic roots of Bufo, the lizard Sphaerodactylus, and the chick. From a primary motor-cell in the embryo of Xenopus an axon process grows along the surface of the cord and finally turns outwards to traverse a myocommatal plane, thereby forming a ventral root. As in other larval Amphibia, the longitudinal motor-tract and the ventral roots originate together, though not necessarily by identical methods in all. In the recently hatched larva, movement is inhibited by transection of the central nervous system behind the otocyst. At these levels there must be a centre for the co-ordination of swimming movements. In mid-larval stages the ventral roots of Xenopus and Bufo arise from the longitudinal motor-tract of the cord; cell-body and myocommatal terminal of the axon are longitudinally displaced, though the precise arrangement varies at different levels in the cord. The ventral roots of the trunk of Eleutherodactylus are wholly separate and distinct from the longitudinal motor-tract, the fibres of which they cross at right angles. The arrangement of the ventral roots of the tail resembles that in other Anura. In embryos of the lizard Sphaerodactylus the ventral-root fibres arise directly from cells of the basal plate of the cord and run at various angles through the white matter to emerge as spinal motor-roots. In the chick embryo ventral-root fibres run directly at right angles through the white matter. On the basis of observations on the behaviour of nerve fibres in tissue culture, it is suggested that there is a general correlation between the angle of approach of two growing fibres and their chances of permanent anastomosis.
X-ray Inactivation of Nuclei as a Method for Studying their Function in the Early Development of Fishes
Authors: Neyfakh A. A.
Published: April 2021

The effect of high radiation doses (20-60 kr.) on different stages of the early development of the loach (Misgurnus fossilis L.) was studied. Analysis of dose dependence shows that a radio-sensitive component (presumed to be the nuclei) is affected maximally by such doses, whereas a radio-resistant component (presumed to be the cytoplasm) is not affected significantly. The use of such radiation doses is, therefore, a means of investigating the role of nuclei in development. Irradiation with these doses at any time from fertilization to early blastula leads to the arrest of development at one stage—the late blastula—and to death some hours later. Irradiation at any time during the period from late blastula to mid-gastrula similarly leads to arrest of development at one stage—the end of gastrulation. Irradiation during the period from early to late blastula results in the arrest of development at different stages of gastrulation depending on the moment of irradiation. Irradiation after the mid-gastrula results in the arrest of development at different stages of organogenesis, depending also on the moment of irradiation. The results cannot be explained by changes of nuclear sensitivity, nor by non-specific critical periods in development. They can be explained by changes in the role of nuclei in development, by periods of specific dependence on the function of nuclei. The independence of the stage of developmental arrest on the stage of irradiation, when irradiating from fertilization up to early blastula and from late blastula up to mid-gastrula, shows the relative inactivity of nuclei during these periods of normal development. The strong dependence of the stage of development reached at arrest on the stage of irradiation, when irradiating the early to late blastula and after the mid-gastrula stages, demonstrates the activity of nuclei in development during these periods. The conclusion may be drawn that in the early development of the loach the nuclei function periodically, each period of activity ensuring a subsequent episode of development. Nuclear activity during ovogenesis ensures the development of the egg up to the stage of the late blastula; nuclear activity during the early and mid-blastula stages ensures gastrulation. Development of axial organs and further organogenesis is ensured by nuclear function beginning from the mid-gastrula stage.
Tail Regeneration in the Geckonid Lizard,Sphaerodactylus
Authors: Hughes Arthur , New Denis
Published: April 2021

Tail regeneration in the Geckonid Lizards Sphaerodactylus goniorhynchus and argus is described. The rate of growth of a first regenerate, after a latent period of 10–12 days, is about 0·47 mm. per day. Subsequent regenerates grow more slowly. The tissues of the new tail are derived from a regenerative blastema which is formed beneath the epidermis covering the broken surface of the tail. A flaskshaped outgrowth of the ependymal epithelium is a centre for the proliferation of new cells. The outer part of the regenerative blastema is a zone of myogenesis, which becomes divided into the same number of muscle bands as in the original tail. Each muscle band becomes segmented, and motor nerves enter the intersegmental planes. At these sites a positive reaction for esterases is first seen. Multinucleate muscle fibres, which stretch from one intersegmental plane to the next, arise by the fusion of myoblastic cells. The regenerate is innervated by branches of the last three remaining pairs of spinal nerves. These branches keep pace with the growth of the regenerate, and form longitudinal nerves. Their terminal fibres enter the new ectoderm on the 4th day. Nitrogen mustard applied in solution to the outer surface of the regenerating area may inhibit, or slow down, the new growth. Degeneration of each type of cell within the regenerate is caused by nitrogen mustard, but melanocytes become more abundant than normal. A regenerate subsequent to one inhibited by nitrogen mustard grows as fast, or even faster, than a normal first regenerate, and again contains an excess of melanocytes.
The Development of the Cornea in the Chick
Authors: Meyer David B. , O’rahilly Ronan
Published: April 2021

The development of the cornea in the chick, based on the microscopical examination of serial sections of 108 morphologically staged chick embryos between stage 26 and hatching, is described. A description of the adult cornea is also provided. Correlations between the internal histogenesis of the cornea and the external morphology of the chick embryo have been established from the use of staged embryos, so that the probable state of development of the cornea can be assessed from surface appearances only. The cornea of the chick, at stage 26, consists of an anterior epithelium, an acellular postepithelial layer, and a mesothelium. Mesenchymal cells (corneal ‘corpuscles’) begin to infiltrate the postepithelial layer at stage 27. By stages 29–31 these cells occupy a continuous layer, the substantia propria, which comprises the entire extent of the postepithelial layer except for an anterior, acellular band subjacent to the anterior epithelium. The anterior band becomes progressively thinner and disappears at stage 36, the substantia propria then extending across the entire distance between the anterior epithelium and the mesothelium. The anterior limiting lamina first appears at stage 39. It closely resembles and is often confused with the temporary anterior band of the postepithelial layer. The posterior limiting lamina was not identified with certainty in any of the embryonic corneae examined. It has been stressed that embryological studies in which external staging and internal development are correlated provide a more precise interpretation of developmental processes, and are an essential prelude to experimental, physiological, biochemical, and histochemical investigations of embryonic development.