bluuebunny/crossref_metadata_2025 huggingface dataset:
X-chromosome inactivation mosaicism in the three germ layers and the germ line of the mouse embryo
Authors: McMAHON A. , Fosten M. , Monk M.
Published: April 2021

Electrophoretic variant forms of the X-linked enzyme phosphoglycerate kinase (PGK-1, E.C.2,7,2,3) have been used to examine X-chromosome mosaicism in tissues from -day post coitum heterozygous female mouse embryos. Samples of yolk-sac endoderm, neural ectoderm, heart (mesoderm), liver (endoderm) and germ cells were analysed from each embryo. In all tissues except yolk-sac endoderm, both PGK-1 isozymes were expressed. The extent of covariance among tissues with respect to the PGK-1 isozyme contribution is consistent with all tissues being derived from the same pool of cells after X-inactivation. The covariance among tissues gives an estimate of the size of this pool (47 cells) and places the earliest time of X-inactivation in epiblast cells between and days post coitum. From the independent variance among tissues within an individual, the average primordial precursor pool size for the three germ layers and the germ line itself was estimated as 193 cells.
The mechanism of feather pattern development in the chick: II. Control of the sequence of pattern formation
Authors: Davidson Duncan
Published: April 2021

During the development of the dorsal feather pattern, a wave of morphogenesis sweeps across the skin forming successive anteroposterior rows of feather primordia. The preceding paper in this series showed that the morphogenetic wave is almost immediately preceded by a wave of determination at which feathers sites are established row by row, (Davidson, 1983). The present paper reports an in vitro experimental investigation of the movement of these waves across the skin.

The waves pass undisturbed across a cut made before the pattern forms. Although cultured skin does not grow and consequently forms only a few rows of primordia, the morphogenetic wave takes the same time to cross the prospective feather tissue as in vivo, indicating that the passage of this wave through cultured skin reflects its traverse of the entire pattern in vivo.

These results show that the movement of the waves of determination and morphogenesis does not depend on the propagation of any signal across the skin immediately ahead of primordium formation. Their movement derives from a gradient in the temporal differentiation of the skin, established before stage 29. In this respect, the temporal control of feather development in the chick skin resembles the control of somite development in the amphibian paraxial mesoderm (Pearson & Elsdale, 1979). The present results therefore suggest that a programmed gradient of temporal differentiation across the prospective patterned tissue is a common component of the mechanisms which form regular, repetitious patterns in vertebrate embryos.
A prestalk-cell-specific acid phosphatase in Dictyostelium discoideum
Authors: Oohata Akiko A.
Published: April 2021

A simple and reliable method of separating and quantifying acid phosphatase activities in D. discoideum is described, and one of the electrophoretically distinguishable forms of the enzyme is shown to be specific for prestalk cells. Accumulation of this product commences some 2-3 h later in development than the prespore specific enzyme UDP-galactose polysaccharide transferase. This finding is discussed in terms of recent observations on the control of prestalk cell differentiation in this organism.
Restriction of developmental potential and trochoblast ciliation in Patella embryos
Authors: Janssen-Dommerholt C. , Wijk R. Van , Geilenkirchen W. L. M.
Published: April 2021

At the 64-cell-stage embryos of Patella develop a prototroch consisting of four groups of four cilia-bearing cells. Ciliogenesis of isolated blastomeres and trochoblasts was studied, as well as the effect on it of cleavage arrest caused by cytochalasin B treatment. Isolation of blastomeres or trochoblast cells has no influence on ciliogenesis; neither has arrest of cleavage in whole embryos after the third cleavage. However, cleavage arrest before third cleavage completely prevents ciliogenesis. Thus, third cleavage is decisive for the expression of the developmental potential of the primary trochoblasts. Impairment of DNA synthesis by aphidicolin in the S-phase preceding third cleavage also prevents ciliogenesis. It is concluded that a determinant for ciliogenesis as well as certain nuclear factors must be segregated into the micromeres at third cleavage for ciliogenesis to occur in the prototroch cells.
An SEM analysis of neural crest migration in the mouse
Authors: Erickson C. A. , Weston J. A.
Published: April 2021

The cellular morphology and migratory pathways of the trunk neural crest are described in normal mouse embryos, and in embryos homozygous for Patch in which neural crest derivatives develop abnormally. Trunk neural crest cells initially appear in -day embryos as a unique cell population on the dorsal neural tube surface and are relatively rounded. Once they begin to migrate the cells flatten and orient somewhat tangentially to the neural tube, and advance ventrad between the somites and neural tube. At the onset of migration neural crest cells extend lamellipodia onto the surface of the tube while detaching their trailing processes from the lumenal surface. The basal lamina on the dorsal neural tube is discontinuous when cell migration begins in this region. As development proceeds, the basal lamina gradually becomes continuous from a lateral to dorsal direction and neural crest emigration is progressively confined to the narrowing region of discontinuous basal lamina. Cell separation from the neural tube ceases concomitant with completion of a continuous basement membrane. Preliminary observations of the mutant embryos reveal that abnormal extracellular spaces appear and patterns of crest migration are subsequently altered. We conclude that the extracellular matrix, extracellular spaces and basement membranes may delimit crest migration in the mouse.
Transfilter studies on the mechanism of epithelio-mesenchymal interaction leading to chondrogenic differentiation of neural crest cells
Authors: Smith Linda , Thorogood Peter
Published: April 2021

Interaction with an epithelium is a prerequisite for avian cranial neural crest (NC) cells to differentiate into cartilage and bone (Bee & Thorogood, 1980). In order to investigate the causal mechanism we have selected one such interaction - that between mesencephalic NC and retinal pigmented epithelium (RPE) for further study. Premigratory NC cells were grown transfilter to RPE explants of different developmental ages and on Nuclepore filters of different pore size which either allowed or prevented penetration by cell processes. Initial scanning electron microscopy (SEM) observations established that pores of 0·8μm allowed the passage of cell processes through the filter whereas 0·2 μm pores did not.

The transfilter experiments demonstrated that chondrogenic differentiation of NC cells will occur only if the Nuclepore filters have a pore size large enough to permit the passage of cell processes. Furthermore SEM observations established that cell processes do traverse the Nuclepore filter when NC and RPE are grown in transfilter combination. The results indicate that the mechanism is not mediated by diffusable factors but rather is mediated either by direct contact between NC cells and non-diffusable matrix closely associated with RPE or by direct plasmalemmal contact between RPE and NC cells through discontinuities in the basement membrane. The results of these experiments also demonstrate that younger (stage 17) RPE is more effective at eliciting chondrogenesis from premigratory NC cells than older (stage 24) RPE and that the interaction between RPE and NC cells is a prolonged one, taking place over days rather than within hours. Both of these in vitro observations are compatible with the timing of events leading to scleral cartilage formation in vivo.
Nature of the hypoblastic influence on the chick embryo epiblast
Authors: Mitrani E. , Shimoni Y. , Eyal-Giladi H.
Published: April 2021

Stage XIII chick blastoderms deprived of the marginal zone, the area opaca and the posterior half of the hypoblast, when incubated further developed axes whose orientation in 50 % of the cases was according to the original blastoderm’s orientation, whilst in 50 % of the cases they developed at 90° from the posterior side. Those results illustrate the quantitative differences in inductivity between the anterior and the posterior hypoblastic halves. Normally the posterior region has the highest effect but other regions can also bring about the development of an embryonic axis if allowed to act upon the epiblast for a sufficiently long period of time. The possible ways in which a chick hypoblast influences the epiblast to develop an embryo are examined in the light of recent findings and of new experiments described below.
Expression of the yolk-protein genes in the mutant doublesex dominant (dsxD) of Drosophila melanogaster
Authors: Bownes Mary , Dempster Maureen , Blair Mairearad
Published: April 2021

Adult flies mutant for doublesex dominant (dsxD) are intermediate in phenotype between males and females. The dsxD mutation acts in the heterozygous state to transform only flies with two X chromosomes into intersexes, XY flies are unaffected by the mutation. Yolkprotein synthesis, which normally occurs in the ovaries and fat bodies of females, but not in males unless stimulated with 20-hydroxy-ecdysone, is reduced. The dsxD fat body synthesizes less yolk proteins throughout adult life, and the gonads rarely make yolk proteins. Using cloned yolk-protein genes as probes for measuring transcript levels we have shown that expression of these genes in dsxD is regulated both transcriptionally and post-transcriptionally. We suggest that the dsxD locus regulates the expression of the yolk-protein genes from within the fat body cells and does not operate by modulating ecdysteroid titres in the adults.
A boundary model for pattern formation in vertebrate limbs
Authors: Meinhardt Hans
Published: April 2021

We postulate that positional information for secondary embryonic fields is generated by a cooperative interaction between two pairs of differently determined cell types. Positional information is thus generated at the boundaries between cells of different determination. The latter are assumed to result from the primary pattern formation in the embryo. The application of this model to vertebrate limbs accounts for the pairwise determination of limbs at a particular location, with a particular handedness and alignment to the main body axes of the embryo. It accounts further for the gross difference in the regeneration of double anterior and double posterior amphibian limbs as well as for the formation of supernumerary limbs after certain graft experiments including supernumeraries in which the dorsoventral polarity changes or which consist of two anterior or two posterior halves. Our model provides a feasible molecular basis for the polar coordinate model and successfully handles recently found viola-tions, for instance formation of supernumerary limbs after ipsilateral grafting with 90° rotation. The most frequent types of developmental malformations become explicable. The models allow specific predictions which are fully supported by recent experiments (see the accompanying paper of M. Maden).
Tissue interactions in the organization and maintenance of the muscle pattern in the chick limb
Authors: Mauger Annick , Kieny Madeleine , Hedayat Ihsan , Goetinck Paul F.
Published: April 2021

Recent investigations on a hereditary muscular dysgenesis (cn/cn) in the chicken (Kieny, Mauger, Hedayat & Goetinck, 1983) have suggested that limb muscle pattern development and subsequent maintenance are two independent steps in the formation of the musculature. The respective activities or muscle cells and connective tissue cells in the ontogeny of the musculature have been investigated in avian embryos 1) by in ovo administration of drugs interfering with collagen biosynthesis, and 2) by heterogenetic somite-exchange experiments between normal and mutant embryos.

None of the drugs administered to the chick embryo caused any disturbance of muscle pattern formation or maintenance whether treatment occurred before (5 days) or after (7-5 days) the muscle splitting period.

Heterogenetic implantations were performed at 2 days of incubation either at the leg or at the wing level. Somitic mesoderm from non-mutant quail embryo was grafted to replace a piece of somitic mesoderm in putative mutant (cn/cn) chick embryos. The introduction of normal myogenic cells into a mutant leg or wing led to a normally patterned musculature, which demonstrates that the muscular dysgenesis cn/cn results from a defect of the somitic myogenic cell line.
Role of theesc+gene product in ensuring the selective expression of segment-specific homeotic genes inDrosophila
Authors: Struhl Gary
Published: April 2021

The product of the extra sex combs+ (esc+) gene is required during embryogenesis for the correct determination of segments in Drosophila. If this product is absent, most segments develop like the normal eighth abdominal segment. Here, I extend previous results (Struhl, 1981a) showing that this phenotype results in large part from indiscriminate expression of the bithorax-compiex genes which are normally active only in particular segments of the thorax and abdomen. In addition, I test whether the esc+ gene product is required for the correct expression of other homeotic genes. First, I have examined two genes of the Antennapedia- complex (Sex combs reduced+ and Antennapedia+): I find that both genes are normally required in only some of the body segments, but that in the absence of the esc+ gene product, both appear to function adventitiously in other segments. Second, comparing esc+ and esc+ embryos lacking both these genes as well as the bithorax-compiex, I find that additional homeotic genes (possibly those normally involved in specifying head segments) appear to be expressed indiscriminately when the esc+ gene product is absent. Finally, I present evidence that the products of the esc+ gene and the Poly comb+ gene (a second gene required for the correct regulation of the bithorax-complex) act independently. On the basis of these results, I propose a tentative outline of the roles and realms of action of all of these genes.
An analysis of contractile proteins in developing chick heart by SDS polyacrylamide gel electrophoresis and electron microscopy
Authors: Lim Soo-Siang , Woodroofe M. Nicola , Lemanski Larry F.
Published: April 2021

Chick heart development was studied using transmission electron microscopy and SDS-polyacrylamide gel electrophoresis in combination with densitometry. Myosin heavy chain, α-actinin, actin and tropomyosin accumulations were analysed in developing hearts from preheartbeat stage 9 (Hamburger-Hamilton staging series) through 2 days after hatching. At the preheartbeat stage, electron microscopy revealed a significant number of thin filaments scattered throughout the cytoplasm of the myoblasts; however, very few thick filaments were seen. There was no obvious association between the two filament types. SDS-polyacrylamide tube gels of heart muscle homogenates demonstrated the presence of all five proteins in hearts at the preheartbeat stage. Further analyses of the proteins by gel densitometry indicated that both actin and myosin accumulated rapidly during heart development while a-actinin and tropomyosin levels remained relatively static. Our results show that detectable quantities of myosin heavy chain, α-actinin, actin and tropomyosin accumulate in myocardial cells prior to the appearance of myofibrils and initiation of the contractile function.
Evidence for a functional role of the cytoskeleton in determination of the dorsoventral axis in Xenopus laevis eggs
Authors: Ubbels Geertje A. , Hara K. , Koster C. H. , Kirschner M. W.
Published: April 2021

A normal table of events of the first cleavage period in the fertilized egg (cf. Gerhart, 1980) has been completed (cf. Table I) by studying external and internal features. Through a cytological study of eggs fixed after video time-lapse observation such features can directly be correlated and it has been shown that the first postfertilization wave (PFW) reflects spermaster growth, which causes rearrangements of animal yolk material. This may, in conjunction with the interaction of the spermaster rays with the cortex, define, in time as well as in space, the asymmetric cortical contraction which we suppose to evoke asymmetry in the animal hemisphere by formation of the vitelline wall (Pasteels, 1964) and in the vegetal hemisphere by formation of the Vegetal Dorsalising Centre (Kirschner et al. 1981).

Neither prick-activated eggs nor fertilized eggs incubated in vinblastine develop a spermaster. Under these conditions abnormal cytoplasmic segregation may be directed by gravity alone. For normal development the activated egg must in some way, for instance through the sperm centriole, organize microtubule assembly into a monaster. The centriole acts as a microtubule-organizing centre in structuring the egg’s cytoskeleton, and through this directs localization of the various yolk components, in time as well as in space. In egg rotation experiments performed under appropriate conditions, the cytoskeleton is disturbed and yolk rearranges under gravity till a new equilibrium is established which determines a new dorsoventral polarity. Such experiments also show that neither the dorsal cytoplasm nor the grey crescent cortex act as the ultimate dorsal determinants, since their localization is unaltered upon rotation, whereas the overall yolk distribution is significantly changed.
Cytoplasmic and cortical factors participating in cleavage furrow formation in eggs of three amphibian genera; Ambystoma, Xenopus and Cynops
Authors: Sawai Tsuyoshi
Published: April 2021

A cytoplasmic factor and a cortical factor participating in cleavage furrow formation had been previously found in Cynops eggs (Sawai, 1972). These were investigated in the present study in Ambystoma and Xenopus eggs, by the method of cytoplasmic or cortical transplantation. Results were practically similar to those previously obtained with Cynops, indicating that in all the species of eggs during cleavage, the cytoplasm localizing along the cleavage furrow possessed furrow-inducing activity, and the cortex was competent to form the furrow in response to the activity of the cytoplasmic factor. In the present work, the species specificity of the two further factors was examined among Cynops, Ambystoma and Xenopus eggs, and the factors were found to act across species.
The effect of vitamin A on the regenerating axolotl limb
Authors: Maden M.
Published: April 2021

These experiments describe further investigations into the effects of vitamin A on regenerating limbs. The effects of different retinoids, the time of administration, concentration of vitamin A and histological, autoradiographic and histochemical studies are reported. The most obvious result of vitamin A treatment is to cause proximal elements to regenerate from distal amputation levels, that is to cause serial reduplication of pattern in the proximodis-tal axis. Retinoic acid was the most potent of the analogues tested and longer times of administration or higher concentrations cause a greater amount of serial reduplication. Various tissue changes have been found which include the inhibition of cell division, loss of cartilage metachromasia, changes in the mucous-secreting properties of the epidermis and an increased packing in the blastemal cells. The significance of these cellular effects in relation to the pattern-formation changes is discussed.
The fifth cell cycle of the mouse embryo is longer for smaller cells than for larger cells
Authors: Macqueen Hilary A. , Johnson Martin H.
Published: April 2021

Newly-formed pairs of 16-cell blastomeres were collected by periodic observation of isolated 8-cell blastomeres. Any pairs formed by division were recovered and classified as being composed of 1/16 blastomeres that differed in size or were of similar size. All of the latter and some of the former were then cultured for periods of up to 20 h. The remaining pairs of different-sized blastomeres were disaggregated to larger or smaller cells. Some of these were reaggregated as smaller: smaller or larger: larger pairs, and these, together with the remaining isolated smaller and larger blastomeres were also cultured for up to 20 h. At hourly intervals, cultured cells were sampled and analysed for incidence of division. It was found that larger cells divided on average after 12 h whereas smaller cells divided on average after 14 h.
Sodium transport and the control of epiblast polarity in the early chick embryo
Authors: Stern Claudio D. , MacKenzie Debora O.
Published: April 2021

The sodium transport properties of chick epiblast during gastrulation were studied by various techniques. It was found that the epiblast is capable of unidirectional apical to basal sodium transport, in towards the underlying intraembryonic space. The Na-K-ATPase was localized by [3H]ouabain binding and autoradiography near the basal surfaces of the cells, and the number of pump sites was quantified. The transport rate of sodium was determined with 22Na. Electrophysiological studies on embryos at primitive streak stages showed a trans-epithelial potential of about +16 ±5 mV (basal side positive) which was sensitive to strophanthidin. Applying similar voltages but of reverse polarity to isolated sheets of epiblast caused a rapid reversal of some of their morphological polarity markers as well as some of their physiological functions. The relevance of these results to development is discussed.
Neuronal cell death in grasshopper embryos: variable patterns in different species, clutches, and clones
Authors: Loer Curtis M. , Steeves John D. , Goodman Corey S.
Published: April 2021

Previous studies showed that cell death plays an important role in adjusting the segmentspecific number of ganglionic neurones during grasshopper embryogenesis (Bate, Goodman & Spitzer, 1979; Goodman & Bate, 1981). In every segment, the single midline precursor 3 (MP3) divides once to produce two progeny. In some segments, one or both of these two progeny die; there is a general pattern of cell death of the MP3 progeny across the thoracic and abdominal segments.

In the present study we examined the pattern of cell survival versus death of the MP3 progeny in 472 embryos from four different species, from the genetically related offspring within different clutches of the same species and from the genetically identical offspring within isogenic clones of the same species. We find variability in the pattern of cell survival versus death amongst embryos of the same species, clutch and clone, suggesting a significant epigenetic influence on this pattern. However, our results also show significant differences in the pattern of cell death between different genera and species, and between different clones and clutches within a single species, suggesting a genetic influence on this pattern as well.
Light microscope observations on actin distribution during morphogenetic movements in the chick embryo*
Authors: Ostrovsky David , Sanger Joseph W. , Lash James W.
Published: April 2021

The cellular distribution of actin during two morphogenetic processes in the chick embryo has been observed, using a high-resolution fluorescent technique, with heavy meromyosin as a probe. These cytoskeletal elements have been implicated in all cell and tissue movements in the embryo. It is now commonly accepted that microfilaments are necessary to provide the motive force for morphogenesis. Two morphogenetic movements in the early embryo have been studied at the light microscope level. During somitogenesis, the mesenchymal segmental plate becomes transformed into a meristic series of transient epithelial vesicles. Again, actin distribution is diffuse and random before the morphogenetic event. During epithelialization, actin becomes prominent in the apical regions of the epithelial cells. Cells in the somitic epithelial vesicles, the core cells, appear to be passive participants in this process, and consequently show no distinct cellular localization of actin.
Normal adenylate ribonucleotide content in mouse embryos homozygous for the t12 mutation
Authors: Spielmann Horst , Erickson Robert P.
Published: April 2021

The recently improved firefly luciferase assay was used to determine ATP, ADP or AMP in single preimplantation mouse embryos from crosses yielding lethal t12/t12 embryos. Normal values of the three adenylate ribonucleotides were found in freshly collected 2-cell and 4-cell embryos and during in vitro culture to the blastocyst stage. A decrease in adenylate ribonucleotide content was seen in putative t12/t12 embryos only when they were degenerating.
Morphogenesis of the amphibian limb blastema: The relationship between pattern and form
Authors: Holder Nigel , Reynolds Susan
Published: April 2021

A relationship between pattern formation and field shape is established following the formation of rounded blastemas on lower arm limb stumps after treatment with vitamin A. Pattern formation is not affected by alteration in blastemal shape caused by removal of the dermis from the thigh region of the leg. We conclude, therefore, that blastemal shape does not play a causal role in establishing limb pattern. Data relating the number of cells present between the cardinal axial poles of blastemas and the size of blastemas is discussed in terms of short arc intercalation and short range cell-cell interactions during pattern regulation.
Vibrissa dermal papilla cell aggregative behaviour in vivo and in vitro
Authors: Jahoda Colin A. B. , Oliver Roy F.
Published: April 2021

Parallel cultures of adult rat vibrissa dermal papilla cells and skin fibroblasts revealed differences between the two cell types with respect to a number of criteria. In particular the dermal papilla cells demonstrated a distinctive single cell morphology, and at confluence formed cell aggregates radically different from regular fibroblast multilayering and patterning. This finding confirmed repeated observations of papilla cell clumping in short-term culture. The dermal papilla cells which are mitotically quiescent in situ were also shown to have a lower proliferative capacity than the skin fibroblasts. The affinity shown by papilla cells towards each other in culture reflected the behaviour demonstrated by isolated dermal papillae transplanted into ear dermis and into the collagenous capsule of the vibrissa follicle. In the absence of epidermal contact the papilla cells remained as recognizable rounded aggregates for the experimental period of up to nine months. Synthesis of extracellular material typical of that seen in situ was observed, particularly during the first weeks following transplantation. The collective behaviour of the dermal papilla cells revealed in this study may be significant for the morphogenetic activity of the papilla, and for papilla size during the hair cycle. It may also reflect the retention of embryonic-like properties by the dermal component of adult hair follicles.
The origin of intrahepatic bile duct cells in the mouse
Authors: Shiojiri Nobuyoshi
Published: April 2021

The origin of the intrahepatic bile ducts in the embryonic mouse liver was investigated. At 12·5 and 13·5 gestation days in the C3H/Tw strain mouse, the liver parenchyma contains morphologically and histochemically homogeneous immature hepatocytes but not bile duct cells. When the liver fragments were cultured in the testis, immature hepatocytes differentiated into large hepatocytes for the most part and also into bile duct cells. In contrast, when the similar liver fragments were cultured under the skin of newborn mice, bile duct cells differentiated much earlier in all transplants than those cultured in the testis. These bile duct cells were considered to be the intrahepatic bile duct cells, since they did not form biliary glands but possessed a basal lamina and histochemical characteristics of intrahepatic bile duct cells of the normal liver. The origin of the endodermal epithelial cells in the mouse liver is discussed with special attention to the differentiation of the intrahepatic bile duct cells from the immature hepatocytes.
Skin glands in the axolotl: the creation and maintenance of a spacing pattern
Authors: Holder Nigel , Glade Richard
Published: April 2021

The morphogenesis of skin glands in the larval axolotl is described at the light microscope level. The glands are derived from the epidermis, but are eventually located in the dermis. The glands are non-randomly arranged within the skin and the spacing pattern tends towards a hexagonal array in two dimensions. Analysis of the spacing pattern in animals of different sizes reveals that a clear relationship exists between gland size and the distance between glands. Occasionally, new small glands are inserted into the pattern, suggesting that the spacing of glands in under a dynamic control throughout the growth of the axolotl. The possible mechanisms underlying the creation and maintenance of the pattern are discussed.
Experimental Analysis of the Eye Morphogenesis in Mammals
Authors: Stroeva O. G.
Published: April 2021

Owing to the great difficulties of experimental interference with the embryogenesis of mammals, the morphogenetic potentialities of the mammalian eye remain almost unstudied up to the present. The elucidation of whether the developing mammalian eye obeys the same rules that have been established for the lower vertebrates, or whether its development proceeds in another way, is interesting in many respects. It might allow us to answer a number of questions, e.g. how stable are the morphogenetic interactions within the vertebrates which result in the formation of homologous organs? How do the morphogenetic potentials of the parts of an organ alter in the course of evolution? Light might also be thrown on the development or loss of regenerative capacity in various forms. Lastly, we may find out to what extent the experiments on lower vertebrates, easily carried out on a large scale, are of use for the understanding of those processes which cause regularly recurring inborn malformations in man.
Néoblastes et limitation du pouvoir de regeneration céphalique chez la planaire Dendrocoelum lacteum
Authors: Kolmayer Simone , Stéphan-Dubois Françoise
Published: April 2021

The regeneration of the planarian Dendrocoelum lacteum has been tested at three different levels of amputation : just behind the eyes, half-way between the eyes and the pharynx, and just in front of the pharyngeal base. The plana-rians always regenerate in the first case, never in the last case, and about 7 times out of 10 in the intermediate case. Experiments involving amputations and irradiations show that there are regeneration cells (neoblasts) in the regions behind the pharyngeal base, regions which are unable to regenerate. When they are not irradiated, these neoblasts are able to move towards the head and to restore the irradiated regions. They reconstitute a blastema with eyes, the number of cases directly depending on the prepharyngeal level of the section. The histology confirms the experimental results and demonstrates the processes of regression, of necrosis, and then of colonization of the irradiated regions.
The Developmental Capacity of Nuclei Taken from Differentiating Endoderm Cells ofXenopus Laevis
Authors: Gurdon J. B.
Published: April 2021

The developmental potentiality of embryonic endoderm nuclei in X. laevis is shown to change as the tissue to which they belong becomes differentiated. This change has been demonstrated by taking nuclei from endoderm tissue in different stages of differentiation, and transplanting them into enucleated unfertilized eggs; the development of the resulting transplant-embryos indicates the developmental capacity of their nuclei. Since the proportion of total transplantations which become late blastulae is affected by the technique, the main conclusions have been drawn from the further development of late blastula transplant-embryos. The quality of recipient eggs, which is always variable, may also affect transplant-embryo development, and conclusions have therefore been mainly derived from selected experiments in which control donor nuclei have shown that egg quality was good. Reasons have been given for believing that non-hereditary nuclear qualities, such as their size and stage in mitosis, do not affect the conclusions drawn from transplantembryo development; their development is therefore solely dependent on the specific genetic qualities of the donor nuclei used. No decline in the developmental potentiality of endoderm nuclei was found in blastulae and gastrulae. However, the capacity of nuclei to form normal tadpoles decreased progressively from after gastrulation until the beginning of torsion in the gut of swimming tadpoles; at this late stage there was still a small proportion of undifferentiated nuclei from which normal tadpoles have been obtained. Thus nuclear differentiation affects an increasing proportion of nuclei to an increasing extent, as the endoderm becomes differentiated. Serial transplantation has shown that the changes involved in nuclear differentiation are heritable and, at least to a large extent, irreversible. These results are compared with those of Briggs & King who transplanted nuclei from endoderm cells of R. pipiens. In both Xenopus and Rana, nuclei are undifferentiated at the late blastula stage, but after this the rate and time of onset of nuclear differentiation is very different for the endoderm of the two species. These differences show that there is no exact correlation between nuclear differentiation and tissue differentiation. It is suggested that nuclear differentiation may be concerned in the processes which take place when individual cells become differentiated into their final functional state.
The distribution of endocrine cell progenitors in the gut of chick embryos
Authors: Rawdon B. B. , Kramer Beverley , Andrew Ann
Published: April 2021

The aim of this experiment was to find out whether or not, at early stages of development, progenitors of the various types of gut endocrine cells are localized to one or more specific regions of the gastrointestinal tract. Transverse strips of blastoderm two to four somites in length were excised between the levels of somites 5 and 27 in chick embryos at 5- to 24-somite stages and were cultured as chorioallantoic grafts. The distribution of endocrine cells in the grafts revealed confined localization of progenitor cells only in the case of insulin-immunoreactive cells. The progenitors of cells with somatostatin-, pancreatic polypeptide-, glucagon-, secretin-, gastrin/CCK-, motilin-, neurotensin- and serotonin-like immunoreactivity were distributed along the length of the presumptive gut at the time of explantation; indeed, in many cases they were more widespread than are their differentiated progeny in normal gut of the same age. This finding indicates that conditions in grafts must differ from those that operate in the intact embryo. Also it may explain the occurrence of ectopic gut or pancreatic endocrine cells in tumours of the digestive tract.
Stages in the development of cat muscle spindles
Authors: Milburn Alice
Published: April 2021

The structure of developing spindles has been examined in cat peroneal muscles by light and electron microscopy, beginning at the 34- to 38-day foetal stage.

By this stage α motoneurons have formed end-plates on primary myotubes. Secondary extrafusal myotubes then develop beneath the basal lamina of primary myotubes, and are innervated by motor axons early in their assembly. First-series secondary myotubes separate from primary myotubes prior to the development of subsequent series. The assembly of extrafusal fibres is completed by birth.

Intrafusal fibres assemble in a similar manner. At the 34- to 38-day foetal stage developing spindles consist of a single primary myotube containing a small accumulation of myonuclei beneath the terminals of the la afferent axon. Simple motor nerve terminals also innervate this myotube, which will ultimately become the bag2 fibre of the mature spindle. Secondary intrafusal myotubes then assemble beneath the basal lamina of the primary bag2 myotube, in the order presumptive bagi, long-chain, intermediate-chain and typical-chain fibres. Their assembly begins at the equator, beneath the sensory terminals, and spreads to the poles. The bagi and long-chain myotubes separate from the bag2 in the spindle pole prior to the development of the other chain fibres. The assembly of intrafusal fibres is completed by birth. The periaxial space begins to develop in the first postnatal week.

The development of tandem spindles containing b2c units is described. The role of sensory and motor innervation in the assembly and differentiation of mammalian intrafusal fibres is discussed.
Mutational analysis of patterning of oral structures in Tetrahymena: II. A graded basis for the individuality of intracellular structural arrays
Authors: Frankel Joseph , Nelsen E. Marlo , Bakowska Julita , Jenkins Leslie M.
Published: April 2021

The ciliary arrays of the oral apparatus of the ciliated protozoan Tetrahymena thermophila each have their own unique ‘pattern signature’, which varies little so long as the number of arrays remains the same. In this study, we analyse the consequence of increases in the number of these arrays (membranelles) brought about by certain mutations. In oral apparatuses of mutant cells, the addition of a membranelle is associated with specific alterations in at least one of the other membranelles. The features that are altered include the relative lengths of membranelles, the state of ciliation of basal bodies located at specific positions within these membranelles, and the spatial configurations resulting from displacement of ciliary units during late oral development. The final organization of each membranelle depends upon its relative position along the length of the oral apparatus. This indicates that the membranelles are not individually ‘named’ by the organism, and suggests that the unit of pattern organization is the membranelle field as a whole. In the Discussion, we consider means for testing whether the same underlying idea might also apply to multicellular systems, such as the vertebrate limb, in which spatially ordered differences appear to be superimposed upon a fundamental repeating pattern.
Effects of radius—ulna removal on forelimb regeneration in Xenopus laevis froglets
Authors: Korneluk Robert G. , Liversage Richard A.
Published: April 2021

Regeneration of boneless amputated forearms of adult newts was found to progress at a rate and to a degree comparable to amputated control limbs in which stump bones were not removed. In contrast, regeneration of boneless amputated Xenopus froglet forearms was significantly delayed and did not occur until two to three weeks following amputation. This is in comparison with the initiation of distal cartilage formation observed one week postamputation in control forelimbs of Xenopus froglets. The regeneration of cartilage in boneless forearms of adult newts was found to occur distal to the amputation level. In contrast, distal as well as proximal (centripetal) regeneration of cartilage was observed in the amputated boneless forearms of Xenopus. In froglets and newts, unamputated forelimbs in which forearm bones were extirpated did not initiate cartilage regeneration. Our findings support the hypothesis that forelimb regeneration in Xenopus froglets is primarily a tissue response. In comparison, limb regeneration in the adult newt is predominantly an epimorphic response.
The distribution of cytoplasmic actin in mouse 8-cell blastomeres
Authors: Johnson M. H. , Maro B.
Published: April 2021

Three non-homogeneous patterns of cytoplasmic actin distribution have been demonstrated in pairs of 8-cell blastomeres. Newly formed blastomeres showed an actin distribution associated with the remnant of the previous mitotic spindle. Subsequently blastomeres showed a zonal clearing of actin from regions of intercellular contact, the extent of the clearing increasing with the extent of contact. A polarized distribution of actin was evident from the early to mid 8-cell stage and coincided with the movement of nuclei towards the point of intercellular contact. The detection of polar actin preceded by 2−4 h the detection of a surface polarity as assessed by the FITC-Con A binding pattern and the distribution of cortical microvillous actin. However, once a surface pole of microvilli had formed, it persisted under conditions which led to loss of polar cytoplasmic actin. Incubation in cytochalasin D (CCD) resulted in a dispersed homogeneous pattern of actin distribution but did not prevent the formation of surface poles as assessed both by the Con A binding pattern and detection of polar microvilli. However, the poles formed were less clearly defined and the density and length of microvilli within them was variable. Moreover, when CCD was added early during the 8-cell stage the position of the poles was frequently not on an axis perpendicular to the point of intercellular contact. Cytochalasin D also affected the movement of the nucleus that occurs during the process of polarization. On the basis of these experiments, we conclude that actin is likely to be involved in the events of polarization, but that its precise role remains to be determined.
Induction of hair follicles in mouse skin by rat vibrissa dermal papillae
Authors: Pisansarakit P. , Moore G. P. M.
Published: April 2021

Rat vibrissa dermal papillae were transplanted between the epidermis and dermis of isolated embryonic mouse skin and then grafted onto nude mice. The papillae induced the formation of hair follicles which were larger than those of the host skin but smaller than vibrissa follicles. The potential of isolated dermal papillae to induce follicles with characteristics of those from which the papillae originated is discussed. One of the major factors affecting the sizes of induced follicles may have been related to the splitting of the papilla mass and dispersal of the cells by invading cords of epidermal cells from the host skin during induction.
Branching morphogenesis in the avian lung: electron microscopic studies using cationic dyes
Authors: Gallagher Betty C.
Published: April 2021

The developing chick lung was examined in the electron microscope for intimate cell contacts between epithelium and mesenchyme, discontinuities in the basal lamina and substructure of the basement membrane. Cell filopodia were seen which crossed the basal lamina from both the epithelial and the mesenchymal cells. Ruthenium red and tannic acid staining of the basal lamina of the chick lung showed it to be thin and sometimes discontinuous at the tips compared to the more substantial basal lamina in the interbud areas. The bilaminar distribution of particles seen with ruthenium red is similar to those seen in the cornea and lens. With tannic acid staining, filaments could be seen which crossed the lamina lucida and connected with the lamina densa. Spikes perpendicular to the basal lamina were sometimes seen with a periodicity of approximately 110 nm. Alcian blue staining revealed structure similar to that seen by ruthenium red staining in the salivary and mammary glands, although the interparticle spacing was closer.

Collagen was located in areas of morphogenetic stability, as has been seen by other investigators in different tissues. Collagen was coated with granules (probably proteoglycan) at periodic intervals when stained with ruthenium red. The fibrils were oriented circumferentially around the mesobronchus and were assumed to continue into the bud, but the fibres curve laterally at the middle of a bud. This orientation is opposite to that seen by another investigator in the mouse lung.

In general, the observations made in the avian lung are similar to those seen in branching mammalian tissue. It is likely, therefore, that the chick lung uses strategies in its morphogenesis that are similar to those that have been elucidated previously in developing mammalian organs.
Positional signalling by Hensen’s node when grafted to the chick limb bud
Authors: Hornbruch Amata , Wolpert Lewis
Published: April 2021

Hensen’s node from stage 4 to stage 10 shows polarizing activity when grafted to the anterior margin of the chick limb bud. It can specify additional digits though its action is somewhat attenuated when compared with the effect of a grafted polarizing region. At stage 10 the activity disappears from the node and is found both posterior to the node and in the future wing region of the flank. The ability of Hensen’s node to generate a positional signal suggests that the signal in the limb and early embryo may be similar. The results support the view of the polarizing region as a discrete signalling region.
What do dissociated embryonic cells of the starfish, Asterina pectinifera, do to reconstruct bipinnaria larvae?
Authors: Yamanaka H. , Tanaka-Ohmura Y. , Dan-Sohkawa M.
Published: April 2021

The cellular events that take place during reconstruction of larval forms from dissociated embryonic cells of the starfish are investigated by thick and thin sections. Dissociated cells reaggregate, form an external epithelium (ectoderm), internal epithelial vesicles (endoderm), the blastocoel and the mesenchyme. The internal vesicles continue to fuse until there is only one large one suspended in the centre of the blastocoel. Eventually, the ectoderm invaginates at one or more sites and fuses with the endoderm to form blastopore(s).

Special emphasis is placed on the differences in cell behaviour during endoderm-to-endoderm and endoderm-to-ectoderm fusion.
Replacement of posterior by anterior endoderm reduces sterility in embryos from inverted eggs of Xenopus laevis
Authors: Cleine J. H.
Published: April 2021

The genital ridges of Xenopus laevis tadpoles reared from eggs kept in an inverted position contain less than 40 % of the number of primordial germ cells (PGCs) of controls (Cleine & Dixon, 1985). It has been suggested that this reduction is caused by the germ cells’ ectopic position in the anterior endoderm of larvae from inverted eggs, from where they may be unable to migrate into the genital ridges (Cleine & Dixon, 1985). This hypothesis is tested here by interchanging anterior and posterior endodermal grafts between pairs of inverted embryos at the early tailbud stage. Replacement of anterior by posterior endoderm has no effect but replacement of posterior by anterior endoderm increases the number of PGCs in the genital ridges and significantly reduces the proportion of sterile embryos. In a control series, in which the same type of grafting was done with normal embryos, replacement of posterior by anterior endoderm reduced the number of germ cells to almost zero, but replacement of anterior by posterior endoderm nearly doubled it. These findings are explained in terms of the distribution of the germ cells in the endoderm at the time of grafting. The results firstly show that the position of the germ cells is crucial to successful migration and secondly they support the notion that germ plasm has a determinative role during early germ cell differentiation.