bluuebunny/crossref_metadata_2025 huggingface dataset:
The response of the brachial ventral horn of Xenopus laevis to forelimb amputation during development
Authors: Fortune Joanne E. , Blackler Antonie W.
Published: April 2021

The normal development of the brachial ventral horn of the frog Xenopus laevis and the response of the brachial ventral horn to complete forelimb extirpation at five developmental stages were assessed histologically. Differentiation of brachial ventral horn neurons occurred in pre-metamorphic tadpoles between stages 52/53 and 57. Mean cell number in the brachial ventral horn reached a peak of 2576 (S.E.M. = ± 269, n = 2) per side of the spinal cord at stage 55 and decreased to 1070 (S.E.M. = ± 35, n = 7) by the end of metamorphosis. Cell degeneration was presumed to be the mode of cell loss since it was most prevalent during the period of rapid decrease in cell numbers. The response of the ventral horn to forelimb removal varied with the stage of the animal at amputation. Following amputation at stage 52/53 or 54 the ipsilateral ventral horn neurons appeared less differentiated than those on the control side and a rapid cell loss of about 80% occurred on the operated side. These effects occurred more rapidly after ablation at stage 54 than at stage 52/53. Amputation at stage 58, 61, or 66 caused chromatolysis in the ventral horn, a period of relative cell excess on the operated side, and a delayed neuronal loss of 32–66%. It was concluded that excess cell degeneration accounted for cell loss and that suppression of normal neuronal degeneration caused the relative cell excess on the operated side. The data indicate that the brachial ventral horn was indifferent to the periphery before stage 54, was quickly affected by limb removal between stages 54 and 58, and by stage 58 had entered a phase in which a delay preceded cell death. No forelimb regeneration occurred.
Three-dimensional anatomy of the 8-day mouse conceptus: a study by scanning electron microscopy
Authors: Tamarin A. , Boyde A.
Published: April 2021

The three-dimensional anatomy of the 8-day mouse conceptus was studied by scanning electron microscopy aided by microdissection within the microscope specimen chamber. Attention was given to the relationship of the extra-embryonic membranes and their subtended compartments and particular emphasis was placed on the ‘inverted’ condition of the embryo at this stage of development.

The main points brought forth in this study are: the five basic brain segments are discernible on the basis of surface contours;the cervical fold, extending from the ventrum of themetencephalon to the so ma top leu re, forms a partition which separates the branchial region from the rest of the amniotic space;the procephaiic membrane bifurcates in a vertical plane to form the splanchnopleure andsomatopleure lateral to the forebrain, and it bifurcates horizontally to form the dorsal and ventral coverings of the pericardial coelom;the antrum of the pericardial-peritoneal canal opens into the lateral coelom posterior to the cervical fold;the midgut of the embryo is delineated laterally by longitudinal grooves connecting the foregut and hindgut antra;embryonic ectoderm in the neural-fold region is formed by a single layer of pseudostratified columnar cells;the allantois is hollow near its base and the inner surface is formed by a discontinuous layer of squamous cells;blood islands in the extra-embryonic mesoderm form a ring of bulges around the middle of the exocoel.

Other structures such as the ectopiacental cavity, the ectoplacental cone and the parietal capsule are also described.
Ultrastructural observations of preimplantation stages of the sheep
Authors: Calarco Patricia G. , Mclaren Anne
Published: April 2021

Sheep embryos were examined with the electron microscope in order to characterize their organelles and the changes that occur during the preimplantation period. The first sign of differentiation of trophoblast cells was the appearance of junctions between external cells at the 16-cell stage. Nucleoli developed a granular component suggesting the synthesis of ribosomal RNA at the 16-cell stage also. Centrioles were seen as early as the 8-cell stage. Jntra-cytoplasmic vesicles were present in large numbers in all cleavage stages but disappeared at blastulation. Mitochondria progressed from a very electron-dense hook-or U-shaped form with a few cristae to a cylindrical or spherical form of light density with many transverse cristae. Microvilli were not seen until the blastocyst stage and then only on the exterior surface of the trophoblast cells. Crystalloid or virus inclusions were not observed. It was concluded that the fine structure and developmental changes in the early sheep embryo are very similar to those of other mammalian species.
Cell patterning in migrating slugs of Dictyostelium discoideum
Authors: Sampson J.
Published: April 2021

When front quarters of migrating slugs of Dictyostelium discoideum are isolated by surgery and induced to fruit immediately they produce fruiting bodies with disproportionately large stalks (Raper, 1940). The data in this communication show that the ‘stalky’ character of fruits derived from front quarters persists even if the cells of the front quarters are disaggregated and hence have to reaggregate before fruiting. The data also demonstrate that fruits derived from rear quarters of slugs have disproportionately large spore heads, and that this effect becomes more pronounced with increasing age of the slugs. These observations support the view that the cells of the front and rear of migrating slugs are to some extent committed to different fates.
The structure of the mitochondrial cloud of Xenopus laevis oocytes
Authors: Billett F. S. , Adam Elizabeth
Published: April 2021

The ultrastructure of the mitochondrial cloud (Balbiani body) of the pre-vitellogenic oocytes of Xenopus laevis has been examined using transmission and stereoscan electron microscopy. Examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands of mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 μm in diameter, contain relatively more vesicles. Using a standard electron microscope at 100 kV very long and coursing arrays of mitochondrial profiles can be detected. The presence of very long mitochondrial elements has been confirmed using a high voltage microscope operating at 500–1000 kV. Stereoscan preparations, isolated from pre-vitellogenic oocytes, lend some support to the view that the mitochondrial cloud may consist of a mass of long filamentous mitochondria and the possibility that there are large continuous regions of mitochondrial material cannot be ruled out.
Binding and uptake of trypan blue by developing oocytes of Locusta migratoria migratorioides
Authors: Wajc Esther , Bakker-Grunwald Tilly , Applebaum Shalom W.
Published: April 2021

Resorbing oocytes are heavily stained by trypan blue injected into the haemolymph; this selves as a basis for a quick and convenient method for measuring the degree of resorption. Oocytes in the beginning of their development are most susceptible towards resorptive tendencies.

The uptake of trypan blue by normally developing oocytes is proportional to the oocyte surface. From ‘double-marker’ experiments, in which trypan blue is injected into the haemolymph together with [3H]inulin (which does not bind to the oocyte membrane) it is estimated that the contribution of binding in the interiorization of trypan blue is in the order of 80 %, under the conditions given.

In vitro incubations show the interaction of trypan blue with the membrane to be electrostatic in nature.
The eversion and differentiation of Drosophila melanogaster leg and wing imaginai discs cultured in vitro with an optimal concentration of β-ecdysone
Authors: Milner Martin J.
Published: April 2021

The stages of the eversion and differentiation of prothoracic leg and wing discs of Drosophila melanogaster, in Shields and Sang’s medium 3, are described. The range of specific imaginai structures produced, including patterns of sensilla trichodea and sensilla campaniformia, are noted, and the relationship of these structures to those differentiated in situ is discussed.
Regulation of pre-natal haemopoiesis: evidence for negative feedback control of erythropoiesis in the foetal mouse
Authors: Cole R. J. , Regan T.
Published: April 2021

The effects of medium conditioned by erythrocytes on in vitro differentiation of mouse prenatal erythroblasts were examined. Haem synthesis was inversely proportional to the concentration of erythrocyte-conditioned medium (ECM) in either presence or absence of erythropoietin (EP), but concentrations of ECM which limited haem synthesis to 50% of normal had no effect on changes in erythroblast numbers. ECM reduced uridine incorpora-tion into RNA and limited the rise in incorporation due to stimulation by EP. ECM enhanced thymidine incorporation into DNA. This enhancement was additive with that due to EP, but appeared earlier. Thymidine labelling indices of liver cells were not changed by ECM in vitro. Serum from polycythaemic animals limited haem synthesis by EP stimulated foetal liver cells in vitro. These observations provide evidence for susceptibility of foetal liver erythroblasts to negative feedback control of differentiation, dependent on the concentration of circulating erythrocytes. Characteristic changes in kinetics of prenatal erythropoiesis in vivo can also be related to increasing erythrocyte concentration.
The effect of synchronous and asynchronous egg transfer on foetal weight in mice selected for large and small body size
Authors: Aitken R. J. , Bowman P. , Gauld I.
Published: April 2021

The weight difference between large, small and unselected strains of mice were maintained when blastocysts of each genotype were transferred to unselected control recipients, suggesting that foetal genotype was an important factor in determining prenatal body size. The asynchronous transfer of large, small and unselected embryos resulted in a highly significant (P < 0·001) elevation of foetal weight compared with synchronously transferred groups, genetically small mice attaining a foetal weight greater than the normal large strain. This result suggested that foetal genotype did not limit the capacity of each strain for prenatal growth. It is postulated that foetal genotype exercises its control over embryonic growth by affecting the state of embryonic development at implantation.
Pattern and polarity of sclerites in adult abdominal segments of Calliphora erythrocephala (Diptera): anlage rotation experiments
Authors: Pearson M. J.
Published: April 2021

The anlagen of imaginal histoblasts in the abdominal segments of Calliphora (higher Diptera) present an interesting problem, which bears on recent concepts employed in the consideration of spatial patterning in insects. They differ from imaginal discs with respect to larval organization and activity, and in the absence of the progressive pattern of genetic determination during the larval period, characteristic of imaginal discs. How is the adult pattern in the abdominal segments determined?

The experiments presented here seek to clarify the spatial parameters involved in control of adult pattern and polarity in the adult segment. A series of 180° rotations of hypodermal grafts bearing the anlagen singly, or in combination, or of larval intersegmental hypodermis, indicate that polarity is determined within the anlagen, through interaction with local larval epidermis either before or during histoblast migration. The nature of the sclerites, too, is primarily carried by the anlagen rather than determined by intersegmental information.

The whole question of ‘determination of polarity’ is set out more carefully than hitherto in the light of (a) observations of the movement of epidermal cells in other systems in response to disturbance of pattern, and (b) the obvious vectorial nature of the phenomenon, which cannot be a genetic matter, but one of cell axes and of the relation of cells to segment/organism.

The demonstration that (i) hemitergite and hemisternite are primarily determined by the anlagen themselves, and not by larval intersegmental membranes; and (ii) evidence indicates an influence of epidermal cells of the larva on the differentiation (as well as polarity) of imaginal histoblasts, leads to the conclusion that neither of two models considered will account for the establishment of the adult abdominal pattern among the histoblasts at metamorphosis. These models are (a) of a segmental gradient, set by the intersegmental boundaries of the previous instar, to which imaginal cells respond by interpretation of positional information; and (b) of progressive compartmentalization of pattern within the anlagen, without reference to epidermal context.
An experimental investigation into the early development of the chick elbow joint
Authors: Holder N.
Published: April 2021

The theory that differential growth of opposed chondrogenic centres is important in early joint formation has been tested experimentally by removing structures in relation to the chick elbow joint. The humerus and its cap of differentiating joint cells were found to develop independently of structures distal to them. Removal of the presumptive joint region at early stages resulted in fusion of the humerus with the radius and ulna. Results are discussed in terms of concepts concerning pattern formation of cell types in the early wing-bud.
Redifferentiation, cellular elongation and the cell surface during lens regeneration
Authors: Hornsby Sharon , Zalik Sara E.
Published: April 2021

Dorsal irises from normal and lentectomized eyes of the newt Notophthalmus viridescens were cultured in vitro in the presence of colchicine (1·25 × 10−3 to 2·5 × 10−6 M), vinblastine sulfate (4·4 × 10−8) and cytochalasin B (20 μg/ml). Explants were treated for 24 h and implanted into host eyes of previously lentectomized newts. In regenerates treated with colchicine at stages prior to the onset of lens fiber formation, cellular elongation was inhibited or considerably delayed. Cytochalasin B has no effect on lens fiber differentiation when compared with regenerates treated with its solvent, dimethyl sulfoxide. Colchicine-treated regenerates showed no detectable fluorescence when stained with anti-newt lens fluorescent antibodies, suggesting that cells in which cellular elongation was inhibited were unable to synthesize lens specific proteins. Ultrastructural observations of elongating lens regenerate cells showed microtubules present in the cytoplasm parallel to the axis of elongation. Microtubules were not observed in depigmented cells from colchicine-treated regenerates. Characteristic vinblastine-induced microtubule crystals were present in depigmented cells from vinblastine-treated regenerates. Experiments using cell electrophoresis showed that neuraminidase-sensitive groups were detectable at the ionic double layer of cells from implanted regenerates at stages where lens fiber differentiation occurs. Cells from colchicine-treated regenerates showed no significant reduction of their electrophoretic mobility after neuraminidase treatment. This suggests that the appearance of some cell surface components in the redifferentiated cell may also be colchicine sensitive and probably mediated by microtubules.
Recent findings in oogenesis ofDrosophila melanogasterIII. Lysosomes and yolk platelets
Authors: Giorgi F. , Jacob J.
Published: April 2021

The role played by the vitellogenic oocytes of Drosophila melanogaster in relation to the elaboration of material taken from the haemolymph is examined by ultrastructural cytochemistry.

As revealed by the Gomori procedure, acid phosphatase occurs widely over the forming yolk platelets of the cortical and central ooplasm. A number of Golgi apparatuses in the cortical ooplasm are also positively stained with lead precipitates.

With the proceeding of the ovarian development it becomes progressively more difficult to demonstrate cytochemically the enzyme over the yolk platelets. In stage 9-10 chambers the acid phosphatase is restricted to the so-called associated body, while the rest of the yolk platelet appears devoid of lead deposits.

By using a osmium zinc iodide (OZ1) complex as a preferential staining method for the Golgi apparatus, it has been shown that, apart from the apparatus itself, a number of OZI deposits occur over the superficial layer of the forming yolk platelets. When mature yolk plate-lets are formed at later stages, the OZI deposits in the yolk platelets come to be restricted to the cap-like region of the superficial layer which contains the associated body.

In vitellogenic oocytes, both the internal lining of the limiting membrane of the forming yolk platelets and the associated body of the mature yolk platelets react positively, to cyto-chemical methods to demonstrate carbohydrates.

The present findings are interpreted as indicating the involvement of lysosomal enzymes in the process of maturation of the yolk material. The suggestion is also made that such an involvement is required to accomplish a selective hydrolysis of those blood proteins which have been taken in by vitellogenic oocytes along with yolk precursors.
Further studies on skull growth in achondroplasie (cn) mice
Authors: Brewer A. K. , Johnson D. R. , Moore W. J.
Published: April 2021

The morphology of the basioccipital, basisphenoid and mandibular bones in achondroplasie (cn/cri) mice was compared with that of normal siblings. The two bones of the cranial base were markedly reduced in length but not in width. The percentage reduction in the basisphenoid was twice that in the basioccipital bone and of the same magnitude as that previously observed in the long bones of the limbs. This difference may arise because the basisphenoid, like the long bones, grows in length from two cartilaginous growth sites while the basioccipital grows from one cartilaginous and one periosteal site. The mandible of the cn/cn mice was also reduced in size, although to a lesser extent than were the cranial bones and without the ensuing disproportion. The scale of the mandibular changes suggests that they are largely attributable to regulatory responses to the shortened cranium. The finding that the condylar cartilage of the cnjcn mice is reduced in thickness indicates, however, that the cn gene may have a direct effect on condylar chondrocytes.
Intercellular contacts at the epithelial-mesenchymal interface of the developing rat submandibular gland in vitro
Authors: Cutler Leslie S.
Published: April 2021

An ultrastructural study of the development of the rat submandibular gland (SMG) anlage in vitro was undertaken to determine if epithelial-mesenchymal and epithelial-nerve contacts were integral events in the differentiation of the gland in vitro as they are in vivo. SMG rudiments were removed at the stalk-bulb stage (15 days in utero) and cultured for 6 days on a millipore filter in supplemented McCoy’s 5A media. Rudiments were taken at daily intervals, fixed and processed for electron microscopy. The overall development of the explanted rudiments closely paralleled their maturation in vivo although cultured glands lagged 24-36 h behind their normal counterparts. Direct epithelial-mesenchymal contacts were seen after the morphogenetic patterning of the gland bad been established but prior to functional differentiation of the rudiment. Epithelial-nerve contacts were not seen although healthy axons were seen in the stroma throughout the culture period. The study indicates that epithelial-nerve contacts are probably not required for morphogenesis of cytodifferentiation of the rat SMG. However, direct epithelial-mesenchymal contacts appear to be an integral part of the developmental sequence of the rat SMG.
In vitro chondrogenesis in mouse limb mesenchymal cells; changes in ultrastructure and proteoglycan synthesis
Authors: Royal Patricia D. , Goetinck Paul F.
Published: April 2021

Mouse chondrocytes were allowed to differentiate from 11-day dissociated limb-bud mesenchymal cells cultured at high density. Over a period of 5 days in culture these cells differentiated from a culture containing a population of mesenchymal cells and myoblasts into one containing cartilage nodules. Chondrogenesis, as demonstrated by the sulfated proteoglycans (PGS) synthesized, was monitored quantitatively and qualitatively by molecular sieve chromatography on polyacrylamide and 1 % agarose columns, and by examination of cultures with phase contrast and transmission electron microscopy. Chromatographically, the PGS synthesized could be separated into three fractions (la, lb, and II). In the 24 h cultures a small amount of PGS was synthesized and was predominantly of fraction II. As time in culture elapsed there was, concomitant with chondrogenesis, an increase in PGS synthesis with a preferential increase in peaks la and lb. Peaks la and Ib were shown to have an aggregate-subunit relationship. Fraction la could be dissociated to chromatograph at the Ib position, but the disaggregation was not reversible. Digestion of the various chromato-graphic fractions extracted from the cell layer of the 5-day cultures by chondroitinase ABC and AC revealed that fraction I contained 80 % chondroitin-4-sulfate, 20 % chondroitin-6-sulfate, and negligible amounts of dermatan sulfate, while chondroitinase ABC and AC digestion of fraction II showed 55 % chondroitin-4-sulfate, 0-3-7 % chondroitin-6-sulfate, and 20 % dermatan sulfate. Cytological studies revealed that as nodule development pro-gressed there was a concurrent development of the endoplasmic reticulum and extracellular matrix, and a reduction in mitochondria.
Inhibition of Glyceraldehyde Phosphate Dehydrogenase by Salts other than Lithium Chloride
Authors: Ham Richard G. , Eakin Robert E.
Published: April 2021

Lallier (1954) has shown that 0·4 M lithium chloride strongly inactivates glyceraldehyde phosphate dehydrogenase—a finding which might partially explain some of the developmental changes found in lithium-treated embryos. In an attempt to establish an enzymatic basis for the morphological effects of lithium ion on Hydra which have been observed in this laboratory (Ham & Eakin, 1955), we have repeated the enzyme study with lithium chloride and extended it to include a number of other salts as controls.
Compensation in the Remaining Pronephros of Triturus after Unilateral Pronephrectomy
Authors: Fox H.
Published: April 2021

Larvae of Triturus cristatus survive unilateral pronephrectomy at the early caudal bud stage. The remaining pronephros compensates and in the main the results confirm those of Howland (1921) on Amblystoma punctatum. A comparison between control and operated specimens by an analysis of covariance showed that the pronephros of the pronephrectomized group had significantly higher values for all the measurements made, within the range studied (5·5–7·5 mm. nose to cloaca; 10–17 days after operation). The measurements include the means of: the nuclear population; total cell volume; total lumina volume; overall volume of pronephros; internal surface area of tubules; antero-posterior length of pronephros; volume of individual cell of pronephros. The slopes of the regression lines in the two groups demonstrate that in all measurements except that of individual cell volume, the pronephroi of the operated group grow faster than those of the controls. During development the individual cell volume significantly falls in the control pronephroi, in contrast to the operated group where the mean volume does not significantly change. The duct of the compensating pronephros is expanded in cross-section along its entire length. The duct of the operated side atrophies from the anterior region towards the posterior, becoming a degenerate strand of cells, subsequently losing its lumen throughout its length.
Factors Affecting Vertebral Variation in Mice: 3. Maternal Effects in Reciprocal Crosses
Authors: McLaren Anne , Michie Donald
Published: April 2021

All six possible reciprocal crosses were made between C57BL, C3H/He, and C3H/Bi mice. The last group differs from the other two in having predominantly 5 lumbar vertebrae. The offspring of the C3H/He ♀ ♀ × C57BL ♂ ♂ cross had a lower average number of vertebrae than either parental population. The other crosses gave offspring falling within the range between the parental means. There was a significant difference between reciprocals in the two pairs of inter-strain crosses. The F1 offspring tended towards the vertebral type of the maternal strain. No significant effect was apparent in the inter-substrain cross. The evidence from the reciprocal crosses suggests that, although the C3H/He substrain has since 1930 diverged from the C3H/Bi substrain in the direction of a higher number of lumbar vertebrae, the two substrains continue to show similar maternal effects when crossed with the C57BL strain. Hence the genetic control of maternal influence upon vertebral type can operate independently of the genetic control of vertebral type itself.
Growth and Function in the Foetal Liver
Authors: Dick D. A. T.
Published: April 2021

A method is described for estimating the total population of hepatic cells in the liver of a sheep foetus. Use of this method has shown that during development there is a real decrease in the relative number of hepatic cells in the sheep foetus. The relative number of hepatic cells in the foetus is directly proportional to the specific growth-rate of the foetal body. It is suggested that the relative number of hepatic cells in the foetus is determined by functional requirements, partly to perform normal metabolic processes and partly to maintain growth.
On the Neural Crest of the Lamprey Embryo
Authors: Newth D. R.
Published: April 2021

Those parts of the branchial basket of the ammocoete larva that have chondrified by the time the animal is 7 mm. long are of neural crest origin. Those parts of the trabeculae cranii (anterior parachordals) of the ammocoete that have chondrified by this time are not of neural crest origin, nor do they depend upon the presence of the crest for their normal formation. The factors governing the development of the visceral arch skeleton are, as far as is known, equivalent to those operating in Amphibia. The pre-migratory crest of the branchial region is competent to form cartilage, but not determined to do so. It is probable that the normal development of the visceral arch skeleton is dependent upon the early establishment of contact between branchial ectoderm and endoderm. The cranial neural crest is necessary for the normal development of the ventral arteries of the head. In its absence they are much dilated. It is probable that the walls of these vessels are normally, at least in part, of crest origin. In the absence of the neural crest in the trunk region the dorsal fin of the larva is not formed. Absence of the neural crest leads to absence of the dorsal root ganglia in the trunk and, usually, to a reduction in size of those of the head. The neural crest is a source, if not the only source, of larval melanophores.
Differences in rotation-mediated aggregation between wild-type and homozygous Brachyury (T) cells
Authors: Yanagisawa K. O. , Fujimoto H.
Published: April 2021

Rotation-mediated aggregation was studied in dissociated cells from 9- and 10-day-old (‘12-40 somite’ stage) mouse embryos homozygous for the Brachyury (T) mutation. Average diameter of the aggregates formed by wild-type cells increased up to the 27-somite stage. In T/T cells, however, a completely different pattern was observed. The disappearance of free cells and the process of aggregate formation were also followed. The possibility that T/T cells have different adhesive properties from +/+ cells is discussed.
Regulation of deficiencies along the proximal distal axis of the chick wing-bud: a quantitative analysis
Authors: Summerbell Dennis
Published: April 2021

The wing-bud shows zero regulation following removal of a whole slice of the proximaldistal axis from stage 22 or later. Prior to this it is possible that it may show some regulation. Some of the apparent regulation may be explained by the way in which the limb grows. The bud never shows perfect size regulation or morphallaxis. The proximal-distal axis of the bud between shoulder and wrist expands uniformly from stage 20.
Waves and periodic events during primitive streak formation in the chick
Authors: Stern Claudio D. , Goodwin Brian C.
Published: April 2021

Morphogenetic movements occurring during formation of the primitive streak in the chick embryo are of a periodic nature, with a mean frequency of one pulse every 2·6 min. The period of the oscillatory movement is shown to be temperature-dependent. The onset of these pulses of movement can be seen as a slow wave starting at the posterior end of the embryo and making its way towards the anterior end. An interpretation of this behaviour is discussed.
On the differentiation of prospective ectoderm to a ciliated cell pattern in embryos ofAmbystoma mexicanum
Authors: Landström Ulf
Published: April 2021

The differentiation of the ectoderm in Ambystoma mexicanum (Harrison stage 26-27) was examined under in vivo and in vitro conditions by scanning electron microscopy under different experimental conditions. About one out of three flank epidermal cells was found to be ciliated in the undisturbed or control embryos. The shape of ciliated cells in the explants from the animal region was only slightly affected. In no case was it possible to find two adjacent ciliated cells, implying that these cells prevent the appearance of cilia in the cells in direct contact. Transformation to ciliated cells is suppressed by hypertonicity but favoured in a hypotonic medium. The differentiation of epidermis is also dependent upon the synthesis of RNA and some kind of sulphated glucosaminoglycan, corroborated by the inhibitory effect of actinomycin and selenate.

The differences between the test series and the controls are discussed with regard to factors controlling embryonic epidermal differentiation.
Limb-somite relationship: origin of the limb musculature
Authors: Chevallier Alain , Kieny Madeleine , Mauger Annick
Published: April 2021

Quail-to-chick grafting experiments performed during the third day of incubation demonstrate that somites can contribute to limb development. In orthotopic recombinations, migrating cells originating from the grafted unsegmented or segmented somitic mesoderm adjacent to the wing or leg field end up in the musculature respectively of the wing or the leg, where they express exclusively myogenic properties. Thus, in these heterospecific recombinations, the anatomical muscle has a double origin: muscle bulk of somitic origin; tendons and connective tissues of somatopleural origin. Similar features are observed in heterotopic recombinations with (segmented or unsegmented) somitic mesoderm located cranially or caudally to the limb levels.

In the reverse chick-to-quail grafting experiments, the somitic participation to the limb mesoderm can also be observed. But it is less regular than that obtained in the quail-to-chick recombinations, and the muscle bulk is made up in various proportions of graft-originated somitic cells and of host somatopleural cells.

The possible existence of juxtaposed and interdigitated myogenic and tendinogenic compartments is discussed in view of the dissimilarity between the results of the two kinds of heterospecific recombinations.
The ultrastructure of the mesenchymal element of the palatal shelves of the fetal mouse
Authors: Innes Peter B.
Published: April 2021

The ultrastructure of the mesenchymal element of the palatal shelves of C3H mouse embryos aged 13 days 18 h and 14 days 18 h in utero was studied. At 13 days 18 h the mesenchyme showed a high density of cells. The cells contained a well developed system of rough endoplasmic reticulum and Golgi complex; many were ciliated and multi-vesicular structures were common. By 14 days 18 h, many of the mesenchymal cells contained large numbers of glycogen particles. These cells also possessed long cytoplasmic processes which sometimes were seen to contain many filaments 5–7 nmin diameter. Some of the cells also contained a fine filamentous network just below the plasma membrane. Developing mononuclear and binucleate skeletal muscle cells containing myofibrils were present in the posterior region of the palate, with groups of cells which consisted of typical peripheral neurons and their surrounding satellite cells. Both the muscle and nerve cells were only observed in the 14 day 18 h material. It is suggested that both the myofibrils in the skeletal muscle cells and the filamentous network in the mesenchymal cells may play a role in shelf reorientation.
Growth and sexual differentiation in the gonads of chick and duck embryos
Authors: Gasc Jean-Marie
Published: April 2021

The sex-dependent morphological asymmetry between gonads of bird embryos is generally considered to represent the critical point at which the definitive pattern of sexual differentiation is established. A quantitative study of growth in gonads of chick embryos (6- to 11-day-old) and of duck embryos (7- to 11-day-old) has been carried out in order to clarify in what manner growth of gonads is involved in sexual differentiation. Growth has been estimated by the determination of total protein and DNA content, and of DNA synthesis [3H]Tdr incorporation in vitro).

Increase of protein and DNA content follow different growth curves according to the sex and the laterality of gonads. As early as day 6 (chick) or day 7 (duck) significant differences of protein content exist between gonads: left > right in both sex embryos, and male > female on both sides. Differences in DNA content of gonads are large even at the earliest stages. In the 6-day-old chick embryo both testes contain less DNA than the left ovary and more DNA than the right ovary. In the 7-day-old duck embryo both testes contain the same amount of DNA as the left ovary and twice as much DNA as the right ovary. Consequently, the protein/ DNA ratio has a different value according to the sex of the gonad.

In the 6-day-old chick embryo and in the 7-day-old duck embryo absolute values of DNA synthesis (cpm/gonad) are higher in left gonads than in right gonads, and higher in male than in female gonads. When calculated as a ratio to the protein content (cpm/protein) DNA synthesis is lower in the left ovary than in the three other types of gonads, both in chick and duck embryos. When calculated as a ratio to the DNA content of gonads (cpm/DNA), DNA synthesis is lower in the left ovary than in the three other gonads in the chick, and lower in the left ovary and in testes than in the right ovary in the duck.

The results show that growth of gonads is sex-dependent at a very early stage. The meaning of this sex character is discussed with special reference to the role of steroid hormone secretion.
Temporal and spatial patterns of the synthesis of tissue-specific polypeptides in the preimplantation mouse embryo
Authors: Handyside A. H. , Johnson M. H.
Published: April 2021

Mouse embryos at different morphological stages in the transition from morula to blastocyst were analysed for the qualitative pattern of their polypeptide synthesis. The first appearance of the individual species of polypeptides specific to trophectoderm or ICM occurred progressively over this developmental period. Populations of inside cells recovered from morulae and early blastocysts synthesized those polypeptides previously shown to be characteristic of ICMs at days, but not those characteristic of trophectoderm.
Scanning electron microscopy of the developing chick anterior corneal epithelium
Authors: Waggoner Phillip R.
Published: April 2021

The anterior corneal epithelium of the developing chick was observed with the scanning electron microscope at various stages of development. In the earlier stages, up to about 15 days of incubation, the cells are characterized by regular polygonal outlines and a proliferation of microvilli on the surface. The microvilli then begin to coalesce and flatten so that the surface is rather smooth by about 19 days of incubation. Just prior to hatching, however, the cells begin to round up and once again become covered by microvilli. The cells then lift off the surface and expose the underlying cells. After hatching, the surface cells lose the synchrony of development that characterized the embryo and are found in various stages of senescence. The cells eventually lose their regular polygonal outlines and the corneal surface takes on a patchwork appearance.
A study of spermatozoan defects in wild-type and T:t-bearing mice
Authors: Hillman Nina , Nadijcka Mary
Published: April 2021

A comparative light and electron microscopic study was done on cauda epididymal spermatozoa from + /tx, T/ +, T/tx, C5TBL/6J, BALB/c and randomly breeding Swiss Albino mice. The results show that all of the males contain abnormal spermatozoa and that all contain the same types of defective gametes. No unique defect was found which can be correlated with the increased transmission frequency of the tx -bearing allele.
Isolation and characterization of flightless mutants in Drosophila melanogaster
Authors: Koana Takao , Hotta Yoshiki
Published: April 2021

Since animal behaviour is executed through neuronal circuits including sensory receptors and muscle, genes vital for their development and differentiation must be found among mutants having behavioural anomaly. After mutagenesis with ethyl methanesulphonate (EMS), we screened for X-linked flightless mutants of Drosophila melanogaster by using a column-type flight tester. Approximately 104 individuals were screened and 21 mutant genes were isolated. Chromosomal mapping and complementation experiments revealed that they belong to 15 cistrons randomly located on X chromosome, three cistrons having more than two alleles. Two of the isolated mutants (fltO2 and fltH, which are recessive both behaviourally and morphologically) were analysed with the mosaic fate mapping technique, and both were found to have their primary foci in mesodermal region of blastoderm, suggesting that the genes exert their primary effect in indirect flight muscle.

Electronmicroscopic studies on the muscles from four alleles of the fltO2 cistron revealed an abnormality in myofibrillar arrangement. A possible deficit within Z-band components is discussed in relation to wings-up B mutants. The indirect flight muscle of flltH was also examined, and it was found that sarcomere length and diameter of myofibrils were abnormal. It was postulated that a possible factor which controls size of myofibrils is defective in this mutant. These examples indicate the advantage of combining ultrastructural examination with genetic mosaic mapping technique.
Ultrastructural analysis of preimplantation lethal yellow(Ay/Ay)mouse embryos
Authors: Cizadlo Gerald R. , Granholm Nels H.
Published: April 2021

Embryos recovered at 62 and 80 h post coitum from reproductive tracts of yellow (Ay/a) and black (a/a) female mice mated to Ay/a males were examined ultrastructurally to define the developmental defect of lethal Ay homozygotes.

No abnormalities were observed in five embryos from control matings (♀ a/a × ♂ Ay/a). Of 24 morulae and blastocysts from Ay/a × Ay/a matings, six were observed to possess some morphological aberration. Two of the six abnormal embryos were morulae and contained isolated blastomeres which had developmental features typical of younger embryos; remaining cells of these embryos were normal. The third, an early blastocyst, contained a degenerating trophoblast cell; other cells of this embryo were also abnormal but not in an advanced stage of degeneration. The fourth abnormal embryo (late cleavage stage) was in an advanced stage of degeneration affectingall blastomeres. Finally, the remaining two abnormal morulae had a unique nucleolar morphology and an unusual abundance of intra-cisternal A particles.

Presumably, one or more of the six abnormal embryos from Ay/a × Ay/a matings were Ay homozygotes. However, no single ultrastructural alteration characteristic of Ay/AV embryos was found.
The paths and destinations of the induced ipsilateral retinal projection in goldfish
Authors: Easter Stephen S. , Schmidt John T. , Leber Steven M.
Published: April 2021

Adult goldfish had one tectal lobe removed surgically, and several months later, the eye contralateral to the missing tectum was injected with radioactive proline. Radioautographs of the brains were studied to trace the paths and termination sites of the optic fibers.

The optic tract decussated at the chiasm, as normally, but then ran caudally in a large neuroma on the tectum-less side of the brain. Substantial numbers of fibers left this neuroma to enter two or more of five commissures, through which they recrossed the midline. These commissures: transverse, minor, horizontal, posterior and ansate, ordinarily contain few or no optic fibers. All are normally linked with the tectum. Negligible numbers of aberrant optic fibers recrossed the midline elsewhere. On the intact side of the brain, ipsilateral to the injected eye, the optic fibers innervated some or all of the nuclei and areas normally served by contralateral retinal fibers. An earlier behavioral study of these same fish had shown that some of them made reversed optokinetic nystagmus in response to stripe movement seen by the eye projecting ipsilaterally; others failed to respond to stimuli through this eye. In all the reversed responders, a caudal group of retinal projection sites was labeled ipsilaterally. This included the basal optic nucleus and the caudal portions of nucleus dorsolateralis thalami and area pretectalis. In the non-responders, these targets were not labeled ipsilaterally. Together, these results suggest that one or more of these three sites is or are responsible for optokinetic nystagmus in normal goldfish.
Isolation and development of the inner cell mass after exposure of mouse embryos to calcium ionophore A23187
Authors: Surani M. Azim H. , Torchiana David , Barton Sheila C.
Published: April 2021

Compacted morulae and blastocysts were obtained from CBA, BALB/c and CFLP strains of mice. The embryos were incubated in medium containing 2 × 10−5 M or 2 × 10−6 M ionophore A 23187. With 2 × 10−6 M ionophore, morulae survived for up to 12 h showing slight decompaction. Normal development resumed when the morulae were explanted to fresh medium. There was no detectable effect on blastocysts. With 2 × 10−5 M ionophore, morulae survived for about 20 min and then extensive cell death occurred after this time. With blastocysts however, selective lysis of trophectoderm cells occurred after approximately 30 min following their swelling and vesiculation but the inner cell mass cells (ICM) remained apparently intact and viable. Nearly 80 % of the early blastocysts obtained 87 h post-ovulation and all of the late blastocysts used after 12 h in culture (99 h blastocysts) showed this response. Individual fluid accumulating cells were detected in a few isolated ICMs after their overnight culture in vitro, especially in those obtained from early blastocysts, but the majority of the ICMs did not have these cells. All aggregates of three to five ICMs, except one which reformed into a blastocyst, developed as embryoid bodies after 2 days in culture and these survived for up to 10 days; in some cases they developed into cystic embryoid bodies or attached to the culture dish displaying a variety of cell types. The development of the isolated ICMs in vivo was judged to be normal after their transfer to intact host blasto-cysts as these developed as chimaeric embryos to term.
Anatomical mapping of retino-tectal connections in developing and metamorphosed Xenopus: evidence for changing connections
Authors: Longley Alison
Published: April 2021

Neural connections between the eye and optic tectum in Xenopus laevis were anatomically traced by observing the tectal location of Wallerian degeneration after discrete retinal lesion. These retinotectal connections were mapped in post metamorphic frogs and tadpoles at stage 51, the stage at which retinal axons have grown into about the rostral one-half of the tectum. The course of the experimental degeneration was the same in frogs and tadpoles, but degeneration proceeded faster in the younger animals.

In the frogs, connections were ordered, with nasal retina mapping to the caudal part of the tectum and temporal retina mapping to the rostral tectum. In the tadpoles, within the innervated area at the rostral tectum, the retino-tectal connections were generally organized as in the adults, with the temporal retina mapping to the rostral part of the innervated tectum and nasal retina mapping primarily to the caudal part. But a portion of the nasal fibers consistently mapped to the far rostral tectum as well. Electron microscopic observations showed degenerating synaptic terminals at both rostral and caudal portions of the innervated tectum after lesion of just the nasal retina. Degeneration was not seen in control animals. These results indicate that some fibers (particularly from nasal retina) may shift their terminals caudally on the tectum to match tectal growth and produce the adult pattern of connections. If there is such connection readjustment, the ‘aberrant’ connections from nasal retina in tadpoles may be an indication of this process.
Serum-dependent avian skin differentiation in vitro: time sequence of induced events
Authors: Carinci P. , Stabellini G. , Becchetti E.
Published: April 2021

Information concerning the developmental mechanisms involved in skin differentiation have been mainly derived from in vitro experiments. We have previously observed that 6-day chick embryonic thigh skin keratinizes in vitro in chicken serum-containing medium, but does not do so in chick embryo extract-containing medium. This system seems adequate in many respects for investigating the mutual regulative relationship between epithelium and mesenchyme (so called epithelio-mesenchymal interactions).

We have therefore attempted better to define the time course of differentiative events and their dependence upon the time of serum administration.

Skin explants have been sequentially supplemented with differentiation-stimulating or non-stimulating nutrient, removed at different intervals and examined by histological and histochemical procedures.

Different epithelial and mesenchymal behaviour results according to serum supplementation time. Serum administered in the first 48 h of in vitro maintenance is unable to stimulate either the subsequent epidermal keratinization or the correlated changes in dermal histochemical pattern. On the other hand, serum-containing medium induces keratinization and changes in dermal intercellular composition (glycoproteins accumulate to a greater extent than glycosoaminoglycans, as does hyaluronic acid relative to chondroitin sulphuric acids), if added for only the second two days. In the last 48 h, serum may promote epidermal keratinization provided that in vitro incubation has been prolonged.

Administration of actinomycin D with serum in the second 48 h prevents epidermal keratinization and modifies dermal histochemical reactivity, but is ineffective if added in the last 48 h.

The above findings demonstrate that serum factor(s) stimulating epidermal differentiation act(s) on skin explants in the central incubation period and that correlatively mesenchyme acquires a characteristic histochemical pattern, supporting the possibility that the effect of serum may be mediated by changes in the composition of dermal ground substance.