bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidermal metaplasia of proamnionic epithelium induced by dorsal skin dermis in the chick embryo
Authors: Mizuno Takeo
Published: April 2021

Proamnionic epithelium of the chick embryo cultivated directly on Wolff and Haffen’s medium in the absence of mesenchymes fails to differentiate. Cultivation of the dorsal dermis of 6 ·5-day chick embryos in the absence of epithelium also results in lack of differentiation of dermal cells.

When proamnionic epithelium taken from embryos before the 10-somite stage is cultivated combined with dorsal dermis of 6 ·5-day embryos for 6 days, the epithelium invariably undergoes metaplastic changes, forming stratified epidermis, sometimes with keratinized superficial layer. The underlying dermal cells are condensed and this often leads to the formation of feather germ-like structures.

The competence of the epithelium for changing into the epidermis is gradually lost after the 10-somite stage, and the dorsal dermis from 8 ·5-day embryos is not very effective in inducing the epidermal metaplasia.

Proamnionic epithelium cultivated on heat-killed dorsal dermis seems healthy but shows no sign of differentiation. Dorsal dermis combined with heat-killed proamnionic epithelium spreads and remains almost undifferentiated. These observations suggest that reciprocal induction mechanisms are involved in the epithelial and dermal differentiation.

Cultivation of proamnionic epithelium with various heterologous mesenchymes or fragments of embryonic organs shows that this epithelium is only competent for epidermal differentiation when combined with dorsal dermis.

When proamnion (proamnionic epithelium plus hypoblast) is directly combined with 6 ·5-day dorsal dermis it undergoes metaplastic changes. The same result is obtained when inverted (upside-down) proamnion is combined with the dermis. Hypoblast does not seem to affect the inductive interaction between the epithelium and the dorsal dermis.
Chondrogenesis in chick embryo somites grafted with adjacent and heterologous tissues
Authors: O’hare M. J.
Published: April 2021

A variety of heterologous tissues have been tested for the ability to promote cartilage differentiation in isolated chick-embryo somites, using a modified chorioallantoic grafting technique. Of the 12 tissues tested only 3- and 4-day embryonic ectoderm promoted somite chondrogenesis in somites that fail to chondrify when grafted in isolation. This activity of ectoderm was evident in grafts of somites isolated with adjacent ectoderm, and in grafts of somites recombined with ectoderm derived from several sources. Four-day embryonic limbbud ectoderm, including the apical ridge, was capable of promoting somite chondrogenesis, but to no greater extent than dorsal trunk ectoderm of the same age. It is suggested that the ability of embryonic ectoderm to promote cartilage differentiation in isolated somites is associated with its ability to synthesize basement membrane material (sulphated glycosaminoglycans and collagen), in association with adjacent somite mesoderm.
Ultrastructural changes during transition of larval to adult intersegmental muscle at metamorphosis in the blowfly Calliphora erythrocephala
Authors: Crossley A. C.
Published: April 2021

Dissolution of the contractile apparatus derived from larval muscle occurs when pupal morphogenetic movements are complete, but a residual myofibre remains. Synapses with nerves are retained by degenerating myofibres, although the nerves are not structurally normal. Within the myofibre, the appearance of several types of unit membrane aggregate is coincident with the disappearance of normal sarcoplasmic reticulum. One type of aggregate consists of stacked cisternae, separated by a gap of 300 Å which is traversed by a three-dimensional connecting lattice of regularly arranged rods. These latticed cisternae appear to be derived from sarcoplasmic reticulum, and they interconnect with smooth-surfaced cisternae. Structures akin to latticed cisternae have been described by others in a variety of cells. Of particular interest is a report of their formation as a result of denervation in rat muscle. This report, coupled with the evidence presented here, suggests that latticed cisternae are indicative of changed nervous stimuli in degenerating muscle.

Changes in the membrane systems are rapidly followed by resorption of the myofilaments. Thick myofilaments disappear first, followed by thin myofilaments, with the eventual disappearance of Z-discs completing the dissolution of the sarcomere. No evidence was obtained for the segregation of myofilaments in membrane-bound vacuoles, or for the presence of lysosomes in muscle at this time. It is suggested that these observations are consistent with theories developed by others for retention of protein structure, rather than disassembly into amino acids, at metamorphosis in insects.

Formation of surface blebs is correlated with loss of organelles to the haemolymph. Morphological evidence supports the proposition that coated vesicles are involved in exchange of proteins with the haemolymph, shortly before adult myofilaments form.

Insect myoblast fine structure is described. The bipolar shape of these cells is shown to be associated with an oriented fascicle of microtubules. Attention is drawn to the plasma membrane of the myoblast, which bears folds at the points where flexion of the cell can be demonstrated by time-lapse microscopy. Myoblasts do not contain recognizable microfilaments other than microtubules.

Fusion of free-floating myoblasts with the residual myofibre is demonstrated by light and electron microscopy, and the stages of fusion are described. Ultrastructual manifestation of a cell recognition process was not detected. The process of multinucleation of developing muscle cells in insects is directly comparable with myoblast fusion in vertebrate cells. How ever, in Calliphora the resulting myofibre contains two classes of nucleus, easily recognizable on basis of size. The structure of these nuclear classes, and the role played by each in adult myofibril formation, is investigated in an accompanying paper.
Immunochemical study of hypoxanthine-dehydrogenase in different organs of the chick
Authors: Croisille Yvon
Published: April 2021

Immunotitration of hypoxanthine-dehydrogenase confirms earlier findings according to which, in the liver, HXDH activity stays low throughout embryonic life and increases suddenly at the period of hatching.

Whether from liver, kidney, intestine, pancreas or mesonephros, HXDH appears to have the same electrophoretic mobility (in agar, agarose and starch gels), the same molecular weight (estimated to be about 290000 by Sephadex G 200 filtration) and the same immunochemical properties (as tested with 24 anti-liver, 18 anti-kidney, and 4 anti-mesonephros sera).

Various attempts to interfere with HXDH synthesis in vivo or in vitro (injection of substrate or liver extracts; explantation of fragments of mesonephros, metanephros or intestine from 9-to 12-day-old chick embryos on substrate-containing culture media; direct association of tissues containing high and low levels of enzyme) have so far failed.
Rôle du nerf et du territoire cutané dans le développement des corpuscules de Herbst et de Grandry
Authors: Saxod Raymond
Published: April 2021

Role of nerve and cutaneous tissue in the development of Herbst’s and Grandrfs corpuscles

Frontal buds or pieces of the bill of duck and chick embryos have been explanted on the chorioallantoic membrane, transplanted as homo- or xeno-plastic grafts to the flank, the frontal bud and the limb bud of early host embryos, or associated as coelomic grafts with various isolated nerve sources. Results show that :

These results are discussed in connexion with what is known about peripheric sense organs in vertebrates. A schematic model is proposed for the mechanism of the morphogenesis of the corpuscles.
Cell movements in morphogenesis of hydroid polypes
Authors: Beloussov L. V. , Badenko L. A. , Katchurin A. L. , Kurilo (Filatcheva) L. F.
Published: April 2021

Growth, morphogenesis and cell movements were studied in Obelia loveni, O. geniculata and Dynamena pumila with the use of time-lapse cinematography, visual observations of vitally stained objects and by histological techniques. Growth pulsations with the period around 14 min and the amplitude around 15 μm exist in Dynamena pumila and with the period 5–8 min and amplitude up to 5 μm in Obelia loveni. It was demonstrated that the rhythm of growth pulsations does not coincide with the rhythm of periodical contractions of the proximal part of coenosarc. The distalwards movements of individual cells in the ectoderm of growing stems and hydranth rudiments are described. A considerable variability in the rates of movements of ectodermal cells has been demonstrated. Different kinds of cell reorientations in developing rudiments are described. As a rule, they precede the alterations of growth directions or of rudiment shapes. The mechanisms involved in deformations of epithelial layers are discussed. The possibility of the existence of passive, elastico-plastic structures in the deforming epithelial sheets is suggested.
The role of neurohumours in early embryogenesis
Authors: Buznikov G. A. , Sakharova A. V. , Manukhin B. N. , Markova L. N.
Published: April 2021

The 5-hydroxytryptamine concentration changes insignificantly in the course of each of the first cleavage divisions, except at prometaphase when a sharp short-term fall occurs. According to the data obtained by the simplified gaseous formaldehyde method of Falck and Hillarp, 5-HT is present in all embryonic and larval cells up to the stage of prism. In plutei 5-HT is detected by this method only in the digestive tube, ventral ciliary band and possibly in pigment cells. According to the data obtained by the aqueous formaldehyde method, at the gastrula stage 5-HT is localized in the archenteron and vegetative ectoderm and at the stages of prism and pluteus in cells of the digestive tube, ventral ciliary band and, possibly, in pigment cells. The aqueous method gives negative results at pregastrular developmental stages.

On the basis of the data obtained a suggestion is put forward about the presence of two 5-HT pools in developing sea-urchin embryos and larvae. It is suggested that the first of them, not detected by the aqueous method and present in embryos beginning from the earliest developmental stages, performs intracellular regulatory functions whose character is discussed. The second pool detected by the aqueous method arises with the onset of gastrulation and appears to be related to morphogenetic processes.
Cytodifferentiation of the mouse secondary palate in vitro: morphological, biochemical, and histochemical aspects
Authors: Idoyaga-Vargas Victor , Nasjleti Carlos E. , Azcurra Julio M.
Published: April 2021

Previous investigations had indicated that the epithelial cells at the medial surface of the palate differentiate prior to fusion. An increase in adhesiveness and signs of partial autolysis were reported to be part of the differentiation. It was not determined, however, whether or not the autolytic processes may result in the total lysis of the cells, even if fusion is prevented. This problem was approached in the present investigation by culturing shelves in isolation, thus preventing fusion. The morphological properties of the presumptive fusing cells were then observed during and after the actual time of fusion. Differentiation was assessed in vivo at equivalent developmental ages. In addition, the role of the lysosomes in the process of fusion was investigated. This was done by measuring the activities of two lysosomal enzymes, glucosaminidase and arylsulfatase, before, during, and after fusion in vivo and at the equivalent times in vitro. Glucosaminidase activity was also localized histochemically.

The in vitro and in vivo differentiation were similar. The cells of the mesenchyme produced intramembranous bone and loose mesenchyme. The nasal surface differentiated into a pseudostratified columnar ciliated epithelium, while the oral surface became stratified squamous epithelium. At the medial surface, however, the morphological changes during fusion in vivo were different from those observed at the equivalent time in vitro. Few, if any, of the presumptive fusing cells forming a bi-layered or multilayered epithelium degenerated in the explants, while many cells forming the epithelial seam in vivo underwent complete degeneration. In addition, after fusion, the medial surface of the palatal expiants was covered by a stratified squamous and/or pseudostratified columnar ciliated epithelia. In vivo, the mesenchyme merged as a consequence of the total destruction of the seam. The specific activity of glucosaminidase increased progressively, reaching a peak three days after fusion. In all cases no statistically significant differences were found between the in vivo and in vitro values. Arylsulfatase specific activity remained the same both in vivo and in vitro. Histochemically glucosaminidase activity was localized in the cells undergoing degeneration during fusion. It is concluded that fusion is a necessary condition for the completion of the autolysis of the presumptive fusing cells. The cells may alter their developmental fate, forming a stratified squamous and/or pseudostratified columnar epithelia, if fusion is prevented.
Neurotrophic dependence of macromolecular synthesis in the early limb regenerate of the newt, Triturus
Authors: Singer Marcus , Caston J. Douglas
Published: April 2021

The well-documented nerve dependence of limb regeneration in the newt was analysed by study of accumulation of newly synthesized macromolecules following denervation. The specific activity of RNA and DNA in the denervated early regenerate bud was determined following intraperitoneal injection of [3H]-uridine and [3H]-thymidine. Results showed an outburst in the incorporation into RNA and DNA which reached a peak 3 h after denervation for the former and 7 h for the latter. There was then a decline in incorporation to a plateau about 50-60% of the control non-denervated side within 48 h. Combining these results with our previous demonstration of a similar outburst in the accumulation of newly synthesized protein with a peak at 4 h, the sequence of the outbursts was in order RNA, protein and DNA. The results are interpreted to mean that the nerve influences either macromolecular synthesis or macromolecular processing and turnover, and therefore accumulation in the regenerate.
Properties of the primary organization field in the embryo ofXenopus laevisI. Autonomy of cell behaviour at the site of initial organizer formation
Authors: Cooke J.
Published: April 2021

The work presented, in this and the subsequent papers of a series, was begun in order to re-examine the properties of the amphibian primary embryonic field, in the light of current theories concerning the nature of individuation fields in developing animal systems. A detailed description is given of the basic operation whose results are described in this and the subsequent paper. This involves the transplantation, into a late blastula or stage-10 gastrula host, of a supernumerary stage-10 organizer region. The consequences of such operations during the following 4–6 h, up to the late gastrula stage, are also described.

Evidence is presented that, from a time some 2·5 h before the organizer site first becomes externally visible, its presumptive region is immune from interference by the proximity of another, implanted organizer, even one which is itself 2·5 h older. That is to say, the final site of development of host organizer activity is not altered by the presence of such an implant.

Pairs of early organizers at comparable stages of activity appear to set up competing fields of cellular orientation and immigration, which show a fairly sharp boundary at their interface. This is most obvious for pairs of organizers fairly close together, since the cell polarization and stretching is most pronounced in the region near to the apex of the field, i.e. the initial site of cell immigration. Independent initial fields of immigration due to two organizers can reliably be distinguished in cases where they are as little as 30° of angular distance apart in the marginal zone of the host.

These results are to be considered in relation to those of Paper II, for the same series of operations, where the final patterns of cell differentiation are studied, and to those of Paper III, where evidence is given for the development of autonomous polarity in the region of the organizer.
Rôle du mésoderme somitique dans le développement du plumage dorsal chez l’embryon de Poulet:I. Origine, capacités de régulation et détermination du mésoderme plumigène
Authors: Mauger Annick
Published: April 2021

The role of somitic mesoderm in the development of dorsal plumage in chick embryos. I. Origin, regulation capacity and determination

The role of somitic mesoderm in the development of the dorsal plumage has been studied in chick embryos. The operations were performed at 2–2·5 days of incubation.

The replacement of a portion of somitic mesoderm by somitic mesoderm labelled with [3H] thymidine or obtained from Japanese quail embryos (whose nuclei bear distinctive specific markers) showed that cells originating from the dermatomes build up the dermis of the dorsal skin only. They do not migrate farther than approximately midway down the flank. Beyond this limit, dermal cells originate from the somatopleural mesoderm.

The unsegmented somitic mesoderm is capable of extensive regulation, which leads to the development of a dorsal plumage, normal in the number and arrangement of its feathers according to the characteristic pattern of the spinal pteryla. Uni-or bilateral excision of segmented somitic mesoderm resulted in dorsal plumage deficiencies, the extent and frequency of which was related to the state of differentiation of the excised mesoderm. Thus, the excision of somites generally led to an incomplete spinal pteryla (absence of feather rows, apteria). However, the somitic mesoderm is still capable of regulation even though it has already undergone its differentiation into dermatome, myotome and sclerotome. These results show that somitic mesoderm retains its regulative capacity, even though it has already acquired its feather-forming determination.

The replacement of unsegmented somitic mesoderm by various implants (agar, tantalum, gut, neural tube, somatopleural mesoderm), intended to block the regulation processes, abolished the differentiation of the spinal feathers on the operated side. In some cases, the implantation of somatopleural mesoderm resulted in the formation of a supernumerary tract. No tissue other than somitic mesoderm -not even the somatopleural mesoderm, which is normally in part feather-forming -is able to give rise to region-specific spinal pteryla dermis.

The excision and replacement of somitic mesoderm prevented the differentiation of dense dermis, whereas these operations had no effect on the early histogenesis of the epidermis, with the formation of arches and anchor filaments.
Energy metabolism in isolated rat embryo hearts: effect of metabolic inhibitors
Authors: Cox Steven J. , Gunberg David L.
Published: April 2021

Hearts isolated from 11-and 12-day rat embryos were incubated in a simple salt solution to which was added the metabolic inhibitors iodoacetate, malonate, 2,4-dinitrophenol or trypan blue. Comparisons were made between the two age-groups and it was observed that both 11-and 12-day hearts exhibited depressed contractile activity with the glycolytic inhibitor iodoacetate. Malonate did not depress contraction rate in the younger hearts but significantly depressed the rate in the older hearts. A greater inhibitory action on the older hearts as compared with the younger hearts was also produced by 2,4-dinitrophenol. These results were interpreted as further evidence of a shift in dependence on pathways other than glycolysis between days 11 and 12 of development.

The teratogenic agent trypan blue was shown to depress contraction rate when added to the incubation medium. This effect could be reversed by adding glycolytic intermediates such as fructose-l,6-diphosphate or alpha glycerophosphate. These results were suggestive of a direct inhibitory effect of trypan blue either on glucose uptake or its complete catabolism.
Evidence for a two-step mechanism operating duringin vitromouse kidney tubulogenesis
Authors: Gossens Carol L. , Unsworth Brian R.
Published: April 2021

The process of kidney tubulogenesis was investigated in mouse metanephrogenic mesenchyme, differentiating in tissue culture under the influence of an inductive stimulus from embryonic mouse brain. The metanephrogenic mesenchyme was separated from the brain by a membrane filter. The time of exposure to the inductive stimulus was controlled by removing the brain from the filter.

Restricting the period of transfilter association of metanephrogenic mesenchyme and brain resulted in incomplete tubulogenesis. A 30 h interaction time with brain led to the formation of small tubules. These small tubules were at an unstable stage of differentiation, and regressed during the 6-day culture period. Stabilization and elongation was achieved by the addition of mesenchymal tissues or chick embryo extract. Induction was clearly not a one-time triggering event, and as the degree of differentiation increased so the specificity for mesenchymal requirement decreased.

Embryo extract did not mimick the inductive event that initiated tubulogenesis, but supported the later stages of tubulogenesis. This was interpreted to indicate a certain specificity in the induction reaction.

The incidence of tubule elongation was related to both the initial mass of metanephrogenic mesenchyme and to the total contact time with brain. The greater the initial mass of mesenchymal tissue, the less contact time with brain needed for complete tubulogenesis.

The morphology of the elongated tubules depended on the nature of the mesenchyme with which the small tubules were associated. This suggested that the expression of tubule morphology may be under the control of the surrounding mesenchymal cells. Possible mechanisms operating during tubule elongation were discussed.

It was concluded that an integrated two-step mechanism was operating during kidney tubulogenesis. The first step, cell condensation, was induced by contact with brain. The second step, tubule elongation, was dependent upon the association of the condensates with the surrounding non-induced mesenchymal cells.
The growth of transplanted mouse vertebrae: effects of transplantation under the renal capsule, and the relationship between the rate of growth of the transplant and the age of the host
Authors: Noel Janet F. , Wright E. A.
Published: April 2021

The tail vertebrae of 7-to 8-day C3H mice were transplanted under the renal capsules of syngeneic animals of various ages. Morphological effects of transplantation included degeneration of the intervertebral joints, increase in the diaphyseal haemopoietic marrow and decreased formation of bone trabeculae. The growth rate of the transplanted vertebrae depended upon the age of the host. Those transplanted into animals of the same age as the donor grew faster than controls left on the tail. Those transplanted into young adults (aged 4 months) and senile adults (aged 17 months) grew at 71% and 64% respectively of the rate of those transplanted into 7-to 8-day hosts. These differences are interpreted as due primarily to age dependent changes in blood hormone levels.
Development in culture of rat foetuses explanted at 12·5 and 13·5 days of gestation
Authors: Cockroft D. L.
Published: April 2021

As a result of the relatively simple operation of opening the yolk sac and thus exposing the foetal capillary circulation to flowing medium, it has proved possible to grow 12·5- and 13·5-day rat foetuses for a period of 42 h in culture. 25% rat serum, 75% Tyrode has been found to be a satisfactory and economic culture medium, and has the added attraction that foetal survival is improved compared with that obtained in whole rat serum. For both 12·5- and 13·5-day foetuses grown with open yolk sacs, a gas mixture of 95% O2, 5 % CO2 in equilibrium at 1 atm with culture medium flowing at about 15 ml/min has been found to give the best results. Under these conditions, foetuses explanted at 12·5 days increased their protein content from 1·0–1·3 mg to 2·3–2·7 mg during culture. Their somite number was 40–44 at explantation and reached 50–55 during culture. Foetuses explanted at 13·5 days increased their protein content from 3·2–4·0 mg to 6·1–7·5 mg during culture. Their somite number was 51–55 at explantation and reached 60–63 during culture.
Anaerobiosis in the Rana pipiens Embryo
Authors: Cohen Adolph I.
Published: April 2021

Evidence is presented demonstrating that although a short burst of oxygen uptake follows transfer of Rana pipiens embryos from a nitrogen to an oxygen atmosphere, a similar burst follows transfer from air to oxygen. Since the material being oxidized exists in the reduced state in gastrulae raised in air, it cannot constitute a major source of anaerobic oxidations in gastrulae. Data and considerations suggesting that the amphibian embryo is normally partially anaerobic in the usual temperature range employed in physiological experiments are presented. A detailed description of the respiratory and lactate level changes of embryos transferred to an oxygen atmosphere after anaerobiosis is given and the significance of the findings is discussed.
Morphogenetic Effects of a Heat Shock on the Eggs of Limnaea stagnalis
Authors: Raven Chr. P. , Roon A. C. De , Stadhouders A. M.
Published: April 2021

Eggs of Limnae stagnalis were subjected to a heat shock (37° C.) for or 3 hours at the 2-to 4-cell stage. Both exogastrulae and head malformations were produced. The exogastrulae produced by a heat shock differ considerably from those caused by lithium treatment in showing a much more serious disturbance of development, leading to the appearance of greatly atypical differentiations. No typical cyclocephalic malformations were produced by this treatment. Apparently a heat shock does not primarily act by depressing the animal gradient field. Local eye reductions were produced preferentially on the right side. Presumably the left-right asymmetry at early cleavage stages in Limnaea is attended with differences in physiological conditions between both sides. Lateral eye reduplications, leading to the formation of two eyes in a single tentacle field, occurred on both sides. The most characteristic heat-shock effect consists in a reduplication of the posterior part of the apical plate, with the formation of a median tentacle field containing an eye, and sometimes a tentacle. The splitting of the apical plate is not attended with a decrease in the number of apical plate cells, but in at least some of the cases with an increase. It is concluded that these median reduplications are caused by a strengthening of the animal gradient field, leading to the splitting of the apex of the gradient. It is possible that the lateral eye reduplications are due to a splitting of a secondary field apex. Dislocations of head organs, especially of the nervous ganglia, encountered in the treated embryos, show that the differentiation of cerebral ganglion, pedal ganglion, and statocyst does riot depend on the presence of a normal cerebropedal connective on that side of the body.
Histogenetic and Organogenetic Processes in the Development of Specific Characters in some South African Tadpoles1
Authors: Balinsky B. I.
Published: April 2021

The tadpoles of four species of Anura used for the experiments (Pyxicephalus adspersus, Pyxicephalus delalandii, Phrynobatrachus natalensis, and Xenopus laevis) differ in the structure of their adhesive organs, external gills, and mouth parts, as well as in size and other properties. To investigate whether the distinctions in the above organs are due to different reactive abilities of the ectoderm or to differences in inducing systems, parts of the presumptive ectoderm were transplanted in the early gastrula stage from one species to another. Adhesive organs, gills, and mouth parts-were developed from grafted ectoderm in conformity with its position in the host embryo, as a result of inducing influences from the underlying parts of the host. The organs developed from the grafts partly retained the characters of the donor species and partly acquired the characters of the host species. In respect of all characters concerned with the differentiation of special types of cells and with their mutual arrangement the graft ectoderm strictly retained the peculiarities of the donor species. These characters were: presence or absence of horny jaws and horny labial teeth; rhythm of differentiation of the labial teeth; shape of the adhesive organ; subdivision of the rudiment of the adhesive organ into two lateral organs or retention of an organ that is continuous across the midline (i.e. is single and median); branching of the external gills. It is proposed to distinguish processes of this type as histogenetic processes. They are presumably based directly on the genotype of the cells. The size of all induced graft structures, such as the mouth, the gill rudiments, or the adhesive organ, showed various degrees of approximation to the size of corresponding organs of the host, and this not through retarded or accelerated growth but through an increased or decreased initial size of the rudiments. Ectoderm of a species having only one pair of gills developed gills of a second pair when transplanted to an embryo having normally two pairs of gills. The length of the gill filaments was predominantly determined by the host. Processes controlling characters of this second type, that is characters involving the number or mass of cells and the position of areas differentiating in a specific way, I call organogenetic processes. Differences in organogenetic processes between related species may thus be due to a modification of the inducing systems and not to changes in reactive abilities of cells.
Studies on the Development of the Foregut in the Chick
Authors: Bellairs Ruth
Published: April 2021

Mitotic counts have been made in the area pellucida endoderm of 10 chick embryos. In the head process stage embryos there was no evidence that any region of the endoderm consistently possessed a mitotic rate which was statistically significantly different from that of any other. In all the early somite stage embryos a region possessing a high mitotic rate was found in either the foregut floor or the presumptive foregut floor. It is suggested that as the histological structure of the developing foregut floor of the embryo changes from cubical to columnar, and the individual cells become narrower, a proliferation is needed to maintain the width of the region. There is no evidence that this high mitotic rate is necessary for the morphogenetic movements leading to the ventral closure of the foregut. There is no evidence to suggest that a lowering of the mitotic rate plays any part in the thinning of the roof of the developing foregut.
Dissociation and Reaggregation of Embryonic cells of Triturus alpestris
Authors: Feldman M.
Published: April 2021

The dissociation of cells of neurulae of Triturus by means of sodium citrate or potassium oxalate and glycine is described. Suspensions of isolated cells of neural, mesodermal, and endodermal tissues were made to reaggregate in a slightly acid solution, and the aggregates were cultured within explants of ectoderm. Reintegration of some histogenetic patterns was observed. Differentiation of structures resembling neural tube and archenteron are described in aggregates of neural and endodermal tissues. Some factors involved in the dissociation and reaggregation processes are briefly discussed.
Abnormal microtubular systems in mouse spermatids associated with a mutant gene at the T-locus
Authors: Dooher Gerald B. , Bennett Dorothea
Published: April 2021

Fine structural observations of spermiogenesis in sterile mice homozygous for the t-allele tw2 reveal that spermatids develop severe morphological abnormalities during spermiogenesis. In a small proportion of late spermatids the nuclear envelope develops broad areas of discontinuity except at the level of the acrosome. Manchette microtubules, which in normal spermatids form an orderly perinuclear array, appear to undergo premature depolymerization in cells of this type although flagellar structures differentiate normally.

The majority of late spermatids, on the other hand, contain unusually large numbers of disorganized microtubules. Spermatid head shapes likewise become very abnormal. Both acrosomal and post-acrosomal portions of the nucleus exhibit malformations. The presence of disorganized microtubular arrays is believed to contribute to the observed nuclear deformations.

Although condensation of the chromatin occurs in these cells, the spermatids seldom survive to maturity. Most of the cells are phagocytized by Sertoli cells.

Late spermatids from tw2 homozygotes are abnormal in that they fail to maintain a precisely ordered array of microtubules during the concluding stages of spermiogenesis. This defect may reflect an underlying abnormality in the structural or biochemical characteristics of the plasma membrane with which the microtubules become associated.
Ontogeny and localization of the lens crystallins inXenopus laevislens regeneration
Authors: Brahma Samir K. , McDEVITT David S.
Published: April 2021

Ontogeny and localization of the lens crystallins, especially the γ-crystallins were investigated in Xenopus laevis lens regenerating system by the ‘indirect’ immunofluorescence staining method. Antibodies directed against Rana pipiens γ-crystallin antigen were used for the detection of this crystallin; the validity of such an experiment has been shown in a previous report. To detect total lens proteins we used X. laevis anti-total lens protein antibody.

The regenerates were staged according to Freeman (1963) and the first positive reaction with both the two antisera was observed in an early stage-4 regenerate. The site of the immunofluorescence reaction was nearly identical in both, suggesting that γ-crystallins are one of the first, if not the first of the lens crystallins to appear during lens regeneration.

The secondary fibres, when developed, showed less immunofluorescence than the primary fibres with R. pipiens anti-γ crystallin antibody, though the reaction was intense in the secondary fibres with X. laevis anti-total lens protein antibody.

The intensity and distribution of immunofluorescence increased with the growth of the lens. With the R. pipiens anti-γ crystallin antibody, the lens epithelium did not show any immunofluorescence reaction at any stage of lens regeneration. With X. laevis anti-total lens protein antibody, the epithelium showed an immunofluorescence reaction earlier than in the normal lens development. With the two antisera we used, we did not observe any immunofluorescence outside the lens tissue.
Morphogenesis in Micrasterias: II. Patterns of morphogenesis
Authors: Lacalli T. C.
Published: April 2021

The final form of the polar lobe and lateral wings of developing semicells of M. rotata results from combined action of three growth processes: tip growth, branching and lobe broadening. Tip giowth unaccompanied by branching or broadening occurs during normal development in M. radiata, but is observed only under abnormal conditions (e.g. raised temperature) in M. rotata. When branching and broadening do occur, they occur together and for this reason may be causally related. Autoradiograms demonstrate that specific patterns of cell wall incorporation can be associated with each of the three processes in M. rotata. Autoradiographic patterns found in the polar lobe differ from those found in wings. The growing polar lobe also responds to laser irradiation differently from the wings; lasings occasionally cause duplication of the polar lobe.
The development of trophoblast in vitro from blastocysts containing varying amounts of inner cell mass
Authors: Ansell J. D. , Snow M. H. L.
Published: April 2021

When intact mouse blastocysts are cultured in vitro in medium supplemented with foetal calf serum, trophoblast cells proliferate and undergo giant cell transformation such as occurs in vivo. If the amount of inner cell mass in the blastocyst is decreased by culture with [3H]-thymidine then giant cell transformation occurs normally but proliferation is reduced. In the absence of inner cell mass no proliferation occurs, and giant cell transformation is more rapid than in undamaged blastocysts.
Demonstration of cytoplasmic processes in Millipore filters permitting kidney tubule induction
Authors: Lehtonen E. , Wartiovaara J. , Nordling S. , Saxén L.
Published: April 2021

The presence of cytoplasmic material inside thin Millipore filters between interacting mouse metanephric mesenchyme and spinal cord was investigated using different fixation methods. .

The transmission of induction was studied from sections of Zenker-fixed paraffin-embedded expiants. Formation of kidney tubules was taken as evidence for induction. Filters with 0·8 and 0·22 μm pores permitted induction, whereas only 6 out of 31 filters with 0·1 μm pores did so.

Glutaraldehyde-fixed Epon-embedded explants were used for study of cytoplasmic penetration into filters. In thick sections, filters with large pores were seen to contain cytoplasmic material at all levels. Filters with 0·1 μm pores usually showed only shallow ingrowth, but those which had permitted passage of induction contained material at least half way from the spinal cord and shallow ingrowth from the mesenchyme. With 0·8 μm filters the ingrowths from both sides met first after 18 h of transfilter cultivation. This has previously been shown to be the minimum time needed for induction to take place in this system.

In electron microscopy cytoplasmic processes were seen deep inside the 0·8 and 0·22 μm filters regularly permitting induction. In small pores such material was only preserved by certain glutaraldehyde fixatives.

Diffusion studies did not reveal major differences between induction-permitting 0·22 μm filters and induction-preventing 0·1 μm filters.

Thus in the kidney tubule induction system this and our previous work speak in favour of a mechanism based on close apposition of cells rather than on long-range diffusion of inductive substances or on matrix interaction.
Reconstitutive ability of axial tissue in early rat embryos after operations and culture in vitro
Authors: Deuchar E. M.
Published: April 2021

Longitudinal incisions have been made in the axis of 10-day-old rat embryos (post-neurula stage with 5–10 pairs of somites) at mid-trunk levels, dividing the axis into right and left halves. The embryos have then been cultured in vitro by New’s method and their ability to reconstitute tissues in each half has been studied.

After 20 h culture at 37 °C, there was no longer any external sign of the division of the axis. Histological studies showed that in nearly all cases, however, the neural tube was duplicated in the operated region. The two neural tubes lay in close contact in the midline, and ventral to them the gut was single. Apart from four cases in which the gut roof was slightly broadened and forked, all other tissues were normal.

The reconstitutive ability of the neural and gut tissue has been compared with that of amphibian and avian embryos, as observed in ‘twinning’ experiments by other workers.

The apparent delay in axial rotation in the operated rat embryos, as compared with controls, is attributed to the inability of the two separated halves of the somite series to co-ordinate their contractions. Further details of the rotation process in operated embryos will be the subject of a future study.
The tip of the Dictyostelium discoideum pseudoplasmodium as an organizer
Authors: Rubin Jonathan , Robertson Anthony
Published: April 2021

We have extended Raper’s original work on the organizing ability of the tip of the Dictyostelium discoideum slug.

Our new results are that tips from all multicellular (pseudoplasmodial) stages act as organizers; that the structure organized by a tip depends on the developmental stage of the cells responding to the tip’s signal; that tips from all stages release a qualitatively similar signal which is continuous, most probably a gradient of c-AMP; and that the signal from fruiting-body tips appears stronger than that from conus tips.

We discuss these results with reference to the control of morphogenetic movement and patterned differentiation and point out that the D. discoideum tip is analagous to a classical organizer, whose signal is interpreted according to the state of determination of cells in its field of influence.
Quantitative studies of germ plasm and germ cells during early embryogenesis of Xenopus laevis
Authors: Whitington P. McD. , Dixon K. E.
Published: April 2021

The germ plasm in the egg is partitioned between the first four blastomeres by the first two cleavage planes. Although the blastomeres divide 10–11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. During and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. At subsequent mitoses, the germ plasm is localized at one of the poles of the spindle and hence is segregated to only one of the daughter cells, thus explaining how mitosis occurs without increase in the number of cells with germ plasm. Early in gastrulation, the germ plasm moves to a perinuclear position, therefore ensuring that as mitosis continues, both daughter cells receive germ plasm and the number of p.p. germ cells increases. Direct counts of the number of p.p. germ cells and measurements of their volume suggest that they divide twice between early gastrula and the stage at which they leave the endoderm. The p.p. germ cells behave similarly to the adjacent endodermal cells until they begin to migrate to the gonad, an event which may represent the first overt signs of differentiation. Measurements of the volume of germ plasm suggest that there is no change through cleavage. The general conclusion is drawn that during cleavage, the morphogenetic determinant germ plasm is segregated to a few cells by the normal processes of cleavage and that subsequently these cells undergo a small number of cloning divisions which are contemporaneous with the first signs of differentiation.
In vitrochondrogenesis of limb mesoderm from normal and brachypod mouse embryos
Authors: Elmer William A. , Selleck David K.
Published: April 2021

This paper describes the cytodifferentiation of hind limb mesodermal cells from 12-day-old normal and brachypod (bpH) mouse embryos grown in vitro at high densities. Over a 3-day culture period normal cells underwent aggregation, nodule formation, and coalescence of nodules into large masses of cartilage. This was associated at the biochemical level with a cessation of cell division, with a concomitant increase in metachromatic matrix, and synthesis of collagen. Under the described culture conditions the collagen synthesized by 48 h cultures was predominantly of cartilage type with an αl: α2 ratio of 9:1. A change in the collagen synthetic program was observed when the entire medium was replaced after 48 h incubation with fresh, serum-free medium. Under these conditions the αl: α2 ratio was 4:1.

In contrast, brachypod cells plated at the same density appeared large, flattened, and stellate. Upon aggregation, normal nodule morphology was only rarely observed. More often large, irregular clusters formed from suspended cells loosely attaching to the surface aggregates. Concomitant with the marked changes in the morphology of the mutant cells was a linear increase in DNA synthesis and the appearance of many mitotic figures. A biochemical transformation in matrix synthesis was not observed, however. After a 24 h delay, mutant matrix accumulated and stained intensely with toluidine blue. Collagen was synthesized at approximately the normal rate and was of the cartilage type with an αl: α2ratio of 9:1. When incubated in fresh, serum-free medium, the response of collagen subunit synthesis was identical to the normal cultures. In view of these results the possible manner in which brachy-podism causes developmental anomalies of the limb skeleton is suggested.
Ultrastructural features of chondrogenesis in the human hand plate: a cytochemical and autoradiographic study
Authors: Kelley Robert O.
Published: April 2021

Ultrastructural features of chondrogenesis are correlated with the appearance of collagen and proteoglycan components of the cartilage matrix in the developing human hand (stages 16-18).

Prechondral mesenchymal cells comprising the digital plate (stage 16) exhibit euchromatic nuclei, sparse granular endoplasmic reticulum, few polysomes, broad cell to cell associations, little enhancement of electron density after postfixation with osmium tetroxide/potassium ferrocyanide and scanty incorporation of 3H-proline. Extracellular matrix is electron-lucent.

During stage 17, early chrondroblasts acquire affinity for OsO4/K4Fe(CN)6, develop filopodia, lose broad intercellular attachments, assemble cytoplasmic polysomes, incorporate 3H-proline and the extracellular matrix acquires electron-dense particles (10-20 nm in diameter).

By stage 18, chondrogenic cells of digital blastemata exhibit affinity for osmium-ferrocyanide, and particles (10-20 nm in diameter) and filaments (5 nm in diameter) are present in the extracellular matrix. Mature chondrocytes are present.
Developmental changes in the composition and amount of mouse fetal fluids
Authors: Renfree Marilyn B. , Hensleigh Hugh C. , McLaren Anne
Published: April 2021

Fetal fluid was studied in mice of the Q, C57BL/McL, C3H/Bi/McL and JU/Fa strains. The amount increases to day 16 of gestation, and then decreases. Amniotic fluid and fetal plasma contain three transferrins, five α-fetoproteins and albumin. Protein concentration in both increases during gestation; glucose decreases in amniotic fluid although it rises in fetal plasma; urea levels remain constant. The regulation of volume and biochemical composition of amniotic fluid, and its relation to the yolk-sac membrane, are discussed.
Cell death during the formation of tubular heart of the chick embryo
Authors: Ojeda J. L. , Hurle J. M.
Published: April 2021

Light and electron microscopical examination of the heart of the chick embryo between stages 9 and 11 (Hamburger & Hamilton) revealed degenerating and dead cells specifically localized in the midline of endocardial tubes. The morphology of cell death in this system does not differ from that described in other embryonic tissues and organs. Phagocytosing cells are rarely seen.

The results of this study show that a destruction of midline cells of both endocardial tubes takes place during the fusion of heart anlages. The possible roles of this cell death in the morphogenesis of the tubular chick heart are discussed.