bluuebunny/crossref_metadata_2025 huggingface dataset:
Foetal haemopoiesis during the hepatic period; II. Topographic histology
Authors: Nessi Analía C. , Bozzini Carlos E.
Published: April 2021

Serial sections of mouse foetal liver, during the 9th and 16th days of gestation, were studied.

The erythropoietic process starts in the central area of the growing hepatic lobes, and subsequently spreads towards the periphery. Each lobe passes successively through an undifferentiated, proliferating and differentiating period, but does not proliferate and differentiate in a homogeneously synchronized way, since the onset of both histogenesis and erythropoiesis is delayed at the periphery, when compared with the central area. As a consequence, in sections it is possible to find three different zones, namely: marginal, which is the most undifferentiated; intermediate (transitional); and a central area, which is the most mature, since it is the first site where erythropoiesis arises. These zones are distinguishable not only by their cell distribution, but also by the biological behaviour of their elements, specially in the transitional areas between undifferentiated and proliferating zones.

The hepatic lobes do not start their organogenesis at the same time; but those of them in which histogenesis is delayed, repeat courses of development similar to those previously organized. The first interstitial erythropoiesis appears in the central area, after the development of an organized network of sinuses, and in close relation to vascular channels. Dynamic images of immature blood cells, between interstitial and vascular spaces, suggesting passage through the endothelium, are often seen. These steps are followed, in a concentric form and spreading towards the periphery, by each hepatic lobe.
Time-dependent effects of α-amanitin on blastocyst formation in the mouse
Authors: Braude P. R.
Published: April 2021

Early compacting mouse morulae were placed in α-amanitin at various times after HCG and the effect of this transcriptional inhibitor during formation of the blastocyst was noted. No cavitation was observed in those embryos transferred into α-amanitin before 77 h after HCG but the percentage of cavitation increased dramatically in those embryos transferred after 80 h post HCG. The large increase in amino acid incorporation which normally occurs during formation of the blastocyst was blocked in those embryos placed in the inhibitor before 80 h post HCG. Two-dimensional polyacrylamide gel electrophoresis of radiolabelled embryos showed that the changes in synthesis of certain polypeptides normally associated with blastocyst formation did not occur in those embryos placed in α-amanitin before 80 h after HCG. Only one cleavage division appears to occur in the presence of α-amanitin. However, groups of embryos which had completed their fifth division before exposure to the drug subsequently were able to form blastocysts and showed the quantitative and qualitative changes associated with blastocyst formation despite the continued presence of the inhibitor. These results suggest that a critical transcriptional event concerned with blastocyst formation occurs around 80 h after HCG and may be associated with the fifth cleavage division.
Cytoplasmic and nuclear protein synthesis in preimplantation mouse embryos
Authors: Howe C. C. , Solter D.
Published: April 2021

Cytoplasmic and nuclear proteins synthesized by mouse embryos at different stages of preimplantation development were analyzed by two-dimensional polyacrylamide gel electrophoresis. Several nuclear-specific proteins (i.e. proteins more abundant in the nucleus than in the cytoplasm) and numerous cytoplasmic-specific proteins were observed. The trends of changes in the nuclear and cytoplasmic protein synthesis are similar. Moderate changes occur between the unfertilized egg and the zygote. Striking changes characterized by the disappearance of numerous major oocyte-specific proteins and the appearance of a large number of new, stage-specific proteins occur between the zygote and the 4- to 8-cell stages. Tn contrast, between the 4- to 8-cell and early blastocyst periods, only a few new proteins appear, and a small number of oocyte-specific or other stage-specific proteins disappear. Minor differences in protein synthesis were observed between the trophoblast and inner cell mass.
An experimental investigation into the possible origin of pancreatic islet cells from rhombencephalic neurectoderm
Authors: Andrew Ann , Kramer Beverley
Published: April 2021

To determine whether or not any pancreatic islet cell type arises from rhombencephalic levels of neurectoderm, lengths of presumptive rhombencephalon (containing potential neural crest) of Black Australorp chick embryos at 6-to 9-somite stages were replaced iso-topically and isochronically by neural tube of Japanese quail embryos. Some transplants included mesencephalic regions. In some cases various levels of the rhombencephalon were deleted and not replaced.

The quail nuclear marker was detected in cranial ganglia in operated embryos sacrificed at days of incubation and in enteric ganglia and cells accompanying some pancreatic nerves, in embryos killed at 7 days of incubation. This provided evidence of normal migration of crest cells from the grafts. Dopa was administered to the younger embryos, which were submitted to the formaldehyde-induced fluorescence procedure to demonstrate APUD (Amine Precursor Uptake and Decarboxylation) cells. No pancreatic APUD cells exhibited the quail nuclear marker. In 9-to 11-day embryos, A and B cells were identified by specific light and electron microscopic features. None showed the quail marker. The marker was also absent from those D cells seen and from cells of an as yet unidentified type, but not enough of these were found to warrant a conclusion. All islet cell types were found in embryos from which various levels of the rhombencephalon had been deleted.

It is concluded that at least A and B islet cells are not derived from the rhombencephalic neurectoderm and probably not from mesencephalic levels. Their most likely origin remains the endoderm, which was the accepted source until recently.
The development of hepatogenic potency in the endoderm of quail embryos
Authors: Fukuda Sumiko
Published: April 2021

Hepatogenic potency of the endoderm is detectable in the anterior half of the endoderm of quail embryos older than 2-somite stage when endodermal fragments are cultured with or without heterologous chick mesenchymes, in the coelomic cavity of 3-day chick embryos. On the other hand, the posterior half of the endoderm never has hepatogenic potency. The hepatogenic potency of the endoderm is gradually stabilised with increasing age. However, expression of hepatogenesis can be affected when the endoderm is associated with inductively active digestive tract mesenchymes.

Mesenchyme taken from the presumptive cardiac region (‘cardiac’ mesenchyme) of chick embryos is necessary for the uncommitted anterior endoderm to acquire hepatogenic potency, and this effect is specific for the ‘cardiac’ mesenchyme. The ‘cardiac’ mesenchyme, however, fails to induce hepatic epithelium in the allantoic endoderm, which can differentiate heterotypically when cultured in combination with digestive tract mesenchymes. The evidence presented in this study suggests that the effect of ‘cardiac’ mesenchyme on the acquisition of hepatogenic potency in the endoderm is limited.
Étude autoradiographique de l’incorporation de 14CO2 dans des gastrulas d’Axolotl
Authors: Tencer R.
Published: April 2021

Regional incorporation of 14CO2 into Amphibian gastrulae has been followed by autoradiography. Differences in uptake of the tracer in different parts appear already in the early gastrula. These differences only affect the cytoplasm while the nuclei, heavily labelled, show very similar radioactivities. In the late gastrula, however, the nuclei show the same gradients of activity as the cytoplasm.
Interaction ectoderme-mésoderme dans la formation des invaginations uropygiennes des Oiseaux
Authors: Gomot Lucien
Published: April 2021

The culture in vitro of the tail-bud of duck embryos aged 8,9, and 10 days permits the formation of uropygial invaginations (rudiments of the preen gland) that normally appear on the 11th day of incubation. The separation of the various tissues of the tail-bud of 10-day duck embryos and their culture in association with some other duck embryonic tissues has made it possible to locate, at this stage, the ‘organizer’ of the preen gland in the superficial stratum of the dermis. The formation of the glandular invaginations results from an interaction between ectoderm and mesoderm, in which, at the beginning, only the mesoderm is specific. The ectoderm of chick embryos and rabbit embryos is able to react to contact with this mesoderm in the same way as the ectoderm of duck embryo.
The Formation of the Second Maturation Spindle in the Eggs ofLimnaea, Limax, andAgriolimax
Authors: Raven Chr. P. , Escher Frouke C. M. , Herrebout W. M. , Leussink J. A.
Published: April 2021

Egg maturation has been studied in Agriolimax reticulatus, Limax flavus, and Limnaea stagnalis with special regard to the formation of the second maturation spindle. In the three species the second maturation spindle arises by direct transformation from the deep centrosphere of the first maturation amphiaster. In Agriolimax reticulatus and Limax flavus there is a pair of centrioles moving apart to opposite poles of the developing spindle. In Limnaea stagnalis there is only one centriole, which remains undivided and moves as a whole to the outer pole of the spindle. The developing spindle in Agriolimax and Limax is symmetrical and gets an aster at both ends, arising in the cytoplasm outside the original centrosphere. The developing spindle of Limnaea stagnalis is asymmetrical, egg-shaped, and aster formation occurs at its pointed outer end only. The inner aster of the second maturation spindle in Limnaea is provided by the sperm aster, which fuses secondarily with the blunt inner end of the spindle. There are some indications that the fusion between these two structures is accompanied by a certain cytochemical activity in the region of fusion. The sperm aster in Limax flavus appears some time after the extrusion of the first polar body; it does not fuse with the second maturation spindle but disintegrates by vacuolization soon after the extrusion of the second polar body. In Agriolimax reticulatus no sperm aster has been observed. In the three species the dyads apply themselves closely against the centrosphere but do not penetrate into it. In Agriolimax and Limax they lie as a compact group on one side against the equatorial region of the developing spindle. In Limnaea they become arranged into an irregular ring, which encircles the outer pole of the developing spindle and gradually shifts to the equatorial region of the spindle. In the three species the dyads only penetrate into the spindle when the latter has been completely formed. The results are discussed with reference to the relationships in the Pulmonates in general. It is concluded that the sperm aster is a more or less rudimentary structure in this group. In Limnaea the sperm aster has taken on a new function in the mechanism of polar body extrusion. The primary cause of the atypical development of the second maturation spindle in Limnaea is, presumably, the precocious inactivation of the egg cyto-centre, which divides no more after the completion of the first maturation division.
Regional Differences in Catheptic Activity inXenopus laevisembryos
Authors: Deuchar E. M.
Published: April 2021

The total catheptic activity per embryo in X. laevis increases during gastrulation and early neurulation, decreases slightly during late neurulation, then increases again at the early tail-bud stage. When dorsal and ventral parts of gastrulae, neurulae, and tail-bud stages are compared, the catheptic activity per unit dry weight is highest in dorsal parts, but the absolute activity per part, and the activity per cell, are highest in ventral parts of the embryos. The catheptic activity is increased in the presence of 0 0024 M cysteinehydrochloride. The yolk platelets, separated from other cell-constituents by centrifuging, carry a considerable proportion of the catheptic activity, though not as much as the supernatant fraction. The possibilities that the catheptic activity gives rise to increased concentrations of free amino acids and that it assists in yolk breakdown are discussed.
Effect of a Leucine Analogue on Incorporation of Glycine into the Proteins of Explanted Chick Embryos
Authors: Schultz Phyllis w. , Herrmann Heinz
Published: April 2021

Amino acid analogues have been observed to give rise to abnormal forms of development of chick and amphibian embryos (Herrmann, 1953; Rothfels, 1954; Waddington & Sirlin, 1954; Feldman & Waddington, 1955; Herrmann, Rothfels-Konigsberg, & Curry, 1955). Assuming that these disturbances may be due to interference with the utilization of amino acids for protein formation, we have attempted an analysis of this effect by comparison of the protein contents and of the uptake of glycine into the proteins of chick embryo explants in the presence and absence of amino acid analogues. The results of such experiments are reported in this paper.
On Regeneration after the Amputation of Abnormal Structures
Authors: Newth D. R.
Published: April 2021

The bilateral removal of the posterior neural folds of axolotl neurulae may lead to the development of larvae in which a greater or lesser length of the ventral fin of the tail between the cloaca and a point just short of the tail-tip is missing. In other cases regulation permits the development of a normal-looking tail. The later amputation of such ‘normal’ tails, or of defective ones where the plane of amputation lies anterior to the defective region, is followed by the formation of normal regenerates. The amputation of defective tails where the plane of amputation passes through a region lacking ventral fin is followed by the formation of a regenerate lacking ventral fin as far posteriorly as a point just short of the tail-tip. The presence or absence of a ventral tail-fin in the regenerate depends upon its presence or absence in the plane of amputation, and is not otherwise related to the degree of abnormality of primary urogenesis. Tails which have defective ventral fins and poorly developed somitic musculature (as a consequence of simultaneous removal of posterior neural folds and part of the posterior medullary plate) behave in regeneration as do those lacking ventral fin only, even where the plane of amputation passes through a region with deficient somites. The removal of the dorsal half of the tail-bud of embryos of R. temporaria may also be followed by almost normal urogenesis as a consequence of regulation. In most cases, however, the resulting tails are extensively defective lacking a region of the dorsal fin, parts of the spinal cord, and having poorly developed somitic musculature. In nearly every case the amputation of these tails was followed by the formation of a regenerate that was normal if the original tail was ‘normal’ or if the plane of amputation lay anterior to the region of the tail which lacked a dorsal fin. Where the plane of amputation passed through a region lacking dorsal fin the regenerate was formed without one. In a very small number of cases exceptional and defective regenerates were formed, either after a first or a subsequent amputation, where normal ones were to be expected. The occurrence and significance of these exceptions are discussed. It is concluded that the successful completion of normal primary urogenesis in amphibians is not a prerequisite of the formation of a normal regenerate. It remains possible that the formation of normal regenerates from abnormal tails involves regulative properties in the blastema. The need for representation of tail-fin at the plane of amputation if it is to be present in the regenerate is further confirmation of the departure of amphibian tail regeneration from the pattern established for the urodele limb.
Recherches sur l’action tératogène du refroidissement temporaire de l’œuf de Poule au cours de l’incubation
Authors: Ancel P.
Published: April 2021

De très nombreux auteurs ont signalé les effets tératogènes de divers agents physiques sur l’œuf de Poule (incubation à des températures élevées ou basses, vernissage des œufs, secouage, prélèvement d’albumine, réalisation d’une fenêtre dans la coquille, radiations diverses, ultra sons etc.) avant ou pendant les premiers jours de l’incubation. Nous avons cherché à savoir si des malformations différentes de celles qui avaient été ainsi obtenues pouvaient l’être après la soixante-douzième heure de l’incubation. Nous avons choisi comme agent un choc thermique qui n’a pas d’action tératogène dans les premiers jours de l’incubation.
Cell Mixtures of Different Species and Strains of Cellular Slime Moulds
Authors: Bonner John Tyler , Adams Marcia Shaw
Published: April 2021

The cells of various species and strains of cellular slime moulds have been mixed by making grafts at the aggregation stage and by thoroughly mixing the cells at the migration stage. Depending upon the strains used, varying degrees of cell compatibility or adhesion between the cells was observed. There was either (l)a complete separation of the strains; (2) a partial merger to form a double fruiting body, one standing on the sorus of the other; (3) a single fruiting body on which the pre-spores of both strains regrouped to form two cohesive blocks of cells within one sorus.

This regrouping phenomenon is also characteristic of many dissociated animal cells where partially or completely differentiated cells will regroup with their kind. It is suggested that the basis of this regrouping phenomenon is the result of an intermediate degree of surface compatibility—not so great as to produce a complete separation of the cells, and not so little as to permit a random intermingling of the cells.
A Note on the Effects of some Cytotoxic Substances on Amphibian Embryos
Authors: Waddington C. H.
Published: April 2021

In connexion with the experiments of Jurand (1958) on the action of TEM on avian embryos, it seems worthwhile describing very shortly some observations on the effects of this substance, and also of Myleran, on early amphibian embryos. Bodenstein (1954 and earlier) has described some of the cytological results of the administration of various ‘radio-mimetic’ substances to amphibian embryos, including nitrogen mustards and TEM. The effects on the development of the eye were particularly considered, and they have also been discussed and illustrated by Töndury (1955). Two main types of damage were noted, the formation of giant cells, and of cellular degeneration accompanied by nuclear breakdown and the formation of deeply staining cytoplasmic lumps. The giant cells presumably arise from the suppression of cell-division followed by the formation of a restitution nucleus. These nuclei stain rather palely, and appear to be lacking in DNA. On the other hand, the cytoplasmic globules which are commonly met with appear to consist of RNA, and to indicate an over-production of that compound.
Experimental Tetraploidy in Newts 1
Authors: Fischberg M.
Published: April 2021

A simple method has been devised for producing tetraploid newts by means of a ‘heat’ treatment. The eggs of T. palmatus (helveticus) and T. vulgaris were at different stages, varying from 3 hours to hours after artificial insemination, exposed to warm water of 34° –38°C. for a duration of 10–12 minutes. A temperature treatment of 35 ·6° –36·0° C. proved to be the most successful for the production of tetraploid embryos and larvae. Treatment at the stage when the first cleavage furrow closes at the vegetative pole was found to be the only effective one. The eggs contain at this stage two interphase nuclei. The described treatment causes up to 24 per cent, of all treated eggs, or up to 93·7 per cent, of all analysed newts to develop into tetraploids. The probable cytological mechanism which leads to tetraploidy is discussed. Factors which seem to be of importance for the production of tetraploidy in other amphibian species, and some important problems which might be investigated with the help of this method, are mentioned.
Intestinal Development
Authors: Coulombre Alfred J. , Coulombre Jane L.
Published: April 2021

A description of chick duodenal morphogenesis is given. It is based on (a) quantitative measures of the change in size and shape of the duodenum, (b) a histogenetic study of the duodenal musculature, and (c) a quantitative description of changes in size, shape, and number of the duodenal villi throughout their development.

Correlation of these data on a developmental time-scale has led to the following hypotheses:

Mesenchymal cells are oriented by mechanical forces acting to distort a tissue. The orientation of smooth muscle is determined by the orientation of the premuscle mesenchyme in which it differentiates. In the wall of a hollow viscus such as the duodenum the contraction of the first layer of muscle to form will orient the remaining mesenchymal cells at right angles to itself, thus determining the orientation of the muscle-layers which subsequently differentiate. The duodenal villi are shaped by mechanical forces which act on the mucosa and which arise from epithelial expansion, on the one hand, and muscular contraction, on the other.
Genetical Studies on the Skeleton of the Mouse
Authors: Deol M. S.
Published: April 2021

A pilot experiment by Weber (1950) established the fact that the minor skeletal variations universally present in strains of tame mice are also encountered in wild populations; and that the incidence of individual variants may differ widely from population to population. In the decade since Weber’s work many new variants have come to light, and it seemed desirable to repeat his observations on the more extensive range of variants now available. An opportunity to do so presented itself in 1956 when wild mice from various localities in the eastern U.S.A, became available for study.
Inherited Retinal Dystrophy in the Mouse: its Appearance in Eyes and Retinae Cultured in vitro
Authors: Lucas D. R.
Published: April 2021

Certain strains of mice, such as C3H, exhibit a recessively inherited retinal dystrophy. This takes the form of a degeneration and complete disappearance of the visual cell layer; it begins on or about the 11th day of life and is nearly complete by the 19th day (Sorsby, Koller, Attfield, Davey, & Lucas, 1954). The process is remarkably uniform from litter to litter (Lucas & Newhouse, 1957).
An Ultra-Violet Light Method for Producing Haploid Amphibian Embryos
Authors: Selman G. G.
Published: April 2021

For several years in this laboratory, ultra-violet light has been used to produce haploid amphibian embryos, sometimes to provide haploid nuclei for transplantation experiments, as in Pantelouris & Jacob (1958). The ultra-violet method gives a high proportion of haploids, is very simple and speedy to carry out and involves the use of only inexpensive apparatus. Our method and results are described here to help others choose between this and alternative methods such as the use of toluidine blue by Briggs (1952), or X-rays by Lehman (1955) and Rugh (1939). Other methods are reviewed in Fankhauser (1937) and Drebinger (1951).
Cell differentiation in a temperature-sensitive stalkless mutant of Dictyostelium discoideum
Authors: Amagai Aiko , Ishida Shuji , Takeuchi Ikuo
Published: April 2021

A temperature-sensitive aggregateless and stalkless mutant was isolated from Dictyostelium discoideum NC-4. The mutant cells cannot aggregate at 27 °C, but aggregate and form normal fruiting bodies at 21 °C. When the temperature was shifted to 27 °C after aggregation at 21 °C, almost all of the cells in the aggregate differentiated into spores. Neither stalk cells nor stalk tubes formed at 27 °C. Inhibition of stalk formation was not lifted by addition of cyclic AMP.

Nevertheless, the proportion of prespore to total cells within the mutant slugs was normal, at both 21 °C and 27 °C. At 27 °C, a slug was transformed into a spherical cell mass at the end of migration, within which pre-existing prespore cells differentiated into spores. The remaining prestalk cells were then converted to prespore cells which later became spores. As the celltype conversion continued, formation of a spore mass resulted. The development of the mutant is thus consistent with the idea that the presumptive cell differentiation is directly related to the terminal cell differentiation.

During migration at 27 °C, the number of prestalk cells decreased in the anterior part of the slug but instead increased at the foot or the rear part, whereas the prestalk-prespore pattern remained normal at 21 °C. The fact that a normal proportion of prespore cells was maintained in spite of their deranged distribution at 27 °C indicates that the regulation of proportion is independent of the formation of pattern.
Growth and morphogenesis of the fibula in the chick embryo
Authors: Archer Charles W. , Hornbruch Amata , Wolpert Lewis
Published: April 2021

The development of the avian fibula was studied both histologically and experimentally. It was found that from the onset of chondrogenesis, the fibula possessed a smaller diameter than the neighbouring tibia. The truncated growth of the fibula was a result of the loss of its distal epiphysis between stages 27– 31. This epiphysis subsequently became fused to the tibia and formed the fibulare of the tibiotarsus. The experiment of Hampé (1960) was repeated by inserting tantalum barriers into the limb between stages 18 and 23: this sometimes prevented the separation of the fibula distal epiphysis, thus giving rise to an elongated element. A similar result was obtained from grafts of polarizing region into the leg bud at stages 18– 20. It was concluded that there was no evidence for competitive interaction between the blastemata of the tibia and fibula. In addition, the differential growth in diameters between the tibia and fibula was largely a result of differential osteogenesis rather than chondrogenesis as previously thought.
Proportion regulation without pattern formation in Dictyostelium discoideum
Authors: Oyama Masakazu , Okamoto Koji , Takeuchi Ikuo
Published: April 2021

When shaken in a glucose-albumin-cAMP medium, dissociated aggregative cells formed small clumps, in which both prespore and prestalk cells differentiated in essentially the same proportions as in a slug. Immunocytochemical staining of sections of such clumps revealed that the two types of cells showed no particular pattern of distribution, unlike the two-zoned prestalk-prespore pattern as observed in the slug.

Cells dissociated at stages later than the onset of aggregation always produced a constant proportion of prespore cells, irrespective of the initial proportion when transferred to the culture. Furthermore, prestalk cells fractionated from slugs and transferred to the culture restored almost the normal prespore proportion through conversion of the cell types, whereas proportion of unfractionated slug cells remained unchanged. We conclude from these findings that the normal prestalk-prespore pattern is not required for proportion to be regulated.
Somitogenesis in amphibia : IV. The dynamics of tail development
Authors: Elsdale Tom , Davidson Duncan
Published: April 2021

Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue.

Presegmental extension is entirely the result of activity within a narrow zone of extension that occupies the central region in the tail bud. Within the zone of extension, a minimum of six prospective somites undergo an eightto ten-fold extension along the axis. The zone passes posteriorly across the tissue of the tail tip. The anterior of the tail bud contains three extended prospective somites in the course of segmentation. The anterior boundary of the zone of extension coincides in space exactly with the anterior boundary of the zone of abnormal segmentation that results from temperature shock. This means that extension ceases immediately before the sudden tissue change associated with segmentation.
Postnatal muscle fibre histochemistry in the rat
Authors: Ho K. W. , Heusner W. W. , Huss J. Van , huss W. D. Van
Published: April 2021

Histochemical techniques were used to study the postnatal muscle fibre differentiation patterns in the plantaris and soleus muscles of male Sprague-Dawley rats. Nine groups of animals (n = 6/group) were killed at 1, 6, 11, 16, 21, 26, 31, 36, and 140 days of age. Serial transverse sections of the two muscles were stained with H & E, NADH-D, and myofibrillar ATPase with acid (pH 4·35) or alkali (pH 10·4) preincubation. In each of the age groups, all available fibres across the muscle sections were classified. Obtained data show that fibre types are basically undifferentiated at birth in both muscles.

In the plantaris muscle there are about 99 % type IIA and less than 1 % type I fibres at 6 days of age. Type IIB fibres can be identified at 11 days of age. There are increases in the percentages of type I fibres (from 0·7 % to 3·5 %) and type IIB fibres (from 1·1 % to 6·5 %) between 6 and 11 days and between 16 and 21 days respectively. By 36 days of age the relative numbers of type IIA, IIB, and type I fibres in the plantaris are approximately 80 %, 14 %, and 6 %, respectively. A gradual change in fibre-type composition continues until it becomes 47 % for type IIA, 43 % for type IIB, and 10 % for type I at 140 days of age.

In the soleus muscle there are approximately 73 % type IIA and 26 % type I fibres at both 6 and 11 days of age. However, type IIA fibres decrease to 44 % and type I fibres increase to 56 % at 16 days of age. This rapid shift in fibre composition continues up to 31 days of age when the distribution becomes 25 % for type IIA and 74 % for type I fibres. Thereafter, the differentiation rate is much slower. At 140 days of age, there are 17 % type IIA and 83 % type I fibres in the soleus muscle.

The results of this study show that the fibre populations in the plantaris and soleus muscles of the rat undergo a postnatal differentiation process. In both muscles the adult fibre population is established by 140 days of age. Although relatively rapid increases of type I and type IIB fibres occur in the plantaris during the second and third weeks of life, differentiation in that muscle appears to be an essentially continuous process. There is a notable shift in the fibre composition of the soleus muscle during the second postnatal week. Differences between the patterns of differentiation in the two muscles are apparent.
Further analysis of the effect of ultra-violet irradiation on the formation of the germ line inXenopus laevis
Authors: Thomas V. , Heasman J. , Ford C. , Nagajski D. , Wylie C. C.
Published: April 2021

Ultra-violet (u.v.) irradiation of the vegetal pole of newly fertilized eggs has three documented effects: reduction of primordial germ cells (PGCs), cytological damage to the vegetal hemisphere and disruption of the normal mechanism by which the vegetal yolk mass induces the formation of the dorsal axis of the embryo.

In this study, we find that 90° rotation of the egg for various periods after irradiation rescues the dorsal axial structures but does not restore the number of PGCs found in the dorsal mesentery of the gut; neither is there any correlation between reduced numbers of PGCs and disruption of cleavage at the vegetal pole. We therefore conclude that the effect on the germ line is separate from the other two phenomena.

Secondly, 90° rotation of non-irradiated eggs was found to significantly reduce germ cell numbers migrating in the dorsal mesentery of the gut.
H-2 antigens as markers of cellular genotype in chimaeric mice
Authors: Ponder B. A. J. , Wilkinson M. M. , Wood Maureen
Published: April 2021

We describe an immunohistochemical method, using monoclonal anti-H-2 antibodies, for demonstrating H-2 antigens in cryostat sections of a variety of mouse tissues. Double staining allows simultaneous demonstration of both cell populations in tissue sections from H-2b H-2k aggregation chimaeras.
Evidence for specific feedback signals underlying pattern control during vertebrate embryogenesis
Authors: Cooke Jonathan
Published: April 2021

Experiments are described in which sectors including dorsolateral mesoderm from early-neurula-stage amphibian embryos are grafted to the mid-ventral region of gastrula-stage hosts. The grafted tissue pursues an autonomous developmental sequence, though integrated into the host mesodermal mantle, so that such embryos develop a ventral strip of ectopic somite tissue, occasionally with a pronephric formation at one side. When the proportions in which mesodermal tissue has been assigned to the four basic territories of the host’s mediolateral pattern are assayed, a significant deficit in somite is characteristically found, though the phenomenon is variable in magnitude. It seems that the size of the host’s prone-phric territory may be diminished in a similar way, if an earlier differentiating ectopic pronephros is already joined to the system. These phenomena are discussed in relation to theories of biological pattern formation.
Transplantation of turtle embryonic thymus, into quail embryo : colonization by quail cells
Authors: Vasse J.
Published: April 2021

Turtle (Emys orbicularis L. ) embryo thymuses grafted in the somatopleure or onto the quail embryo chorioallantoic membrane developed in these heterotopic sites for 2–12 days.

When the thymus was removed from embryos at early stages such that no thymocytes were yet present during normal development, epithelial cells with mitoses were observed in the explants but no turtle thymocytes developed whatever the duration of explantation. An extrinsic origin of lymphoid precursor cells can explain such results. Quail lymphoid-like cells distinguishable from turtle cells by their nuclear structure began entering the explants 5 days after grafting. Their number increased progressively until the 12th day, when all the grafts were retrieved.

When an already lymphoid thymus was removed from embryos at later stages, turtle thymocytes remained fairly abundant in the explants until 5 days. Beyond this period, they gradually disappeared. After 11–12 days, none were left and only epithelial tissue from the turtle was present, showing excellent development. Quail lymphoid-like cells entered this more mature thymus following the same time course as they did in the early rudiment.

Thus we observed no difference between attraction of quail lymphoid cells by the precolonization thymic epithelium or by the lymphoid thymus.
Brachial muscles in the chick embryo: the fate of individual somites
Authors: Beresford Bonnie
Published: April 2021

The wing and wing-associated muscles of the shoulder and thorax in the bird all cleave from common myogenic masses in the developing wing bud and are referred to collectively as brachial muscles. In this study the precise embryonic origin of the brachial muscles was determined using chick-quail chimaeras. Such chimaeras consisted of a graft of one somite taken from a 2-day quail donor embryo transplanted to the equivalent location in a 2-day chick host embryo. The chimaeras were analysed at 9·5-10·0 days in ovo to determine the location of the grafted cells and therefore the structures that were derived from the transplanted somite. The somites that were studied in this manner were somites 13 to 23 inclusive. The results show that only somites 16 to 21 inclusive contribute cells to the brachial musculature; moreover, the cells from a given somite are not distributed randomly among the brachial muscles but populate specific muscles only: thus it has been possible to map the somitic origin of individual brachial muscles. Moreover, there is an indication that each somite plays a unique role in the development of the brachial muscles.
Non-random X-chromosome inactivation in mouse X-autosome translocation embryos—location of the inactivation centre
Authors: Rastan Sohaila
Published: April 2021

X-chromosome inactivation was investigated cytologically using the modified Katida method which differentially stains inactive X-chromosome material at metaphase in balanced -day female embryos heterozygous for four X-autosome rearrangements, reciprocal translocations T(X;4)37H, T(X;11)38H and T(X;16)16H (Searle’s translocation) and the insertion translocation Is(7;X)1Ct (Cattanach’s translocation). In all cases non-random inactivation was found. In the reciprocal translocation heterozygotes only one translocation product ever showed Kanda staining. In addition in a proportion of cells from T(X;4)37H, T(X;11)38H and Is(7;X)1Ct the Kanda staining revealed differential staining of X-chromosome material and attached autosomal material within the translocation product.

In a study of -day female embryos doubly heterozygous for Searle’s translocation and Cattanach’s translocation two unbalanced types of embryo were found. In one type of unbalanced female embryo of the karyotype 40(X(7)/X16;16/16) no inactivated X-chromosomal material is found. A second unbalanced type of female embryo, of the presumptive karyotype 40(X(7)/XN;16x/16) was found in which two inactivated chromosomes were present in the majority of metaphase spreads. A simple model for the initiation of X-chromosome inactivation based on the presence of a single inactivation centre distal to the breakpoint in Searle’s translocation explains these findings.
20-hydroxyecdysone stimulates tissue-specific yolk-protein gene transcription in both male and femaleDrosophila
Authors: Bownes Mary , Blair Mairearad , Kozma Robert , Dempster Maureen
Published: April 2021

The yolk polypeptides of Drosophila are normally synthesized in the fat body and ovarian follicle cells of adult females. In response to 20-hydroxyecdysone males synthesize yolk polypeptides. The actual level of yolk polypeptides synthesized in males is not always a direct reflection of the YP-transcripts present. Initially YP-transcripts are efficiently translated into polypeptides whereas later they are not and the YP-transcripts can have a half-life of less than 8h in males. We suggest that the expression of the genes coding for the yolk polypeptides in males may be regulated at transcriptional and translational levels. Treatment of females with 20-hydroxyecdysone leads to a transient increase in YP-transcript accumulation, but the response is difficult to assess in whole flies due to the high variability in transcript levels during normal development.

Analysing the response to 20-hydroxyecdysone at the level of specific tissues shows that transcript accumulation is dramatically increased in body walls (fat-body cells, epidermis and oenocytes) of both males and females. Gut, Malpighian tubules, testis and ovaries are not affected. Treatment of females with 20-hydroxyecdysone followed by measuring YP-transcript accumulation over the next 24 h in ovaries and body walls separately, confirms that only body walls respond to the hormone. There is an increase in yolk-polypeptide synthesis during the period of increased YP-transcript accumulation in females.

We conclude that the response of the YP-genes to 20-hydroxyecdysone is tissue-, but not sex-specific.
Dorsalization and neural induction: properties of the organizer inXenopus laevis
Authors: Smith J. C. , Slack J. M. W.
Published: April 2021

We have studied the action of the organizer in Xenopus laevis using grafts labelled with horseradish peroxidase (HRP). Orthotopic grafts of the dorsal marginal zone (the organizer) from an HRP-labelled embryo into an unlabelled host showed that this region contributes to the anterior archenteron wall, to the entire craniocaudal extent of the notochord and to a few cells in the somites. Little or no contribution was made to the neural tube. Orthotopic grafts of the ventral marginal zone (the tissue that responds to a grafted organizer) indicated that it only contributes to the posterior half of the embryo. Within this region it spreads around the entire ventrolateral mesoderm, occasionally contributing a few cells to the somites. The posterior endoderm was also heavily labelled.

When the dorsal marginal zone from an HRP-labelled embryo was inserted into a slit cut in the ventral marginal zone of an unlabelled host a mirror-symmetrical double-dorsal duplicated embryo resulted, in which only the notochord and a few cells in the somites of the secondary embryo were derived from the graft. The bulk of the secondary somites was, therefore, derived from host ventral marginal zone tissue which normally makes very little contribution to the somites. This indicates that host ventral marginal zone becomes dorsalized by the graft. The neural tube of the secondary embryo was also unlabelled, showing that it was induced by the influence of the graft on the overlying ectoderm, which normally forms ventral epidermis.

We have also grafted ventral marginal zone tissue into a slit cut into the dorsal marginal zone of a host embryo. HRP-labelled tissue was grafted into an unlabelled embryo and vice versa. This graft did not produce a double ventral embryo and this reinforces the traditional view that the dorsal marginal zone is a special signalling region. Instead, the resulting embryos usually had a twinned notochord with the graft tissue in between, differentiated as somite. This confirms that juxtaposing ventral and dorsal marginal zone ‘dorsalizes’ the ventral tissue but does not affect the dorsal tissue which differentiates, as usual, as notochord. Thus, our results allow us to conclude that the organizer mediates two distinct interactions in bringing about the formation of duplicated embryos. The first is dorsalization of adjacent ventral mesoderm and the second is the induction of neuroepithelium from ectoderm overlying the new archenteron roof.
Homeotic transformations of the abdominal segments ofDrosophilacaused by breaking or deleting a central portion of the bithorax complex
Authors: Morata Gines , Botas Juan , Kerridge Stephen , Struhl Gary
Published: April 2021

In Drosophila, genes in the centromere-proximal portion of the bithorax complex (BX-C) have been shown to control the development of the metathorax, and parts of the mesothorax and first abdominal segment. Here, we explore the roles of genes positioned more distally by examining the larval and adult phenotypes caused by a breakpoint and deletion in the middle of the complex. We find that both aberrations affect only abdominal segments, transforming the more anterior segments towards the first abdominal segment, and the remaining segments into a graded series of novel segment types which are partially transformed towards more anterior abdominal segments. Moreover, the adult transformations, which we have observed in somatic clones of mutant cells, are in close accord with the transformations observed in mutant first instar larvae, and appear to be expressed in a cell autonomous fashion. We discuss these results in the light of current views of the organization and function of the complex.
Development and motor innervation of a distal pair of fast and slow wing muscles in the chick embryo
Authors: Laing N. G. , Lamb A. H.
Published: April 2021

The chick wrist muscle ulnimetacarpalis dorsalis (umd) has two heads. Using myosin ATPase and acetylcholinesterase (ACh.E) staining it was shown that one of the heads is composed almost entirely of acid-stable muscle fibres with multiple end plates (slow muscle fibres) and the other of acid-labile fibres with single end plates (fast muscle fibres). The development of the muscle was traced from E7 (Stage 32-33) when it is a relatively homogeneous mass, to E18. The two heads of the muscle are first distinguishable, by ATPase staining, at E8 (Stage 33-34) prior to their cleaving. Both heads of the muscle are innervated by motoneurons positioned laterally in the lateral motor column in spinal segments 15 and 16. There is no observable difference in the positions of the motoneuron pools to the two heads. At E18 the motoneurons innervating the fast head tend to be slightly larger than those innervating the slow head.
Epithelial enhancement of connective tissue differentiation in explanted somites
Authors: Swalla Billie J. , Solursh Michael
Published: April 2021

This paper examines the differentiation of somites from stage-16 or -17 chick embryos cultured with or without notochord in explant cultures. Histological sections of the cultures were stained with a trichrome stain to identify the different kinds of connective tissues formed. Both anterior and posterior (epithelial) somites made muscle, cartilage and loose connective tissue in explant culture. The extent of cartilage differentiation was enhanced by the presence of the notochord, confirming earlier studies. The presence of 1 mM-dibutyryl cAMP in the culture medium increased the amount of muscle found in the explants but by histological criteria did not inhibit chondrogenesis, contrary to earlier reports. The addition of quail ectoderm to the explants stimulated loose connective tissue to form directly beneath it, suggesting for the first time a role of the ectoderm in dermatome differentiation. These results suggest that the epithelial somite has the capacity to differentiate into all three connective tissue types even before it has separated into sclerotome and dermamyotome. The relative amount of different connective tissue types can be influenced by environmental factors, such as adjacent epithelia like the notochord or ectoderm.
The nature of intercellular coupling within the preimplantation mouse embryo
Authors: Goodall H. , Johnson M. H.
Published: April 2021

The changing nature of intercellular coupling during the 4- and 8-cell stages of mouse early development has been investigated by iontophoretic injection of carboxyfluorescein, horseradish peroxidase and current into individual blastomeres in either the intact embryo or after their disaggregation and reaggregation into pairs. Coupling junctions that allowed only molecules of low molecular weight (putative gap junctions) were found not to appear until 2– 5 h beyond the 3rd cleavage division (8-cell stage). However, intercellular junctions that were not size selective were detected in intact embryos only throughout the 4- and 8-cell stages. It is proposed that this junctional communication results from the persistence of midbodies through all or part of the two, and in a few cases the three, cell cycles following their formation at the first and second cleavage divisions. We conclude that the cells of the early mouse embryo may be linked in a more extensive syncytial network than was hitherto suspected.
La compétition entre les éléments osseux du zeugopode de Poulet
Authors: Hampé par Armand
Published: April 2021

En traitant les bourgeons de patte de Xenopus avec une substance toxique, Tschumi (1954) observe une réduction progressive du nombre de doigts à mesure que la dose de substance toxique augmente. C’est d’abord le premier doigt qui disparaît, puis le quatrième et ensuite le deuxième. Le troisième doigt subsiste en dernier lieu. Cette règle s’observe aussi chez les Oiseaux. L’irradiation aux rayons X du bourgeon de patte par M. Schué (1951) conduit à une perte successive des 1er, 4ème, 2ème et 3ème doigts; cet ordre est toujours respecté. Étant donné que tous les éléments osseux présumés sont touchés et partiellement détruits par l’irradiation, on peut admettre que tous les éléments cellulaires disponibles, quelle que soit leur origine, sont mobilisés par priorité vers la formation du troisième doigt. S’il y en a davantage, ce sont les 2ème, 4ème et 1er doigts qui seront constitués.