bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental expression of the mouse Evx-2 gene: relationship with the evolution of the HOM/Hox complex
Authors: Dollé Pascal , Fraulob Valérie , Duboule Denis
Published: April 2021

The mouse Evx-2 gene is located in the immediate vicinity of the Hoxd-13 gene, the most posteriorly expressed gene of the HOXD complex. While the Evx-1 gene is also phys ically linked to the HOXA complex, it is more distantly located from the corresponding Hoxa-13 gene. We have analysed the expression of Evx-2 during development and compared it to that of Evx-1 and Hoxd-13. We show that, even though Evx-2 is expressed in the developing CNS in a pattern resembling that of other Evx-related genes, the overall expression profile is similar to that of the neigh bouring Hoxd genes, in particular with respect to the devel oping limbs and genitalia. We propose that the acquisition of expression features typical of Hox genes, together with the disappearance of some expression traits common to Evx genes, is due to the close physical linkage of Evx-2 to the HOXD complex, which results in Evx-2 expression being partly controlled by mechanisms acting in the HOX complex. This transposition of the Evx-2 gene next to the Hoxd-13 gene may have occurred soon after the large scale duplications of the HOX complexes. A scheme is proposed to account for the functional evolution of eve-related genes in the context of their linkage to the HOM/Hox complexes.
Insect embryogenesis - what is ancestral and what is derived?
Authors: Tautz Diethard , Friedrich Markus , Schröder Reinhard
Published: April 2021

The systematic genetic analysis of Drosophila development has provided us with a deep insight into the molecular pathways of early embryogenesis. The question arises now whether these insights can serve as a more general paradigm of early development, or whether they apply only to advanced insect orders. Though it is too early to give a definitive answer to this question, we suggest that there is currently no firm reason to believe that the molecular mechanisms that were elucidated in Drosophila may not also apply to other forms of insect embryogenesis. Thus, many of the Drosophila genes involved in early pattern formation may have comparable functions in other insects and possibly throughout the arthropods.
Factors affecting Vertebral Variation in Mice
Authors: McLaren Anne , Michie Donald
Published: April 2021

By means of X-ray photography the number of lumbar vertebrae was counted in samples of mice from 11 colonies of the C3H inbred strain. The results confirm Green’s (1953) finding that, of the three main substrains of the C3H strain, one (C3H/He) has predominantly 6 lumbar vertebrae while the other two (C3H/St and C3H/Bi) have predominantly 5 lumbar vertebrae. In addition, the new data have revealed three factors with significant effects on vertebral variation within substrains of the C3H strain: A fluctuating variable of the mother’s physiology which affects the prenatal development of the offspring. A difference between the sexes. The percentage of mice with 5 lumbar vertebrae is higher among males than among females. Divergences between colonies of the same substrain. The available data are not competent to distinguish the relative contributions to these divergences of nature and nurture.
The Significance of Inductive Relationships in the Development of Vertebrates
Authors: Medawar P. B.
Published: April 2021

One of the most conspicuous characteristics of the development of vertebrates is the adaptive specialization of pre-gastrular larvae. The eggs of vertebrates are laid upon land, in fresh water, in the sea, or within the mothers; the quantity of yolk they contain varies from the minute to the almost prodigious; they may develop at temperatures ranging from little above zero to little below 40° C., and at very different rates; the membraneous investments of egg and embryo are of widely different kinds; and so on. And accordingly we find that, although the strategy of pre-gastrular development is much the same in all vertebrates (inasmuch as all early development is directed towards the establishment of an axiate neurula of very uniform pattern), the overt tactics are in the very highest degree diverse. One need only reflect upon the variety of manœuvres that lead to the formation of endoderm, or upon the very different patterns of chorda-mesodermal invagination, to be convinced that this proposition is a truism.
Localisation et dosage du lithium dans les embryons d’Amphibiens
Authors: Ficq Adrienne
Published: April 2021

An estimate of content and localization of lithium within lithium-treated amphibian embryos has been made by means of autoradiography after neutron irradiation.

An accumulation of lithium in the dorsal part of the embryo and a concentration associated with the pigment granules was observed.

Nous tenons à remercier le Centre de Physique nucléaire de Bruxelles et en particulier M. le Dr Picciotto pour l’aide et les conseils qu’il nous a prodigués à l’occasion de ce travail. Notre gratitude va également au Service de la Pile de Châtillon et à Mme H. Faraggi grâce à qui les irradiations ont pu être effectuées.
Chlorure de lithium et biochimie du développement de l’œuf d’Amphibien
Authors: Lallier R.
Published: April 2021

The action of lithium chloride on the metabolism of carbohydrates was investigated in the amphibian Rana temporaria. Anaerobic glycolysis was inhibited in lithium-treated embryos. Lithium chloride had no action on the activity in vitro of hexokinase and aldolase, but inhibited the activity of triosephosphate-dehydrogenase. Lithium chloride inhibited the increase in oxygen consumption during embryonic development. Lithium treatment did not modify the respiratory quotient. Normal gastrulae, in the presence of intermediary substrates of carbohydrate breakdown, showed an increased oxygen consumption. This increase was slight or absent in lithium-treated gastrulae. Potassium ions compensated for the inhibition of respiration in lithium-treated gastrulae, and restored oxygen consumption to normal. Dehydrogenase activity was 25 per cent, inhibited in lithium-treated gastrulae. Lithium chloride did not affect the activity of cytochrome-oxidase. The intracytoplasmic sedimentable particulate material, mitochondria and microsomes, suffered a considerable loss of ribonucleic acid in lithium-treated gastrulae. This effect of the lithium ion on the particulate material seems to be fundamental in the development of the morphological and metabolic alterations appearing in the course of embryonic development.
The role of neurohumors in early embryogenesis
Authors: Buznikov G. A. , Chudakova I. V. , Vyazmina N. M. , Berdysheva L. V.
Published: April 2021

In a previous paper (Buznikov, Chudakova & Zvezdina, 1964) it has been reported that serotonin (5-hydroxytryptamine, 5-HT) may be involved in early embryogenesis in various groups of animals. This conclusion was confirmed by Baker’s recent publication (Baker, 1965) concerning 5-HT synthesis in Xenopus laevis embryos.
Natural and synthetic materials with insect hormone activity
Authors: Masner P. , Sláma K. , Landa V.
Published: April 2021

The juvenile hormone of insects is known to inhibit the process of insect metamorphosis. It is also known to stimulate ovarian growth in adult females of some species. It has been found recently that some substances with juvenile hormone activity also influence embryonic development. In the bug Pyrrhocoris apterus such substances, which prevent imaginai differentiation in metamor-phosis, also affect the differentiation process of embryos at a certain stage of egg development (Sláma & Williams, 1966). This has been confirmed with other juvenile hormone analogues on embryonic development of silkworm eggs (Riddiford & Williams, 1967) and grasshoppers (Novák, 1967).
Action of nuclear and cytoplasmic fractions of liver homogenate on liver growth in the chick embryo
Authors: Tumanishvili G. D. , Salamatina Naira V.
Published: April 2021

A number of observations have been made during a study of the regulation of organ growth which lead to the conclusion that there is a certain correlation between the density of cell packing and mitotic activity in the tissue (Tumanishvili, 1964, 1965a, b;Tumanishvili & Tabidze, 1962, 1963). The density of cell packing is expressed as the concentration of nuclei (CN), reflecting not only the number of cells in a given tissue volume, but an aspect of interrelation of nuclei and cytoplasm as well. Observations have shown that an increase in mitotic activity always leads to an increase in the concentration of nuclei, and a decrease to a decrease. At the same time an increase in the concentration of nuclei appears to cause suppression of mitotic activity, while a decrease of the nuclear concentration to cause vigorous cell division. Thus mitotic activity and nculear concentration form a typical circuit with a negative feed-back mechanism where M is mitotic activity and CN is the nuclear concentration in the tissue.
Cell adhesion and movement in relation to the developing limb pattern in normal and talpid
3 mutant chick embryos
Authors: Ede D. A. , Agerbak G. S.
Published: April 2021

Descriptive studies of the talpid2 chick embryonic lethal mutant (ta3//a3) have suggested that the multiple effects produced by this gene are of mesodermal origin, and that they arise from defective mesenchymal cell movement and condensation (Ede & Kelly, 1964a, b). It may be argued that condensation in vivo is comparable to cell reaggregation of dissociated cells in vitro, and that defects in the former are likely to be reflected in the latter. In this case it should be possible to obtain experimental verification of this effect of the gene at the cellular level, using the quantitative methods for assessing aggregation developed by Moscona (1961a, b) and Curtis & Greaves (1965). The experiments reported here show a clear genetic effect upon cell adhesion in the wing-bud mesenchyme of the talpid3 mutant.
An electron-microscope study of centrioles in differentiating motor neuroblasts
Authors: Lyser Katherine M.
Published: April 2021

Mature neurons with centrioles were first described at the end of the nine-teenth century and have been observed in many animals (see Cajal, 1911; Ariens Kappers, Huber & Crosby, 1936). As mitosis rarely, if ever, occurs after morphological differentiation of the neuroblast begins, the function of the centrioles in nerve cells posed a problem which has yet to be resolved. Held (1909) described centrosomes in differentiating neuroblasts as being associated with the ‘fibrillogenous zone’, which suggests a role for the centriole in the differen-tiation of neurofibrils.
The effect of hydrocortisone acetate on the development of mouse embryos
Authors: Jurand A.
Published: April 2021

Hydrocortisone (Kendall’s compound F, 17-hydroxycorticosterone, Cortisol) and cortisone (Kendall’s compound E, 17-hydroxy-ll-dehydrocorticosterone) have been widely used in medicine for about 20 years, first as adrenal hormones in substitution therapy. Since the discovery of Hench, Kendal, Slocumb & Polley (1949) that cortisone is beneficial against a wide range of rheumatic diseases and against all forms of arthritis, many more types of diseases have been added in later years to the list of ailments curable with cortisone, namely bronchitis, bronchial asthma, pulmonary tuberculosis, colitis, various inflammatory conditions and certain skin, blood and eye diseases. Hydrocortisone is used against the same diseases as cortisone; in fact, it is believed that cortisone becomes pharmacologically active only after conversion to hydrocortisone in the liver (Cope, 1964). Particularly in the inflammatory conditions cortisone must be converted to hydrocortisone to become antiphlogistic (Applezweig, 1962).
Enzyme ontogeny in normal and hemimelic limbs of mice
Authors: Long Sally Y. , Johnson E. Marshall
Published: April 2021

The appearance of electrophoretically separable isozyme patterns is specific both to type of tissue and to its stage of development (Markert & Moller, 1959), In abnormally developing embryonic systems there are alterations in the time of initial appearance and the persistence of isozymes from a variety of metabolic areas (Johnson &Spinuzzi, 1966, 1968). In malformed embryos from folic-acid-deficient rats the altered zymogram patterns of esterases from abnormal limbs were different from those of abnormal kidneys, yet differentiation of zymograms from the normal hearts of these embryos was unaltered. This implies a correlation between altered tissue-specific zymogram patterns and abnormally developing systems, though no causal relationship has as yet been shown (Johnson, 1968), Moreover, when tibial hemimelia in the rat was elicited by two different teratogens—a folic acid antagonist, 9-methylpteryol-glutamic acid (PGA), and the alkylating agent N-nitroso-iV-methylurea (NNMU)—there were similar changes in the non-specific esterases after electrophoretic separation of homo-genates from the defective limbs (Johnson & Lambert, 1968).
Nucleic acid and protein synthesis and pattern regulation in hydra: II Effect of inhibition of nucleic acid and protein synthesis on hypostome formation
Authors: Clarkson S. G.
Published: April 2021

In a previous paper (Clarkson, 1969) data were presented which indicate that hypostome determination is accompanied by a large and rapid burst of RNA synthesis, a slight stimulation of protein synthesis, and no increase in DNA synthesis. More direct evidence concerning the relative importance of these metabolic activities in hypostome determination is reported in this paper.
Polysyndactyly, a new mutant gene in the mouse
Authors: Johnson D. R.
Published: April 2021

Our understanding of the mechanisms underlying mutant genes affecting the limb skeleton is very incomplete. At this stage description of new phenotypes is still valuable, especially when they differ markedly from those previously described and have counterparts in man.
RNA synthesis in the early embryogenesis of a fish (Misgurnus fossilis)
Authors: Kafiani C. A. , Timofeeva M. J. , Neyfakh A. A. , Melnikova N. L. , Rachkus J. A.
Published: April 2021

Synthesis of ribonucleic acids in early embryos has been extensively studied during recent years in a number of laboratories and has been shown to begin shortly after fertilization (Kafiani, Tatarskaya & Kanopkayte, 1958; Wilt, 1963; Brown & Littna, 1964; Decroly, Cape & Brachet, 1964; Glišin & Glišin, 1964; Kafiani & Timofeeva, 1964, 1965; Nemer & Infant, 1965). Early embryos of Xenopus (Brown & Gurdon, 1964; Brown & Littna, 1964, 1966) and of sea urchins (Wilt, 1963; Glišin & Glišin, 1964; Nemer & Infant, 1965) synthesize up to gastrula stage predominantly or exclusively polydisperse RNA of a non-ribosomal nature usually referred to as DNA-like RNA (dRNA).
Myogenesis in chick embryo somites in vitro
Authors: Ellison M. L. , Ambrose E. J. , Easty G. C.
Published: April 2021

Evidence from a number of studies (e.g. Holtzer, 1964; Coon & Cahn, 1966; Konigsberg, 1963) has suggested that the differentiation of some types of cells in vitro may be influenced by environmental factors. Culture conditions can permit or prevent the phenotypic expression of characteristics already determined in the cells.
The influence of the nucleus on sequential determination in frog ectoderm following induction by lithium ion
Authors: Ansevin Krystyna D.
Published: April 2021

It appears certain that the process of cellular differentiation is an outcome of interactions between the cell nucleus and cell cytoplasm. Differentiation of embryonic amphibian ectoderm involves two fairly distinct phases: during the first short period an inductor (or some intrinsic factor, if an inductor is absent) determines the course of future differentiation in a multipotential cell; during the second, longer interval of time presumably a complex sequence of reactions leads to physiological and morphological differentiation. Little is known about the nature of reactions which take place during the first phase when the cells become developmentally determined by the inductor. It appears that the first step in translation of the inductive instruction in the competent cell is accomplished during the first 2 or 3 h following the treatment with the inductor (Ansevin, 1966). The step is not actinomycin-sensitive (Ansevin, 1965), as was shown by cells that completely recovered after actinomycin treatment (in conditions when it was unlikely that they could have failed to take up some inhibitor). This suggests that transcription of RNA does not have to occur during cell determination, but it does not exclude the possibility that induction removes biological repressors from specific genes which thus become available to direct cellular differentiation along a specific line. Barth (1965) has drawn attention to a striking similarity between the power of several inorganic ions to bind to DNA and the capacity of the same ions to act as embryonic inductors. He suggested that ions might compete with histones for active sites on DNA molecules, and by binding on these sites protect the molecules from the inactivating action of histones.
Differentiation capacities of the prospective tail somite region of the neural plate in the embryos of Ambystoma mexicanum
Authors: Niazi I. A.
Published: April 2021

The hind part of the neural plate in amphibian embryos has a mesodermal significance although it occupies an ectodermal position till late neurula stage. In anurans it gives rise to the posterior tail somites (Smithberg, 1954) and in urodeles the somites of the posterior trunk region and of the entire tail together with several other mesodermal structures (Bijtel, 1931; Nakamura, 1938; Aufsess, 1941; Spofford, 1945; Chuang, 1947; Ford, 1949). Presence of mesoderm in the neural plate is an interesting developmental problem. During normal gastrulation this region is at first underlaid by the future anterior part of the archenteric roof which exerts a neuralizing inductive influence. It is only later that the posterior part of the notochord with its mesodermalizing influence comes to lie under it. According to Eyal-Giladi (1954), who worked on gastrula stages of the Axolotl, even a short and transient contact of the invaginating archenteric roof with the overlying ectoderm produces archencephalic induction in the latter. It is therefore relevant to ask whether the posterior part of the neural plate does or does not pass through a phase of neuralization before assuming mesodermal properties. This specific question has not been investigated although a number of workers have studied the determination, differentition capacities or inductive properties of the caudal portion of the neural plate in amphibians (Bytinski-Salz, 1931; Bijtel, 1936, 1958; Chuang, 1947; Nakamura, 1947; Spofford, 1948; Smithberg, 1954). Spofford (1948) demonstrated that in Ambystoma mexicanum neurulae the tail notochord induces the overlying ectoderm to acquire mesodermal properties. He replaced the posterior part of the neural plate by a piece of competent ectoderm which itself had never been subjected to the influence of a neural inductor. This technique could demonstrate that, under experimental conditions, the so-called transformation or mesodermalization need not be preceded by activation or neuralization. These results, however, do not show whether this is also true during normal embryogenesis.
Nouvelles observations sur les facteurs qui contrôlent l’érythropoïèse in vitro
Authors: Salvatorelli Germano
Published: April 2021

Nous avons démontré précédemment que l’association de fragments de foie embryonnaire à des expiants de moelle osseuse de poulet s’est montrée très favorable au maintien du processus de l’érythropoïèse médullaire. Dans ces conditions expérimentales en effet, même après 15 jours de culture la structure et la composition cellulaire des expiants sont comparables à celles existant in vivo. En particulier, en ce qui concerne la série rouge tous les stades de la différencia-tion cellulaire depuis la cellule souche jusqu’à la cellule sanguine mûre sont présents dans nos expiants et dans des proportions comparables à celles qu’on retrouve dans la moelle osseuse normale.
The formation of somites in Xenopus
Authors: Hamilton Louie
Published: April 2021

The cell movements and contacts in somite formation in Xenopus are unusual. The vertebrate somite as seen in section is traditionally described as a rosette and is formed by pinching off a group of cells from the paraxial mesoderm; these cells then increase intercellular contacts. Typical rosettes with cells radiating from the myocoel may be seen in the Axolotl (Fig. 1 A). Not all the cells of a rosette have the same fate. The lateral ones become dermis and spread out under the epidermis forming a continuous sheet with their counterparts from neighbouring somites. The majority of the somitic cells, which are myotomal, will elongate antero-posteriorly and fuse end to end with other cells of the same somite (Przybylski & Blumberg, 1966; Riabova, 1966). In this way myotubes are formed which stretch from one end of the somite to the other and obliterate the myocoel. Somites are formed in an orderly anterior-posterior succession.
Histogenesis of lymphoid organs in larvae of the South African clawed toad, Xenopus laevis (Daudin)
Authors: Manning Margaret J. , Horton John D.
Published: April 2021

Before embarking on a study of the lymphoid system of an amphibian larva, it is necessary to realize that lymphoid tissue may occur in many organs of the body and that in all immature vertebrates and in adult poikilotherms separation of lymphoid tissue from myeloid tissue is incomplete (Yoffey, 1960). Jordan (1938) reviewed the early work on the haemopoietic tissues of Amphibia.
Le rôle du mésoderme somitique dans la morphogenèse précoce des membres de l’embryon de Poulet
Authors: Pinot Par Madeleine
Published: April 2021

La morphogenèse des membres a fait l’objet de nombreux travaux chez l’embryon de Poulet. Les recherches récentes concernent surtout les processus intervenant après l’apparition de l’ébauche du membre, et conduisant à sa morphologie définitive. Le premier stade de développement du membre consiste en une condensation localisée du mésoderme de la somatopleure. Par la suite seulement, l’ectoderme sus-jacent acquiert un aspect morphologique particulier: une crête épaissie à l’extrémité distale. Les causes de la condensation initiale du mésoderme ne sont pas connues. Le rôle déterminant du constituant mésodermique comme initiateur du développement du membre a été clairement mis en évidence par Kieny (1959, 1960). Le constituant mésodermique isolé, greffé sous l’ectoderme du flanc, peut induire la formation d’une crête apicale dans l’ectoderme sus-jacent, et provoquer ainsi le développement d’un membre surnuméraire. A quel moment et sous quelles influences le mésoderme acquiert-il cette propriété ?
The inhibitory effect of tetracycline on osteogenesis in organ culture
Authors: Kaitila Ilkka , Wartiovaara Jorma , Laitinen Ossi , Saxén Lauri
Published: April 2021

Two characteristics of the tetracycline-group antibiotics have recently focused the special attention of teratologists: these drugs are known to pass readily across the placental ‘barrier’ (Charles, 1954; Frost & Villanueva, 1960; Gibbons & Reichelderfer, 1960; Hughes, Lee & Flood, 1965; Simpson, Burnette & Bawden, 1967), and they are incorporated into the foetal skeleton, where they may remain for long periods and can be detected owing to their brilliant fluorescence (Rail, Loo, Lane & Kelly, 1957; Milch, Rail & Tobie, 1957, 1958; Bevelander, Rolle & Cohlan, 1961; Urist & Ibsen, 1963; Michelson, 1964). The question of whether they exert a harmful effect on bone formation and mineralization in mammals, however, is still a matter of controversy. There is no doubt that tetracycline interferes with mineralization of the skeletal tissue in certain lower vertebrates (Bevelander, Goldberg & Nakahara, 1960; Bevelander & Cohlan, 1962), and prevents calcification of mammalian bones in organ culture (Saxén, 1966a, b). Reports of in vivo studies in mammalian species have yielded more confusing results.
The role of the zona pellucida in the development of mouse eggs in vivo
Authors: Modlński Jacek A.
Published: April 2021

Up to the present time the function and significance of the zona pellucida in the development of mammalian eggs has not been fully explained. Zona-free mouse eggs will develop in vitro from the 2-cell stage, or later, up to the blastocyst stage (Tarkowski, 1961; Mintz, 1962; Gwatkin, 1963). Single blastomeres isolated at the 2-cell (Mulnard, 1965), 4- and 8-cell stage (Tarkowski & Wrób-lewska, 1967) will also develop in vitro up to the blastocyst stage. Similar experiments on development in vitro of 1- and 2-cell rabbit eggs (Edwards, 1964) showed that in this species also cleavage can occur when the zona pellucida is absent, although the blastomeres exhibit a tendency to fall away from each other.
The role of neurohumours in early embryogenesis
Authors: Buznikov G. A. , Kost A. N. , Kucherova N. F. , Mndzhoyan A. L. , Suvorov N. N. , Berdysheva L. V.
Published: April 2021

In previous papers (Buznikov, Chudakova & Zvezdina, 1964; Buznikov, Chudakova, Berdysheva & Vyazmina, 1968) we reported that fertilized eggs of the sea-urchin Strongylocentrotus dröbachiensis synthesized a number of neurohumours, such as serotonin (5-hydroxytryptamine, 5-HT), acetylcholine (ACh), adrenalin (A), noradrenalin (NA) and dopamine. Synthesis of 5-HT was also demonstrated in the fertilized eggs of the loach Misgurnus fossilis and some marine Invertebrata. In experiments with sea-urchin embryos we were able to trace regular changes in the level of 5-HT, ACh, A and NA, related to the first cleavage divisions. This early onset of neurohumour synthesis, as well as regular changes in their level, suggests their direct involvement in the regulation of the first cleavage divisions.
Cleavage rate of mouse embryos in vivo and in vitro
Authors: Bowman Patricia , McLaren Anne
Published: April 2021

Mouse embryos (Q strain) developing in vivo from the 2-cell to the blastocyst stage showed a constant cell doubling time of about 10 h. Embryos cultured in vitro over the same period showed a rate of cleavage which was initially almost as great as in the reproductive tract, but subsequently declined to give a doubling time of about 24 h. Addition of oestrogen to the culture medium increased the diameter of blastocysts but did not increase cell number.
Thyroid hormone effects on chick scale morphogenesis and keratinization
Authors: Lawrenz Nancy K. , Johnson Leland G.
Published: April 2021

The effects of thiourea injection on scale development were studied in New Hampshire Red × White Leghorn Cross chick embryos.

Normal morphogenesis and keratinization of scales were significantly delayed in thioureatreated specimens. Subsequent thyroxine injection resulted in normal or even precocious scale development.

The thyroid hormone responsiveness of scale development is discussed in relation to other studies of endocrine effects on differentiation of skin and skin derivatives.
Effect of temperature differentials upon reconstitution of embryonic primordia in Ambystoma
Authors: Piatt Jean
Published: April 2021

Eggs of Ambystoma maculatum in early stages of development were separated into two groups and maintained at 5 and 14 °C, respectively. In one series of animals comprising both temperature groups, the right otic vesicle was extirpated at stage 27. In another series the right forelimb disc was extirpated at stage 30. Following operation, animals of both groups were kept at 18 °C. Frequency and extent of reconstitution were compared between the two temperature groups.

The 5° group was superior to the 14° group in the number of ears and forelimbs reconstituted. The extent of ear reconstitution and the initial quality of forelimb reconstitution were also superior in the 5° group. Statistical analysis of the data indicates that the difference between the two temperature groups is highly significant in both series.

It is concluded that a slower pre-operative rate of development, caused by hypothermia, enhances the regenerative capacity of both ear and forelimb fields in the salamander embryo.
Influence de la thiourée sur la charge en glycogène du foie de l’embryon de poulet
Authors: Daugéras Nicole
Published: April 2021

Influence of thiourea on the glycogen content of the liver of the chick embryo

In the developing chick embryo, liver glycogen appears on the sixth day of incubation. The glycogen content increases from the sixth day, but decreases on the twelfth day before increasing again.

This decrease on day 12 might be related to the onset of thyroid activity, which would be responsible for an increased rate of utilization of the substrates.

An antithyroid drug, thiourea, has been injected on day 6·0. The liver glycogen concentration of the thiourea-treated chick embryos was determined from the tenth to the fifteenth days and compared with that of the control embryos.
Etude de l’origine et de la différenciation du pharynx au cours de la régénération chez l’annélide Eisenia fœtida
Authors: Chapron Claude
Published: April 2021

Study of the origin and differentiation of the pharynx during regeneration in Eisenia foetida (Annelida)

A study has been made in Eisenia foetida of the regeneration of the pharynx, a complex organ with an epithelium, muscular fibres and glandular cells. We have investigated the origin of these constituents and analysed the ultrastructural aspects of their differentiation.

The epithelium derives from oesophageal endoderm and not from stomodeal ectoderm as during embryogenesis. Muscular fibres form from myoblasts which result from dedifferentiation of the muscular coats of the alimentary canal and dorsal vessel. Glandular elements come from the peritoneal coat of the dorsal vessel, and in particular from stem cells of chlora-gogen cells.

Each of these cellular classes synthesizes specific substances but this differentiation is always preceded by a period in which all the three cell types undergo similar modifications. They change shape to the adult form, then the electron density of the cytoplasm diminishes considerably.

A general hypothesis is formulated to try to explain these preliminary phenomena of differentiation. An inducer would determine a modification in the cell surface which would become permeable to enzymes. These enzymes would be able to hydrolyse the ‘coat’ of inactive mRNA pre-existing in the cells. Then the mRNA would control the synthesis of specific proteins.
The analysis of spatial distributions in mixed cell populations: a statistical method for detecting sorting out
Authors: Elton R. A. , Tickle C. A.
Published: April 2021

This work presents a quantitative measure, α, of the degree of segregation of two cell types in sections of aggregates, and some results obtained with the measure relating to ‘sorting out’. The method is designed particularly for the case where labelling of one type of cell is incomplete, and the importance of this effect is assessed. Possible problems in formulating such a model are discussed. The measure α is compared with methods used in investigations of segregation in plant communities. Segregation of chick heart and limb-bud cells in mixed aggregates has been analysed using α. In control aggregates of mixtures of labelled and unlabelled cells of one type, α is near to its random value of 1, and we suggest that the departure from random can be adequately accounted for by cell division. In mixed aggregates, significant segregation is consistently found, even in aggregates formed after 2 and 4 h. Both disaggregation procedures (EDTA, trypsin or trypsin+ EDTA) and reaggregation methods (reciprocating or gyratory shaker) are found to have an effect on the degree of segregation. Possible reasons for these findings are discussed. Positioning of the cells relative to the outside of aggregates is also investigated for some of the aggregates.
Stimulation of haem synthesis by erythropoietin in mouse yolk-sac-stage embryonic cells
Authors: Bateman A. E. , Cole R. J.
Published: April 2021

Cultures of disaggregated cells from mouse embryos at the stage of yolk-sac erythropoiesis have been used to test sensitivity of primary erythroid cells to erythropoietin, the hormone which controls adult red cell production. Synthesis of haem was stimulated by 89% in cells of 8-day embryos, 23 % in cells of 9-day embryos and by 19% in peripheral nucleated blood cells of 12-day embryos. Differentiation of primary embryonic erythroid cells may therefore be controlled by erythropoietin in situ. The haem precursor δ-aminolaevulinic acid (ALA) did not stimulate haem synthesis under similar conditions.
The behaviour of the egg pigment in wild-type and ‘rusty’ tadpoles of Xenopus laevis
Authors: Uehlinger V. , Beauchemin M. L. , Droin A.
Published: April 2021

The behaviour of the egg pigment was studied by histological analysis of wild-type and ‘rusty’ embryos and tadpoles of Xenopus laevis as well as by experimental procedures.

The histological analysis of the wild-type animals showed that the various tissues, notably the skin, neural tube, alimentary system and cement gland go through progressive stages of egg pigment migration and concentration at the apical ends of the cells. In the ‘rusty’ mutants the migration and concentration of pigment occur to a slight extent only, the majority of the pigment granules remaining dispersed.

The experiments (tail cultures, squashes of cement gland mucus and of meconium) showed that in wild-type animals the pigment, after migration and concentration, is eliminated from the cells by expulsion. In ‘rusty’ animals, this expulsion does not take place.

Parabiotic tadpoles of a ‘rusty’ wild-type combination possess a coloration corresponding to their genotype. Ectodermal grafts performed at the neurula stage between ‘rusty’ and wild-type embryos develop according to their origin.

The amount of egg pigment found in wild-type and ‘rusty’ tadpoles, and the exceptional case of the cement gland are discussed.

It is concluded that the behaviour of the egg pigment is an active cell-specific process, and that the pigment is eliminated by expulsion. The non-elimination of the egg pigment in the ‘rusty’ mutant, accounting for its characteristic colour, appears to be due to a failure of the expulsion mechanism.
Cytological and cytochemical studies of centrifuged eggs of the slug Avion ater rufus L.
Authors: Sathananthan A. H.
Published: April 2021

The stratification of various cell organelles and of important chemical substances have been studied in the eggs of the slug, after moderate centrifugation.

As in other molluscs the egg contents stratify typically into three well-defined zones - lipid, hyaline and yolky zones - but a distinct equatorial band of inclusions consisting mainly of phagosomes and associated lysosomes was detected in the most centrifugal region of the hyaline zone.

The sub-stratification of various cell inclusions in their respective zones was determined in some detail.

The role of the cell membrane and egg cortex in the redistribution of these inclusions and the nature of the ergastoplasm are discussed in the light of electron-microscope studies of eggs of this slug and of the sea urchin.
Les relations épithélio-mésenchymateuses au cours de l’organogenèse gastrique du fœtus de Lapin
Authors: David Par Danielle
Published: April 2021

The epithelio-mesenchymal relations during the gastric organogenesis of the rabbit foetus

The experimental study of the epithelio-mesenchymal relations during the gastric organogenesis shows the following facts:

Completely deprived of mesenchyme, the cultured or grafted isolated epithelium cannot develop. On the other hand the mesenchyme free of epithelium can survive and differentiate its muscular layer. Isolated after the 18th day, it possesses sufficient autonomy to form chorionic villi when covered only by vitelline membrane. The epithelium and the mesenchyme, dissociated by treatment with trypsin, then reassociated in culture (with or without subsequent grafting), develop identically to those of untreated controls. From the 19th day the mesenchyme shows a polarity and only the zone normally adjacent to the epithelium can form chorionic villi. The heterochronic associations of gastric epithelium and mesenchyme demonstrate the existence of two types of mesenchymal inductors: (a) a primary inductor, responsible for the epithelial morphogenesis, elaborated early in embryonic life (10th day); it acts till about the 21st day. (b) A secondary inductor, produced at a later time (15th day), provokes the epithelial cytodifferentiation; its activity is still strong at the 23rd day.

These experiments again show the early competence of the epithelium to react to the two mesenchymal inductors. The presumptive gastric endoderm of the 10-day-old rabbit foetus has a developmental potential such that it can respond as well to the stimuli elaborated by a young mesenchyme as to those of an older mesenchyme.
Aspects of spinal cord induction of chondrogenesis in chick embryo somites
Authors: O’hare M. J.
Published: April 2021

The specificity of the chondrogenic inductive activity of chick embryonic spinal cord has been examined in chorioallantoic culture. It has been found that the 2-day spinal cord is capable of inducing somites to chondrify even after lethal X-irradiation (5000 rads, i.e. 50 J/l kg); this dose of X-radiation resultingin the inhibition of mitosis in the spinal cord and its complete necrosis within 48 h of irradiation.

The unirradiated spinal cord is capable of promoting the chondrogenesis of stage 9 –12 posterior lateral mesoderm, but to a lesser extent than when it is combined with stage 9 –12 posterior somite mesoderm. Irradiated spinal cord, however, possesses no chondrogenic activity with respect to lateral mesoderm. Thus it would appear that the 2-day spinal cord possesses a general cartilage-promoting activity dependent on its continued viability and proliferation, in addition to a somite-specific chondrogenic activity that survives a lethal dose of X-radiation.

The inclusion of enzymes in the Millipore filter used as a graft vehicle has been used to demonstrate that collagenase and hyaluronidase when combined, but not individually, are capable of interfering in the induction of somite chondrogenesis by irradiated spinal cord. Grafts of somites with unirradiated spinal cord show that these enzymes do not directly reduce the chondrogenic potential of the somites or interfere in the subsequent deposition of cartilage matrix. The activity of the spinal cord in inducing somite chondrogenesis appears to be associated with the synthesis of basement membrane materials by either or both of the interacting tissues during the first 24 h of the interaction.

No influence of the 2-day spinal cord on the morphogenesis of non-somitic cartilage could be detected.
Patterns of cell division, cell death and chondrogenesis in cultured aggregates of normal and talpid3 mutant chick limb mesenchyme cells
Authors: Ede D. A. , Flint O. P.
Published: April 2021

Aggregates were prepared from dissociated mesenchyme cells obtained from normal and talpid3 mutant chick limb buds at stage 26 and were maintained for 4 days in culture. They were shown by autoradiographic techniques to consist initially of populations of uniformly dedifferentiated cells within which chondrogenesis was initiated between 1 and 2 days, leading to the formation of areas of precartilage in the interior of the aggregates.

Measurements of cell population density, cell death and cell division were made in precartilage and non-cartilage regions on sections prepared from normal and mutant aggregates fixed at 1-day intervals and were related to the pattern of chondrogenesis.

Non-cartilage areas consisted of cells surrounding the precartilage areas and extended to the surface of the aggregate; these cells showed no special pattern or histochemical reaction. Precartilage areas consisted of one or more ‘condensations’, comprising cells arranged in concentric rings around a central cell or group of cells, characterized by uptake of [35S]sulphate and taking up alcian blue stain in the intercellular matrix. Chondrogenesis was initiated at the condensation foci and spread centrifugally.

Condensations were arranged in a simple pattern, roughly equidistantly from each other and never at the surface of the aggregate. The shape and arrangement of the cells comprising them suggested that they were formed by a process of aggregation towards the condensation foci. The relation of these observations to events in the intact limb bud developing in vivo is discussed.
Budding in hydra: the role of cell multiplication and cell movement in bud initiation
Authors: Webster Gerald , Hamilton Susan
Published: April 2021

The work described in this paper is concerned with the role of cell multiplication and cell movement in relation to the initiation of buds in hydra. .

Hydra starved for 6 days do not initiate new buds ; in such animals the mean mitotic index is only 10% of that in well-fed animals. When starved animals are re-fed, there is a rapid rise in mitotic index which reaches a maximum 12 h after feeding and thereafter declines. This cell division causes an increase in the cell population of about 30% in the 24 h following the meal. New buds are initiated at 24–72 h, i.e. at some time after the major part of the cell multiplication.

Cell division occurs in all parts of the axis to more or less the same extent and there is no sign of a growth zone in the budding region. However, the cell population in the budding zone of re-fed animals shows a significantly greater increase than in other parts of the axis and this can only be accounted for if it is assumed that cells have moved into this region from other parts of the axis.

Some cell multiplication is a necessary prerequisite for bud initiation, but grafting experiments with starved animals suggest that division per se is not necessary; the important factor seems to be the increase in size resulting from division.

The mechanics and causes of the cell movement which results in bud initiation are briefly discussed. It is suggested that changes in intercellular adhesion may be important.
The innervation of the hind limb of Eleutherodactylus martinicensis : further comparison of cell and fiber numbers during development
Authors: Hughes Arthur , Egar Margaret
Published: April 2021

In montages of electron micrographs of the sciatic nerve of Eleutherodactylus martinicensis, the numbers of fibers of all classes have been counted, from the 8·5 day embryo, through the early juvenile to the adult. These counts have been compared with the total numbers of cells in the lumbar ventral horn plus those in the lumbar spinal ganglia 8, 9 and 10.

In the embryo, both sets of counts rise to a peak on the 13th day, and fall early in the 14th day. In the embryo, the cell count is 600–1000 more than the fiber count, while in the 6-day juvenile onwards, the fiber count is the greater.

These differences are held to arise from the play of two independent factors, namely production of axons in the embryo by only a minority of cells in ganglia and ventral horns, and secondly, the extent to which axons branch between spinal roots and sciatic nerve at all stages.

In the embryo, numbers of cells and fibers maintain a parallel course up and down the 13-day peak, indicating that many cells which are lost by degeneration had already sent axons into the nerve.

Myelinated fibers first appear in the limb nerves at 8-5 days, when limb motility is first seen. The course of formation of the earliest myelin in the sciatic nerve resembles that of fibers in the central nervous system.

In spinal roots there are both myelinated and unmyelinated fibers, the proportion of the latter in ventral roots being the greater.
Malformations des membres dues à des lésions vasculaires chez le fœtus de rat déficient en acide pantothénique
Authors: Giroud par A. , Lefebvres J. , Prost H. , Dupuis R.
Published: April 2021

Female rats were given a synthetic diet devoid of pantothenic acid. They were then mated and the foetuses were examined on the 21st, 18th, 16th, and 15th days of gestation. Many foetuses were malformed. They exhibited exencephaly, anophthalmia, oedema, and alterations of the limbs. The extremities of the limbs on the 21st day were red and irregularly swollen. Histological examination on the 16th day showed that an arrest of blood circulation in the dilated marginal veins had occurred. The vascular endothelium had then disappeared, and the coagulated blood had come in direct contact with the tissues. Some skeletal elements may be distorted by the resulting pressure. Above all, there is a degeneration of the tissues in contact with the blood. The skele-togenous tissues of the digits degenerate and this results in ectrodactyly. The epidermis in some areas degenerates and the accumulated fluids and blood may be eliminated. These data are compared with other data concerning embryonic hemorrhagic processes, especially those producing limb amputation. Travail facilité par une aide de la Sécurité Sociale.
Foetal Death in the Rat
Authors: Frazer J. F. D.
Published: April 2021

Pregnant rats were laparotomized 9 days after mating, and the number of implantation sites and conceptuses noted. These rats were killed at the end of pregnancy, and the numbers of foetuses noted. From these findings assessments were made of the degree of death before and after the 9th day of pregnancy. Different factors were found to be associated with loss of whole litters and of individual foetuses from litters. Different factors were associated with loss before and after the 9th day of pregnancy. Factors associated with loss of whole litters before the 9th day of pregnancy were the number of ova implanted and (in one strain of rat only) the time of year. Loss of part litters before the 9th day was associated with high numbers of ova implanted, with older mothers, and with the time of year. Loss of whole litters after the 9th day was associated with implantation of abnormal numbers of ova and with some previous loss of foetuses. Loss of part litters after the 9th day was associated with some previous loss of foetuses and with maternal coat colour. These findings are discussed.
The Uptake of Methionine-S35 by the Chick Embryo and its Inhibition by Ethionine
Authors: Feldman M. , Waddington C. H.
Published: April 2021

The distribution of S35 in the proteins of the chick embryo was studied with labelled methionine. The various tissues were found to differ significantly from each other in their incorporated S35. Ethionine inhibited the uptake of methionine and higher dosages of ethionine retarded differentiation, and caused abnormalities. Methionine was shown to alleviate the effect of ethionine. Glycine did not. The specificity of the morphogenetic processes affected by ethionine, and the biochemical aspects of this inhibition, are briefly discussed.
Factors Affecting Vertebral Variation in Mice
Authors: Mclaren Anne , Michie Donald
Published: April 2021

As a test for genetic differences within that part of the C3H inbred strain of mice which has predominantly 5 lumbar vertebrae, males from each of three C3H(5) colonies were crossed to C57BL females. The F 1 offspring differed in vertebral type according to paternal origin, showing that genetic divergences between colonies and substrains have occurred within that section of the C3H strain which has predominantly 5 lumbar vertebrae. These matings also gave further evidence, in the form of significant hetero-geneity between litters, that vertebral type is in part determined by a fluctuating variable of the mother’s physiological state. We have summarized published data on the variation of the number of lumbar vertebrae in mice in the C3H and C57BL inbred strains and their F1 and F2 hybrids. On certain assumptions we find that the inbreds are about twice as variable as the F1 hybrids.