bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformations in the abdominal muscles of the blue blow-fly,Calliphora erythrocephala(Meig), during metamorphosis
Authors: Crossley A. C. S.
Published: April 2021

A re-examination of the changes at metamorphosis of certain abdominal hypodermal muscles in Calliphora is described. Methods of preparation of insect hypodermal muscles for anatomical, histological and electron microscopical studies are outlined. The anatomical changes in the abdominal hypodermal muscles were traced from larval to adult instars. Two major phases of histolysis occur. Certain larval muscles transform to adult muscles. Histological changes have been followed with various light and electron microscopical techniques. The relative importance of haemocyte phagocytosis and autolysis are considered for different groups of muscles. Evidence indicating that free-floating myoblasts, almost certainly derived from abdominal histoblast tissues, can invade modified larval muscles is presented, and electron micrographs of the invasion process are given. Redifferentiation of imaginai muscles associated with myoblast nuclei is described. Experimental denervation did not affect muscle histolysis. The results are compared with those reported in the earlier literature. Certain similarities of metamorphic and early embryonic development are pointed out.
Nouvelles recherches concernant le rôle du canal de Wolff dans la différenciation du mésonéphros de l’embryon de poulet
Authors: Bishop-Calame par Simone
Published: April 2021

Au cours de recherches antérieures, Caíame (1961), nous avons mis en évidence le rôle inducteur du canal de Wolff dans la différenciation du mésonéphros de l’embryon du Poulet confirmant ainsi les résultats de Grünwald (1937):
Teratogenic action of the thyroid stimulating hormone and its interaction with trypan blue
Authors: Beaudoin Allan R. , Roberts James M.
Published: April 2021

The role that the thyroid gland may play in embryonic development has been under investigation for many years. A direct relationship between thyroid gland function and development is best illustrated in the amphibia (see Kollros, 1961, for pertinent literature). Attempts to demonstrate a similar influence of thyroxin on development in mammals has led to controversial results, in part due to the difficulty of separating the metabolic from the possible developmental effects of the hormone. In order for thyroxin to exert a direct effect upon the mammalian embryo it must cross the placenta. The bulk of the evidence seems to favor the viewpoint that the placenta is rather impermeable to thyroxin during the early stages of gestation and that this permeability increases near term. This is apparently true of the rabbit and man (Osorio & Myant, 1960) and the rat (Hamburgh, Sobel, Koblin & Rinestone, 1962; Roy & Kobayashi, 1962).
The 45Ca turnover in the membranous labyrinth of chick embryos during development
Authors: De Vincentiis Mario , Marmo Francesco
Published: April 2021

An autoradiographic study of the 45Ca turnover in the membranous labyrinth of chick embryos has shown the following.

An early presence of 45Ca in the surface of the endolymphatic duct and of the lower part of the otocyst from which the sacculus and the ductus cochlearis will originate. 45Ca is always connected to an organic matrix of mucopolysaccharide. The turnover of 45Ca in these zones is very active in embryos of 5,6,7 days of incubation (a period in which otolithic morphogenesis is occurring), while it is very low in embryos of 12 days of incubation (in which the otoliths are already formed and mineralized in large amount). These results are discussed, together with the problem of the origin of otoliths.
Enzymic differentiation of rat yolk-sac placenta as affected by a teratogenic agent
Authors: Johnson E. Marshall , Spinuzz1 Ralph
Published: April 2021

Electrophoretic and biochemical techniques were applied to homogenates of the rat’s visceral yolk-sac. Non-specific esterase, acid phosphatase, malate and lactate dehydrogenases were shown, by electrophoretic techniques, to undergo sequential enzymic differentiation from day 10 through day 20 of gestation. The enzyme repertory on a particular day was achieved through both additions to and deletions from the repertory of the preceding day. The greatest staining intensity by esterase and acid phosphatase was late in gestation but for both malate and lactate dehydro-genase it was most intense during days 11–13. A teratogenic folic acid deficiency resulted in delayed appearance of several enzyme forms but also resulted in some forms persisting beyond their normal time for disappearance. The effects of the vitamin deficiency were quite selective in that some enzyme forms appeared on time and in apparently normal concentration in the PGA-deficient material.
Production élective de la phocomélie sous Finfluence d’ypérite azotée, chez l’embryon de Poulet: IL—Etude histologique des bourgeons de membres au cours du développement
Authors: Salzgeber par Berthe
Published: April 2021

The production of phocomelia in the chick embryo by the action of nitrogen mustard. IL Histological study of developing limb buds Nitrogen mustard at a concentration of 3x 10−4M was administered to chick embryos of days incubation (stages 18-20 of Hamburger & Hamilton). The solution was deposited either over the whole embryo or locally on the limb rudiments. Some limb buds were examined in situ during the period 24-48 h after the administration and were subject to examination at autopsy at the 11th day of incubation. Others, both wing and leg-buds, were taken for histological examination at times between 1 h and 120 h of the beginning of treatment. The first detectable morphological lesions appear between 24 and 30 h of the administration of the nitrogen mustard. The growth of the bud is inhibited and haematomata of varying sizes are seen at the centre of the bud or near its base. Histological study of limb rudiments fixed within the first hours or days of treatment gives a more detailed picture of the changes suffered by them. The dense central mesenchyme with small cell nuclei is replaced by a vacuolated tissue with large cell nuclei. Forty hours after treatment the disorganization of the limb bud is characterized by the absence of the central mesenchymal condensation and the presence of lacunae, of vacuoles and pyknotic nuclei. Chondrogenesis is inhibited or delayed. Four or five days after treatment there is a reorganization of the limb rudiment. The distal structures appear, as do nodules of precartilaginous cells and muscle rudiments. Nerves and blood vessels enter the limb which is of reduced size. In those cases where the mesoderm is greatly reduced the buds degenerate. This gives rise to ectromelia, the complete absence of limbs. The ectoderm, including the apical cap, develops normally in most cases. In cases of extreme mesodermal atrophy the ectodermal covering shows signs of degeneration. These results suggest a specific action of nitrogen mustard on mesodermal structures. They are compared with the results of other authors and their relevance to problems of mesodermal-ectodermal interactions is discussed.
The effect of mitomycin C on developing chicken embryos
Authors: Kury George , Craig John M.
Published: April 2021

The effect of mitomycin C before completion of organogenesis was studied in chicken embryos. The injection of mitomycin C into the yolk sac produced developmental anomalies which varied with the time of injection. Embryos treated on the 3rd day of development (2–16 μg/egg) had retardation of growth, bilateral microphthalmia, cerebral hemorrhage, malformations of lower extremities, lower beak and defect of calvarium. Specimens treated on the 4th day of development (2–28 μg/egg) had retardation of growth, abnormalities of beak, lower extremities and calvarium. Histological examination of viable embryos sacrificed 2–6 days after injection revealed necrotic changes involving the developing retina, lens, cerebral vesicles, mesenchyme and heart. Histological examination of 19-to 20-day-old treated embryos showed depression of hematopoietic and osteoblastic tissues. The skeletal abnormalities produced included shortening and curvature, deformity of the bones of lower extremities, especially the tibia. Absence of other bones of the lower extremities was also encountered.
Ectopic regeneration of whiskers in the hooded rat from implanted lengths of vibrissa follicle wall
Authors: Oliver R. F.
Published: April 2021

A method is described for isolating and removing lengths of follicle wall, composed of the inner root sheath, outer root sheath and mesenchymal layer, from vibrissa follicles. These segments of follicle wall were transplanted into ear skin and, in one case, into an ovarian capsule. Seven of the thirteen implants originally dissected from the lower third of the follicle produced short whiskers up to 6 mm in length. Two further implants had also regenerated dermal papillae but not whiskers. The dermal papillae regenerated at the proximal end of the implants and appeared to derive from cells from the mesenchymal layer. None of the four implants obtained from above the lower third of the follicle regenerated dermal papillae or produced whiskers. The outer root sheaths of all of the implants which did not regenerate papillae or whiskers did, however, maintain their typical histological character. The possibility that maintenance of the implants was dependent on the presence of the mesenchymal layer is discussed. Whisker growth from transplanted lengths of follicle wall logically isolates the outer root sheath and/or the mesenchymal layer as the essential prerequisites for papilla regeneration.
The differentiation of epidermis:I. The interrelationship of epidermis and dermis in embryonic chicken skin
Authors: Dodson J. W.
Published: April 2021

Experiments were made on the tarso-metatarsal skin of 12-day chicken embryos to determine the relative importance of different dermal constituents for the continued growth and differentiation of the epidermis. The two tissues were separated after exposure to Versene and the isolated epidermis was either recombined with the dermis which had previously been subjected to various treatments, or explanted on different gels, including acetic acid-extracted collagen. After growth in organ culture on natural medium, the explants were examined histologically. The isolated epidermis did not survive in culture when laid directly on a plasma-embryo extract clot, but it grew and keratinized when placed with the basal surface downwards on dermis killed by freezing and thawing or on a gel of collagen; when frozen-killed dermis was trypsinized, the epidermis differentiated at first, but then degenerated. The epidermis did not survive on heat-killed dermis, on agar, alginate, or fibrin gels, nor on Gelfilm. The epidermis survived on Millipore filter only in the presence of an increased concentration of embryo extract, when it differentiated to form a s. corneum. A periodic acid-Schiff-reactive basement membrane was formed in the absence of living dermal cells. It is concluded that, under the conditions of the experiments, the survival of embryonic chicken epidermis as an organized, keratinizing tissue depends on the contact of the basal surface with a suitable substratum, but not on the presence of living dermal cells. In the normal substratum provided by the dermis, both collagen and trypsin-labile ground substance are required by the epidermis, yet a gel of collagen can provide a suitable surface on which the epidermis is capable of normal differentiation in vitro. It has been suggested therefore that the epidermis reacts to the flat surface of collagen gels in the same way as to the extracellular moiety of the dermis.
Aspects of the development of yolk spheres in the hen’s oöcyte, studied by electron microscopy
Authors: Bellairs Ruth
Published: April 2021

Yolk-sphere formation in the hen’s oöcyte has been studied by electron microscopy using the following stages: Balbiani body present, Balbiani body dispersed, large vesicles visible, well-defined yolk present. A detailed description is given of each stage. Raw materials from which the yolk is formed appear to enter the oöcyte in two ways. The first is probably by pinocytosis, the second by specialized pieces of follicle cell apparently becoming engulfed by the oöcyte. These pieces of follicle cell have been described in detail elsewhere under the name of ‘lining bodies’. Prior to yolk formation the mitochondria and Golgi bodies migrate to the periphery of the oöcyte, the numbers of free lipid drops in the cytoplasm become reduced and two new structures appear in the oöcyte. These are respectively electron-dense particles measuring 300 Å in diameter and specialized structures that may be termed ‘yolk spindles ‘. The latter are about 700 Å in T.S. and contain within them a rod that is about 50 Å in diameter. The yolk spheres develop from large, membrane-bounded vesicles that appear in the ooplasm. There is no direct evidence as to the origin of these vesicles though several alternative suggestions are made. Yolk spindles cluster around some of the large vesicles and appear to become incorporated into them. It is suggested that the yolk spindles influence the large vesicles to transform into primary yolk spheres, though the mechanism is not understood. As the large vesicles become recognizable as primordial yolk spheres, they acquire osmiophilic subdroplets as well as more granular material. Frequently they also contain many 300 Å dense particles, as well as degenerating lining bodies. The mechanism by which these materials enter the primordial yolk spheres is unknown. Each yolk sphere within the oöcyte is surrounded by a well-defined unit membrane. By the time the egg is laid, however, it has become difficult to demonstrate this membrane. It is suggested in this paper that the unit membrane of the yolk sphere retains its normal appearance so long as it remains in contact with living cytoplasmic structures. This contact is retained only until the oöcyte is about 2·5 mm in diameter, for at about that time the nucleus and cytoplasmic components stream up to the animal pole where they remain.
Studies on growth of the mink blastocyst
Authors: Daniel Joseph C.
Published: April 2021

Mink blastocysts grew in vitro when the culture medium contained estrone or ergosterol, but the growth was slow and of short duration, and believed to be the product of fluid uptake rather than cell proliferation.

Ergosterol failed to shorten the gestation period when administered to mink during the delay phase of pregnancy, the same failure having been reported earlier with estrogen.

Mink blastocysts did not grow in vitro in medium containing other vitamins, enzymes known or suspected to be present in uterine fluids, a variety of energy sources, rabbit uterine or blastocyst fluids or when transplanted to the uterus of 3-to 4-day pregnant rabbits.

A factor inhibiting blastocyst growth is believed to exist in the mink because rabbit blastocysts cease growing and collapse when retained in culture medium whose mink serum component is 5% or higher. Dialysis does not remove the factor.

Collapsed mink blastocysts can reconstitute to their original fluid-filled state in vitro.
Studies on the haemopoietic stem cells of mouse foetal liver
Authors: Silini G. , Pozzi L. V. , Pons S.
Published: April 2021

Cells obtained from the blood-forming organs of donor animals and injected, under appropriate conditions, into heavily irradiated mice, can colonize, among other organs, the spleen of the hosts, giving rise to discrete and differentiated nodules of haemopoietic tissue (Till & McCulloch, 1961). It has been demonstrated that the number of nodules is directly proportional to the number of injected cells and that such nodules may be regarded as clones arising from single cells (Till & McCulloch, 1961; Becker, McCulloch & Till, 1963). The postulate of classical haematological theories (Maximov & Bloom, 1934; Ferrata, 1935) that a proportion of the cells in blood-forming organs is capable of indefinite division with renewal of the stem line and of differentiation into mature blood cells has thus been experimentally demonstrated.
Temperature and other environmental effects on ammocoete organs in culture
Authors: Stephenson E. M. , Potter I. C.
Published: April 2021

Whole hearts of ammocoete larvae of Mor dada mordax were cultured at temperatures ranging from 37 to 5 °C. Rapid death of cultures occurred at 37 °C. A temperature of 30 °C was ultimately lethal but viability as indicated by heart beat could be maintained for up to 6 days. Total viability was usually maintained in temperatures from 25 to 5 °C. Rate of heart beat varied in absolute values but the relative pattern in relationship to incubation temperatures was more or less constant. The optimal temperature was 25 °C. Cell outgrowth occurred at 25, 20 and 15 °C. The optimal temperature for rate of outgrowth appeared to be 25 °C, but cultures at 20 °C were also satisfactory. Chopped kidney and liver explants were also cultured. Successful outgrowth was obtained from almost all kidney cultures at 25 and 20 °C. Outgrowth from liver was extremely rare and occurred only at 25 and 20 °C. Successful outgrowth was obtained in media lacking any homologous component. Dilution of standard media by approximately 10 % appeared to be necessary for outgrowth but viability could be maintained in undiluted media. A correlation appears to exist between the upper limit of temperature suitable for maintenance of ammocoete tissues in vitro and the highest temperatures encountered by the whole animals in their natural environment.
Promoting activity of extracellular materials on sponge cell reaggregation
Authors: Maclennan A. P. , Dodd R. Y.
Published: April 2021

A number of species of sponge showed enhanced aggregation behaviour in the presence of cell extracts prepared under defined conditions previously found suitable for other sponges. The promoting activity of one such preparation appeared to be based on a minor component of the total extract. The specificity of promotion was of a low order and led to mixed aggregate formation from species that segregated specifically in unpromoted mixtures. The observations are discussed in relation to the known antigenic relationships of the cell surfaces of the species examined.
Morphology and development of theDrosophilaeye
Authors: Hanly E. W. , Hemmert Wynn H.
Published: April 2021

The morphological changes which take place in the differentiation of the adult Drosophila eye from the larval imaginal disc have been described from a histological and cytological standpoint by Shatoury (1956, 1963) and Shatoury & Waddington (1957). In addition, Gottschewski (1960), Gottschewski & Querner (1961), and Schneider (1964) have studied these processes in eyes and brains in vitro. These latter workers removed eye-antennal anlage with associated structures, and placed them in culture media. Under these conditions, the imaginal discs can apparently undergo most of the normal differentiation processes, finally attaining nearly all of the adult morphology.
Development of explanted rat embryos in circulating medium
Authors: New D. A. T.
Published: April 2021

A method is described for growing post-implantation rat embryos, explanted with their embryonic membranes, in circulating medium. Embryos cultured by this method grow to about five times the maximum weight attainable in static medium in watch-glasses. Homologous serum, equilibrated with 95 % O2/5 % CO2, has proved to be a satisfactory culture medium, and it makes no difference whether the serum is from pregnant or non-pregnant animals. Good development is obtained in 2–3 ml serum per embryo, and little or no improvement is gained by using more than this. About 50 % of embryos explanted at 7–15 somites develop to 30-to 35-somite stages and synthesize O·3–O·5mg protein during the period in culture. Further development of these embryos appears to be prevented by the abnormal formation of a large blood vessel bypassing the allantoic placenta. About 50 % of embryos explanted at 22–28 somites develop to 40–46 somite stages and synthesize about 1–1·5 mg protein. Embryos explanted at more than 45 somites do not develop. The rate of flow of the circulating medium is critical. Embryos explanted at 7–15 somites develop much better in serum flowing at 1 ml/min (= 2 cm/min through the embryo chamber) than at 10 ml/min. Embryos explanted at 22–28 somites develop much better in serum flowing at > 10 ml/min than at 1 ml/min.
On the orientation of the implanting blastocyst
Authors: Kirby D. R. S. , Potts D. M. , Wilson I. B.
Published: April 2021

The sequence of events in the orientation of the blastocyst is described. Six a priori mechanisms for orientating the blastocyst are presented. It is concluded that the only mechanism fulfilling the available morphological and experimental observations is one in which the inner cell mass is free to travel round the inside of the trophoblast shell once the latter has become fixed to the uterine epithelium.
Effects of histones on morphogenesis and differentiation in chick embryos
Authors: Malpoix P. , Emelinckx A.
Published: April 2021

The transcription of DNA is known to be inhibited in vitro by the presence of histones. This has been shown to be true for isolated nuclei, isolated chromatin, or for DNA alone (Bonner & Huang, 1962; Bonner, Huang & Gilden, 1963; Allfrey & Mirsky, 1963 ; Allfrey, Faulkner & Mirsky, 1964; Sonnenberg & Zubay, 1965). The masking of genomic sites in adult differentiated tissues seems the most probable explanation of the expression of only a fraction of the adult genome (Paul & Gilmour, 1966). Affinities have been observed between certain base sequences in DNA and certain fractions of histones (Liau, Hnilica & Hurlbert, 1965; Skalka, Fowler, Andre & Hurwitz, 1966; Tan, 1966), yet the remarkable similarity in composition between the histones of different species and organs of the same species does not encourage the idea that histones are specific repressors of genomic function. Many authors (Zalokar, 1964; Goldberg & Atchley, 1966; Frenster 1967) have proposed hypotheses tending to reconcile the apparent non-specificity of the relation between DNA and histones and their intervention in gene function : it is thought that polyanions (RNAs, phosphoproteins, phospholipids, non-histone proteins or hormones) may remove histones from binding sites and release specific single-stranded sequences of DNA for transcription.
The developmental potentialities of regeneration blastema cell nuclei as determined by nuclear transplantation
Authors: Burgess Ann M. C.
Published: April 2021

Formerly, many embryologists believed that the blastema cells in regenerating amphibian tails and limbs arose from a reserve of undifferentiated cells, but since the work of Hertwig (1927) and Butler (1935) few modern investigators would support this view. Others have suggested that blastema cells are of epidermal origin (Godlewski, 1928; Rose, 1948). However, this idea has largely fallen into disrepute following the investigations of Karczmar & Berg (1951), Chalkley (1954) and Hay & Fischman (1961). There is now abundant evidence that blastema cells arise by the dedifferentiation of some of the stump tissues, in particular the stump muscle and cartilage (Thornton, 1938 a, b;, Hay, 1958,1959, 1962; Hay & Fischman, 1961), and that contributions may also arise from fibroblasts when they are present.
The experimental induction of whisker growth in the hooded rat by implantation of dermal papillae
Authors: Oliver R. F.
Published: April 2021

Dermal papillae are regenerated and whiskers are produced after the experimental removal of up to the lower third of the vibrissa follicle, but if more of the follicle is removed neither event occurs (Oliver, 1966 a, b). Similarly, when lengths of the lower third of the vibrissa follicle wall are transplanted into ear skin, whiskers are again produced, but not if lengths of wall are taken from within the upper two-thirds of the follicle (Oliver, 1967). From these experiments it was clear that the outer root sheath and the adherent mesenchymal layer, from which the new papillae are apparently derived, are the essential tissues in the regeneration process.
Analysis of the development of the nervous system of the zebrafish, Brachydanio rerio: II. The effect of nerve growth factor and its antiserum on the nervous system of the zebrafish
Authors: Weis Judith Shulman
Published: April 2021

When a nerve growth factor isolated from mouse submaxillary salivary glands is injected into young zebrafish, Brachydanio rerio, it causes enlargement of spinal ganglia due to hypertrophy and hyperplasia. A large part of the response is due to hyperplasia, as compared with that of chicks and mammals, in which the response is primarily hypertrophy of cells. The nature of the response to NGF corresponds to the chief method of normal growth of ganglia in this species. Sympathetic ganglia of B. rerio are also markedly enlarged by treatment with the nerve growth factor. Injections of a specific antiserum to the nerve growth factor cause a reduction in size of the spinal ganglia of the zebrafish. This decrease in size is due to a reduction in the cell population of the ganglia, while the cells in the reduced ganglion appear normal. An effect of antiserum has previously been noted in other animals, but only on sympathetic ganglia.
Glandular metaplasia of hair follicles and other responses to vitamin A excess in cultures of rodent skin
Authors: Hardy Margaret H.
Published: April 2021

This paper reports the effects of excess vitamin A on the development of hair follicles in organotypic cultures of embryonic mouse skin. Pieces of trunk skin, upper lip and lower jaw were cultivated on the surface of a clot of adult cock plasma and chicken embryo extract in slide preparations for 11 – 14 days. Changes in individual living follicles were observed daily and the findings confirmed from complete serial sections. In skin from the trunk of -day embryos the pelage follicles were initiated and underwent some normal differentiation, both in the presence and absence of added vitamin A (6·2 – 37·5 i.u./ml.). In skin from the trunk of 15-day embryos the pelage follicles differentiated normally for 4 days in both treated and untreated groups but then regressed in the vitamin-treated groups (12·5, 25·0 i.u./ml.), while normal differentiation continued and some keratinized hairs were formed in the control groups. Vibrissal follicles in the upper lip from a -day embryo differentiated normally for 4 days in excess vitamin A (12·5 i.u./ml.), and then some follicles became misshapen and developed gland-like lateral buds, while follicles in the control explant continued normal development and produced many keratinized hairs. All the vibrissal follicles originally present in four explants of upper Up from 14-day embryos differentiated normally for about 3 days in excess vitamin A (12·5 i.u./ml.) and then showed metaplastic changes. Many of them underwent a complete glandular metaplasia, being transformed into compound tubular glands with branching duct systems, terminal ‘alveolar’ swellings and occasional signs of mucous secretion. Some follicles retained traces of the original structure, and in a few the follicle eventually recovered its capacity for normal differentiation, producing simultaneously a small keratinized hair and a vigorously growing gland. The metaplastic glands were unlike any normal mammalian skin glands but resembled immature salivary glands. At the time of initiation of the metaplasia there was also an increase in the secretion of sebum or sebum-like material in the same hair follicles. In the control group without excess vitamin A the follicles continued normal differentiation and hair production until the experiment was terminated, and there was no metaplasia. Most of the vibrissal follicles in the explants of upper lip from 15-day embryos continued normal differentiation in the presence of excess vitamin A (12·5 i.u./ml.), although a higher proportion of the hairs were abnormal in structure than in the control group. In excess vitamin A a few of the initially least advanced follicles underwent glandular metaplasia, but no metaplasia was observed in the control group. Some of the differences between the behaviour of explants from embryos of different ages could be explained by the hypothesis that there is only a relatively short critical stage in follicle development during which vitamin A is capable of inducing metaplasia.
The synthetic activity of primordial germ cells in normal and irradiated neonatal male rats
Authors: Lett I. C.
Published: April 2021

Exposure of the testes of rats to 100 r of X-rays at birth inhibits the division of gonocytes but does not prevent them from differentiating into transitional cells. The latter, however, fail to divide to form spermatogonia type-A, but increase markedly in size so that by 8 days post partum (p.p.) the testes of irradiated animals contain numerous giant transitional cells which are destined to degenerate. The metabolic activity of germ cell nuclei in normal and irradiated rats has been studied by the technique of autoradiography, using radioactive precursors of DNA, RNA and protein. The results have demonstrated that synthetic processes continue in cells whose division has been blocked. The synthesis of RNA is largely unaffected by irradiation. DNA synthesis may be prolonged after exposure, but the amount of 3H-thymidine incorporated by the nucleus declines from 5 days p.p. and does not keep pace with nuclear growth. The synthesis of nuclear protein, on the other hand, increases from 5 days after irradiation and the quantity of phenylalanine taken up by giant cells seems to be proportional to nuclear size. Thus the accumulation of nuclear protein appears to be the main factor in nuclear enlargement.
Métabolisme des acides nucléiques et des protéines et formation de cytasters dans les œufs d’amphibiens sous l’action de l’eau lourde
Authors: Assel S. Van , Brachet J.
Published: April 2021

The formation of cytasters and the metabolism of nucleic acids and proteins in amphibian eggs treated with heavy water

Amphibian eggs (Pleurodeles and Xenopus) form cytasters, which are made of astral fibres and probably centrioles, upon treatment with concentrated heavy water (D2O). A study of the importance of nucleic acid and protein synthesis for the formation of cytasters was undertaken; both precursors and inhibitors of these syntheses were used. It was found that D2O completely inhibits the synthesis of nuclear DNA. Hydroxyurea (an inhibitor of DNA synthesis) and X-rays do not inhibit the appearance of the cytasters, which is clearly independent of nuclear DNA replication. Actinomycin D, a classical inhibitor of RNA synthesis, has no effect on cytaster formation. Eggs treated with D2O incorporate 14C-leucine in the nucleus as well as in the cytoplasm, including the cytasters. However, puromycin, which inhibits protein synthesis, has no effect on the formation of cytasters in Pleurodeles and Xenopus eggs. Another inhibitor of protein synthesis, cycloheximide, prevents the formation of cytasters in the eggs of Pleurodeles but not in those of Xenopus. Mercaptoethanol also blocks the appearance of cytasters in the eggs of Pleurodeles without affecting those of Xenopus. The possible reasons for the discrepancies in the results obtained with different species are discussed.
A time-lapse photographic study of chick embryos exposed to teratogenic doses of hypoxia
Authors: Grabowski Casimer T. , Schroeder Robert E.
Published: April 2021

Continuous, long-term observations of amniote embryos have always been difficult. Special culture techniques for young avian and mammalian embryos have been developed (New, 1967) and these have helped to visualize the early stages of development. But studies of normal and abnormal development during the major period of organogenesis have been made largely by tedious indirect methods, such as the examination of a series of embryos preserved at different time intervals. Transitory responses to toxic stimuli have been particularly difficult to detect in this manner. To observe the visible initial effects of terato-genic agents, a photographic time-lapse study of chick embryos in their natural, in ovo, state was initiated. This report compares the changes in normal and hypoxia-treated embryos during the third day of development.
The role of sodium chloride in the process of induction by lithium chloride in cells of the Rana pipiens gastrula
Authors: Barth Lester G. , Barth Lucena J.
Published: April 2021

A study of the effects of a series of monovalent cations, Li+, Na+ and K+, and a series of divalent cations, Mn2+, Ca2+ and Mg2+, upon small aggregates of cells taken from the presumptive epidermis of Rana pipiens gastrulae re-vealed that these ions induce nerve and pigment cells (Barth, 1965). The effec-tiveness of both series of ions as inductors was similar to their effects on decreasing the electrophoretic mobility of DNA as determined by Ross & Scruggs (1964).
A cytological study of Mauthner’s cells in Xenopus laevis and Rana temporaria during metamorphosis
Authors: Moulton J. M. , Jurand A. , Fox H.
Published: April 2021

This paper discusses cytological changes which occur during anuran meta-morphosis in a pair of large hind-brain neurones, the Mauthner cells or M-cells which, in many teleosts and amphibians, innervate the tail musculature via ventral horn cells. The M-cells of fishes, urodeles and anuran larvae are un-usually large neurones of particular interest, and according to Stefanelli (1951) they constitute a ‘true functional system of nervous activity’. The value of a cytological study is enhanced by the fact that amphibian M-cells have not yet been extensively analysed biochemically (Deuchar, 1966).
Gene loss and gain in the evolution of the vertebrates
Authors: Ruddle Frank H. , Bentley Kevin L. , Murtha Michael T. , Risch Neil
Published: April 2021

Homeobox cluster genes (Hox genes) are highly conserved and can be usefully employed to study phyletic relation ships and the process of evolution itself. A phylogenetic survey of Hox genes shows an increase in gene number in some more recently evolved forms, particularly in verte brates. The gene increase has occurred through a two-step process involving first, gene expansion to form a cluster, and second, cluster duplication to form multiple clusters. We also describe data that suggests that non-Hox genes may be preferrentially associated with the Hox clusters and raise the possibility that this association may have an adaptive biological function. Hox gene loss may also play a role in evolution. Hox gene loss is well substantiated in the vertebrates, and we identify additional possible instances of gene loss in the echinoderms and urochordates based on PCR surveys. We point out the possible adaptive role of gene loss in evolution, and urge the extension of gene mapping studies to relevant species as a means of its sub stantiation.
The evolution of arthropod segmentation: insights from comparisons of gene expression patterns
Authors: Patel Nipam H.
Published: April 2021

The comparison of gene expression patterns in a number of insect and crustacean species has led to some insight into the evolution of arthropod patterning mechanisms. These studies have revealed the fundamental nature of the parasegment in a number of organisms, shown that segments can be generated sequentially at the molecular level, and suggested that pair-rule pre-patterning might not be shared by all insects.
Symmetry systems and compartments in Lepidopteran wings: the evolution of a patterning mechanism
Authors: Nijhout H. Frederik
Published: April 2021

The wing patterns of butterflies are made up of an array of discrete pattern elements. Wing patterns evolve through changes in the size, shape and color of these pattern elements. The pattern elements are arranged in several parallel symmetry systems that develop independently from one another. The wing is further compartmentalized for color pattern formation by the wing veins. Pattern development in these compartments is largely independent from that in adjacent compartments. This two-fold compartmentalization of the color pattern (by symmetry systems and wing veins) has resulted in an extremely flexible developmental system that allows each pattern element to vary and evolve independently, without the burden of correlated evolution in other elements. The lack of developmental constraints on pattern evolution may explain why butterflies have diverged so dramatically in their color patterns, and why accurate mimicry has evolved so frequently.

This flexible developmental system appears to have evolved from the convergence of two ancient patterning systems that the butterflies inherited from their ancestors. Mapping of various pattern types onto a phylogeny of the Lepidoptera indicates that symmetry systems evolved in several steps from simple spotting patterns. Initially all such patterns were developmentally identical but each became individuated in the immediate ancestors of the butterflies. Compartmentalization by wing veins is found in all Lepidoptera and their sister group the Trichoptera, but affects primarily the ripple patterns that form the background upon which spotting patterns and symmetry systems develop. These background pattern are determined earlier in ontogeny than are the symmetry systems, and the compartmentalization mechanism is presumably no longer active when the latter develop. It appears that both individuation of symmetry systems and compartmentalization by the wing veins began at or near the wing margin. Only the butterflies and their immediate ancestors evolved a pattern formation mechanism that combines the development of a regular array of well-differentiated symmetry systems with the mechanism that compartmentalizes the wing with respect to color pattern formation. The result was an uncoupling of symmetry system development in each wing cell. This, together with the individuation of symmetry systems, yielded an essentially mosaic developmental system of unprecedented permutational flexibility that enabled the great radiation of butterfly wing patterns.
The hedgehog gene family in Drosophila and vertebrate development
Authors: Fietz Michael J. , Concordet Jean-Paul , Barbosa Robert , Johnson Randy , Krauss Stefan , McMahon Andrew P. , Tabin Cliff , lngham Philip W.
Published: April 2021

The segment polarity gene hedgehog plays a central role in cell patterning during embryonic and post-embryonic development of the dipteran, Drosophila melanogaster. Recent studies have identified a family of hedgehog related genes in vertebrates; one of these, Sonic hedgehog is impli cated in positional signalling processes that show interest-ing similarities with those controlled by its Drosophila homologue.
The evolution of echinoderm development is driven by several distinct factors
Authors: Wray Gregory A. , Bely Alexandra E.
Published: April 2021

We analyzed a comparative data base of gene expression, cell fate specification, and morphogenetic movements from several echinoderms to determine why developmental processes do and do not evolve. Mapping this comparative data onto explicit phylogenetic frameworks revealed three distinct evolutionary patterns. First, some evolutionary differences in development correlate well with larval ecology but not with adult morphology. These associations are probably not coincidental because similar developmental changes accompany similar ecological transformations on separate occasions. This suggests that larval ecology has been a potent influence on the evolution of early development in echinoderms. Second, a few changes in early development correlate with transformations in adult morphology. Because most such changes have occurred only once, however, it is difficult to distinguish chance associations from causal relationships. And third, some changes in development have no apparent phenotypic consequences and do not correlate with obvious features of either life history or morphology. This suggests that some evolutionary changes in development may evolve in a neutral or nearly neutral mode. Importantly, these hypotheses make specific predictions that can be tested with further comparative data and by experimental manipulations. Together, our phylogenetic analyses of comparative data suggest that at least three distinct evolutionary mechanisms have shaped early development in echinoderms.
Neural Activation and Transformation in Explants of Competent Ectoderm under the Influence of Fragments of Anterior Notochord in Urodeles
Authors: Nieuwkoop P. D. , Nigtevecht G. V.
Published: April 2021

The inductive influence of presumptive notochordal tissue (neurula stage) upon competent ectoderm was tested in sandwich-experiments, for which eggs of Triturus alpestris, T. taeniatus, and Ambystoma mexicanum were used. Strong activating and rather weak transforming influences emanate from the anterior portion of the notochord. Both activating and transforming influences have the character of field actions and spread with decrement, probably from cell to cell, in the overlying ectoderm. Both influences, but especially the activation, can spread over an area much larger than the area in which a direct contact between inductor and ectoderm occurs. It is therefore suggested that the more lateral portions of the archenteron roof merely support the activation spread from the dorsal midline, probably as a form of double assurance. The activation leads to a segregation into neural, mesectodermal, activated epidermal, and indifferent epidermal zones, each of which is characterized by a certain threshold value. In the activated epidermal zone differentiation tendencies for prosencephalic placodal development arise. They can be transformed by additional transforming influences into those for rhombencephalic or spinal placodes.
The yolk of Holostean fishes
Authors: Kilarski Wincenty , Grodziński Zygmunt
Published: April 2021

Eggs of some archaic fishes, such as Polypterus, sturgeon or the holosteans, resemble amphibian eggs. Not only has the similarity been found in the amount of yolk (mesolecithal types of eggs), which indicates the manner of egg cleavage (holoblastic) in these vertebrates, but also in the morphological composition of yolk. Fat droplets, yolk platelets and an unidentified fluid in which they are suspended, in fishes sometimes called ichthulin, are three main components of yolk in these eggs.
Myocardial cell death in the embryonic chick ventricle
Authors: Manasek Francis J.
Published: April 2021

The degeneration and death of cells is a normal occurrence in renewing cell systems in mature animals. Cell death is also a frequent event during embryonic development and appears to be a normal, and perhaps necessary constituent process of morphogenesis (see Glucksmann (1951) and Saunders (1966) for reviews). The events of cell degeneration and death during ontogenesis have been observed in many developing tissues, even those which have a relatively static cell population in the adult, such as the nervous system (Hamburger & Levi-Montalcini, 1949).
Development of luxoid (lu) skeletal defects in vitro
Authors: Burda D. J. , Center E. M.
Published: April 2021

Skeletal abnormalities in the hind limb of the homozygous luxoid mutant mouse (lu/lu) have been described by Green (1955) and Forsthoefel (1958, 1959). These defects include a reduction in the size of the tibia, a slight thickening of the fibula and a failure to form normal condyles on the distal portion of the femur. Chondrogenesis and ossification are also slightly retarded in these limbs.
Morphogenesis in hydra: I. Peduncle and basal disc formation at the distal end of regenerating hydra after exposure to colchicine
Authors: Corff Sondra C. , Burnett Allison L.
Published: April 2021

The regenerative ability of hydra has been frequently demonstrated since Trembley (1744) first witnessed the regeneration of a hydranth from the proximal half of an excised animal. Under normal conditions, the hypostome and tentacles always regenerate from the distal cut end, and proximal structures, the peduncle and basal disc, from the proximal cut end. This pattern of regeneration reflects the rigid polarity of hydra. Normal polarity and regeneration can be altered, however, by several techniques. Various graft combinations induce distal structures from regions destined to produce peduncle (Wetzel, 1898; King, 1903; Browne, 1909; Koelitz, 1911; Mutz, 1930; Burnett, 1961). An interspecific graft between the peduncle region of Hydra oligactis and the distal end of Hydra pirardi can result in the production of tentacles at the proximal end of the peduncle, which normally would form a base, and the inversion of polarity (Burnett, 1961). An extract prepared from an homogenate of hydra can induce multiple head and tentacle formation and inversion of polarity in gastric annuli (Lesh & Burnett, 1964; Lentz, 1965a; Lesh & Burnett, 1966). It appears therefore that regions proximal to the hypostome and tentacles are not irreversibly determined, but susceptible to redirection under appropriate stimuli. Although distal structures have been produced from proximal regions, no report exists of peduncle and basal disc formation at the distal end of an excised hydra.
Analysis of follicle cell patterns in dextral and sinistral Limnaea peregra
Authors: Ubbels Geertje A. , Bezem J. J. , Raven Chr. P.
Published: April 2021

Several experiments done in our laboratory make it likely that in the egg of Limnaea stagnalis there is a cortical morphogenetic field (Raven, 1949, 1952, 1966). One of us (Raven, 1963,1964,1967) has studied the origin of this morphogenetic field. In the newly laid egg cell there is a vegetative pole plasm, occupying a sector of about 110 degrees with its apex near the centre of the egg. It is situated somewhat obliquely with respect to the longitudinal axis of the first maturation spindle. Moreover, a circle of six lenticular subcortical patches of cytoplasm are found in the equatorial region of the egg. These ‘subcortical accumulations’ (SCA) are arranged according to a regular pattern. Four of them are situated close together on one side, occupying about 180 degrees of the egg circumference; two somewhat larger SCA lie on the opposite side. The SCA, together with the obliquity of the vegetative pole plasm, define a pattern which is polar, dorsoventral and nearly symmetric, though a slight asymmetry seems to be present.
Aspects of the tabby-crinkled-downless syndrome : II. Observations on the reaction to changes of genetic background
Authors: Sofaer J. A.
Published: April 2021

Two alleles of the sex-linked gene tabby, Ta and Tac, and two autosomal mimics of tabby, crinkled, cr, and downless, dl, each produce a similar mutant syndrome involving the coat and dentition of the mouse. Certain aspects of the development of the mutant defects have already been studied, and some comparisons between tabby and crinkled have been made. The present investigation is concerned with a comparison of all four genes, and with further analysis of the developmental basis for the dental abnormalities.