bluuebunny/crossref_metadata_2025 huggingface dataset:
Insufficient VEGFA activity in yolk sac endoderm compromises haematopoietic and endothelial differentiation
Authors: Damert Annette , Miquerol Lucile , Gertsenstein Marina , Risau Werner , Nagy Andras
Published: April 2021

Vascular endothelial growth factor A (VEGFA) plays a pivotal role in the first steps of endothelial and haematopoietic development in the yolk sac, as well as in the establishment of the cardiovascular system of the embryo. At the onset of gastrulation, VEGFA is primarily expressed in the yolk sac visceral endoderm and in the yolk sac mesothelium. We report the generation and analysis of a Vegf hypomorphic allele, Vegflo. Animals heterozygous for the targeted mutation are viable. Homozygous embryos, however, die at 9.0 dpc because of severe abnormalities in the yolk sac vasculature and deficiencies in the development of the dorsal aortae. We find that providing ‘Vegf wild-type’ visceral endoderm to the hypomorphic embryos restores normal blood and endothelial differentiation in the yolk sac, but does not rescue the phenotype in the embryo proper. In the opposite situation, however, when Vegf hypomorphic visceral endoderm is provided to a wild-type embryo, the ‘Vegf wild-type’ yolk sac mesoderm is not sufficient to support proper vessel formation and haematopoietic differentiation in this extra-embryonic membrane. These findings demonstrate that VEGFA expression in the visceral endoderm is absolutely required for the normal expansion and organisation of both the endothelial and haematopoietic lineages in the early sites of vessel and blood formation. However, normal VEGFA expression in the yolk sac mesoderm alone is not sufficient for supporting the proper development of the early vascular and haematopoietic system.
Skeletal defects in VEGF120/120 mice reveal multiple roles for VEGF in skeletogenesis
Authors: Zelzer Elazar , McLean William , Ng Yin-Shan , Fukai Naomi , Reginato Anthony M. , Lovejoy Stephanie , D’Amore Patricia A. , Olsen Bjorn R.
Published: April 2021

Angiogenesis is an essential component of skeletal development and VEGF signaling plays an important if not pivotal role in this process. Previous attempts to examine the roles of VEGF in vivo have been largely unsuccessful because deletion of even one VEGF allele leads to embryonic lethality before skeletal development is initiated. The availability of mice expressing only the VEGF120 isoform (which do survive to term) has offered an opportunity to explore the function of VEGF during embryonic skeletal development. Our study of these mice provides new in vivo evidence for multiple important roles of VEGF in both endochondral and intramembranous bone formation, as well as some insights into isoform-specific functions. There are two key differences in vascularization of developing bones between wild-type and VEGF120/120 mice. VEGF120/120 mice have not only a delayed recruitment of blood vessels into the perichondrium but also show delayed invasion of vessels into the primary ossification center, demonstrating a significant role of VEGF at both an early and late stage of cartilage vascularization. These findings are the basis for a two-step model of VEGF-controlled vascularization of the developing skeleton, a hypothesis that is supported by the new finding that VEGF is expressed robustly in the perichondrium and surrounding tissue of cartilage templates of future bones well before blood vessels appear in these regions. We also describe new in vivo evidence for a possible role of VEGF in chondrocyte maturation, and document that VEGF has a direct role in regulating osteoblastic activity based on in vivo evidence and organ culture experiments.
Expression of CD41 on hematopoietic progenitors derived from embryonic hematopoietic cells
Authors: Mitjavila-Garcia Maria Teresa , Cailleret Michel , Godin Isabelle , Nogueira Maria Manuela , Cohen-Solal Karine , Schiavon Valérie , Lecluse Yann , Le Pesteur Françoise , Lagrue Anne Hélène , Vainchenker William
Published: April 2021

In this study, we have characterized the early steps of hematopoiesis during embryonic stem cell differentiation. The immunophenotype of hematopoietic progenitor cells derived from murine embryonic stem cells was determined using a panel of monoclonal antibodies specific for hematopoietic differentiation antigens. Surprisingly, the CD41 antigen (αIIb integrin, platelet GPIIb), essentially considered to be restricted to megakaryocytes, was found on a large proportion of cells within embryoid bodies although very few megakaryocytes were detected. In clonogenic assays, more than 80% of all progenitors (megakaryocytic, granulo-macrophagic, erythroid and pluripotent) derived from embryoid bodies expressed the CD41 antigen. CD41 was the most reliable marker of early steps of hematopoiesis. However, CD41 remained a differentiation marker because some CD41– cells from embryoid bodies converted to CD41+ hematopoietic progenitors, whereas the inverse switch was not observed. Immunoprecipitation and western blot analysis confirmed that CD41 was present in cells from embryoid bodies associated with CD61 (β3 integrin, platelet GPIIIa) in a complex. Analysis of CD41 expression during ontogeny revealed that most yolk sac and aorta-gonad-mesonephros hematopoietic progenitor cells were also CD41+, whereas only a minority of bone marrow and fetal liver hematopoietic progenitors expressed this antigen. Differences in CD34 expression were also observed: hematopoietic progenitor cells from embryoid bodies, yolk sac and aorta-gonad-mesonephros displayed variable levels of CD34, whereas more than 90% of fetal liver and bone marrow progenitor cells were CD34+.

Thus, these results demonstrate that expression of CD41 is associated with early stages of hematopoiesis and is highly regulated during hematopoietic development. Further studies concerning the adhesive properties of hematopoietic cells are required to assess the biological significance of these developmental changes.
The reopening process of the esophagus in the normal chick and the crooked neck dwarf mutant
Authors: Allenspach Allan L.
Published: April 2021

The development of the esophagus in the crooked neck dwarf was studied between and 12 days of incubation (stages 26 –38). Esophageal histogenesis in the crooked neck dwarf resembles normal development up to stage 33. Vésiculation alone does not cause the reopening of the esophagus, which depends on the participation of epithelial degeneration to complete the process. Studies of epithelial degeneration in the mutant esophagus emphasize its caudo-cephalic gradient in the reopening process. The appearance of clefts in the intervesicular epithelium suggests that tension plays a role in the reopening process. The occluded segments and persisting epithelial strands of the 18-day mutant embryonic esophagus result from critical developmental failures at 8 days of incubation (stage 34). The crooked neck dwarf mutant has a histogenetic marker in the form of ‘degenerate mesenchyme cells’ as early as stage 30.
Übertragung und Änderung der Determinations-qualitäten in Antennenscheiben-Kulturen vonDrosophila melanogaster
Authors: Gehring Von Walter
Published: April 2021

Cell heredity and changes of determination in cultures of imaginai discs in Drosophila melanogaster
Oligosyndactylism, an early embryonic lethal in the mouse
Authors: Valen Phebe Van
Published: April 2021

In heterozygous condition, the gene for oligosyndactylism (Os) in the mouse (Mus musculus) causes syndactylism on all four feet and sometimes suppression of digit 2. Os/Os homozygotes are inviable and die before the 12th day of gestation (Grüneberg, 1956, 1961). The present study was initiated to identify the Os/Os homozygote and to establish the circumstances of its death.
Déterminations régionales dans l’aire cardiaque présomptive mises en évidence chez l’embryon de poulet par la méthode microélectrophysiologique
Authors: Douarin Georges Le , Obrecht Geneviève , Corabœuf Edouard
Published: April 2021

La répartition des potentialités cardiogénétiques dans le blastoderme d’oiseau aux stades précoces du développement a été étudiée par de nombreux auteurs. Au stade du blastoderme non incubé les parties périphériques, mais non les parties centrales, peuvent fournir en culture in vitro du tissu cardiaque spontanément pulsatile (Olivo, 1928). Les cellules cardiaques présomptives sont plus abondantes dans la région postérieure que dans les régions latérales et antérieure du blastoderme (Butler, 1935). Pendant les premières heures de l’incubation l’aptitude à former du cœur est encore très largement répandue dans le blastoderme mais tend à se concentrer dans la région postérieure (Spratt, 1942). Les potentialités cardiogénétiques se localisent ensuite de part et d’autre de la ligne primitive définitive (Rudnick, 1938; Hunt, 1932). Au stade du prolongement céphalique, les limites du territoire cardiaque présomptif ont été précisées par Rawles (1936, 1943). Les deux aires cardiaques occupent alors une situation bilatérale de part et d’autre du prolongement céphalique et du tiers antérieur de la ligne primitive.
Becs-de-lièvre provoqués chez le rat par un dérivé de la pénicilline, l’hadacidine
Authors: Lejour-Jeanty Madeleine
Published: April 2021

Il est aisé de provoquer des fentes palatines chez les Mammifères de laboratoire. L’action de la cortisone (Walker & Fraser, 1957), l’hypervitaminose A (Giroud & Martinet, 1955), la carence en niacine (Chamberlain & Nelson, 1963), par exemple, ont permis une étude détaillée de ces malformations.
Regeneration from mesenteric arteries in short-term culture
Authors: Feldman J. D. , Gardner D. L.
Published: April 2021

The investigations which are described here were originally undertaken in order to investigate the pathogenesis of early hypertension at a time when no morphological changes were evident in adrenergic arteries on light microscopy. Evidence of functional change was therefore sought by comparing the growth patterns of cells from hypertensive and normal mesenteric arteries in culture. The study of the cells which migrated from the explants form the basis for this paper.
Modification of embryonic development of reproductive and lymphoid organs in the chick
Authors: Erickson Alan E. , Pincus Gregory
Published: April 2021

Following the publication of Lillie’s (1917) observations and theories on the endocrine basis of the development of the bovine freemartin, experiments were initiated to determine if heterosexual gonad grafts to the chorio-alantoic membrane of chicks could stimulate formation of intersexes (Willier, 1927). Hormone extracts of testes and urine were used by Dantchakoff (1935) and Kozelka & Gallagher (1934), and synthetic hormones were tested in the chick by Wolff & Ginglinger (1935). Estrogens feminized the left gonad of male embryos and resulted in retention of Mullerian ducts in males and occasional cystic develop-ment of Mullerian ducts in females. Less extensive feminization of the left testis, dilation of Wolffian ducts, and partial deletion of Mullerian ducts occurred in androsterone-treated embryos (Wolff, 1935). Sensitivity of the genital papilla to exogenous steroids was described by Reinbold (1951). Riddle & Dunham (1942) demonstrated that a single injection of estradiol benzoate into laying birds resulted in feminization of genetic males which developed from ova released shortly thereafter. Lutz & Lutz-Ostertag (1959) described spontaneous chick freemartins developing in double-yolked eggs. Studies of individual male embryos which had access to the resources of two yolks in double-yolked eggs (Ruch, 1961) revealed the occurrence of gonadal modifications similar to those resulting from administration of estrogens or from implantation of female gonads adjacent to the genital ridge of young male embryos (Wolff, 1946–47). When heterosexual implants of gonads of sufficient size were placed on the chorioallantoic membrane, male left testes developed into ovotestes and Mullerian ducts were reduced in the female (Groenedijk-Huijbers, 1960). The immunological consequences of vascular anastomoses between bovine twins discussed by Owen (1945), and more recently by Fecheimer, Herschler & Gilmore (1963) and Goodfellow, Strong & Stewart (1965) afford an additional point of departure in studying the freemartin.
Ontogenesis of serum esterases in Mus musculus
Authors: Pantelouris E. M. , Arnason A.
Published: April 2021

The ‘typical’ serum esterase zymogram, obtained by starch-gel electrophoresis, of adult mouse serum comprises 19 fractions, but undergoes changes related to developmental stage. The main adult fractions are already present in the 18-day foetus. Whilst most are weaker than in the adult, the reverse is true for fractions 16–19. There are also six ‘foetal esterases’ which gradually decrease and disappear after birth, at different rates. The foetus and the young animal, up to 2 weeks, have also alkaline phosphatase (1 or 2 fractions), whilst no such enzyme was detectable in the adult’s serum. Pregnancy is associated with increases in three and decreases in two adult fractions and, more characteristically, with the appearance of a strong specific pregnancy esterase. An esterase zone (6) which is always stronger in the male could be subdivided into three fractions in males and two in females. The exclusively male fraction coincides with a band of acid phosphatase activity.
The effect of embryonic partial decapitation on the developmental sequence of some proteins in the chicken
Authors: Manwell Clyde , Betz T. W.
Published: April 2021

Partial decapitation of chick embryos at 33–36 h of incubation, ‘embryonic hypophysectomy’, markedly decreases the amount but not the electrophoretic mobility of alkaline phosphatase and a cathodal esterase, although several other esterases, acid phosphatase, lactate dehydrogenase, malate dehydrogenase, a cathepsin, lipase, haemoglobin and the major protein components extractable at low ionic strength are essentially unaffected. Electrophoresis of extracts of pituitaries of chicks just prior to hatching, at 4 days after hatching, and adults, suggests that with regard to the major proteins, which most likely include many of the protein hormones, the pituitary becomes well differentiated by hatching in normal embryos. The absence of pituitary hormones is responsible for the ‘foetal’ syndrome of partial decapitates and the reduction in bone formation may well be the result of inadequate amounts of alkaline phosphatase.
The control of growth in transplanted mammalian cartilage
Authors: Noel Janet F.
Published: April 2021

Seven-to eight-day mouse tail vertebrae were transplanted under the renal capsules of syngeneic adult animals and allowed to grow for up to 6 months. Their curve of growth and histological pattern of ageing were similar to those of control vertebrae which had been left in their normal position on young animals.

Slices of the growth cartilage of seven-to eight-day rat tail vertebrae were similarly transplanted into adult syngeneic rats. Though some grafts failed to grow, a considerable number showed similar growth characteristics to the epiphyseal cartilage in intact control vertebrae.

These results have been used to support the view that in the mouse and rat the epiphyseal growth cartilage has a limited potential for growth. This intrinsic growth-limiting mechanism seems to be of relatively greater importance than age-dependent changes in blood hormone levels in determining the changes in the rate of growth of the vertebrae as the animals approach adulthood.
A stereoscan study of the origin of ciliated cells in the embryonic epidermis ofAmbystoma mexicanum
Authors: Billett F. S. , Courtenay T. H.
Published: April 2021

A stereoscan electron microscope has been used to survey the epidermis of axolotl embryos as it becomes ciliated. The observations are consistent with much earlier ones that ciliated cells first occur on the surface of the epidermis at about the time of the closure of the neural folds. The cells are located first in the anterior dorsal region of the embryo at about the one-somite stage. After this they rapidly increase in number and by the three-to six-somite stage ciliated cells, which are isolated from one another, are scattered over the entire surface of the embryo in numbers which approach those of much later stages (18 somites). At the earlier stage, however, most of the ciliated cells lie below the general surface of the epidermis, occupying pit-like depressions. This is in contrast to the later stage when they are raised above the surface. The observations support the view that the precursors of the ciliated cells lie beneath the outer epidermal layer of cells and that the ciliation of the embryonic surface occurs when they move into the outer layer as they complete their differentiation.
Participation of grafted nerves in amphibian limb regeneration
Authors: Wallace B. M. , Wallace H.
Published: April 2021

Irradiated axolotl arms bearing grafts of brachial nerves can regenerate, albeit imperfectly. The origin of the regenerated tissues has been traced by means of the difference between dark and white genotypes. Although the origin of the melanophores cannot be decided in this way, their abundance identifies the genotype of the tissue they occupy. Sections of nine regenerates provide consistent evidence for the following conclusions. (1) The epidermis of the regenerate is probably an extension of the irradiated host epidermis. (2) All other tissues of the regenerate which differentiate from a mesenchymal blastema originate from the non-irradiated graft. Regeneration thus involves a true dedifferentiation and redifferentiation (i.e. a loss of determination and equivalent gain in potency for histological transformation). Irradiated cells apparently also dedifferentiate but cannot undergo the normal sequence of proliferation and redifferentiation, and so are not found in the mesodermal component of the regenerate.
The effect of progesterone and oestradiol on blastocysts cultured within the lumina of immature mouse uteri
Authors: Grant P. S.
Published: April 2021

Ovariectomy-delayed blastocysts flushed from mice treated with medroxyprogesterone acetate were injected into the lumina of immature mouse uterine horns. The horns were then maintained as organ cultures for 1–3 days in media that contained either (a) ethanol or ethanol plus (6) progesterone, (c) oestradiol or (d) progesterone and oestradiol. Trophoblast invasion of the uterine stroma occurred for 13, 10 and 6 % of the eggs injected, in media that contained progesterone, progesterone plus oestradiol, and oestradiol, respectively. The uterine stromal tissue did not decidualize. Embryonic development in invading eggs usually became abnormal during the migration of the distal endoderm. Further development was impeded by the progressive collapse of the yolk cavity which allowed trophoblastic giant cells to intermingle with proximal endodermal cells. The optimal oxygen concentration for trophoblastic invasion and embryonic development in the presence of progesterone and oestradiol was between 26 and 40 %.
Estrogen-induced surface coat and enzyme changes in the implanting mouse blastocyst
Authors: Holmes P. V. , Dickson A. D.
Published: April 2021

Blastocysts from estrogen-stimulated mice tend to be very sticky, a characteristic which can be correlated with estrogen-induced enzyme activation and changes in the surface coat of the trophoblast cells. The blastocyst surface coat was investigated using colloidal iron-Prussian blue stain. In addition, the activity of tyrosine aminotransferase was assayed histochemically in preimplantation blastocysts. The surface and enzyme changes were correlated with the presence of estrogen by investigations in normal blastocysts from intact mice before and after the endogenous estrogen surge and in delayed-implantation blastocysts from ovariectomized mice preceding and following estrogen treatment. Colloidal iron stains the surface coat of the blastocyst after, but not before, the endogenous estrogen surge and the exogenous estrogen treatment. Tyrosine aminotransferase activity also is increased considerably after estrogen induction.
Cell sorting out during the differentiation of mixtures of metabolically distinct populations ofDictyostelium discoideum
Authors: Leach C. K. , Ashworth J. M. , Garrod D. R.
Published: April 2021

The behaviour, during the multicellular phase of the life-cycle, of amoebae of Dictyostelium discoideum grown indifferent media is described. Amoebal populations were marked by growthtemperature-sensitive genetic lesions which do not interfere with developmental phenomena. The fate of cell populations was determined by measuring the relative number of mutant and wild-type cells at various stages in the life-cycle. Cells sort out during development in such a way that they may be ordered in a sequence in which those given early in the following list preferentially appear in the spore population when mixed with those given later in the list: cells grown in axenic medium + 86 mM glucose and harvested when in the exponential phase of growth ; cells grown in axenic medium and harvested when in the exponential phase of growth ; cells grown on bacteria and harvested when in the exponential phase of growth; cells grown in axenic medium+ 86 mM glucose and harvested when in the stationary phase of growth. Chemotactic aggregation and grex migration are not essential for sorting-out to occur but, in the normal life-cycle, the cells of a grex formed from amoebae grown in different media have sorted out anteroposteriorly. The relationship between this sorting out behaviour and the mechanism of pattern formation in fruiting-body morphogenesis is discussed. Differences in density of the amoebae cannot account for the sorting out predispositions we observe.
Etude morphologique de Faction du bromure d’éthidium sur des cellules embryonnaires dePleurodeles waltliien culturein vitro
Authors: Miquel Marie-Therese , Duprat Anne-Marie
Published: April 2021

Morphological studies on the action of ethidium bromide on in vitro cultured Pleurodeles waltlii embryonic cells

Ethidium bromide (EB) induces characteristic and constant nuclear changes on Pleurodeles waltlii embryonic cells cultured in vitro:

At the cytoplasmic level an important alteration of the chondrioma morphology occurs and an inhibition of the utilization of yolk platelets.

On the other hand EB generally inhibits neuroblast and myoblast differentiation. This inhibition appears to be reversible in myoblasts after short treatments.

The chromosomal DNA synthesis (incorporation of [3H]thymidine) does not seem to be affected by EB treatments while [3H]uridine incorporation in RNAs is completely inhibited after 24 h and longer treatments.
Influence of retino-tectal innervation on cell proliferation and cell migration in the embryonic teleost tectum
Authors: Schmatolla Ernest , Erdmann Georg
Published: April 2021

The influence of retino-tectal innervation on cell proliferation and cell migration in the optic tectum of the embryonic teleosts, Brachydanio rerio and Astyanax mexicanus, was investigated in a combined autoradiographic and experimental embryological study.

Unilateral eye Anlage removal was the method used to compare development of the affected non-optic-innervated tectum with that of its normal opposite innervated tectum.

The amount of mitosis as estimated by [3H]thymidine incorporation was not stimulated by retino-tectal innervation. Likewise no increase in cell number was found in the innervated tectum.

Cell migration and differentiation in the marginal zone was enhanced by retino-tectal innervation.

Conflicting results concerning proliferation, migration and differentiation in different species are explained by differences in time of ingrowth of the optic nerves and their depth of penetration into the tectum.
Chronological changes in the cell cycle of chick neuroepithelial cells
Authors: Wilson D. B.
Published: April 2021

Radioautographic data obtained from a total of 103 chick embryos injected with [3H]thymidine suggest that the generation time of neuroepithelial cells in dorsolateral regions of the optic tectum increases from approximately 8 h at 3 days of incubation to 15 h at 6 days of incubation. The most marked change occurs between the 4th and 5th day, when the generation time increases from 9 to 13 h, respectively. Between the 3rd and 6th day of incubation the length of the DNA-synthetic (S) period and of the premitotic (G2) period remains fairly constant; however, the duration of mitosis (M) and of the postmitotic (GJ period appears to be prolonged.
Size determination inHydra: The roles of growth and budding
Authors: Bisbee John W.
Published: April 2021

Hydra pseudoligactis cultured at 9°C for 3 – 4 weeks are one-and-a-half times larger than those cultured at 18°C. The size of Hydra is correlated with the numbers of epithelio-muscular and digestive cells in the distal portion of the animal and with the diameters of the epithelio-muscular cells in the peduncle.

Counts of mitotic figures and tritiated-thymidine-labeled nuclei and determinations of increase in mass of Hydra populations suggest that the difference caused by these temperatures does not affect mitosis. At 9°C buds are initiated at a lower rate and take longer to develop than at 18°C. The surface-areas of buds raised at the two temperatures are similar.

Because Hydra raised at the two temperatures have similar growth dynamics, the differences in sizes of the animals cannot be due to growth rate. The observed effect of temperature on bud initiation and development is probably relevant to the increased size of animals raised at 9°C, since these larger animals may be accumulating more cells while losing fewer to buds.
The ultrastructural effects of excess maternal vitamin A on the primitive streak stage rat embryo
Authors: Morriss Gillian M.
Published: April 2021

A single injection of 100000 i.u. vitamin A palmitate was administered to pregnant female rats on one of the days 0–14 of pregnancy. The litters were examined for malformations and prenatal death. On the basis of the results of this preliminary investigation, treatment on day 8 was selected for detailed study. Day-8 embryos were examined with the electron microscope from 2 to 24 h after maternal vitamin A administration. Ultrastructural abnormalities were: membrane swelling (cytoplasmic vacuoles, ‘budding’, nuclear membrane irregularities, general swelling leading to cell death); changes in the extra-to intracellular fluid ratio; increase in the number of lipid droplets; autophagic vacuoles; condensed and swollen mitochondria. These changes were not equally distributed among the different cell types. It is suggested that this differential effect leads to a loss of synchrony between the development of structures from the different germ layers, in addition to a general retardation. Loss of contact between mesoderm cells may delay normal migratory movements and induction of neural plate. The general retardation is related to the lower birthweights of treated embryos versus controls, and the differential effects to the subsequent abnormal morphogenesis.
Properties of the primary organization field in the embryo ofXenopus laevis: IV. Pattern formation and regulation following early inhibition of mitosis
Authors: Cooke J.
Published: April 2021

Visual observation of early blastulae, and counting of cell suspensions from the late blastula and subsequent stages of Xenopus development, have shown that exposure to either colcemid or mitomycin C can sustain blockage of the mitotic cycle, and hence prevent the normal increase in cell number. Such blockage is essentially complete within a period, following introduction of the drugs, which is short compared with the cell-cycle time normal to post-blastular stages. Although the cell-counting data do not allow a statistical demonstration, there is a suggestion that mitomycin C allows a greater proportion of cells to divide once, after its introduction, than does colcemid. This is in accord with its putative mode of action, in causing only intrachromatid cross-linkage within chromosones, but there are no data on the status of DNA replication within nuclei of the non-dividing cells under either drug. If blockage is begun not earlier than stage 10+, some 20 min after dorsal lip formation, essentially normal morphogenesis ensues up to tail-bud stages around 27, including histodifferentiation of ectodermal structures and notochord, and twitching of somitic muscle. Such embryos are described. In describing those arresting at earlier stages following blockage in blastulae, the possibility is mentioned that morphogenesis may fail for mechanical reasons due to low cell number and large cell size, rather than to lack of a normal field as such. Cell counting reveals that blocked embryos with qualitatively normal pattern formation by stages 22-24, in having a total cell number appropriate to stage 10+ or 10J, show about a seventh or an eighth of the number of cells normal to their stage. Between then and stage 27 when histogenesis, particularly of twitching muscle, is more clearly seen, the direct method of estimating cell number can no longer be used, but histology reveals no mitotic metaphases in any blocked embryos. In the same experiments, operations of two types described in previous papers are performed on early gastrulae so that regulation is required in the embryonic field after the cessation of mitosis. The results are as seen in the normal presence of the cell cycle, revealing that, in response to changes of positional information value, host material may change its presumptive differentiation tendency and final commitment, in the absence of cell division as such. There is some indication that the proportional numbers of cells assigned to different structures in an individuation field may deviate from normal when overall cell number is limiting.
Degeneration of the nerve cord in the tail ofRana temporariaduring metamorphic climax: study by electron microscopy
Authors: Fox H.
Published: April 2021

The preclimactic non-degenerate and climactic degenerate tail nerve cords of larvae of Rana temporaria have been examined by electron microscopy. The nerve cord begins to degenerate at the tip of the tail; the recognizably severe area of necrosis remains relatively discrete and circumscribed as the tail progressively shortens. Initially the nerve cord cells undergo autolysis, and acid phosphatase is active in the necrotic areas probably representing lysosomal intervention. It is likely that disorganized and degraded nerve cord cells are phagocytosed by mesen-chymal macrophages.
Parthenogenetic development of mouse embryosin vivo: I. Preimplantation development
Authors: Witkowska Anna
Published: April 2021

Newly ovulated eggs from CBA-p and CBA-T6T6 inbred strains were activated in situ with an electric shock of 20–50 V. Both spontaneously ovulating females mated with vasectomized males (strain A) and those induced to ovulate and kept apart from males were used. The immediate reaction of eggs was examined 5–7 h after activation and their subsequent development was followed every day up to the 6th day (eggs examined on the 5th and 6th day were tube-locked by a ligature). In spontaneous ovulators the highest yield of activated eggs was obtained following 30 V shock (75%), with a mean for four series (20, 30, 40 and 50 V) of 46·1%. The most common reaction is extrusion of the second polar body (2 PB) and formation of one pronucleus (about 70% of activated eggs). Other types of reaction include: immediate cleavage, suppression of 2 PB with formation of two or, very rarely, one pronucleus. Thus the majority of eggs are potentially haploid. No relationship between the frequency of various types of reaction and the strength of the shock (voltage) was observed. Up to the 3rd day cleavage proceeds at a normal rate and appears to slow down during the 4th day. In spontaneously ovulating females the incidence of blastocysts among developing eggs rises from 3·4% on the 4th day to 52·5% on the 5th day; the corresponding figures for induced ovulations are 10% and 23·6%. Some embryos despite being composed of a large number of cells (40–120) do not undergo cavitation and remain morulae.

On the basis of karyological examination of 60 embryos with analysable metaphase plates 60% were classified as haploid, 16·7% as diploid, 1·7% as tetraploid and 21·6% as haploid/diploid mosaics. During early cleavage binucleate blastomeres (a presumed step in regulation from tt to 2n) were observed only in eggs from induced ovulations. In embryos developed from spontaneously ovulated eggs n/2n mosaics were observed for the first time on the 5th day. In general, spontaneously ovulated eggs developed better after activation (both in quantitative and qualitative terms) than those obtained following hormonal treatment.
Feather pattern stability and reorganization in cultured skin
Authors: Novel Genevieve
Published: April 2021

The formation of the feather pattern has been studied in skin explants obtained from the lumbar region of the spinal pteryla of -to -day chick embryos. Explants were cultured in vivo on the chorioallantoic membrane (CAM) or in vitro, either on semi-solid natural media (containing whole chick embryo extract (JE) or chick brain extract (EC)), or in a liquid synthetic medium (199). Feather pattern development was dependent on the culture method and also on the way the explants were excised and treated before cultivation. When the mid-dorsal initial row of rudiments was preserved at explantation, the feather pattern was stable on all media and initial feather rudiments progressively gave rise to feather buds. When the mid-dorsal initial row of rudiments was damaged at explantation, explants of younger stages (A, B or C) cultured on media JE or EC underwent a complete reorganization of their initial feather pattern; in other explants (of older stage D, or those of any stage cultured in medium 199 or on the CAM) the initial feather pattern was stable. When the initial rudiments were destroyed by dermo-epidermal dissociation and recombination, feather pattern reorganization was observed in explants of any stage cultured in vitro (on medium EC or in medium 199) (Table 1, p. 625). Feather pattern reorganization was characterized by the following events: during the first 24 – 30 h of culture the initial feather rudiments gradually vanished; dermal condensations and epidermal placodes disappeared; after which a new ‘primary’ row differentiated parallel to the longitudinal edges of the explant’s dermis, its distance from the medial dermal edge was larger when the explant was obtained at a more advanced stage. The newly formed feathers were arranged in longitudinal rows parallel to the cephalo-caudal axis of the dermis, which was thus solely responsible for the polarity of the reorganized feather pattern. The capacity of the feather pattern to reorganize shows that it is still labile at the time of explantation and that the site of subsequent feathers is not yet determined in the unpatterned dermis. The pattern is determined progressively from prospective row to prospective row starting from the primary row. In normal development in situ, the role of the primary row is supposedly played by the mid-dorsal row in the lumbar region of the spinal pteryla. Just prior to the formation of feather condensations the dermal cells appear to be the transitory seat of a passing peak of morphogenetic activity moving from the mid-dorsal line to the lateral edges of the spinal tract.
A clonal analysis of segment development inOncopeltus(Hemiptera)
Authors: Lawrence Peter A.
Published: April 2021

X-irradiation of eggs and larvae of Oncopeltus fasciatus results in the development of clonal patches of epidermal cells of unusual pigmentation. The frequency, size and distribution of these patches is dependent on the dose and timing of irradiation. Analysis of these clones in the abdomen has shown that the presumptive epidermis becomes effectively segmented during blastoderm formation and thereafter the clones are restricted to within a segment quadrant (dorsal or ventral, left or right). There are approximately 10 presumptive epidermal cells per segment quadrant. The shape of the clones and the orientation of mitoses in larvae suggest that both early and late cells of the anterior margin of the segments divide with a preferred orientation (cleavage plane parallel to the antero-posterior axis). Elsewhere in the larval segment the mitoses are randomly oriented, and the segment grows evenly all over. The number of mitoses/cell/moult cycle is not precisely determined, but the amount of cell division is perhaps under a general probabilistic control. It is suggested that the segmental gradient may be involved in this control.
Positional information and pattern regulation in hydra: the formation of boundary regions following axial grafts
Authors: Hicklin J. , Hornbruch A. , Wolpert L. , Clarke M.
Published: April 2021

A two-gradient model is proposed for regulation and regeneration of the head end of hydra in terms of positional information. One gradient is set up by a diffusible substance made at the head end, which may be regarded as a positional signal, and the other is a more stable cellular parameter which is the positional value. The rule for head end formation is that the concentration of the diffusible substance falls a threshold amount below the positional value. A variety of instantaneous axial grafts have been carried out which are discussed in terms of this model. Some simple computer simulations of diffusion are provided. There is some evidence that the source of the positional signal is localized at the head end. Some experiments on changes in polarity are given. It also seems that the positional signal from the head end inhibits foot end formation.
Positional information and pattern regulation in hydra: the effect of γ-radiation
Authors: Hicklin J. , Wolpert L.
Published: April 2021

Hydra exposed to high doses of γ-irradiation (25000 rad) are still capable of regeneration although no normal mitotic figures could be seen for up to 48 h after irradiation. Irradiated heads could still inhibit head formation in other regions in graft combinations. The time for head end determination in irradiated animals appeared to be increased. It is concluded that head end regeneration need not involve cell division.
A propos d’un effet paradoxal de la cycloheximide sur l’œuf Anemia salina
Authors: Fautrez J. , Fautrez-Firlefyn N.
Published: April 2021

Cycloheximide, an inhibitor of protein synthesis at the ‘translation’ level, has a very strong antimitotic activity upon the egg of Artemia salina, during segmentation. At extremely low concentrations, on the contrary, it enables eggs, extracted from the uterus just after fertilization, to enter into segmentation, while the controls remain undivided. From these results it is argued that synthesis of a protein in the immature egg could have an inhibitory influence upon too early cell division. The synthesis of this factor could be extremely sensitive to cycloheximide action.
Further observations on the distribution of cytoplasmic substances among the cleavage cells in Lymnaea stagnalis
Authors: Raven Chr. P.
Published: April 2021

The period of development from the 4th cleavage to the 24-cell stage was studied. Both during 4th and 5th cleavage a wave of mitosis passes over the egg from the vegetative to the animal pole. At 5th cleavage it does not spread over the cells of the first quartet, however, and cell division stops for 3 h at the 24-cell stage. Nucleoli are now formed in the interphase nuclei, and many of them are extruded whole into the cytoplasm. After 5th cleavage the cleavage cavity is gradually reduced and finally disappears altogether. All cells then extend towards the centre of the egg. In this process one of the macromeres (3D) finally becomes preponderant, gets a central position and applies itself against the inner side of the animal cells. This is preceded by a period of seemingly haphazard variation in macromere positions. Lipid globules and mitochondria accumulate in the central parts of the first quartet cells. The special cytoplasm (SCA-plasm) found in the most vegetative part of the macromeres at the 8-cell stage is distributed among the cells at the next cleavages. Part of it passes into the 2nd micromeres, another part into the 3rd micromeres, while the rest remains concentrated in the vegetative part of the macromeres around the vegetative cross-furrow. At this place coarse dark composite granules, of a special kind and very rich in RNA, become visible at the 16-cell stage. At the 24-cell stage they begin to move inwards along the cell walls, and finally condense into the compact RNA-rich ‘ectosomes’ at the central ends of the macromeres. The significance of the SCA-plasm and of the ‘ectosomes’ for the determination of dorso-ventrality in Lymnaea is discussed.
Morphogenesis of the trigeminal mesencephalic nucleus in the hamster: cytogenesis and neurone death
Authors: Alley Keith E.
Published: April 2021

The chronology of cellular development in the trigeminal mesencephalic nucleus of the hamster has been studied by light and electron microscopy. Major developmental features are compressed into a two-week period that spans pre- and postnatal maturation. Special emphasis is focused on the sequence of developmental events, with the following points analyzed in this report: cell proliferation, cytological and axonal development, cell death, and cluster formation.

These centrally located primary sensory neurones seem to arise from a separate germinal population found in the alar plate of the midbrain and pons. The neurones are remarkable for their precocious formation and characteristic appearance. In hamster embryos they are first detected when the neural tube is only a couple of cell layers thick. Prenatally, the neurones grow rapidly and have doubled in diameter by birth. Axons form shortly after the cells are formed. This is marked by a sudden upsurge in cytoplasmic tubules and filaments in one end of the soma. Postnatally, cellular growth continues at a reduced rate. However, shortly after birth many small spines protrude from the cell body, thus increasing the surface area available for nutritive exchange. Myelination of the axon commences 6 days after birth.

Cell counts on a series of pre- and postnatal animals detected a considerable overproduction of neurones in the mesencephalic nucleus. Prior to birth there is a rapid elimination of almost 50% of these cells. Degenerating cells were identified in both light and electron microscopes. The temporal relationship between peripheral innervation, cell death and synaptogenesis suggests a developmental mechanism that provides some flexibility in the formation of synaptic connexions in the mesencephalic nucleus.

Clusters of 2 –4 tightly packed neurones are a characteristic feature of the developing and adult mesencephalic nucleus. Specialized junctions connect adjacent neurones and are thought to provide the basis for electrotonic coupling within the nucleus. Macula adhaerens plaques were present in both pre- and postnatal hamsters. However, close appositions were only identified postnatally.
Ein invasives Neoplasma aus embryonalen Zellen vonDrosophila melanogasterin Dauerkulturin vivo
Authors: Hauri Hans-Peter
Published: April 2021

An invasive neoplasm from embryonic cells of Drosophila melanogaster cultured permanently in vivo

The neoplasm H 126, obtained from the posterior half of a 6 ± 1-h-old embryo of Droso-phila melanogaster, was cultivated in adult female flies over more than 120 transfer generations (more than 4 years). Four sub-lines were derived from it.

The neoplasm H 126 invades the ovaries of the host flies, whereas the intestinal tract and the fat body are only surrounded very tightly, but not invaded by these abnormal cells. The neoplasm is lethal to the host 8–14 days after implantation into the abdomen (cultivation temperature: 25 °C).

Egg deposition of neoplasm-bearing hosts decreases 5 days after abdominal implantation.

After 4 years of cultivation the sub-lines differ specifically from one another in their chromosomal content; however, all of them show a karyotype near tetraploidy.

Ultrastructural features of these neoplasm cells are: (a) the nearly complete absence of membrane specializations correlated with weak cell adhesion, (b) the abundance of cyto-plasmic processes and (c) 36 nm virus-like particles in the nucleus and in the cytoplasm.

Invasiveness, alterations of the karyotype, the origin of the neoplasm H .126, and the presence of virus-like particles are discussed.
The structure of a morphogenetic cytoplasm, present in the polar lobe ofBithynia tentaculata(Gastropoda, Prosobranchia)
Authors: Dohmen M.R. , Verdonk N.H.
Published: April 2021

In the first polar lobe of the egg of Bithynia tentaculata a cup-shaped mass of small vesicles is described, which fills the greater part of the lobe. It is named the ‘vegetal body’. With methyl green-pyronin the vegetal body stains clearly, but after treatment with RNase no staining occurs, thus indicating the presence of RNA. The first polar lobe of Bithynia is of great importance for further development of the embryo and it is argued that the vegetal body could be a morphogenetic cytoplasm, responsible for the developmental effects of the polar lobe.
In vitroactivation of mouse eggs
Authors: Graham C. F. , Deussen Z. A.
Published: April 2021

Unfertilized mouse eggs were activated in vitro with hyaluronidase. Subsequently they were exposed to culture medium at different osmolarities. In full strength White’s culture medium they tended to form one pronucleus and a second polar body. The majority of these eggs were haploid. In 4/5 and 3/5 dilutions of this medium, the second polar body formation was sup-pressed and eggs tended to form with one or two pronuclei. Those with one pronucleus were diploid and those with two pronuclei could either form a diploid or form a haploid mosaic. Old eggs tended to immediately cleave and form haploid mosaics.

DNA synthesis was studied in activated eggs using tritiated thymidine and autoradiography. DNA synthesis occurred at a similar time in fertilized and activated eggs.
The effect of osmolarity on mouse parthenogenesis
Authors: Kaufman M. H. , Surani M. A. H.
Published: April 2021

Eggs from (C57BI × A2G)F1 mice were activated by treatment with hyaluronidase, which removed the follicle cells, and cultured in vitro. Observations were made 6–8 h after hyaluronidase treatment to determine the frequency of activation and the types of parthenogenones induced. Cumulus-free eggs resulting from hyaluronidase treatment were incubated for in culture media of various osmolarities. The frequency of activation was found to be dependent on the postovulatory age of oocytes, while the types of parthenogenones induced were dependent on the osmolarity of the in vitro culture medium and their postovulatory age.

Culture in low osmolar medium suppressed the extrusion of the second polar body (2PB). This decreased the incidence of haploid eggs with a single pronucleus and 2PB and immediately cleaved eggs from 97·5% to 42·3 % of the activated population. Where 2PB extrusion had been suppressed, 97·4 % of parthenogenones contained two haploid pronuclei. Very few were observed with a single and presumably diploid pronucleus.

Serial observations from 11 to 18 h after hyaluronidase treatment were made on populations of activated eggs as they entered the first cleavage mitosis after incubation in medium either of normal (0·287 osmol) or low (0·168 osmol) osmolarity. A delay in the time of entry into the first cleavage mitosis similar to the duration of incubation in low osmolar medium was observed.

Further, eggs were incubated in control and low osmolar culture media containing uniformly labelled [U−14C]amino acid mixture to examine the extent of protein synthesis in recently activated eggs subjected to these culture conditions. An hypothesis is presented to explain the effect of incubation in low osmolar culture medium in delaying the first cleavage mitosis.