bluuebunny/crossref_metadata_2025 huggingface dataset:
Positional information and pattern formation in Hydra. Dynamics of regions away from the boundary
Authors: Hicklin J. , Hornbruch A. , Wolpert L.
Published: April 2021

The dynamics of regions away from the head-end boundary have been investigated by a variety of assays, and the changes appear to be slow. If, for example, a head end is grafted onto a peduncle to give H/56F, region 5 does not become a region 1 within 72 h. Such results support a gradient type model, and exclude a head end inducing a region 1 in the tissue adjacent to it. The changes can be interpreted if the positional value were effectively slowly diffusible: about 10 times more slowly than the positional signal. These results also have implications for studies on polarity reversal.
An analysis of the condensation process during chondrogenesis in the embryonic chick hind limb
Authors: Thorogood P. V. , Hinchliffe J. R.
Published: April 2021

An analysis has been made of the pre-cartilaginous condensation stage in the development of the femur and tibia/fibula skeletal blastemata of the embryonic chick hind limb. Light microscopy serial sections were used to ‘map’ the mesenchymal cell condensations of both myogenic and chondrogenic anlagen in the limb-bud from stages 22 to 26 (Hamburger & Hamilton, 1951). Cell counts reveal that an increase in mesenchymal cell number per unit area occurs in the central chondrogenic locus at stage 24 prior to matrix formation. Electron microscopy, using a simultaneous double fixation with osmium and glutaraldehyde, reveals that the pre-chondrogenic cells are characterized by large areas of close surface contact between adjacent cells, as compared with the extensive intercellular spaces associated with undifferentiated mesenchymal cells. The results are discussed and related to other investigations of in vivo chondrogenesis and to analyses of cellular events during in vitro chondrogenesis. These observations are consistent with the theory that condensations are formed by a process of aggregation rather than by localized increased mitosis.
Differentiation in vitro of innervated tail regenerates in larval Ambystoma
Authors: Globus Morton , Liversage Richard A.
Published: April 2021

Larval Ambystoma tail regenerates, innervated by the intact spinal cord, were cultured with their epidermal covering in modified Parker’s medium (CMRL-1415) and the morphological integrity of the explanted regenerates was maintained with consistent success. The results show that the larval urodele tail blastema is capable of undergoing growth and differentiation when isolated in vitro and regeneration follows the normal in vivo pattern. A diffuse aggregate of blastema cells, which extended caudally from the cut end of the notochord at the time of explantation, underwent differentiation in vitro in the presence of the regenerating spinal cord. The importance of the nerve in regeneration is discussed in relation to the in vitro system.
Haploid mouse embryos obtained by microsurgical removal of one pronucleus
Authors: Modliński Jacek A.
Published: April 2021

A pronucleus can be microsurgically removed from the fertilized mouse egg. Out of 145 haploid eggs obtained by this method and transplanted into the oviduct of pseudopregnant recipients, 36 multicellular embryos were recovered on the 4th or 5th day. On the 4th day all embryos were morulae composed of 8-50 cells, with the majority containing 8-16 cells. After an additional 24 h in vivo or in vitro the cell number increased considerably, sometimes up to as many as 80. Out of 36 multicellular embryos only one developed into a blastocyst while the others remained at the morula stage. Karyological investigations confirmed that the embryos were haploid and revealed that all were gynogenetic. Possible reasons for the absence of the androgenones and for the scarcity of blastocysts are discussed.
Developmental precocity in transferred mouse embryos influencing the teratogen response to salicylate
Authors: Marsk L. , Larsson K. S. , Kjellberg M.
Published: April 2021

Asynchronous blastocyst transfer, supposed to equalize the developmental stage of native and alien embryos during the organogenic period, was used as a tool in a teratological investigation.

A spurious protection by the transfer as such was shown to depend on a persisting asynchrony between native and alien foetuses. The initial difference of 24 h was not nullified, but decreased to 8 h. This difference allowed transferred foetuses to pass the period of maximum sensitivity before salicylate treatment.
The structural and functional development of the retina in larval Xenopus
Authors: Chung S. H. , Stirling R. Victoria , Gaze R. M. , Land M. , Stirling R. Victoria
Published: April 2021

The structural transformations of the larval Xenopus retina at successive stages of development, and concomitant changes in response characteristics of retinal ganglion cells, were studied using histological and electrophysiological techniques. The first sign of visually evoked electrical responses appears at about the time when the ganglion cells spread out into a single layer and shortly after the inner and outer plexiform layers become discernible. Initially giving simple ‘on’ responses, the cells progressively change their response characteristics and become ‘event’ units. Subsequently, ‘dimming’ units can be identified. Throughout larval life, response properties of these two types become more distinct from one another and approximate to those found in the adult. So do the arborization patterns of the dendritic trees of the ganglion cells. Two types of branching patterns are identifiable in Golgi preparations. Around metamorphic climax, a new type of ganglion cell appears, coinciding with the emergence of ‘sustained’ units electro physiologically. After metamorphosis, the retina still grows both in thickness (mainly in the inner plexiform layer) and diameter. The three unit types change such that they come to show pronounced inhibitory effects from the peripheral visual field on the receptive field and each unit type acquires a distinct pattern of endogenous discharge.
Xenopus laevis cement gland as an experimental model for embryonic differentiation
Authors: Picard J. J.
Published: April 2021

Explants of the blastocoelic roof of Xenopus laevis embryos were incubated for 6 h in Holtfreter solution containing 10 mM ammonium chloride and 10 HIM sodium bicarbonate. After this incubation they were transferred for 5 days to Barth’s physiological salt solution. Under these conditions the explants underwent differentiation into cement gland tissue. The ability to produce cement gland was highest when explants were dissected from young gastrulae (stage 10). Explants from younger and older embryos displayed much smaller cement glands.

There is no difference in the response of ventral or dorsal portions of the blastocoelic roof of stage-10 embryos under these in vitro conditions involving ammonium chloride stimulation. Although the treatment changed the fate of some ectoblastic tissues, it was unable to force endodermal or mesodermal tissues of the blastoporal lip to differentiate into cement gland.

The amount of cement gland in the ectoblastic explants varied according to the egg-batch and on the average accounted for 55 % of the total tissue. The remaining tissue was undifferentiated. Most of this undifferentiated tissue originates from the adjacent layer of the ectoblast. Therefore it may be estimated that the cement gland accounts for 80 to 100 % of the volume of the competent superficial layer.
Investigation of the determinative state of the mouse inner cell mass
Authors: Rossant J.
Published: April 2021

Inner cell masses (ICMs) were dissected from and day mouse blastocysts and inserted into empty zonae before transfer to the oviducts of pseudopregnant mice. The ICMs survived in the oviduct for at least 2 days with little evidence of reduction in cell number. After 1 day, isolated day ICMs were still viable, since they could form chimaeras when injected into day blastocysts. However, no evidence of trophoblast formation could be detected in any of the isolated ICMs, despite exposure of some of their cells to ‘outside’ conditions. This is further evidence that ICM cells, although not overtly differentiated, are determined by days. Although no trophoblast was formed, day ICMs formed an outer endoderm layer after 1 day in the oviduct, as judged by light and electron microscopical evidence. It is suggested that cell position may be important in endoderm differentiation.
Ultrastructural identification of extracellular matrix and cell surface components during limb morphogenesis in man
Authors: Kelley Robert O.
Published: April 2021

Development of the human hand plate (stages 16–17) has been analyzed with emphasis on differentiation of elements within the extracellular matrix and the composition of the mesenchymal cell surface. The epithelial-mesenchymal interface contains a basal lamina and a sublaminar matrix exhibiting: (a) collagen fibrils with characteristic 63–64 nm banding; (6) non-banded filaments, 10—15 nm in diameter; (c) ruthenium red-positive particles, 12—15 nm in diameter; and (<7) attenuated threads, 3·5–5·0 nm in diameter which interconnect particles, fibrils, filaments and the basal lamina. Processes of mesenchymal cells penetrate this matrix network. In addition to staining with ruthenium red, components of basal laminae bind to ferritin-conjugated Concanavalin A, greatest binding being localized on the mesenchymal surface of the lamina. Asymmetry of binding is removed by incubation of exposed laminae with trypsin (5 /μg/ml). Regional differences in these staining and binding characteristics within the subepithelial matrix have not been observed in the hand plate. However, precartilaginous extracellular zones deep within the plate are notably unstructured in comparison to the sublaminar region. Ruthenium red-positive materials at mesenchymal cell surfaces display sensitivity to testicular hyaluronidase, Pronase and trypsin but resist removal with neuraminidase and EDTA. These features of the substrate in situ may be important in the regulation of mesenchymal cell behavior during limb morphogenesis in man.
Immunofluorescence studies on amphibian myoblast differentiation
Authors: Duprat A. M. , Romanov’sky A. , Hurychová D. , Machá J.
Published: April 2021

Differentiating myoblasts from urodele amphibians were cultivated in vitro and treated by immunofluorescence techniques and (or) inhibitors of RNA and protein syntheses. These experiments lead to the conclusion that the differentiation of these cells is directed by long-lived m-RNAs which are already present in morphologically undifferentiated cells and may act for at least 6 days.

Contrary to observations on cultivated myogenic cells from other groups, the fusion of urodele myoblasts is not a prerequisite for a normal and functional differentiation (contractions) since isolated myoblasts differentiate quite normally.

The appearance and further evolution of myosin and actin occur synchronously in this biological system.
Analysis of gene expression during development in the homeotic mutant Contrabithorax of Drosophila melanogaster
Authors: Morata Gines
Published: April 2021

Contrabithorax, a mutant of the bithorax system in Drosophila melanogaster produces a partial homeotic transformation of mesothorax (wing) into metathorax (haltere). The wing of a fly homozygous or heterozygous for the mutant is a mosaic of wing and haltere structures. A genetic analysis of the mutant suggests that its phenotype is due to some form of derepression in the wing of two other genes of the bithorax system (bithorax and postbithorax) which are not normally active there. This repression is not complete. The activity of the two genes is below the normal level resulting in only a partial transformation of wing into haltere.

Clones of marked cells were generated by X-rays and were found to include both transformed (haltere) and untransformed (wing) territory; this was true even for those generated late in development. Thus the final expression of a cell depends not on its immediate ancestry but perhaps on the level of the products of the wild-type alleles of bithorax and postbithorax.
The role of microtubules in chick blastoderm expansion—a quantitative study using colchicine
Authors: Downie J. R.
Published: April 2021

Since their discovery, cytoplasmic microtubules have been much studied in the context of cell movement and cell shape change. Much of the work has used drugs, particularly colchicine and its relatives, which break down microtubules - the so-called anti-tubulins. Colchicine inhibits the orientated movements of many cell types in vitro, and disrupts cell shape change in several morphogenetic situations.

The investigation reported here used chick blastoderm expansion in New culture in an attempt to quantify the colchicine effect on orientated cell movement. However, although colchicine could halt blastoderm expansion entirely, a simple interpretation was not possible. Colchicine at concentrations capable of blocking mitosis, and of disrupting all or most of the cytoplasmic microtubules of the cells studied, inhibited blastoderm expansion, often resulting in an overall retraction of the cell sheet.Though blastoderm expansion does normally involve considerable cell proliferation, the colchicine effect could not be ascribed to a block on cell division since aminopterin, which stops cell division without affecting microtubules, did not inhibit expansion.Blastoderm expansion is effected by the locomotion of a specialized band of edge cells at the blastoderm periphery. These are the only cells normally attached to the vitelline membrane - the substrate for expansion. When most of the blastoderm was excised, leaving the band of edge cells, and the cultures then treated with colchicine, expansion occurred normally. The colchicine effect on blastoderm expansion could not therefore be ascribed to a direct effect on the edge cells.An alternative site of action of the drug is the remaining cells of the blastoderm. These normally become progressively flatter as expansion proceeds. If flattening in these cells is even partially dependent on their cytoplasmic microtubules, disruption of these microtubules might result in the inherent contractility of the cells resisting and eventually halting edge cell migration. That cell shape in these cells is dependent on microtubules was demonstrated by treating flat blastoderm fragments with colchicine. On incubation, the area occupied by these fragments decreased by 25-30 % more than controls.

The significance of these results in the general context of orientated cell movements and cell shape determination is discussed, with particular emphasis on the analogous system of Fundulus epiboly.
The hormonal control and morphology of blastocyst invasion in the mouse uterus in vitro
Authors: Grant P. S. , Ljungkvist I. , Nilsson O.
Published: April 2021

When mature and immature uteri from ovariectomized mice were cultured in chemically defined media, blastocyst invasion occurred in the presence of progesterone but not in media containing only oestradiol.

The invaded stromal tissue did not decidualize unless the uteri were taken from mice pretreated with progesterone and oestradiol. Fibrillar material was, however, concentrated in the stromal tissue adjacent to the invasive trophoblast.

Neither progesterone nor oestradiol, had any ultrastructural effect on the endometrium of cultured uteri from ovariectomized mice, other than closure of uterine lumina in the presence of progesterone.

Embryogenesis became abnormal, probably owing to the failure of formation of a suitable implantation chamber.
Electron microscopic studies on chick limb cartilage differentiated in tissue culture
Authors: Goel Suresh C. , Jurand A.
Published: April 2021

The hind limb-bud mesenchyme of chick embryos days old was cultured in Eagle’s Minimum Essential Medium supplemented with both horse serum and fresh chick embryo extract. Whereas no differences are seen at the light-microscope level, at the electron-microscope level the chondroblasts differentiated in tissue culture are noticeably different from those differentiated in vivo, particularly in the possession of some cytoplasmic fibrils and vacuoles. It is proposed that the secretion of the extracellular matrix alone is not sufficient to account for the pattern of cellular arrangement in a cartilaginous condensation.
Activities of haem synthetic enzymes in blood cells of pre-natal flexed-tailed (f/f) anaemic mice
Authors: Cole R. J. , Garlick J. , Cheek E. M.
Published: April 2021

Levels of activity of δ-aminolaevulinate synthetase, δ-aminolaevulinate dehydratase, porphyrinogen synthetase and haem synthetase in circulating reticulocytes of pre-natal FL4/Re + /+ and congenitally anaemic FLl/Re f/f mice have been determined. The activities of δ-aminolaevulinate synthetase and δ -aminolaevulinate dehydratase were found to be decreased in proportion to the hypochromia observed in mature liver-derived erythrocytes in neonatal f/f mice, but activities of enzymes later in the haem synthetic pathway were relatively undisturbed. No significant differences were found in levels of haem synthetic enzymes in foetal livers of +/+ and f/f mice. These results indicate that the severe anaemia of late prenatal and neonatal f/f mice is due both to reduction in haem synthesis expressed at the reticulocyte stage of erythroid differentiation and to restricted production of erythroid progenitor cells. Retarded foetal growth and skeletal abnormalities, both characteristic of the pre-natal expression of the f/f gene complement, can also be related to reduced levels of haem synthesis, but the abnormal distribution of pigment cells seen in f/f animals appears to be a secondary effect of reduced tissue oxygenation resulting from pre-natal anaemia.
‘Immobile’ (im), a recessive lethal mutation of Xenopus laevis tadpoles
Authors: Droin A. , Beauchemin M. L.
Published: April 2021

‘Immobile’ (im) is a recessive lethal mutation discovered in the F3 of a Xenopus (Xenopus laevis laevis) originating from a mesodermal nucleus of a neurula transplanted into an enucleated egg. The im embryos do not contract after mechanical stimulation nor do they present any spontaneous contraction from the neurula stage onwards. Development proceeds normally during the first days after which deformation of the lower jaw and tail are observed. The im tadpoles die when normal controls are at the feeding stage. Nervous and muscular tissues are histologically normal in the mutant tadpoles; at advanced stages, however, an irregularity in the path of the myofibrils is observed which is especially conspicuous in the electron microscope. Cholinesterases and ATPase are present in the mutant muscles.

Parabiosis and chimerae experiments have shown that parabionts and grafts behave according to their own genotype. Cultures of presumptive axial systems with or without ectoderm lead to the conclusion that, first of all, the abnormality is situated in the mesodermal cells and secondly that the first muscular contractions in normal Xenopus laevis are of myogenic origin. The banding pattern of the myofibrils is normal as was shown by obtaining contractions of glycerol extracted im myoblasts with ATP. It seems therefore that in this mutation, the abnormality is situated in the membranous system of the muscular cell, sarcoplasmic reticulum and/or tubular system as is probably the case in the mdg mutation of the mouse.
Progesterone-induced in vitro maturation in oocytes of Notophthalmus viridescens (Amphibia Urodela) and some observations on cytological aspects of maturation
Authors: Pilone Giuseppina Barsacchi , Humphries A. A.
Published: April 2021

Maturation in vitro of oocytes of the newt, Notophthalmus viridescens, is inducible with progesterone after in vivo treatment of females with gonadotropin; few oocytes mature in vitro in the absence of such gonadotropin treatment. Chromosomes of most large oocytes of animals not receiving gonadotropin are still in the lampbrush condition; chromosomes from gonadotropin-treated animals are shorter and the lateral loops are less profuse and somewhat retracted. The chromosome condition, then, can be correlated with susceptibility to progesterone induction of maturation in vitro. As maturation progresses, the germinal vesicle moves toward the surface and decreases in size, with an apparent loss of nuclear material from the centripetal end. Although lateral loops of most chromosomes disappear during the changes in the germinal vesicle, profuse loops develop during this period at the sphere loci, which were previously devoid of loops.
A new in vitro system for studying secondary palate development
Authors: Brinkley L. , Basehoar G. , Branch A. , Avery J.
Published: April 2021

An in vitro system was devised which supports palate development in partially dissected embryonic mouse heads. The heads were suspended in the culture chamber so that they were not held in a fixed orientation and were constantly surrounded with a fluid medium. Under these circumstances the developing palate must effect closure without the aid of gravitational forces. The culture medium was constantly circulated, gassed with 95 % O2, 5 % CO2 using hollow fiber gas permeation devices, and kept at 34 °C. Swiss-Webster mouse embryos of 12 days 12 –18 h (ca. 48 h prior to expected in vivo closure) or 13 days 8 –14 h (ca. 24 h prior to closure) were used to test the ability of the system to support palatal development. Embryonic heads were dissected in one of two ways before culture: brain and tongue removed, or brain, tongue and mandible removed. After 24 h in culture, preparations of either age with only the brain and tongue removed had made substantially greater progress than their counterparts with the brain, tongue and mandible removed. With only the brain and tongue removed, the palatal shelves were contacting, adhered or fused in 67 % of the older embryos, whereas most of the embryos of the same age cultured with the brain, tongue and mandible removed had shelves that were not fully elevated and still separated by a moderate gap. Thus for maximal progress in the present system, the oral cavity must be intact except for the tongue.
Cell cycle parameters in dedifferentiating iris epithelial cells
Authors: Yamada Tuneo , Roesel Marion E. , Beauchamp John J.
Published: April 2021

After lentectomy of the adult newt eye, non-dividing iris epithelial cells re-enter the cell cycle. Some of the iris epithelial cells become completely depigmented while they are in the cell cycle, and then differentiate into lens cells. The remaining iris epithelial cells become partially depigmented in the induced cell cycle, but resynthesize melanosomes and recover the normal state of iris epithelial cells. The two groups of cells are spatially separated within the iris epithelium. The cell cycle parameters of both groups of iris epithelial cells were estimated by a mathematical procedure on a computerized programme from the percentage of labelled mitotic cells as a function of time after peritoneal injection of [3H]methyl-thymidine on day 6 after lentectomy. The total cell cycle time was found significantly shorter in the cell population with complete depigmentation as compared with that with partial depigmentation. Based on these results the possible role of differential cell cycle time in the control of dedifferentiation was discussed. Grafting of unlabelled iris into the optic cavity of host animals injected 6 h beforehand with [3H]methyl-thymidine, followed by a study of radioactivity of iris epithelial cells of the graft demonstrated incorporation at a low level during the whole period of the experiment in which the cell cycle parameters were estimated. The data used for the estimation were corrected for the delayed incorporation.
Epithelio-mesenchymal interface during mouse kidney tubule induction in vivo
Authors: Lehtonen E.
Published: April 2021

Transmission and scanning electron microscopy were used to study the epithet io-mesen-chymal interface between the interacting mouse ureter-bud and the metanephric mesenchyme.

The gap between the epithelial and mesenchymal cells varied in width. At the stalk of the ureter-bud the interspace was often about 1 μm, but in the inductively active areas at the tips of the branching ureter-bud epithelio-mesenchymal contacts were seen through discontinuities in the basal lamina. At these points the gap between the interacting cells was often less than 20 nm, in places less than 10 nm. The amount of electron-dense, ruthenium-red-positive material was greatest at the stalk of the ureter-bud, but only a small amount of extracellular material was found between the interacting cells at the tips.

Whether epithelio-mesenchymal cell contacts play a role in kidney tubule induction is not yet known, but their existence in the inductively active areas and their absence in inactive zones suggests that they are morphogenetically significant. The finding also obviates the need to postulate long-range transmission of inductive signals to explain this example of embryonic induction.
The formation of the gonadal ridge in Xenopus laevis: II. A scanning electron microscope study
Authors: Wylie C. C. , Bancroft M. , Heasman J.
Published: April 2021

This paper studies the surface morphology of the developing gonadal ridge in X. laevis between stages 44 and 49 (Nieuwkoop & Faber, 1956). During this period the primordial germ cells (PGCs) move laterally from the dorsal mesentery of the gut to the position of the presumptive gonadal ridge. As they do so the coelomic lining cells lateral to the mesentery differentiate into a specialized, longitudinally orientated band, stretching nearly the full length of the dorsal mesentery on each side. The PGCs migrate beneath this band of cells, which thus becomes the germinal epithelium of the gonadal ridge. We have demonstrated by irradiation experiments that this specialized band of cells can differentiate independently, in the absence of the PGCs.
The formation of the gonadal ridge inXenopus laevis: III. The behaviour of isolated primordial germ cellsin vitro
Authors: Wylie C. C. , Roos T. B.
Published: April 2021

Previous studies have described the morphology, including the ultrastructure, of primordial germ cells (PGCs), and the cells with which they associate to form the gonadal ridge, in Xenopus laevis. In order to test their capacity for active movement we have studied single, isolated PGCs in vitro. Time-lapse studies of these cells reveal that they are motile, using broad cytoplasmic processes. The fact that these cells are very large and easy to manipulate in vitro makes them an attractive subject of study, particularly with respect to the mechanism of their movement and the surface phenomena which guide them to the site of the gonadal ridge.
The effect of 5-bromodeoxyuridine on cell division and differentiation of preimplantation mouse embryos
Authors: Pollard D. R. , Baran M. M. , Bachvarova R.
Published: April 2021

Mouse embryos exposed to concentrations of 5-bromodeoxyuridine (BUdR) ranging from 0·01 to 10 μg/ml in vitro for two days from the 8-cell stage exhibit a concentration-dependent decrease in the frequency of normal blastocysts and a decrease in average cell number per embryo. A 20-h exposure was adequate to achieve the full BUdR response. Both effects were eliminated in the presence of excess thymidine.

Autoradiographs demonstrated that BUdR[3H] was incorporated into DNA during the first and second day of culture. Thus, BUdR appears to act through incorporation into DNA; and, in this system, cell division is at least as sensitive to BUdR as is differentiation.
Influence of conceptus number and weight on the amount of foetal fluid in the mouse
Authors: McLaren Anne , Renfree Marilyn B. , Hensleigh Hugh C.
Published: April 2021

The relation of extra-embryonic fluid weight to litter number and foetal and placental weight was studied in mice on the 18th day of pregnancy, in litters both of experimentally reduced and of normal number. Partial regression analysis showed that litter number and foetal weight both exerted a negative effect on fluid weight; placental weight had no significant effect. Increased foetal weight reduced weight locally; on the other hand the effect of litter number was exerted systemically, throughout both horns of the uterus.
Reorganization of retinotectal projection of compound eyes after various tectal lesions in Xenopus
Authors: Straznicky K.
Published: April 2021

The retinotectal connexions of double nasal (NN), double temporal (TT) and double ventral (VV) eyes in juvenile Xenopus were mapped after post-metamorphic removal of the rostral, caudal, medial or lateral tectal halves with the subsequent cutting of the optic nerve of the operated eye.

A whole visual field projection occurred from NN eyes on to residual caudal tectum, from TT eyes on to residual rostral tectum and from VV eyes on to residual medial tectum. When optic fibres from NN, TT or VV eyes grew into inappropriate rostral, caudal or lateral tectal halves respectively, there was a projection deficit in the nasal and temporal or in the dorsal and ventral poles of the visual field. The persisting scotomas in the visual field indicated that only the optic fibres of the central retinal fundus had succeeded in connecting with an inappropriate tectal half whereas the peripheral optic fibres had not. The incongruous results of optic nerve regeneration obtained in the various recombinations may be taken to indicate that the assumption of early embryonic pattern regulation is inadequate to explain the findings in this experimental situation.
The nature and distribution of serologically detectable alloantigens on the preimplantation mouse embryo
Authors: Muggleton-Harris Audrey L. , Johnson Martin H.
Published: April 2021

The nature and distribution of surface alloantigens on preimplantation mouse embryos has been examined by immunofluorescence. Non-H-2 alloantigens were detected at all stages examined, from the 2-cell to the -day blastocyst. Cleaving blastomeres, inner cell mass cells and cells of the primary trophectoderm were all positive. In Fx embryos maternal non-H-2 alloantigens were detectable at all stages, whereas paternal antigens first became evident at the 6-to 8-cell stage. No convincing evidence of the presence of alloantigens associated with the H-2 haplotype was found at any stage or on any cell type, suggesting that if these antigens are present they are in low quantity or are masked.
The distribution of melanocytes in the dorsal coats of a series of chimaeric mice
Authors: West J. D. , McLaren Anne
Published: April 2021

Chimaeras, made by aggregating two embryos from the randomly-bred Q-strain, and X-inactivation mosaics both have similar, balanced distributions of pigmentation in the dorsal coat, while (C57BL x C3H)F1 ↔ Recessive chimaeras tend to have an unbalanced pigment distribution, with a higher proportion of F1 pigmentation in the posterior than in the anterior part of the coat. This observation can be explained if differences in the timing of the migration of the two melanocyte populations from the neural crest cause anterior-posterior differences in selection pressures.
The effect of short-term labelling in [3H] thymidine on the viability of mouse blastomeres: alone and in combination with unlabelled blastomeres
Authors: Kelly Susan J. , Rossant Janet
Published: April 2021

A method of labelling 8-celI-stage mouse blastomeres with [3H]thymidine is described, which allows them to be followed to the late blastocyst stage and is compatible with normal postimplantation development. However, the [3H]thymidine does affect the postimplantation vigour of the cells when placed in competition with unlabelled cells in blastomere aggregates. This suggests that caution should be used in interpreting results using [3H]thymidine as a label for early mammalian cells.
Adult haemoglobin in developmentally retarded tadpoles ofXenopus laevis
Authors: Maclean Norman , Turner S.
Published: April 2021

Tadpoles of Xenopus laevis reared in water containing 0·01% propylthiouracil continue to grow but fail to develop or metamorphose. The haemoglobin of such tadpoles has been extracted in buffer, converted to a cyanmet form, and run on polyacrylamide gels. The developmentally retarded tadpoles are found to possess adult-type haemoglobin rather than the tadpole type which normally characterizes their developmental stage.
Culmination in the slime mouldDictyostelium discoideumstudied with a scanning electron microscope
Authors: Watts D. J. , Treffry T. E.
Published: April 2021

Myxamoebae of Dictyostelium discoideum were allowed to develop on cellulose acetate filters, and specimens taken at various stages of fruiting body formation were prepared for study by scanning electron microscopy.

In the immature fruiting body where the mass of pre-spore cells has just been lifted off the substratum by the developing stalk, the pre-spore cells are irregular in shape and are similar in appearance to cells in aggregates at earlier stages of development. As the stalk lengthens, the pre-spore cells gradually separate from one another and become rounded and elongate, but mature spores are not visible until the fruiting body reaches its maximum height. It is concluded that, contrary to previous reports, spore maturation is a slow process and is not completed until the sorus becomes pigmented.

The mature stalk is surrounded by a smooth cellulose sheath but this does not envelop the cells of the basal disc, which remain discrete. The fruiting body is enclosed in a slime sheath and this may be important in holding together the mass of spores.
Activité génétique au cours de l’embryogenèse de l’OligochèteEisenia fœtida(autoradiographie à l’uracile-3H et traitement à l’actinomycine D)
Authors: Devriès J.
Published: April 2021

Gene activity during embryogenesis of the earthworm Eisenia foetida ([3H]uracil autoradiography and actinomycin D treatment)

Embryos of Eisenia fœtida (Spiralia) have been cultivated with [3H]uracil precursor of RNA at different stages of development from egg to gastrula. The results show that ribonucleic acid synthesis detected by autoradiography begins precociously. During segmentation messenger RNAs are produced by interphase nuclei and liberated in cytoplasm cyclically at mitosis. After the blastula stage rRNAs (nucleoli), which can migrate through the nuclear membranes, predominate. The blastomeres, which contain polar plasm and also mesoderm, already known for its controlling part in embryogenesis after gastrulation, are the seats of the increasingly important ribonucleic acid synthesis.

These genetic transcriptions, which are inhibited by actinomycin D, are implicated in the determination of the blastomeres and postblastular differentiation. Only the messages required for the segmentation divisions pre-exist in the undivided egg.
Quantitation of the spatial distribution of ‘prespore vacuoles’ in pseudoplasmodia ofDictyostelium discoideum
Authors: Farnsworth Paul A. , Loomis William F.
Published: April 2021

The axial distribution of an organelle, the prespore vacuole (PV), previously reported absent from the prestalk region, was determined in pseudoplasmodia of varying sizes, under differing conditions of photostimulation of migration.

The distribution of these organelles, determined quantitatively by electron microscopy of sections from known axial locations, was found to have a spatial pattern which varied with pseudoplasmodial size. The total complement of these organelles appeared constant for any size of pseudoplasmodium under similar conditions of illumination. Increased illumination decreased the total number of the organelles.

The spatial distribution of PV varies with total cell number, and the size of the region with no PV bears no relationship to the proportion of the cell mass which would form stalk cells. Similarly, the number of cells containing PV bears no fixed relationship to the number of cells which will form spores.

On these grounds, the reported role of PV, that of directing or reflecting spore differentiation, appears unlikely.
The mechanism of chick blastoderm expansion
Authors: Downie J. R.
Published: April 2021

At the time of laying, the domestic fowl blastoderm measures 4 mm across. After 4 days’ incubation, the extra-embryonic yolk-sac tissues have expanded to encompass the whole yolk mass. This expansion involves the migration over the inner surface of the vitelline membrane of a specialized band of ‘edge cells’ at the blastoderm periphery. As they move, they pull out the blastoderm behind them, setting up a considerable tension. Expansion also involves cell proliferation and changes in cell shape. This paper attempts to show how locomotion, tension, proliferation and changes in cell shape all contribute to the orderly process of expansion. As a simplification, only the extra-embryonic epiblast is considered here.

The findings are:

Expansion does not occur at a constant rate, but starts slowly, rises to a peak (over 500 μm/h) at around 3 days, and then slows as coverage of the yolk mass nears completion. During the first day of incubation, edge-cell migration produces a tension in the blastoderm. This rises to a peak at 20 –24 h, then declines. This tension may be due to an imbalance between expansion by migration and expansion by proliferation. Migration of edge cells can be affected by tension in the blastoderm, i.e. very high tension may hold them back. However, the tension level normally found in the blastoderm seems not to do so. The low rate of expansion in the first day is therefore not due to the high level of tension. It may instead be due to changes in edge-cell organization. Proliferation occurs throughout the extra-embryonic epiblast during the expansion period. It is not restricted to the blastoderm periphery. After the yolk has been covered, the epiblast continues to grow, with proliferation restricted largely to a band just distal to the advancing edge of the area vasculosa. Cell shape and arrangement change considerably during expansion. The epiblast of the unincubated embryo is a monolayer of tall cells. During expansion, these become considerably flattened so that each contributes a larger amount to yolk-sac surface area.
Abnormalities in somite segmentation following heat shock to Xenopus embryos
Authors: Elsdale Tom , Pearson Murray , Whitehead Margaret
Published: April 2021

The typical abnormality induced by a 15 min shock at 37 °C is a single discrete length along the somite file within which segmental boundaries are absent or irregular. The two sides of the same embryo present a similar but not necessarily identical appearance. Usually all the embryos in a treated batch show abnormalities of similar severity. Survival of treated embryos, the details of the visible malformations, and temporal aspects of the phenomenon have been studied.

The results indicate a temperature sensitive period that traverses the neurula, from head to tail at about the same rate as the somites form, but some hours beforehand. The temperature sensitive process is not associated with cell determination and differentiation, and there are reasons for thinking that the specification of the normal somite number occurs independently.

The results are discussed in relation to Cooke & Zeeman’s model of a wave front interacting with an oscillator.
Stabilité de la determination et de la différenciation des caractères sexuels somatiques chez Nereis pelagica L. (Annélide Polychèté)
Authors: Boilly-Marer Yolande
Published: April 2021

Stability of determination and differentiation of the somatic sexual characters in Nereis pelagica L. (Annelida polychaeta)

Experiments of regeneration in situ or on grafts were carried out to test the stability of determination of the somatic sexual characters in Nereis pelagica.

The sexual characters of the parapodial cirri (male and female swellings, male crenellations) are always expressed on stump or regenerate according to the genetic sex. Super-numary parapodia which developed at the site of junction of the heterologous faces of host and graft of opposite sexes, might have the characters of either sex; this result can be interpreted by supposing that a supernumary parapodium is derived from tissues of either host or graft, of the corresponding sex.

Conversely, the pygidial papillae, which normally occur only on the heteronereid male, will appear on regenerating female pygidia, triggered to transform to the heteronereid condition naturally or by decerebration, with a frequency depending on the age of the regenerate, the length of the regenerate, and the genital condition of both the stump and the regenerate. It is concluded that the presence of the papillae is not a sex-specific character, but that their development is normally inhibited in the maturing female.
Observations on the migration and proliferation of gonocytes in Xenopus laevis
Authors: Kamimura Michiko , Ikenishi Kohji , Kotani Minoru , Matsuno Toru
Published: April 2021

The process of primordial germ cell formation in the normal course of development of Xenopus laevis was examined with a light microscope on paraffin and Epon sections of embryos or tadpoles, extending over the period from the gastrula to the feeding tadpole stage. Positional changes of gonocytes with development were nearly the same as those reported on the same species by Blackler (1958) and Whitington & Dixon (1975). The following points were newly demonstrated. Gonocytes which have been located in a deep endodermal position till mid tail-bud stage come to be located in a rather peripheral region of the endoderm cell mass at stage 31 (late tail-bud), suggesting that the initial step of migration of the gonocytes towards the future genital ridge has already begun at this stage. Gonocytes at stages 33/34 and 35/36 were observed in a more dorsal part of the endoderm than at stage 31. Gonocytes which seem to have begun their migration are roundish in external shape and have a large intercellular space around them. At stage 40 gonocytes were located in the dorsal endodermal crest, and at stage 41 gonocytes were found with cell bodies extending over both the dorsal endoderm crest and the dorsal mesentery, indicating that the separation of the gonocytes from the endoderm was in progress at this stage. The present results seem to indicate that gonocytes migrate not passively but actively from the deep endodermal position to the genital ridge, passing through the dorsal mesentery. Counting the number of gonocytes at successive stages of development revealed that gonocytes proliferated exponentially throughout the developmental stages from gastrula to tadpole.
Cytological and microspectrophotometric analysis of mesodermalized explants of Triturus gastrula ectoderm
Authors: Noda Shinichi , Kawakami Izumi
Published: April 2021

Using isolated presumptive ectoderm of the newt (Triturus pyrrhogaster) embryos as a reactor and extract of rat bone marrow as a mesodermal inductor, changes of cell number and mitotic index of the reactor cells were studied. In early stages of cultivation the increase in cell number in the mesodermalized ectodermal piece was slower than in the non-mesodermalized epidermal piece; but after 24 h it showed abrupt increase and reached a cell population equal to that of the control at 48 h of cultivation. In the experimental series, the mitotic index was 0 at 4 h after the application of the inducing stimulus, but increased precipitously in the next 8 h and reached a level of 4·4 % at 12 h and thereafter decreased gradually. The cell cycle stopped at the S phase and stayed in it for several hours after the application of inductor. A sudden fall in cell number, observed in the mesodermalized epidermal piece between the 4th and the 8th h after the application of inducing stimulus, seems to be attributable to cell death which was brought about by the inducing stimulus. In the histogenetic process phases of repression on mitosis by an inducing stimulus, cell proliferation and nonproliferation seem to succeed each other.
Properties and development of erythropoietic stem cells in the chick embryo
Authors: Samarut Jacques , Nigon Victor
Published: April 2021

When injected into irradiated chickens, haemopoietic stem cells give rise to well-defined erythrocytic colonies in the host marrow. Such stem cells (CFU-M — Colony Forming Unit in Marrow) have been found in different tissue of the chick embryo (yolk sac, blood, marrow). Analysis of the properties of CFU-M reveals that they represent two classes of stem cells: pluripotent stem cells mainly in adult marrow and erythrocytic-committed stem cells present in yolk sac. Yolk sac contains the main pool of CFU-M during the major part of embryonic life. In the blood of 6-day-old embryo, there are three or four times more CFU-Ms than in the yolk sac; they are no longer detected in the blood after the 16th day of incubation. During development of the marrow, stem cells are actively differentiating and their total number remains the same from 16 days to hatching.
Experiments on blocking and unblocking of first meiotic metaphase in eggs of the parthenogenetic stick insect Carausius morosus Br. (Phasmida, Insecta)
Authors: Pijnacker L. P. , Ferwerda M. A.
Published: April 2021

The eggs of the parthenogenetic stick insect Carausius morosus, which remain arrested in first meiotic metaphase until oviposition, must be activated in order to develop. The activating agent is oxygen from the air, which enters the egg cell through the micropyle. An exposure shorter than one minute is sufficient to release the blockage.

In non-activated (micropyle-less) eggs the first metaphase chromosomes either degenerate or change into an interphase nucleus. This nucleus polyploidizes by endoreduplication, and then either degenerates or multiplies by amitosis. Similarly more generations of nuclei may arise resulting in a chaotic development. These nuclei survive better in the anterior region of the egg.

The question of whether the cytoplasmic factors which control nuclear behaviour, also operate in eggs of C. morosus is discussed.
The effects of a t-allele (t
AE5) in the mouse on the lymphoid system and reproduction
Authors: Vojtí škový M. , Viklickí V. , Vorácová B. , Lewis S. E. , Gluecksohn-Waelsch S.
Published: April 2021

Mice homozygous for tAE5, a recessive allele at the complex T-locus, are characterized by their unique short-tailed phenotype as well as by runting and low fertility. Histological and histochemical studies of the lymphoid and reproductive systems disclosed structural changes in the mutant spleen resembling those found in autoimmune conditions. Involution of the mutant thymus was greatly accelerated compared to normal. Necrotic changes occurred during spermiogenesis whereas ovarian structure was normal in mutants. The possible mechanisms of the mutant effects are discussed in the framework of other similar syndromes and the mode of action of alleles at the complex T-locus.