bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal distribution of vinculin and talin in migrating avian neural crest cells and their derivatives
Authors: Duband Jean-Loup , Thiery Jean Paul
Published: April 2021

Neural crest cells express different adhesion modes at each phase of their development starting with their separation from the neural tube, followed by migration along definite pathways throughout the embryo, and finally to settlement and differentiation in elected embryonic regions. In order to determine possible changes in the cytoskeleton organization and function during these processes, we have studied the in situ distribution of two major cytoskeleton-associated elements involved in the membrane anchorage of actin microfilaments, i.e. vinculin and talin, during the ontogeny of the neural crest and its derivatives in the avian embryo. Prior to emigration, neural crest cells exhibited both vinculin and talin at levels similar to the neighbouring neural epithelial cells, and this expression apparently did not change as cells became endowed with migratory properties. However, vinculin became selectively enhanced in neural crest cells as they further migrated towards their final destination. This increase in vinculin amount was particularly striking in vagal and truncal neural crest cells entering cellular environments, such as the sclerotome and the gut mesenchyme. Talin was also expressed by neural crest cells but, in contrast to vinculin, staining was not conspicuous compared to neighbouring mesenchymal cells. High levels of vinculin persisted throughout embryogenesis in almost all neural derivatives of the neural crest, including the autonomous and sensory ganglia and Schwann cells along the peripheral nerves. In contrast, the non-neural derivatives of the neural crest rapidly lost their prominent vinculin staining after migration. The pattern of talin in the progeny of the neural crest was complex and varied with the cell types: for example, some cranial sensory ganglia expressed high amounts of the molecule whereas autonomic ganglia were nearly devoid of it. Our results suggest that (i) vinculin and talin may follow independent regulatory patterns within the same cell population, (ii) the level of expression of vinculin and talin in neural crest cells may be consistent with the rapid, constant modulations of their adhesive properties, and (iii) the expression patterns of the two molecules may also be correlated with the genesis of the peripheral nervous system.
Head morphogenesis in embryonic avian chimeras: evidence for a segmental pattern in the ectoderm corresponding to the neuromeres
Authors: Couly G. , Le Douarin N. M.
Published: April 2021

Areas of the superficial cephalic ectoderm, including or excluding the neural fold at the same level, were surgically removed from 3-somite chick embryos and replaced by their counterparts excised from a quail embryo at the same developmental stage. Strips of ectoderm corresponding to the presumptive branchial arches were delineated, thus defining anteroposterior ‘segments’ (designated here as ‘ectomeres’) that coincided with the spatial distribution of neural crest cells arising from the adjacent levels of the neural fold. This discrete ectodermal métamérisation parallels the segmentation of the hindbrain into rhombomeres. It seems, therefore, that not only is the neural crest patterned according to its rhombomeric origin but that the superficial ectoderm covering the branchial arches may be part of a larger developmental unit that includes the entire neurectoderm, i.e., the neural tube and the neural crest.
Expression of the Drosophila gonadal gene: alternative promoters control the germ-line expression of monocistronic and bicistronic gene transcripts
Authors: Schulz Robert A. , Miksch Jennifer L. , Xie Xiaoling , Cornish Judith A. , Galewsky Samuel
Published: April 2021

The Drosophila gonadal (gdl) gene is differentially expressed in the male and female germ lines. In males, expression in the gdl™ mode results in a 1200-/1500-nucleotide RNA pair, whereas in females, expression in the gdlF mode results in a 1000-/1300-nucleotide RNA pair. Since the two expression modes are a result of alternative promoter usage, the sex-specific transcripts differ at their 5’ ends. These sequence differences affect the coding capacity of the gene. A common open reading frame (ORF) of 193 codons (ORF193) is present in all four gdl transcripts; a consequence of the additional sequences at the 5’ end of the gdlM transcripts is the presence of an additional ORF of 39 codons (ORF39). Translation of gdlF and gdlM cRNAs in a reticulocyte lysate reveals that these transcripts can serve as mono-cistronic and bicistronic mRNAs in vitro. An analysis of germ-line transformants harboring gdl-lacZ gene fusions provides information on gdl gene expression during gametogenesis. The fusion genes are transcribed and translated in the germ line; β-galactosidase activity is detected in premeiotic and postmeiotic spermatogenic stages in males, and in nurse cells and oocytes of developing egg chambers in females. Both gdl™ ORFs are used because transformant lines expressing the lacZ gene, fused in frame with either ORF39 or ORF193, are positive for β-galactosidase activity in the testes. These studies also reveal that separable transcription control elements are responsible for gdl expression in the male and female germ lines.
Topographical control of cell behaviour: II. multiple grooved substrata
Authors: Clark P. , Connolly P. , Curtis A. S. G. , Dow J. A. T. , Wilkinson C. D. W.
Published: April 2021

Electronics miniaturisation techniques have been used to fabricate substrata to study contact guidance of cells. Topographical guidance of three cell types (BHK, MDCK and chick embryo cerebral neurones) was examined on grooved substrata of varying dimensions (4-24 μm repeat, 0.2-1.9 μm depth). Alignment to within 10° of groove direction was used as our criterion for guidance. It was found that repeat spacing had a small effect (alignment is inversely proportional to spacing) but that groove depth proved to be much more important in determining cell alignment, which increased with depth. Measurements of cell alignment and examination by scanning electron microscopy showed that BHK cells and MDCK cells interacted differently with grooved substrata, and also that the response of MDCK cells depended on whether or not the cells were isolated or part of an epithelial cell island. Guidance by a multiple topographical cue is greater than could be predicted from cells’ reactions to a single cue (Clark et al. Development 99: 439-448, 1987). Substratum topography is considered to be an important cue in many developmental processes. Cellular properties such as cytoskeletal organisation, cell adhesion and the interaction with other cells are discussed as being factors determining a cells susceptibility to topography.
The Xenopus MyoD gene: an unlocalised maternal mRNA predates lineage- restricted expression in the early embryo
Authors: Harvey Richard P.
Published: April 2021

Expression of the mouse MyoD gene appears to represent a critical point in the commitment of cultured cells to muscle. In Xenopus, myogenic commitment begins during mesoderm induction which is initiated early in development by endogenous growth factors. To study MyoD gene expression during induction, a Xenopus MyoD gene and homologous cDNAs were selected from Xenopus libraries and analysed. Two different cDNAs have been sequenced. They code for proteins closely related to each other and to mouse MyoD and are likely to be expressed from duplicated Xenopus MyoD genes. Surprisingly, MyoD mRNA is first detected during oogenesis and the maternal species is not localized exclusively to the region of the blastula fated to muscle. Zygotic MyoD mRNA accumulates slowly above maternal levels beginning at the MBT and new transcripts are localized to the somitic mesoderm. Expression outside of somites has been detected in developing heads of tailbud embryos and can be induced in blastula animal pole expiants treated with mesoderm-inducing factors. The early expression of MyoD in Xenopus development suggests that it may play a part in the induction of muscle mesoderm and generally strengthens the evidence that MyoD is determinative in muscle commitment. In addition, the initiation of MyoD transcription at the MBT and its stimulation by mesoderm-inducing factors implies that MyoD gene expression is an immediate early response to mesoderm induction.
Identification of early developing axon projections from spinal interneurons in the chick embryo with a neuron specific β-tubulin antibody: evidence for a new ‘pioneer’ pathway in the spinal cord
Authors: Yaginuma Hiroyuki , Shiga Takashi , Homma Shunsaku , Ishihara Rieko , Oppenheim Ronald W.
Published: April 2021

The early development of interneurons in the chick embryo spinal cord was studied using a monoclonal antibody against a neuron-specific β-tubulin isoform. Early developing interneurons were divided into two cell groups on the basis of their location and the pattern of growth of their axons. One group is composed of cells that establish a primitive longitudinal pathway (PL-cells), whereas the other group contains cells constituting a circumferential pathway (C-cells). The onset of axonal development in both cell groups occurs at stage (st.) 15 (embryonic day, (E), 2) in the brachial segments, which is prior to axonogenesis of motoneurons. PL-cells develop in the region between the floor plate and the motoneuron nucleus. Their axons are the first neuronal processes (‘pioneer axons’) to arrive in the ventrolateral marginal zone and they project both rostrally and caudally to establish a primitive longitudinal association pathway at the ventrolateral surface of the neural tube. This pathway is formed before axons of C-cells arrive in the ventrolateral region. The first C-cells are initially located in the most dorsal portion of the neural tube, whereas later appearing C-cells are also located in both intermediate and ventral regions of the neural tube. The axons of C-cells project ventrally, without fasciculating, along the lateral border of the neural tube. Some of their axons enter the ipsilateral ventrolateral longitudinal pathway at st. 17. We often observed apparent contacts and interactions between preexisting axons of PL-cells and newly arriving axons of C-cells. The axons of commissural C-cells first enter the floor plate at st. 17 and cross the midline at st. 18. Axons of C cells begin to join the contralateral ventrolateral longitudinal pathway at st. 18+ to st. 19. In the floor plate region, contacts between growth cones and axons were often observed. However, axons in the floor plate at these stages were not fasciculated.

These observations establish the timing and pattern of growth of axons from two specific populations of early developing interneurons in the chick spinal cord. Additionally, we have identified an early and apparently previously undescribed ‘pioneer’ pathway that constitutes the first longitudinal pathway in the chick spinal cord.
Heterochromatization and euchromatization of whole genomes in scale insects (Coccoidea: Homoptera)
Authors: Nur Uzi
Published: April 2021

In several families of scale insects (coccids), the sex of an embryo is determined by the number of genetically active genomes present (one=males, two=females). In mealybugs (Pseudococcidae), both males and females develop from fertilized eggs but, in the embryos that develop into males, the set of chromosomes (genome) of paternal origin (PG) becomes heterochromatic (H) and genetically inactive and is not transmitted to the offspring. The mechanism that reduces the number of active genomes in male embryos may vary between families and even between congeneric species. Thus, in male embryos of most armored scale species (Diaspididae), the PG is eliminated, while in a few species it becomes H. In two genera of soft scales (Coccidae), males develop from unfertilized eggs when one of two identical genomes of maternal origin becomes H. In most male tissues, one genome remains H. However, in several tissues that become polyploid by endoreduplication, the PG becomes E and genetically active. The tissues in which the PG becomes E often vary between species and the analysis of hybrid males demonstrated that whether the PG becomes H or remains E is determined by the genome of maternal origin. The euchromatization of the PG in the haploid sector of mosaic male embryos and the presence of spermatocytes with two E genomes (instead of one E and one H), following the irradiation of young mealybug males, strongly suggest that the maintenance of the H state requires the presence of a genetically active genome.
The development of handedness in left/right asymmetry
Authors: Brown Nigel A. , Wolpert Lewis
Published: April 2021

The development of handed asymmetry requires a special mechanism for consistently specifying a difference between left and right sides. This is to be distinguished from both random asymmetry, and from those left/right differences that are mirror symmetrical. We propose a model for the development of handedness in bilateral animals, comprising three components. (I) A process termed conversion, in which a molecular handedness is converted into handedness at the cellular level. A specific model for this process is put forward, based on cell polarity and transport of cellular constituents by a handed molecule. (Ii) A mechanism for random generation of asymmetry, which could involve a reaction-diffusion process, so that the concentration of a molecule is higher on one side than the other. The handedness generated by conversion could consistently bias this mechanism to one side. (iii) A tissue-specific interpretation process which responds to the difference between the two sides, and results in the development of different structures on the left and right. There could be direct genetic control of the direction of handedness in this model, most probably through the conversion process. Experimental evidence for the model is considered, particularly the iv mutation in the mouse, which appears to result in loss-of-function in biasing, and so asymmetry is random. The model can explain the abnormal development of handedness observed in bisected embryos of some mammalian, amphibian and sub-vertebrate species. Spiral asymmetry, as seen in spiral cleavage and in ciliates, involves only conversion of molecular asymmetry to the cellular and multicellular level, with no separate interpretation step.
The Xenopus XIHbox 6 homeo protein, a marker of posterior neural induction, is expressed in proliferating neurons
Authors: Wright Christopher V. E. , Morita Elaine A. , Wilkin Douglas J. , Robertis Eddy M. De
Published: April 2021

XIHbox 6 is an early spatially restricted marker for molecular studies of neural induction. The sequence of the full-length XIHbox 6 protein is reported. An antibody raised against a β-galactosidase/XIHbox 6 fusion protein was used to analyze the expression of XIHbox 6 proteins during frog embryogenesis. The anterior border of XIHbox 6 expression lies just posterior of the hindbrain/spinal cord junction. Immunostalnlng extends the entire length of the spinal cord. A much weaker transient expression with a similar anterior border is observed in mesoderm. Almost all nuclei in the newly closed spinal cord contain XIHbox 6. The number of positive nuclei decreases over the next stages of development, until in later embryos XIHbox 6 is restricted to nuclei of the dividing neuroepithelium, and not the mantle or marginal zones of the spinal cord. When the limb buds begin to grow, there is a second burst of XIHbox 6 expression in proliferating neurons of the cervical and lumbar enlargements, where nerves arise that supply the limbs. The data suggest that XIHbox 6 expression is spatially and temporally restricted to immature neurons of the spinal cord, before their differentiation into mature neurons.
Permissiveness to murine leukemia virus expression during preimplantation and early postimplantation mouse development
Authors: Savatier P. , Morgenstern J. , Beddington R. S. P.
Published: April 2021

Permissiveness to Moloney Murine Leukemia Virus (MoMuLV) expression was examined during preimplan tation and early postimplantation development of the mouse embryo. Blastocysts and 8th, 9th and 10th day postimplantation embryos were infected in vitro with a MoMuLV-based retroviral vector expressing the lacZ gene driven off an internal rat beta-actin promoter. Beta-galactosidase-positive cells were identified in all embryonic tissues including inner cell mass, epiblast, mesoderm, endoderm and definitive ectoderm. In con trast, embryos infected with a MoMuLV-based vector expressing the lacZ gene driven off the viral LTR showed beta-galactosidase-positive cells only in mesoderm and definitive ectoderm. We conclude that permissiveness to transcriptional activity of the LTR is acquired immedi ately upon differentiation of epiblast during gastrulation of the mouse embryo.
Morphological and Functional Development of the Ovary of the Mouse: I. Morphology and Histochemistry of the Developing Ovary in Normal Conditions and after FSH Treatment
Authors: Ben-Or Sarah
Published: April 2021

Maturation and maintenance of ovarian function are under the control of the pituitary gonadotrophins. The capacity of the ovary to respond to FSH stimulation develops gradually with age, and is most pronounced when the animal approaches sexual maturity. In very young animals reactivity to gonadotrophins is found to be lacking, and up to a certain age, which is characteristic for each species, sexual maturity cannot be accelerated by exogenous gonadotrophic stimulation (for references see Price & Ortize, 1944). However, in transplantation experiments of young ovarian tissue into adult spayed hosts, the grafted ovary reaches maturity much earlier than in its normal surroundings (Goodman, 1934; Dunham, Watts & Adair, 1941).
Immunological Attack by Adult Cells in the Developing Chick Embryo: Influence of the Vascularity of the Host Spleen and of Homograft Rejection by the Embryo on Splenomegaly
Authors: Solomon J. B. , Tucker D. F.
Published: April 2021

Adult chicken spleen was implanted on to the chorio-allantoic membrane of chick embryos at 8,9,11,13 and 15 days of incubation. The initial manifestation of graft against the host attack by these adult cells was an increase of host spleen weight (splenomegaly). No splenomegaly appeared in the embryonic hosts before 15 days of incubation. The appearance of splenomegaly roughly coincided with the appearance of reticulum cell foci in the chimaeric spleens. Varying latent periods between the time of introduction of donor cells and the first appearance of increased spleen weights necessitated comparison of the host spleen weights 3 days after the onset of splenomegaly. This showed that implantation at 13 days produced the greatest splenomegaly. Only very slight splenomegaly was obtained after implantation of spleen at 15 days. A possible homograft rejection by the host and poor ‘take’ of the splenic implant on the chorio-allantoic membrane are both thought to be responsible. Intravenous injection of adult chicken spleen cells into embryos at 6, 8, 11 and 13 days of incubation again produced no splenomegaly before 15 days of incubation. Comparison of the host spleen weights 3 days after onset of splenomegaly showed that injection at 13–15 days gave the greatest splenomegaly. Injection before this time gave very slight splenomegaly and injections after 13 days produced a decreasing degree of splenomegaly with increasing age of embryo injected. Increasing the number of adult spleen cells at 15 days or giving large doses of blood at 8, 9, 11, 15 and 17 days of incubation and in the 1-and 2-day-old chick failed to increase the splenomegaly greatly or markedly to alter the above pattern. When 1-day-old chicks were injected with allogenic blood only slight splenomegaly occurred and when 2-day-old chicks were injected there was no splenomegaly 6 days later. The suitability of the chick embryo as an environment for the proliferation of immunologically competent cells is discussed. The reduction in splenomegaly when embryos older than 13-15 days are injected is discussed in relation to the appearance from this time of a weak homograft response by the embryo and to the greater difficulty of induction of both splenomegaly and tolerance to skin grafts soon after hatching. It is proposed that very small numbers of immunologically competent cells appear in the embryo soon after 15 days and progressively increase from this time until onset of competence of the host at 10 days post-hatching. Possible effects of such cell growth on the degree of induction of tolerance are discussed.
The Culture of Small Aggregates of Amphibian Embryonic Cells in vitro
Authors: Jones K. W. , Elsdale T. R.
Published: April 2021

Methods are described for the short term culture of disaggregated amphibian embryonic cells in a medium consisting of about 0·1 per cent protein in Steinberg’s physiological salt solution. In a medium containing whole serum or serum protein cells differentiate according to their presumptive fate in the embryo. The use of a particle-free extract of mouse bone marrow causes ectoderm cells to develop as mesoderm. Gastrula ectoderm cells will differentiate ciliated epidermis providing they are permitted to reaggregate into balls of about thirty cells and upwards. Gastrula mesoderm cells and induced ectoderm cells likewise do not differentiate unless aggregated, but the majority of aggregates fail to differentiate. This seems to be because these cells have exacting requirements for precise concentrations of the protein component in the medium. There is some variation between species in this respect, and requirements vary between ovulations in the case of Rana pipiens and Xenopus laevis. Ciliated epidermal cells differentiate in cohesive balls that detach from the glass. All other cell types differentiate as thin outgrowths of cells attached to the glass by cytoplasmic fringes or pseudopodia. The first visible event in the differentiation of non-epidermal cells is their attachment to the glass by pseudopodia or cytoplasmic fringes, and the rapid expansion of these contributes to the deformation of the cell from the spherical embryonic form to that approximating to the form of the differentiated cell. This rapid change in form and activity is termed germination. It appears to be a necessary preliminary for cytodifferentiation, the rapid utilization of yolk and the build up of large mitochondrial populations. Germination precedes the formation of striated muscle fibres, vacuoles in chordal cells and other indications of cytodifferentiation by a time interval that is characteristic for each cell type within a species. The time and order in which cells differentiate in culture is related to the behaviour of comparable cells in the embryo. It is concluded that, by the neurula stage, the control of the time of germination is vested in the individual cells. It is concluded that the development of neural and mesodermal cells involves two necessary periods of decisive change, one at the end of gastrulation unconnected with any gross morphological changes in the cells, the second, closely following neural closure and involving the in vivo counterpart of germination in culture, by which the potentialities of the cells are mobilized in the interests of cytodifferentiation. Both these important epigenetic events coincide with changes in the adhesive properties of cells.
The Effects of β-Mercaptoethanol on the Morphogenetic Movements of Amphibian Embryos
Authors: Malpoix P. , Quertier J. , Brachet J.
Published: April 2021

Explant systems and vital staining have been used to study the specific effects of various concentrations of β-mercaptoethanol on the morphogenetic movements of amphibians. Three different types of effect were observed. (a) rapid but reversible inhibition of neurulation, becoming irreversible after prolonged treatments; (b) slow, progressive inhibition of epiboly, convergent stretching and ingression; (c) very slight inhibition of invagination, occurring only at high concentrations or after prolonged treatments. The significance of these results is discussed.
The Preparation and Teratogenic Properties of Pure Trypan Blue and its Common Contaminants
Authors: Beck F. , Lloyd J. B.
Published: April 2021

Starting with impure commercial samples of the dye, methods for the preparation of pure trypan blue and each of its chief contaminants are presented. The teratogenic component of the commercial mixture is shown to be the blue fraction, which is presumably trypan blue itself. The impurities are not active teratogens and do not modify qualitatively the teratogenic activity of the blue fraction.
Studies on Hydroid Differentiation, II. Colony Growth and the Initiation of Sexuality
Authors: Braverman Maxwell H.
Published: April 2021

When grown on microscope slides under controlled conditions, the marine hydroid Podocoryne carnea provides excellent material for the investigation of the origin of difference, regulation and the control of pattern during development. The growth of both stolons and hydranths is exponential and the ratio of hydranths to stolons is constant. Qualitative analysis of colony growth during a 5-month period delimits five discrete states that arise in the center and spread peripherally in the radially organized system during the first 3 months. When colony expansion stops, the centrifugal pattern of differentiation is replaced by an apparently random one and the number and proportion of zooids in the colony change. Extirpation and isolation experiments indicate that sexuality is not transmitted from sexual to asexual portions of the colony, and that it is associated with the dense stolon matte. A theory accounting for the origin of sexuality in terms of decreased permeability of the stolon to substances that necessitate sexual differentiation is suggested.
Groupes Sulfhydriles et Morphogénèse: IV. Effets du β-Mercaptoéthanol et de l’Acide-α-Lipoïque sur le Métabolisme des Acides Nucléiques chez les Embryons de Batracien et de Poulet
Authors: Pohl par V. , Quertier J.
Published: April 2021

A study has been made of the incorporation of nucleic acid precursors (thymidine, uridine, cytidine) in two embryonic materials: Pleurodeles and Chicken, in the presence of two substances known to have a morphostatic effect on the closure of the neural plate: β-mercaptoethanol and lipoic acid. The results reveal a marked similarity of action. Thymidine incorporation into DNA is stimulated by mercaptoethanol and lipoic acid. Both substances also stimulate the incorporation of cytidine and uridine into RNA. But there is a difference in the case of DNA : mercaptoethanol has a slight stimulatory effect on the incorporation of the two nucleosides, whereas lipoic acid is definitely inhibitory. All the evidence suggests a specific effect of lipoic acid on the reduction of ribonucleosides to deoxyribonucleosides. The results have been discussed.
Some Effects of Cold and of Hybridity on the Growth of Mice
Authors: Barnett S. A. , Scott Sybil G.
Published: April 2021

Mice of strains A and A2G, born and reared at an environmental temperature of − 3°C, were lighter at the ages from 3 to 16 weeks than controls at 21°C. The body-weight of mice of strain C57BL was unaffected by the low temperature. F1 mice from the cross A × C57BL were heavier than those of the parent strains at both temperatures. Mice from the cross C57BL × A2G, and from the reciprocal cross, were intermediate in weight between the parent strains in the warm, but superior in the cold. The growth of F1 mice was not depressed by cold. Outbred mice, derived from crossing the above inbred strains and G FF, were selected for superior breeding performance in the cold environment. After twelve generations these mice were heavier than controls kept at 21 °C. A2G mice transferred from −3°C to 21 °C at 3 weeks were lighter at that age than controls kept at 21 °C and failed to make up the growth deficit. Their offspring, too, kept at 21 °C, were lighter than the controls. Outbred mice of the twelfth generation in the cold were transferred from − 3°C to 21 °C at 5 weeks. Their offspring, reared at 21 °C, were heavier than the controls which had been bred permanently in the warm; they were also heavier than the outbred mice kept in the cold. This was evidently a result of selection. In all strains the males were heavier than the females. Weights of kidneys, relative to body-weight, were observed in A2G, C57BL and outbred mice. In all three strains they were higher at -3°C. Of the same strains liver weights were raised in the cold in C57BL and outbred mice but not A2G. There was evidence that these two inbred strains had lighter gonads in the cold; but the outbred mice of the twelfth generation had heavier testes in the cold than in the warm. There was no evidence of an effect of heterozygosis on variance in bodyweight. There was some tendency for growth to be more uniform in the cold than in the warm environment.
Regional Organization of Pre-pacemaker Cells in the Cardiac Primordia of the Early Chick Embryo
Authors: Dehaan Robert L.
Published: April 2021

The lateral cardiac primorida of the early chick embryo were cut into anterior, middle and posterior fragments. Each fragment was incubated at 37°C in culture medium, for 48 hours. At the middle and end of the incubation period each culture was examined for the presence of spontaneously beating heart tissue, and its intrinsic pulsation rate was determined. The posterior fragments, which in the intact embryo form atrial and sinus tissue, gain the capacity to produce spontaneously contractile heart vesicles earliest (stage 4+), and exhibit the highest level of heart-forming potency. The middle fragments are first able to form beating hearts at stage 5, but do so in a lower percentage of the cases. The cells in these fragments normally form ventricle. The anteriormost fragments, which represent the presumptive conus and cono-ventricular regions of the heart, are not able to form beating cardiac vesicles until stage 7, and then do so with very low frequency. Vesicles from all three fragments increase in spontaneous pulsation rate with age of the donor. The posterior fragments produce heart tissue which beats at from 90 to 135 beats/min., with a mean of 115 beats/min. Vesicles from the middle pieces range from 40 to 85 beats/min., averaging 65 beats/min. The anterior fragments increase from 10 to 40 beats/min., with an average rate of 36 beats/min. It may be concluded from these results that the various parts of the heart (sinus, atrium, ventricle and conus) are represented in specific, localized portions of the heart-forming regions in the early embryo (stages 5-9), and that each portion contains pre-pacemaker cells which develop an appropriate level of intrinsic rhythmicity. The antero-posterior rate gradient observed in the formed functional heart is already defined in the heart-forming regions of the head-process stage embryo. Whether this early regionalization of pacemaker activity is due to the distribution in the cardiac primordia of pre-pacemaker cells already determined as to their future pulsation rate, or is the result of a gradually emerging, epigenetic pattern of localized interactions between the pre-heart mesoderm and surrounding tissues, cannot be decided on the basis of the present experiments. A test of this question is suggested, and other points of relevance to these results are discussed.
Modification Expérimentale du Développement de l’Ovaire de Souris sous l’influence du Testicule Embryonnaire de Poulet
Authors: Salzgeber par Berthe
Published: April 2021

Mouse ovaries from foetuses 12–21 days of gestation were explanted in vitro in association with gonads of 6–10 days chick embryos. After 2-6 days of culture, the expiants were grafted into the coelom of young chick embryos. Grafts were removed when hosts were 12–19 days old (Plate 1, Figs. 1 and 2). In associations of mouse and chick ovaries, the two organs fused together forming chimeric organs (Plate 1, Fig. 3). The mouse gonad, containing numerous oocytes and primary follicles, lay in the medullary part of the chick gonad (Plates 1 and 2, Figs. 3–7). In associations of mouse ovary with chick testis, the development of the mouse ovary was inhibited (Plates 2 and 3, Figs. 8–14). Cortical structures were very sensitive to the testicular influence; and oocytes degenerated or failed to develop. Follicles when present had an abnormal appearance (Plate 2, Fig. 9). The degree of inhibition depended on the type of association and the age of the gonad when transplanted (Plate 2, Figs. 9 and 10). Some ‘medullary’ structures persisted in these inhibited ovaries. The rete ovarii, which looks like winding cords, was well developed and penetrated into the chick tissue where it established direct connection with testicular tubules (Plate 3, Fig. 16). In some expiants, in the vicinity of the rete, cords of testicular aspect which sometimes contained oocytes or degenerating follicles were observed (Plate 3, Fig. 13). These results demonstrate that mouse ovary associated with chick ovary can develop when transplanted to chick embryos. Oogenesis takes place, the oocytes grow and primary follicles develop.
The Origin and Development of Smooth Muscle and Contractility in the Ductus Epididymidis of the Rat
Authors: Velde Robert L. Van De , Risley Paul L.
Published: April 2021

The smooth muscles of the ductuli efferentes and ductus epididymidis develop from primitive mesonephric mesenchyme. In both ductuli efferentes and ductus epididymidis a proliferation and condensation of the mesenchyme occurs around the ductuli and epididymal duct. This appears in the ductuli efferentes of the 14- and 15-day rat embryo, and by birth it has extended to the cauda epididymidis. Subsequent to the condensation around the ducts, elongation of the mesenchymal cell nuclei beings, and the cytoplasm becomes aligned and extended. This appears first in the circular layer of the caput by the 16th day of gestation, and in the investing layer of the corpus epididymidis by the 20th day. Formation follows lastly in the region of the cauda epididymidis, occurring by parturition or very soon thereafter. After the smooth muscle cells are differentiated, delicate pulsations or contractions may be observed in the ductuli efferentes and ductus epididymidis. They can be seen first at 17 days of gestation in the region of the coni vasculosi, where they occur at intervals of 60 sec. This condition may not be representative of all 17-day embryos as contractions were seen in but three of thirty-three preparations studied. Rhythmic movements of the ductuli and upper and middle caput epididymidis take place with regularity, occurring approximately at 40-45 sec. intervals in the ductuli and upper caput and at 20-25 sec. in the middle caput epididymidis at birth. By the 10th day, a visible contractile wave commences in the region of the ductuli and passes to the upper corpus where it disappears. Inspection of contraction frequency data for the ductuli and upper segments of the epididymis indicates that the interval between successive rhythmic waves diminishes with age. An incidental examination of the Müllerian duct of female neonatal and post-natal animals demonstrated that rhythmic contractions are established by birth.
Production élective de la phocomélie sous l’influence d’ypérite azotée
Authors: Salzgeber par Berthe
Published: April 2021

Chick embryos of to days of age (Stages 17-22 of Hamilton & Hamburger) were injected with nitrogen mustard (methyl-bis-chlorethylamine) dissolved in distilled water. Each embryo received a dose of from 0 · 6 to 1 · 6 μg. Most of the embryos (181 out of 199) showed serious malformations of the limbs of which the most characteristic was phocomelia. Embryos which died, or were sacrificed, before 10 days of age had very short limbs most of which in course of degenerating. Embryos taken at ages greater than 12 days showed various degrees of alterations of wings and legs. In the most severe cases the digits appeared to be inserted directly into the flank of the animal (type I). The least affected cases showed feet or wings shortened and deformed (type III). Between these two types are placed a group whose members approach the phocomélie type but in whom a short segment separates the distal parts of the limb from the body (type II). The digits were also malformed, and both fusions (syndactyly) and regression was observed. There were very few other malformations. There were many aberrations in the development of the skeletal elements. In the foot, the fibula was first to disappear. In the wing, the ulna or the radius was affected. The other elements were generally reduced in size or abnormally developed. Fusions and abnormal bends were seen. The femur and the humerus were generally altered less than the other intermediate pieces of the skeleton. This work brings evidence of a selective action of nitrogen mustard in the limb rudiments. Certain parts of these rudiments are more sensitive than others. Certain elements of the skeleton disappear in a constant order: fibula (foot), radius or ulna (wing), digit I of the foot. The most typical malformation obtained was phocomelia, seen in 65 out of 107 cases. The distal structures, the digits, are least affected. The hypothesis of a selective action upon mesodermal structures is put forward. Other malformations were rare, 26 out of 107 autopsied before the 12th day of incubation showed scoliosis of the neck. Among them, four showed a malformation of the eye.
Developmental Abnormalities in the Rat Induced by Heat Shock
Authors: Škreb N. , Frank Z.
Published: April 2021

A simple method for applying heat shock directly to the uterus of pregnant rats is described. In an experimental series a temperature of 40–41 °C. was maintained for 40 min. A number of malformed foetuses were observed, and the resorption rate was high. In a control series animals were operated upon in the same manner as the experimental ones, but the temperature was kept at 37–38°C. No malformations were found. Deformities of the head and extremities were produced by the heat shock. These malformations are compared with those produced by other teratogens, and the differences are discussed.
Evidence for a Substance Responsible for the Spacing Pattern of Aggregation and Fruiting in the Cellular Slime Molds
Authors: Bonner John Tyler , Hoffman Mary E.
Published: April 2021

In the cellular slime molds, after the individual amoebae have finished their growth and depleted their food supply, they aggregate into centers. Each center ultimately produces a small fruiting body (a spore mass supported by a slender stalk) that rises into the air. In a previous study (Bonner & Dodd, 1962a) it was shown that the size of the aggregation territories remained constant for any one species under a given set of environmental conditions even though the density of the amoebae in the culture dish might vary considerably. From this it was suggested that one of the possible hypotheses might be that a center-inhibiting substance is diffusing outward from the first formed centers and its effectiveness is independent of the number of cells within a territory. In another study (Bonner & Dodd, 1962b) evidence was brought forth to support the notion that as the fruiting body rises into the air it orients with respect to the environment by producing a gas to which it is sensitive and it orients away from regions of high concentration. In the discussion of this second paper we made the point that the adaptive significance of these two phenomena are one and the same; they both tend to space the fruiting bodies, first by keeping the centers separate during aggregation, and then by keeping the sorocarps separate as they rise into the air. Together they produce optimum conditions for effective spore dispersal.
The Development in vitro and in vivo of Fusion of the Palatal Processes of Rat Embryos
Authors: Moriarty Thomas M. , Weinstein Sam , Gibson R. D.
Published: April 2021

The feasibility of employing organ culture and transplantation techniques for obtaining fusion of the lateral palatal processes of the rat embryo was investigated. The methods of obtaining live embryos and the operations upon these embryos to obtain palatal tissues were described. Nineteen organ cultures of the unfused palatal tissues of 15-day Sprague-Dawley rat embryos were made. Five of these palates achieved fusion. Twenty transplantations of the unfused palatal tissues of 15-day Sprague-Dawley rat embryos were carried out. Ten of the heterografted palates developed fusion. Four of the five homografts achieved fusion. The morphology of palatal process closure was observed and photographed at regular intervals in the in vitro and in vivo experiments. The morphology of closure of the secondary palate as found in the experimental tissues differs slightly from that of normal Sprague-Dawley embryos. The tongue appears to have a direct relationship with morphology and mode of closure. Removal of the tongue from between the lateral palatal processes of the experimental tissues immediately modifies process morphology and mode of closure. The abnormal environments of both explants and transplants cause cellular ‘regressions, in them. The histological progress of cellular fusion appears similar for the experimental and normal tissues.
Sur les Structures Différenciées par l’Ectoderme de Batracien après Irradiation aux Rayons X
Authors: Reyss-Brion par MME. M.
Published: April 2021

L’ Ectoderme n’ est capable de réagir à l’ action des inducteurs que pendant un laps de temps assez court et bien déterminé. Waddington (1938) a dé-nommé ‘compétence’, cette réactivité de l’ ectoderme caractérisque d’ un stade du développement embryonnaire.
Mumps Virus Infection of the Pregnant Hamster
Authors: Ferm Vergil H. , Kilham Lawrence
Published: April 2021

The objective of our present studies has been to follow the course of mumps virus when injected intravenously into pregnant hamsters during early stages of gestation, in order to determine possible relations to fetal disease and/or malformations. Several considerations prompted the selection of mumps virus for these investigations. One was that, while rubella (Gregg, 1941) and cyto-megalic inclusion body disease (Weller & Hanshaw, 1962) have been the only two viruses shown to have a definite cause-effect relation in the etiology of human congenital malformations, there has been a continuing suspicion that mumps virus may also act as a teratogenic agent in human pregnancy (Kaye & Reaney, 1962; Blattner & Heys, 1961; Hyatt, 1961). A second reason was that mumps virus has a natural pathogenicity for hamsters (Kilham & Overman, 1953). In addition, this agent is capable of infecting women at term, the strain used in present experiments having been obtained from human milk a few days post-partum (Kilham, 1951).
The Control of Growth of the Chick Embryo Liver Studied by the Method of Parabiosis
Authors: Chaytor Daniel E. B.
Published: April 2021

Chicken embryos of 9 days’ incubation have been parabiosed with partners of 12 days’ incubation and the effects on liver growth during the subsequent 4 days studied. Control 9- and 12-day embryos were parabiosed with partners of their own age.

The younger embryo parabiosed with an older partner was found to show a diminished growth of liver when body weight was standardized.

The mitotic index in liver parenchymal cells of the younger embryo para-biosed to the older was about half that of controls. The liver mitotic index in the older partner did not differ from controls.

Parabiosis per se does not appear to have any adverse effect on the mitotic activity of the liver.

The results have been discussed in terms of a blood-borne liver growth in-hibitor produced by the liver and acting by a feed-back mechanism, of the kind that has been postulated in the adult mammal.
A Quantitative Study of Primordial Germ Cells in the Male Rat
Authors: Beaumont Heather M. , Mandl Anita M.
Published: April 2021

A cytological and quantitative study was made of the testes of foetal and neonatal rats. The population of germ cells was estimated for a total of 111 specimens. A volumetric method (Beaumont & Mandl, 1962) was used for animals aged 14.5 days p.c. to 4.5 days p.p. Counts were made of the numbers of dividing germ cells in foetal testes. Numbers of normal, degenerating and dividing gonocytes, ‘transitional’ cells and spermatogonia type-A were estimated from differential counts made on specimens aged 3-6.5 days p.p. The primordial germ cells divide mitotically up to the age of about 18.5 days p.c. Thereafter they remain at interphase for a period of 6-8 days, during which they enlarge considerably. Although many gonocytes appear to undergo degeneration during this resting period, few ‘disappear’ from the testis until 2-4 days after birth. Differentiation of gonocytes into definitive germ cells sets in about 4 days p.p. The formation of spermatogonia type-A is preceded by the appearance of ‘transitional’ cells and a renewal of mitotic activity. The total population of primordial germ cells rises from about 20,000 at 14..5 days p.c. to.reach a plateau of 120,000-140,000 between 20 days p.c. and 2 days p.p. The number of gonocytes then declines to ca. 50,000 at 6-6.5 days after birth. This decrease is due to (a) the elimination of degenerating germ cells, and (b) the transformation of gonocytes into definitive germ cells. With the re-initiation of mitotic activity, which accompanies germinal differentiation, the total population of germ cells increases to ca. 200,000 at 6-6.5 days, of which spermatogonia type-A number between 50,000 and 90,000.
Ecdysone-dependent proteolysis of an apical surface glycoprotein may play a role in imaginal disc morphogenesis in Drosophila
Authors: Birr Cynthia A. , Fristrom Dianne , King David S. , Fristrom James W.
Published: April 2021

An apical surface glycoprotein, designated gp125 for its apparent molecular weight of 125 000, appears in Ca2+-free, ionic detergent extracts of imaginal discs of Drosophila melanogaster in response to the steroid hormone, 20-hydroxyecdysone (20-HE). Gpl25 is not synthesized in response to 20-HE, but results from modification of an existing macromolecule. Treatment of discs or larval epidermis with serine protease (e.g., trypsin) results in hormone-independent production of gp125. Antiserum raised to electrophoretically purified gp125 recognizes, in addition to gp125, two closely related glycoproteins with higher apparent molecular weights, gp200 and gp180. This family of glycoproteins is localized at the apical surface of imaginal disc cells and of the epidermal epithelium in embryos, larvae and prepupae. Ca2+ affects both the solubility and the proteolytic products of this family of glycoproteins. We discuss the possibility that gp125 is generated through the action of a hormonally controlled serine protease in a process that is necessary for disc morphogenesis.