bluuebunny/crossref_metadata_2025 huggingface dataset:
Normal and abnormal development of an identified leech motor neuron
Authors: Kuwada John Y.
Published: April 2021

In embryonic and mature leeches, the identified L motor neuron, which innervates the longitudinal muscles of the contralateral half body segment, can be identified by the location and relatively large size of its cell body. Here the morphological and physiological development of the L motor neuron has been investigated by intracellular recording and dye-filling techniques in normal and abnormal embryonic leeches. Normally the L motor neuron growth cone projects from the cell body at about the same time as from many other neurons located in the lateral part of the ganglion, including the P mechanosensory neurons. The L motor axon, like many other leech axons, projects directly into the appropriate pathway. The L motor neuron does not initially extend an excessive number of axons followed by elimination of the inappropriate ones. Its growth cone is tapered and relatively free of filopodia and grows out of the ganglion in the contralateral posterior nerve behind the growth cone of the primary peripheral axon of the dorsal P mechanosensory cell, which is one of the earliest axons in the posterior root.

Occasionally the bilateral halves of the germinal plate fail to fuse resulting in an embryo with separated but intact half ganglia, body wall, and skin. In such embryos the L motor neuron axons cannot grow out the contralateral posterior nerve since it is not available. Instead they grow out a variety of ipsilateral nerves and/or connective tracts. The P mechanosensory cells, which normally grow out of the ganglion in specific ipsilateral nerves, extend their axons along their normal pathways. In these abnormal embryos the L motor neurons did not preferentially grow into the ipsilateral posterior nerve, normally the pathway taken by the bilateral homologue and the nerve most similar to the L motor neuron’s normal pathway. The failure of these L neurons to either consistently choose or avoid the ipsilateral posterior root suggests that the bilateral homologues ignore one another’s pathfinding cues or that such cues are missing or changed in these embryos. The axons of the P neurons, however, appear to require no cues or interactions with contralateral structures or cells for normal development.
Fine structure of the interdigital membranes during the morphogenesis of the digits of the webbed foot of the duck embryo
Authors: Hurle J. M. , Fernandez-Teran M. A.
Published: April 2021

Fine structural study of interdigital membranes during formation of the digits of the duck foot reveals that the interdigital necrosis is accompanied by a high deposition of collagenous material in the epithelio-mesenchymal interface, rupture of the basal lamina and detachment of ectodermal cells into the amniotic sac. These changes are similar to those observed in the regressing interdigital membrane of the chick although their intensity and temporal extension are less pronounced in the duck. It is suggested that these changes account for the disappearance of the marginal zone of the duck interdigital membranes. The possible causal relationship between the different structural changes are discussed.
Epithelial induction of osteogenesis in embryonic chick mandibular mesenchyme studied by transfilter tissue recombinations
Authors: Exan R. J. Van , Hall B. K.
Published: April 2021

The initiation of osteogenesis in the mandibular mesenchyme of the embryonic chick at 7 days is dependent upon an epithelial induction which occurs in the mandible up to the fourth day in ovo. In the present study, transfilter tissue recombinations were used to study this inductive mechanism. The epithelial and mesenchymal components of the mandibles were separated before the completion of the induction and recombined to form transfilter explants which were either cultured for 9 days or grafted onto the chorioallantoic membrane for host embryos for 7 days.

Control experiments demonstrated that the tissue separation and recombination techniques did not interfere with the normal epithelial induction, and confirmed that mandibular mesenchyme isolated at this stage was incapable of forming bone.

Bone was observed in 86 % of the CAM-grafted intact mandible controls and in 80 % of the cultured intact mandible controls. Bone failed to form in the mesenchyme of transfilter explants when Millipore filters with 0·45 μm pores were used. Bone was observed as frequently as in control explants when the mandibular mesenchyme was separated from its epithelium by 0·8μm or 0·4μm porosity Nuclepore filters. Only about 30% of the transfilter explants prepared with 0·1μm porosity Nuclepore filters formed bone and none of the explants prepared with 0·03μm porosity Nuclepore filters formed bone. SEM studies demonstrated a distinct correlation between the formation of bone in transfilter explants and the ability of the epithelium and mesenchyme to penetrate the pores of the filters.

Thus, the present study provides evidence that the site of the induction is restricted to the epithelial-mesenchymal interface, and that the induction is not mediated by a diffusible substance. The nature of the inductive mechanism is discussed with respect to this and other recent studies which suggest that the induction may be mediated by a non-diffusible epithelial cell product resident in the epithelial basal lamina.
Electron microscopic evidence for the presence of an asialoglycoprotein receptor on isolated foetal rat hepatocyte surface
Authors: Devirgiliis Laura Conti , Dini Luciana , Russo-Caia Salvatore
Published: April 2021

The ontogeny of asialoglycoprotein receptor was investigated by electron microscopic cytochemistry in hepatocytes isolated from foetal and adult rat. The binding capacity for asialofetuin coupled to horseradish peroxidase was lacking before the 18th day of intrauterine life; it arises at this time and increases with developmental age.

The ligand-receptor complexes form small patches. The distribution pattern of positivity is very similar in pre and postnatal age, covering the entire cell surface.

These results indicate a rather late appearance of the galactose-binding capacity related to the asialoglycoprotein clearance function, which is typical of adult mammalian liver.
Relation between Somite Segregation Rate and ATP-ase Activity in Early Chick Embryos
Authors: Deuchar E. M.
Published: April 2021

In the preceding paper (Deuchar, 1960) it was established that the first-formed somites of the chick embryos at 40–45 hours’ incubation (Hamburger & Hamil-ton’s stage 11, 1951) have a higher calcium-activated ATP-ase activity per unit nitrogen than the somite mesoderm which is not yet segmented at this stage. It was inferred that there is an increase of ATP-ase (possibly connected with myosin synthesis) in the somite tissue as it segments. A question that at once arises is how far the ATP-ase activity is essential to the process of somite segmentation. Besides presaging myosin, the ATP-ase could conceivably play an immediate role during the movements and changes of shape that the mesoderm cells undergo at this time. If so, one would expect some correlation between intensity of ATP-ase activity and the efficiency of segmentation, if either were modified experimentally. To test this possibility, in the work to be described here chick embryos have been grown in media to which the agents ω-bromo-allylglycine, leucine, and adenosine triphosphate had been added, ω-bromo-allylglycine (BAG) is an analogue of leucine which was found by Herrmann, Konigsberg, & Curry (1955) to block completely the segmentation of chick somites. Its effects are reversible by the simultaneous addition of leucine. In the present experiments its effects on ATP-ase activity as well as segmentation rate were measured, both alone and in the presence of leucine. Leucine was also tested by itself to see if it would increase either segmentation rate or ATP-ase activity above the normal level. Finally, ATP was added to some cultures as a possible means of raising both ATP-ase activity and segmentation rate. ATP was then used in combination with BAG to see if it would reverse the effects of this inhibitor.
Some Degenerative Phenomena in Drosophila Ovaries
Authors: Waddington C. H. , Okada Eiko
Published: April 2021

A description is given of degenerative phenomena in the Drosophila ovary. Three types of degeneration are dealt with: (1) degeneration of the follicle cells; (2) degeneration occurring in the unfertilized egg, a major feature of which is the segregation of the different constituents of the egg into comparatively large masses; and (3) degenerative phenomena in the nurse cells and oocytes of abnormal eggs produced in ovaries homozygous for deep-orange.

In all these instances it is noteworthy that a considerable degree of structural organization (formation of double membranes, or sets of parallel or concentric membranes, &c.) occurs in cytoplasm which is clearly degenerating. It is suggested that such organization does not always represent the formation of functioning organelles, but may be a mere consequence of the inherent physicochemical properties of the materials involved.

In degenerating deep-orange ovaries masses of fragmented porous membranes are found. These seem to be derived from the nuclear membranes of the nurse cells, which appear to persist even when the rest of the cell is rather completely destroyed. Fragments of nuclear envelopes tend to lie close together and parallel to one another, and it is suggested that this indicates that there is some force of attraction between them, which may be comparable to the forces involved in the formation of stacks of annulate lamellae, or of concentric or parallel double-membrane structures in ergastoplasm, and in chromosome pairing in healthy functional cells.
La culturein vitrode l’épithélium germinatif isolé des gonades mâles et femelles de l’embryon de Canard
Authors: Haffen Katy
Published: April 2021

Undifferentiated germinal epithelium was isolated following trypsinization from embryonic duck gonads of 5 to 7 days of incubation. This epithelium was associated with ovarian and testicular medullae taken from sexually differentiated embryos. Ovarian cortex differentiates from female germinal epithelium of 5 days, whatever the source of the medullary tissue with which it is associated (Plate 1, fig. 3; Plate 2, figs. 5, 6a, b, c). In control experiments the female epithelium undergoes similar development in the presence of mesonephros (Plate 2, fig. 5). Five-to seven-day male germinal epithelium is influenced by tissues with which it is in contact. In the presence of testicular medulla it gives rise to male medullary cords (Plate 1, fig. 4). In the presence of ovarian medulla, ovarian cortex differentiates (Plate 3, figs. 7a, b, c). When in contact with mesonephros no differentiation of the male epithelium ensues. These results are particularly clear in the case of germinal epithelia explanted between 5 and 6 days of incubation.
The Influence of the Hypophysis and the Thyroid on the Ultimobranchial Body of the Anura of Israel
Authors: Boschwitz Dvorah
Published: April 2021

The ultimobranchial body originates independently of the thyroid, as seen in congenitally athyreotic tadpoles of P. syriacus. Experiments concerning the influence of the hypophysis and thyroid on the ultimobranchial body were performed on H. arborea, R. ridibunda, and B. viridis. With the beginning of metamorphosis, the increasing thyroid secretion inhibits the original growth rate of the ultimobranchial body; experimental hyperthyroidism enhances this physiological interference, so that the follicle shrinks. Experimental hypothyroidism causes hypertrophy of the ultimobranchial body, evidenced by an increase in surface area of the follicle. This effect is negligible before metamorphosis, significant during metamorphosis, and less extreme in young adults, when thyroid activity declines. Hypophysectomy in young adults causes atrophy of the organ. It is assumed that the hypophysis maintains the ultimobranchial body and the thyroid inhibits its growth and activity. The antagonistic effects of both glands produce the normal state of the organ.
Growth and Ascorbic Acid Content of the Chick Embryo
Authors: Rinaldini L. M.
Published: April 2021

Ascorbic acid (ASA) is actively synthesized by germinating plant seeds (see Mapson, 1953), and by the embryos of various animal species (refs, in Needham, 1942).
The roles of node regression and elongation of the area pellucida in the formation of somites in avian embryos
Authors: Stern Claudio D. , Bellairs Ruth
Published: April 2021

Experiments have been carried out on explanted chick embryos to test certain widely accepted concepts about the role of Hensen’s node in somite formation. The relationship between elongation of the area pellucida and regression of Hensen’s node has also been investigated.

We conclude from these experiments that: (a) The timing of somite formation is not controlled by the regression of Hensen’s node, nor by the shearing of the mesoderm into right and left halves.(b) Somite size and shape are probably controlled by local conditions in the chick embryo.(c) Elongation and regression are two different events.(d) The position of the somites probably depends on mechanical tensions in the area pellucida.(e) The notochord is not required for the stability of somites in vivo.
Do larval epidermal cells possess the blueprint for adult pattern in Drosophila?
Authors: Madhavan Mekkara Mandaravally , Madhavan Kornath
Published: April 2021

When the diploid histoblasts, the precursors of adult abdominal epidermal cells, of the larva of Drosophila are deleted by γ-radiation, the polytene larval epidermal cells survive metamorphosis and secrete cuticle and cuticular outgrowths. A comparison of the morphology of the cuticle secreted by the larval epidermal cells in the different regions of the abdominal segments to that secreted by the histoblasts of the unirradiated animal suggests that the former contain the blueprint for the pattern of landscape of the adult abdominal cuticle and possibly could provide this information to the dividing and spreading histoblasts during the normal ontogeny of the fly.
Benzamide on chondrocytic differentiation in chick limb bud cell culture
Authors: Nakanishi Shinobu , Uyeki Edwin M.
Published: April 2021

Benzamide, an inhibitor of (ADP-ribose) transferase, augmented chondrocytic differentiation of chick limb bud mesenchymal cells in micromass cultures; the incorporation of 35SO42- into the trichloroacetic-acid-insoluble constituents of cell masses as well as the formation of cartilage nodules (Nishio, Nakanishi, Doull & Uyeki, 1983) occurred about 24h earlier than in untreated cultures and continued to be enhanced in benzamide-treated cultures of stage 23-to 24-chick limb bud cells. Benzamide also significantly increased cell proliferation. However, benzamide did not affect DNA and RNA syntheses except for one period: 24 to 30 h after the start of culture, RNA synthesis was stimulated. From 48h of culture, (ADP-ribose) transferase activity decreased daily in untreated cultures, whereas benzamide treatment diminished (ADP-ribose) transferase activity 24 h earlier. On the other hand, intracellular NAD levels increased daily in untreated cultures, and benzamide significantly increased the NAD levels above untreated cultures. ATP levels did not differ significantly during the culture period, and benzamide did not affect ATP levels.
Localization of the factors producing the periodic activities responsible for synchronous cleavage in Xenopus embryos
Authors: Shinagawa Atsunori
Published: April 2021

This paper investigates the localization within the Xenopus egg of the factors responsible for the periodic activities such as the cyclic rounding-up and flattening, related to the cleavage cycle. Denuded eggs were bisected along the boundary line between the animal and the vegetal hemispheres immediately after being rotated through 90° off the vertical axis (Early Bisection). The resulting animal halves, though prevented from cell division by colchicine, showed typical periodic rounding-up as previously observed in enucleated egg fragments, whereas the vegetal halves did not. This result indicates that the factors inducing the periodic rounding-up are not distributed uniformly throughout the egg but localized mostly in the animal hemisphere. Furthermore, the distribution of these factors between the cortex and endoplasm of the animal hemisphere was investigated. Eggs were separated into animal and vegetal halves following incubation for 30min after the 90°-off axis rotation (Late Bisection). During this incubation the endoplasmic components become relocated in the rotated egg under the force of gravity. After the rotation, the Late-Bisected vegetal halves showed typical cyclic rounding-up in contrast to those formed by Early Bisection. These results suggest that the factors inducing the periodic rounding-up (and probably also many other cyclic activities, closely linked with the rounding-up movement) are localized in endoplasmic components which can be displaced by gravity from the animal to the vegetal hemisphere of the Xenopus egg.
Origin of the irideal striated muscle in birds
Authors: Nakano Kensuke E. , Nakamura Harukazu
Published: April 2021

The aim of the present study was to elucidate the origin of the striated muscle cells in the avian iris. For this purpose we adopted interspecific transplantation between quail and chick embryos because quail cells can be used as biological markers in this system. We transplanted isotopically and isochronically (6- to 7-somite stage) a fragment of a dorsal part of the quail neural anlage into a chick embryo at the level corresponding to the posterior prosencephalon and the mesencephalon on the right-hand side.

In the chimaeric embryo, the iris epithelium comprised host chick cells, while most of the stromal cells of the iris on the operated side possessed the quail nuclear marker. At 19 days after the operation, the striated muscle cells had differentiated in the chimaeric embryo. These cells, as well as connective tissue cells and the Schwann cells of the iris of the chimaera, were shown to possess typical quail nuclei by light and transmission electron microscopy. From these findings, we conclude that the striated muscle cells originate from the neural crest.
Development of the lateral line system in Xenopus laevis : III. Development of the supraorbital system in triploid embryos and larvae
Authors: Winklbauer Rudolf , Hausen Peter
Published: April 2021

During normal development of the supraorbital lateral line system of Xenopus, an elongated streak of primordial cells becomes subdivided into a linear series of cell groups containing only about eight cells each, thus forming a row of primary lateral line organs (Winklbauer & Hausen, 1983a,b). In triploid Xenopus embryos, cell size is 1 ·5 × normal. When the formation of lateral line organs occurs in triploid primordia, the nascent organs contain only about five or six cells each, i.e. about two thirds of normal. Thus, the increase in cell size is compensated for by a corresponding reduction in cell number, keeping constant the organ size in terms of total cell mass or volume. This result excludes a cell counting mechanism for determining organ size. In diploids, the primary organs, although being of equal size initially, differ vastly in their final size and exhibit a peculiar frequency distribution of organ sizes. A detailed quantitative model for supraorbital lateral line development has been proposed, which accounts for this characteristic frequency distribution (Winklbauer & Hausen, 1983b). This model makes precise predictions as to the frequency distribution of the final size of triploid lateral line organs, where the initial organ size is reduced to five or six cells. These predictions were verified experimentally.
Detection and characterization of spatial pattern in chimaeric tissue
Authors: H. Schmidt Günter , Wilkinson Maureen M. , Ponder Bruce A. J.
Published: April 2021

The mosaic pattern of patches of crypts of Lieberkühn in chimaeric C57BL/6JLac (B6) ↔DDK mouse small intestine, demonstrated using Dolichos bifloras agglutinin as strainspecific marker, is quantitatively examined using the Greig-Smith analysis of variance. This analysis, widely used in ecological research, provides a method to detect and characterize pattern at various scales. The analysis demonstrates that B6 patches are non-randomly distributed at all scales examined. A consistent increase in the intensity of pattern at one particular scale over all replicate samples identifies ‘clusters of clusters’ which probably are territories of ‘descendent’ clones. The sizes of descendent clones, either in terms of numbers of patches or total numbers of crypts, are highly variable. A steady reduction in the strength of pattern from proximal to distal is found. The Greig-Smith analysis of variance provides a valuable method for the analysis of pattern in chimaeric tissue.
The influence of the epithelium on palate shelf reorientation
Authors: Bulleit Robert F. , Zimmerman Ernest F.
Published: April 2021

The intrinsic forces necessary for directing the reorientation of the secondary palate appear to reside in the anterior two thirds of the palate or presumptive hard palate. The hard palate could reorient regardless of whether it was intact or separated from the posterior third or presumptive soft palate. The soft palate could only reorient if the palate shelves are left intact. These intrinsic forces, within the hard palate, may be mediated by the mesenchymal cells, their extracellular matrix, or the epithelium surrounding the shelves. This latter possibly was tested by removing the epithelium, from either the presumptive oral or nasal surface followed by measurement of reorientation in vitro. Only after removal of the oral epithelium was a significant inhibition in reorientation observed. The treatment used to remove the epithelium, EDTA and scraping, was shown to remove 41 % of the oral epithelium leaving the majority of the basement membrane intact. The observed inhibition of reorientation did not appear to be a consequence of wound healing. Creation of wounds twice the area that was observed after treatment with EDTA and scraping inhibited reorientation minimally. These results suggest that the epithelium and particularly the anterior oral epithelium plays a major role in the reorientation of the murine secondary palate.
The development of 12th to 14th day foetuses following reimplantation of pre- and early-primitivestreak-stage mouse embryos
Authors: Beddington R. S. P.
Published: April 2021

This paper describes a technique for transplanting early postimplantation mouse embryos from their own implantation site to a decidua in another pregnant mouse. Evidence is provided that this procedure is compatible with their continued development. At a low frequency both 6th and 7th day embryos can re-establish themselves and continue apparently normal development and placentation for at least 6 –8 days.
Clonal analysis of X-chromosome inactivation and the origin of the germ line in the mouse embryo
Authors: Gardner R. L. , Lyon M. F. , Evans E. P. , Burtenshaw M. D.
Published: April 2021

Cloning of cells from peri-implantation embryos by blastocyst injection was used to investigate the time of X-chromosome inactivation in that part of the ectoderm lineage giving rise to foetal tissues of the mouse. Matings were arranged so that the two X-chromosomes of female donor cells controlled two distinct coat colours and host blastocysts were of a third colour genotype. No coat chimaeras were obtained in experiments using donor cells from the primitive ectoderm of 6th or 7th day embryos or from lactationally delayed implanting or reactivated blastocysts. In contrast, a minimum of 80 unequivocal coat chimaeras were obtained in experiments in which primitive ectoderm cells from 5th day implanting blastocysts were used for injection. The majority of these chimaeras that had received a female cell exhibited both donor colours in addition to host colour in their coats, suggesting that the donor cell had not undergone X-inactivation until one or more cycles after transplantation. The remainder of such chimaeras exhibited only one or other donor coat colour. Determination of the parental origin of the allocyclic X-chromosome in donor metaphase preparations in internal tissues of several chimaeras revealed that the coat pattern did not always reflect the X-activity status of the donor cell clone as a whole. Nevertheless, the findings suggest that X-inactivation takes place shortly after implantation in the primitive ectoderm cell population from which the foetus is derived.

Of the 68 chimaeras in which the sex of both the donor and host component was established 62 proved to be fertile. Furthermore, 21 of the 37 fertile chimaeras whose sex corresponded with that of the donor cell yielded functional gametes of donor origin. Injection of cells from a single donor blastocyst into a series of host blastocysts established that at least 2 cells in 5th day primitive ectoderm can give rise to both somatic cells and functional germ cells among their mitotic descendants.
Fluid transport across the epiblast of the early chick embryo
Authors: Stern Claudio D. , Manning Simon , Gillespie James I.
Published: April 2021

A simple method is described which allows quantitation of the rate of fluid transport across the isolated epiblast of the early chick embryo. This method consists of allowing the tissue to form spheres, which then spontaneously undergo a large volume increase. The rate of fluid uptake into the spheres can be estimated by measuring the dimensions of the spheres. Pharmacological and electrophysiological studies were performed on the spheres to determine the mechanisms of fluid transport. It was found that fluid is driven into the interior of the spheres by the osmotic gradient generated by unidirectional sodium transport and to a lesser extent by another mechanism, as yet unknown. We discuss possible candidates for this mechanism, and consider the significance of these findings to early development.
In vivo and in vitro cultured mouse preimplantation embryos differ in their display of a teratocarcinoma cell surface antigen: possible binding of an oviduct factor
Authors: Gaunt Stephen J.
Published: April 2021

By use of a monoclonal antibody, 2B5, in indirect immunofluorescence experiments, it was found that both fertilized and unfertilized mouse eggs obtained directly from the oviduct commenced expression of a cell surface antigen at about 5h after ovulation. Surface labelling became intense by 16 h after ovulation and persisted over all blastomeres throughout preimplantation development. In contrast, embryos cultured in vitro did not show appearance of 2B5 antigen until about 48 h after ovulation, at which time they were at the 2-to 4-cell stage. Antigen expression in vitro commonly began on a single blastomere and did not appear consistently over all blastomeres until the 8-cell stage (72h after ovulation). Unfertilized eggs maintained for 72 h in culture did not acquire 2B5 antigen. It is postulated that the absence of 2B5 antigen on 1-cell eggs cultured in vitro may be due either to a failure of normal synthesis by eggs as a result of a deficiency in the culture medium, or alternatively, to absence of a soluble oviduct factor which carries the 2B5 antigen, and which normally becomes bound to the surface of eggs after ovulation. The second of these two possibilities was supported by egg transfer experiments which showed that unfertilized eggs within the oviduct became 2B5 antigenpositive even after their prior fixation in glutaraldehyde. By the 2-to 4-cell stage, however, embryos developed their own capacity for synthesis of 2B5 antigen-positive cell surface molecules. This synthesis was inhibited by tunicamycin, suggesting that the antigenic site involved the sugar component of glycoprotein. The range of tissues within the postimplantation embryo and adult reproductive tracts which labelled with 2B5 antibody was found to be very similar to that known for SSEA-1 monoclonal antibody (Solter & Knowles, 1978; Fox et al. 1981; Fox, Damjanov, Knowles & Solter, 1982), and as further evidence of a relationship between 2B5 and SSEA-1 antigens it was found that 125I SSEA-1 antibody could be blocked in its binding to teratocarcinoma cells by preincubation in 2B5 monoclonal antibody.
Quantitation of two-dimensional gel proteins reveals unequal amounts of Tcp-1 gene products during mouse spermatogenesis but no correlation with transmission ratio distortion
Authors: Sánchez Edwin R. , Hammerberg Craig , Erickson Robert P.
Published: April 2021

The discovery of a protein, p63/6.9, that is synthesized by both somatic and germ cells and coded for by a gene, Tcp-1, within the t complex provides a molecular probe for examining transmission ratio distortion in t mice. Two electromorphs of this protein exist. The acidic protein (a) is encoded by t-haplotype chromosomes, while the basic protein (b) is encoded by wild-type 17th chromosomes. We have measured the relative amounts of p63/6.9a and p63/6.9b for various t-complex bearing males and for several stages of spermatogenesis. There was no correlation between the ratio of p63/6.9a to b and the magnitude of transmission ratio distortion but the relative amounts of these proteins present in testicular cells can vary depending on the method of labelling. In vivo labelling results in the detection of two-fold greater amounts of p63/6.9a while in vitro labelling produces equimolar amounts of these two proteins. These data suggest that unequal synthesis or degradation of the p63/6.9 proteins occurs during sperma-togenesis. It is proposed that increased synthesis of p63/6.9a in vivo is an intrinsic property of t-haplotypes.
Cell distributions in the retinal ganglion cell layer of adult Leptodactylid frogs after premetamorphic eye rotation
Authors: Dunlop S. A. , Beazley L. D.
Published: April 2021

In adult Limnodynastes dorsalis and Heleioporus eyrei regions of high cell density in the retinal ganglion cell layer are normally found along the nasotemporal axis and become apparent only after metamorphosis (Dunlop & Beazley, 1981; Coleman, Dunlop & Beazley, 1984). Eye rotations were performed from embryonic to mid-larval life and cell topography mapped after metamorphosis using cresyl violet-stained wholemounts. Mature cell distributions indicated that from stages equivalent to 30/31 in Xenopus (Nieuwkoop & Faber, 1956) alignment of high cell density regions had already been determined and developed to reflect the degree of eye rotation. We conclude that cell topography in the adult ganglion cell layer is determined from the time at which invagination of the eye cup nears completion. Furthermore, the corre-spondence in adults between alignment of high cell density regions and the orientation of the visuotectal projection suggests that these features could not be dissociated by manipulation of the developing eye.
Muscle fibre types and innervation of the chick embryo limb following cervical spinal cord removal
Authors: Laing N. G. , Lamb A. H.
Published: April 2021

Several segments of spinal cord were removed from the cervical regions of stage-13 or -14 (day-2) chick embryos. After further incubation to day 17 or 18, the patterns of end-plate distribution and ATPase typing of muscle fibres in the anterior and posterior latissimus dorsi and the ulnimetacarpalis dorsalis, and the ATPase typing of the forearm muscles were examined. No differences from control embryos were found. The embryos had normal numbers of lateral motor column motoneurons in both the brachial and lumbar enlargements and the positions of motoneurons supplying the biceps as identified with retrograde horseradish peroxidase labelling were consistent with the normal patterns of motor projection into the limb. These results show that the fibre typing of limb muscles and their patterns of innervation are independent of descending inputs until just before hatching in the chick.
Utilization of cytoplasmic poly(A)+ RNA for protein synthesis in preimplantation mouse embryos
Authors: Kidder Gerald M. , Conlon Ronald A.
Published: April 2021

The distribution of cytoplasmic poly(A)+RNA between subribosomal (<80S) and ribosomal/polysomal (⩾80S) ribonucleoprotein particles has been investigated in mouse morulae and blastocysts. After labelling for 24h with [5,6-3H] uridine, late morulae (96h post-hCG), early blastocysts (100h post-hCG), or late blastocysts (120h post-hCG) were homogenized in detergent buffer, and 11000 g supernatants were prepared and centrifuged through 15–40% sucrose gradients. Poly(A)+RNA was isolated from the appropriate gradient fractions by affinity chromatography. In late morulae beginning to undergo cavitation, poly(A)+RNA was evenly distributed between the two types of RNP particles whereas it was almost entirely in the ribosomal/polysomal fraction in early and late blastocysts. The sedimentation profile (in 5–20 % sucrose gradients) of poly(A)+RNA from the ribosomal/polysomal fraction of late morulae and blastocysts was the same, with a range of 4S to greater than 28S and a modal peak slightly smaller than 18S. Roughly 75 % of this RNA was judged to be functional mRNA based on the EDTA sensitivity of the RNP particles containing it. Poly(A)+RNA from the subribosomal fraction of late morulae displayed a similar range of sedimentation values, but was enriched for a component sedimenting at 6–7S. These results demonstrate that the subcellular distribution of poly(A)+RNA shifts as cavitation begins, with the decline of the non-translating, subribosomal fraction. Although most of this fraction in late morulae is probably too small to constitute translatable mRNA, the remainder may represent a reserve available for recruitment into polyribosomes to support blastocyst expansion. Since little non-translating mRNA exists in blastocysts, the increasing rate of protein synthesis during blastocyst expansion must be driven by mRNA accumulation and/or stabilization.
Microgravity simulation as a probe for understanding early Xenopus pattern specification
Authors: Neff Anton W. , Malacinski George M. , Chung Hae-Moon
Published: April 2021

Pattern specification in early amphibians {Xenopus) was monitored in embryos subjected to gravity compensation (microgravity simulation) by constant low-speed rotation on a horizontal axis (clinostat). The useful range of clinostat speeds was determined empirically. The results were interpreted in terms of a set of models which account for the reorganization of the egg cytoplasm that follows fertilization and that correlates with the establishment of dorsal/ventral polarity. Large percentages of clinostated eggs displayed a positive result (normal axial structure morphogenesis). Consequently, normal development of amphibian eggs in the microgravity environment of space should be possible. Models which depend upon gravity-driven rearrangements for cytoplasmic organization (e.g. dorsal/ventral polarization) of the early embryo should, therefore, not be favoured. At several clinostat speeds symmetrization of the egg in accordance with the site of sperm penetration, a natural phenomenon, was altered. The results at those clinostat speeds indicate that models which employ sperm entrance as an obligatory feature of the cytoplasmic rearrangements that generate egg polarity are not applicable.
Identification of proteins and mRNAs in isolated yellow crescents of ascidian eggs
Authors: Jeffery William R.
Published: April 2021

The yellow crescent or myoplasm is a localized cytoplasmic region in eggs of the ascidian Styela that is partitioned to the larval tail muscle and mesenchyme cells during embryonic development. To determine whether the myoplasm contains a specific subset of maternal macromolecules, its abundant proteins and mRNAs were identified and compared to those present in the remainder of the egg. This was accomplished by exploiting a newly developed method for the mass fractionation of yellow crescents which is based on the presence of a unique cytoskeletal domain in the yellow crescent region. The fractionation yields a yellow crescent fraction (YCF) representing the myoplasm and a supernatant fraction representing the non-myoplasmic regions. The YCF comprises structures which contain the characteristic myoplasmic organelles and about 10% of the protein, 8% of the RNA, and 1–3% of the poly (A) of whole eggs. Two-dimensional gel electrophoresis indicated that the YCF contains 15 polypeptides that are undetectable in the supernatant fraction and 43 polypeptides that are significantly depleted in the latter fraction. The proteins restricted to the YCF are both of cytoskeletal and non-cytoskeletal origin. In vitro translation of RNA in a message-dependent lysate and analysis of [35S]methionine-labelled polypeptide products by two-dimensional gel electrophoresis did not reveal qualitative differences between the YCF and the supernatant fraction. Furthermore, the mRNAs coding for two polypeptides that were localized in the myoplasm were not restricted to the YCF. The results suggest that qualitative differences in proteins but not in prevalent mRNAs exist between the yellow crescent and the other cytoplasmic regions of Styela eggs.
The effects of the fibre environment on the paths taken by regenerating optic nerve fibres in Xenopus
Authors: Taylor J. S. H. , Gaze R. M.
Published: April 2021

The paths taken by fibres regenerating to the tectum from various parts of the Xenopus retina were investigated in whole-mount preparations, after localized retinal labelling with HRP. The effects of different environments on the fibres were studied by comparing contralateral with ipsilateral regeneration, in the presence of the other eye or after it had been removed in embryonic life.

Under all conditions fibres from the various parts of the retina regenerated to the corresponding appropriate parts of the tectum, but they took a variety of pathways, some grossly abnormal, to get there. Contralaterally regenerating fibres tended to behave less abnormally than ipsilateral fibres; and regeneration in the absence of the other eye tended to be more abnormal than in its presence. In any one category of regeneration the most nearly normal pathways were those of fibres from temporal retina, followed by ventral, nasal and dorsal fibres.

Fibres regenerating from all parts of the retina, in the presence of the other eye, tended to become gathered into the medial brachium as they approached the tectum. All regenerating fibres approached their tectal terminations by one or more of three main pathways: round one or both brachia, thus encircling the tectum to get to their terminal zone; directly across the tectum; or by passing on to the tectum before changing course. The changes of direction required to enable fibres wrongly positioned in the tract to reach their correct terminal zones were frequently sudden and considerable, and took place on the tectum or at the tectodiencephalic junction. The results are discussed in relation to the differing substrates over which the fibres regenerate.
Chromosome replication in early development of Xenopus laevis
Authors: Laskey R. A.
Published: April 2021

Eggs of Xenopus laevis contain exceptionally large amounts of materials involved in chromosome replication. This maternal stockpile allows an embryo to produce about 80 000 cells in less than 24 h. The adaptations which achieve this involve the mechanisms of both DNA replication and chromatin assembly.
Cytoplasmic localization and chordamesoderm induction in the frog embryo
Authors: L. Gimlich Robert
Published: April 2021

The experiments described here were designed to reveal the distribution in the frog early embryo of components which are sufficient for specification of the dorsal structures of the embryonic body axis. The approach was to allow cleavage planes to divide the embryo into various well-defined regions and to transplant cells from each region into recipient embryos which would otherwise fail to form axial structures. Partial or complete body axis development could then be scored by the use of external criteria or histological methods. Recipients were embryos which had been irradiated before first cleavage with ultraviolet light on the vegetal surface. Irradiated embryos display a well-characterized set of deficiencies in the dorsal structures of the body axis, but their development can be ‘rescued’ toward normalcy in several ways. In particular, transplantation of certain small groups of blastomeres from the normal 32-to 64-cell embryo into irradiated recipients was sufficient to cause partial or complete axis development. Cell groups which could cause rescue were located in the vegetal and equatorial levels of one quadrant of the normal embryo - the quadrant centered on the future dorsal midline. Clonal marking analysis showed that the vegetal-most cells of this quadrant contribute primarily to endodermal structures in normal development. In rescued recipient embryos, these cells also contributed only to the endoderm; the dorsal mesoderm and central nervous system were formed exclusively by host cells which originated near the transplant. Rescue could also result from transplantation of equatorial cells from the dorsal quadrant of the normal embryo. As in normal development, these cells formed primarily the chordamesoderm of the rescued embryo. Host cells were induced to contribute the somitic mesoderm, central nervous system, and other structures which would have been missing but for the presence of the transplanted cells. The frequency and degree of rescue caused by equatorial and vegetal transplants is variable. This was explained by the discovery that the location of components needed for rescue varies among individual embryos without regard to the positions of cleavage planes. This was true even when donor embryos were selected on the basis of a precisely regular pattern of cleavage. In such selected embryos, particular blastomeres make a predictable contribution of progeny to the body axis. Thus it may be that the positions of components which can cause axis formation vary without exact regard to the fate map of prospective areas. The implications of this for the study of cytoplasmic localization in the early embryo are discussed. In any case, it is likely that regional interactions and a degree of developmental autonomy in the area of the prospective chordamesoderm are both involved in formation of the dorsal structures of the embryonic body axis.
Number of Neoblasts in the Intact Body of Euplanaria torva and Dendrocoelum lacteum
Authors: Agnes  , Brøndsted H. V.
Published: April 2021

The total numbers of neoblasts were counted in a specimen of D. lacteum and in a specimen of E. torva. The numbers were respectively 37,826 and 31,320. The distribution of the neoblasts throughout the planarian body does not coincide either with head-regeneration ability or with cross-sectional area along the cephalo-caudal axis of these animals. Although the distribution curve of the neoblasts shows fair agreement in the two species, the time-graded regeneration field is quite different, in Dendro-coelum stopping short just in front of the pharynx, in Euplanaria distributed throughout the animal (A. & H. V. Brøndsted, 1952). The planarian time-graded regeneration field cannot therefore be ascribed to the available numbers of neoblasts at the level of the cut, as is the case in hydroids.
Localization of specific mRNA sequences in Xenopus laevis embryos by in situ hybridization
Authors: Dworkin-Rastl Eva , Kelley Darcy B. , Dworkin Mark B.
Published: April 2021

In situ hybridization of cloned cDNA probes to frozen sections of Xenopus laevis stage-42 tadpoles has been used to determine the tissue localization of several mRNAs. Nine out of sixteen probes tested hybridized to most or all tadpole tissues; seven probes exhibited tissue-specific hybridization. The non-tissue-specific sequences hybridized to RNA species that are also present in maternal RNA while the tissue-specific sequences hybridized to embryonic RNA species induced after gastrulation and undetectable in maternal RNA. Tissue-specific hybridization was observed with muscle (five clones), epidermis (one clone), and the nervous system (one clone). All muscle-specific sequences hybridized to somites and lateral plate muscles, but they differed in their hybridization to heart muscle.
An examination of the evidence for the existence of preformed pathways in the neural tube of Xenopus laevis
Authors: Scott T. M. , Bunt S. M.
Published: April 2021

We have examined the neural tube in Xenopus laevis tadpoles to investigate the anatomical guidance elements which may be present in the presumptive marginal zone. With appropriate fixation protocols the neuroepithelial cells appeared in contact; electron microscopic observations failed to show any specialized intercellular spaces preceding the growing axons. The first fibres were found in the intercellular clefts between the neuroepithelial cells near the surface of the neural tube. Reconstructions of the neural tube from examination of serial 1 μm sections showed that the intercellular clefts are non-aligned at this stage and branching. Scanning electron microscopy of the surface of the neural tube confirmed that the intercellular spaces are non-aligned and often branch caudal to the growing front of descending axons. Thus to grow in a consistent direction the developing axons may have to make consistent and selective (specific) selections of pathway at numerous branch points if their growth is restricted to these intercellular clefts. As more iixons grow along the neural tube, the intercellular clefts become wider, and the neuroepithelial cells bounding the clefts become indented. At later stages many fibres were observed with both scanning and transmission electron microscopy to grow along the surface of the neural tube. These changes in neuroepithelial cell morphology and fibre pathway allow axons to form bundles which take a fairly straight course in contrast to the winding path which must be taken by the first axons to grow through the intercellular clefts.
Comparison of the effects of vitamin A on limb development and regeneration in the axolotl, Ambystoma mexicanum
Authors: Scadding S. R. , Maden M.
Published: April 2021

The objective of this investigation was to compare the effect of vitamin A on limb development and limb regeneration in the same animal, at the same time, thus eliminating the possibility that species differences or different rates of uptake between animals would influence the results. Axolotl larvae had both right limbs amputated and then were treated with retinol palmitate by immersion at 60 or 300 mg l−1 for 4 or 10 days. Intact left developing limbs at the cone, two-digit, or four-digit stages responded to the treatment by deletion of skeletal elements producing hypomorphic limbs. Severity of the deletions was correlated with higher dose, longer times, and earlier stages of limb development. In contralateral right regenerating limbs, the effect of the same treatment was to cause various degrees of proximodistal duplication as well as occasional hypomorphic regenerates. Thus, there is a marked difference in response to vitamin A between developing and regenerating limbs. The implications of this observation are discussed especially with respect to the underlying morphogenetic mechanisms.