bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypothesis: a Y-chromosomal gene causes gonadoblastoma in dysgenetic gonads
Authors: Page David C.
Published: April 2021

The role of the human Y chromosome in the etiology of gonadoblastoma, a gonadal neoplasm, is considered and a two-part model is presented. According to this hypothesis: (1) There is a gene on the Y chromosome that strongly predisposes dysgenetic gonads to develop gonadoblastomas (Page, 1986) and (2) this postulated GBY gene (GonadoBlastoma locus on Y chromosome) has some physiological function in normal males. GBY may, for example, function in or prior to spermatogenesis in normal testes.

Y-DNA hybridization analysis of individuals with gonadoblastoma and partial deletions of the Y chromosome should be of use in testing this proposal. To date, such studies suggest that GBY maps to the region that includes deletion intervals 4B to 7, i.e. it is located near the centromere or on the long arm of the Y chromosome.
Studies of Sl/Sl
d↔ + / + mouse aggregation chimaeras : II. Effect of the steel locus on spermatogenesis
Authors: Nakayama Hiroki , Kuroda Hideya , Onoue Hitoshi , Fujita Jun , Nishimune Yoshitake , Matsumoto Keishi , Nagano Toshio , Suzuki Fumie , Kitamura Yukihiko
Published: April 2021

Mutant mice of Sl/Sld genotype are deficient in melanocytes, erythrocytes, mast cells and germ cells. Deficiency of melanocytes, erythrocytes and mast cells is not attributable to an intrinsic defect in their precursor cells but to a defect in the tissue environment that is necessary for migration, proliferation and/or differentiation. We investigated the mechanism of germ cell deficiency in male Sl/Sld mice by producing aggregation chimaeras from Sl/Sld and +/ + embryos. Chimaeric mice with apparent white stripes were obtained. Two of four such chimaeras were fertile and the phenotypes of resulting progenies showed that some Sl/Sld germ cells had differentiated into functioning sperms in the testis of the chimaeras. In cross sections of the testes of chimaeras, both differentiated and nondifferentiated tubules were observed. However, the proportions of type A spermato-gonia to Sertoli cells in both types of tubules were comparable to the values observed in differentiated tubules of normal +/+ mice. We reconstructed the whole length of four tubules from serial sections. Differentiated and nondifferentiated segments alternated in a single tubule. The shortest differentiated segment contained about 180 Sertoli cells and the shortest nondifferentiated segment about 150 Sertoli cells. These results suggest that Sertoli cells of either Sl/Sld or +/ + genotype make discrete patches and that differentiation of type A spermatogonia does not occur in patches of Sl/Sld Sertoli cells.
Developmental patterning of carbohydrate antigens during early embryogenesis of the chick: expression of antigens of the poly-N-acetyllactosamine series
Authors: Thorpe Susan J. , Bellairs Ruth , Feizi Ten
Published: April 2021

This report describes a striking temporal and spatial patterning of specific carbohydrate sequences in the developing chick embryo. By using oligosaccharide sequence-specific monoclonal antibodies as immuno-histochemical reagents in conjunction with neuraminidase, it was possible to visualize the occurrence, as well as the changes in distribution, of oligosaccharides of the poly-N-acetyllactosamine series. These were (a) long-chain unbranched sequences reactive with anti-i Den, (b) long-chain branched sequences reactive with anti-I Step and (c) short-chain branched sequences reactive with anti-I Ma and (d) their sialylated forms. The salient observations with serial sections of embryos from the unincubated to the 17th stage were as follows.

A pronounced anteroposterior patterning appeared during neuroectodermal development, such that the long-chain unbranched and long-chain branched sequences, which were abundant on the ectoderm of the earlier stages, were replaced by shortchain branched sialo-oligosaccharides in the developing brain and anterior neural tube. A striking anteroposterior and mediolatera) patterning developed in the subectodermal extracellular spaces. The long-chain linear and short-chain non-sialylated sequences demarcated regions favourable for migration of the lateral plate mesoderm. A distinction was made between the dorsal and ventral routes of the trunk neural crest in that the extracellular matrix of the dorsal route only was associated with long-chain linear and short-chain sialylated branched sequences. A circumscribed perinotochordal distribution of the short-chain sialylated branched sequences was observed in the region of the future centra of the vertebrae. An abundance of long-chain linear and long-chain sialylated branched structures was detected in primordial germ cells which permitted their identification during migration.

These observations suggest that oligosaccharides of the poly-N-acetyllactosamine series may have roles as short-range, region-specific information factors during morphogenetic events that take place in the developing embryo, and they open the way to the search for recognition proteins (e.g. endogenous lectins) specific for each of these oligosaccharide structures.
The distribution of tenascin coincides with pathways of neural crest cell migration
Authors: Mackie E. J. , Tucker R. P. , Halfter W. , Chiquet-Ehrismann R. , Epperlein H. H.
Published: April 2021

The distribution of the extracellular matrix (ECM) glycoprotein, tenascin, has been compared with that of fibronectin in neural crest migration pathways of Xenopus laevis, quail and rat embryos. In all species studied, the distribution of tenascin, examined by immunohistochemistry, was more closely correlated with pathways of migration than that of fibronectin, which is known to be important for neural crest migration. In Xenopus laevis embryos, anti-tenascin stained the dorsal fin matrix and ECM along the ventral route of migration, but not the ECM found laterally between the ectoderm and somites where neural crest cells do not migrate. In quail embryos, the appearance of tenascin in neural crest pathways was well correlated with the anterior-to-posterior wave of migration. The distribution of tenascin within somites was compared with that of the neural crest marker, HNK-1, in quail embryos. In the dorsal halves of quail somites which contained migrating neural crest cells, the predominant tenascin staining was in the anterior halves of the somites, codistributed with the migrating cells. In rat embryos, tenascin was detectable in the somites only in the anterior halves. Tenascin was not detectable in the matrix of cultured quail neural crest cells, but was in the matrix surrounding somite and notochord cells in vitro. Neural crest cells cultured on a substratum of tenascin did not spread and were rounded. We propose that tenascin is an important factor controlling neural crest morphogenesis, perhaps by modifying the interaction of neural crest cells with fibronectin.
Embryonic vascular development: immunohistochemical identification of the origin and subsequent morphogenesis of the major vessel primordia in quail embryos
Authors: Coffin J. Douglas , Poole Thomas J.
Published: April 2021

The development of the embryonic vasculature is examined here using a monoclonal antibody, QH-1, capable of labelling the presumptive endothelial cells of Japanese quail embryos. Antibody labelling is first seen within the embryo proper at the 1-somite stage. Scattered labelling of single cells appears ventral to the somites and at the lateral edges of the anterior intestinal portal. The dorsal aorta soon forms a continuous cord at the ventrolateral edge of the somites and continues into the head to fuse with the ventral aorta forming the first aortic arch by the 6-somite stage. The rudiments of the endocardium fuse at the midline above the anterior intestinal portal by the 3-somite stage and the ventral aorta extends craniad. Intersomitic arteries begin to sprout off of the dorsal aorta at the 7-somite stage. The posterior cardinal vein forms from single cells which segregate from somatic mesoderm at the 7-somite stage to form a loose plexus which moves mediad and wraps around the developing Wolffian duct in later stages. These studies suggest two modes of origin of embryonic blood vessels. The dorsal aortae and cardinal veins apparently arise in situ by the local segregation of presumptive endothelial cells from the mesoderm. The intersomitic arteries, vertebral arteries and cephalic vasculature arise by sprouts from these early vessel rudiments. There also seems to be some cell migration in the morphogenesis of endocardium, ventral aorta and aortic arches. The extent of presumptive endothelial migration in these cases, however, needs to be clarified by microsurgical intervention.
Evidence for axonal ‘decision regions’ in the axolotl peripheral nervous system
Authors: Wilson Steve , Holder Nigel
Published: April 2021

Horseradish peroxidase (HRP) was employed to analyse the spatial organization of axons within nerves of the axolotl peripheral nervous system. HRP applications to the lateral motor column, spinal nerves and muscle nerve branches were examined after orthograde or retrograde transport. Axons change relative positions at particular limb regions, notably at the limb plexi, but also at branch points at other limb levels. Such areas of axon reorganization (termed ‘decision regions’ in line with Tosney & Landmesser (1985)J. Neurosci. 5, 2345) are interspersed by lengths of nerve in which axons run parallel to one another. A decision region is also described which involves only axons destined for axial musculature. The detailed anatomy of axon groups is discussed in terms of the likely mechanisms responsible for its formation during development. We conclude that, despite considerable variation in nerve pattern not seen in higher vertebrates, neuromuscular specificity in the axolotl limb is established largely by local pathway cues guiding axons to their appropriate targets.
In situ hybridization reveals differential spatial distribution of mRNAs for type I and type II collagen in the chick limb bud
Authors: Devlin C. J. , Brickell P. M. , Taylor E. R. , Hornbruch A. , Craig R. K. , Wolpert L.
Published: April 2021

During limb development, type I collagen disappears from the region where cartilage develops and synthesis of type II collagen, which is characteristic of cartilage, begins. In situ hybridization using antisense RNA probes was used to investigate the spatial localization of type I and type II collagen mRNAs. The distribution of the mRNA for type II collagen corresponded well with the pattern of type II collagen synthesis, suggesting control at the level of transcription and mRNA accumulation. In contrast, the pattern of mRNA for type I collagen remained more or less uniform and did not correspond with the synthesis of the protein, suggesting control primarily at the level of translation or of RNA processing.
Dietary components modulate yolk protein gene transcription in Drosophila melanogaster
Authors: Bownes Mary , Scott Ann , As Alan Shirr
Published: April 2021

The three yolk proteins of Drosophila melanogaster begin to be synthesized at eclosion. Transcription of the genes is regulated by the genes tra, tra-2 and dsx and also by the insect hormones, juvenile hormone and 20-hydroxyecdysone. We show that there is yet another level of control which is dependent upon feeding. Females that are starved from eclosion show a basal level of yolk protein gene transcription, which is rapidly increased when a complete diet is supplied. We show that the effect is not due to incorrect development of the fat body and is unlikely to be solely due to a general effect on protein synthesis. Later in development, cessation of feeding leads to selective inhibition of yolk protein synthesis and hence egg production.

The effects of starvation can be partially overcome by 20-hydroxyecdysone, juvenile hormone, casein, amino acid mix or sucrose, but only a complete medium or live yeast brings about total recovery. Using ypl-Adh fusions (fusions of the promoter region of ypl to the structural gene for Adh), the DNA sequence required for this diet-enhanced transcription has been located within an 890 bp fragment upstream of the ypl gene. The insect hormones do not operate on this same DNA fragment.
Nuclear and cytoplasmic localization of newly synthesized proteins in the early mouse embryo
Authors: Howlett S. K. , Barton S. C. , Norris M. L. , Surani M. A. H.
Published: April 2021

1-, 2- and 4-cell mouse embryos were labelled with [35S]methionine and the newly synthesized proteins from isolated nuclei were compared with those from cytoplasts and total embryos. There were distinct subsets of translation products present within nuclei compared to those that remained in the cytoplasm. There was no detectable evidence for differences in the presence of newly synthesized proteins in the male and female pronuclei. However, different new proteins associated with nuclei over the time that the embryonic genome becomes active.
Role of segment polarity genes in the definition and maintenance of cell states in the Drosophila embryo
Authors: Arias A. Martinez , Baker N. E. , Ingham P. W.
Published: April 2021

Segment polarity genes are expressed and required in restricted domains within each metameric unit of the Drosophila embryo. We have used the expression of two segment polarity genes engrailed (en) and wingless (wg) to monitor the effects of segment polarity mutants on the basic metameric pattern. Absence of patched (ptc) or naked (nkd) functions triggers a novel sequence of en and wg patterns. In addition, although wg and en are not expressed on the same cells absence of either one has effects on the expression of the other. These observations, together with an analysis of mutant phenotypes during development, lead us to suggest that positional information is encoded in cell states defined and maintained by the activity of segment polarity gene products.
Secretion of collagen types I and II by epithelial and endothelial cells in the developing chick cornea demonstrated byin situhybridization and immunohistochemistry
Authors: Hayashi Masando , Ninomiya Yoshifumi , Hayashi Kimiko , Linsenmayer Thomas F. , Olsen Bjorn R. , Trelstad Robert L.
Published: April 2021

Cells involved in the synthesis of collagen types I and II in the cornea of developing chick embryos have been studied by using in situ hybridization and immunohistochemistry. Corneas processed for in situ hybridization with the type I and II collagen probes demonstrated specific mRNAs in the epithelium of embryos at stage 18 with an increase at stages between 26 and 31, and then gradual decrease to the background level in the next several days. In the endothelium, a small amount of specific mRNA was recognized through these stages. In the stroma, only sections hybridized with the type I probe demonstrated mRNA in fibroblasts. Immunostaining demonstrated specific collagen types in the stroma at sites which were closely associated with cells containing specific mRNAs. Both collagens type I and II were present beneath the epithelium as narrow bands at stage 18; as the thicker primary stroma at stages 20 and 26; and as subepithelial, subendothelial and stromal staining at stage 31. Thereafter, type I collagen was increased in the stroma but it was also noted in the subepithelial and, to a lesser degree, subendothelial regions, whereas type II collagen was gradually confined to the subendothelial matrix. Electron microscopic examination of sections from 5-day-old (stage-27) embryo corneas using antibodies against the carboxyl propeptides of type I and II procollagens revealed the presence of these procollagens within the cisternae of the endoplasmic reticulum and Golgi vesicles in both epithelial and endothelial cells. In the epithelial cells both the periderm and basal cells contained these procollagens within the cytoplasmic organelles. These results indicate that not only the epithelial cells, but also the endothelial cells secrete collagen types I and II during the formation of the primary corneal stroma and for several days after invasion of fibroblasts.
Mechanisms of vertebrate segmentation
Authors: Keynes Roger J. , Stern Claudio D.
Published: April 2021

That all higher organisms possess some segmental organization during their development is presumably no coincidence. Segmentation appears to be an important developmental strategy with which to build and diversify different body regions. It can be studied at many levels, ranging from molecule and genome, through cells and their interactions, to morphogenesis and whole body pattern; and there is no compelling reason for thinking that the study of any one level will prove more revealing than that of any other. The study of vertebrate segmentation in fact provides a particularly good example of this philosophy. The application of classical and molecular genetic analysis to Drosophila development (reviewed by Akam, 1987) has yielded a large amount of information about the genes that play a role in the development of segmental patterns in this organism. Springing directly from this analysis comes the hope that similar methods applied to vertebrate development, exemplified by the discovery of the homeobox in the vertebrate genome, will be just as successful. But will the identification of vertebrate segmentation genes complete our understanding of the segmentation process? We believe not, and our chief purpose in this review is to identify and discuss the variety of different levels at which one can approach the major events involved.
Myoblast migration specifically inhibited in the chick embryo by grafted CSAT hybridoma cells secreting an anti-integrin antibody
Authors: Jaffredo T. , Horwitz A. F. , Buck C. A. , Rong P. M. , Dieterlen-Lievre F.
Published: April 2021

We report a teratological method in which mouse hybridoma cells are grafted into a chick host. CSAT (Cell Substratum ATtachment) hybridoma was used. It produces an antibody directed against the avian integrin complex. The grafts were performed during the second and third days of incubation either at the level of the somites or in the coelom of the chick embryo. The anomalies were revealed by means of a monoclonal antibody that recognizes myogenic cells as soon as they become committed in the myotome. When embryos were grafted at the level of the somites, body wall muscles failed to develop on the side of the graft only. After coelomic grafting, total agenesis of abdominal muscles was induced.

The anomalies were specific since the engraftment of three control hybridoma clones induced no change in muscle formation. These control hybridomas produce antibodies directed against the same molecular complex but not against the same epitope as CSAT.

The injection of hybridoma cells in an embryo appears as a method of general interest to determine the long-term consequences of perturbing a specific developmental process.
Pattern of the insulin-like growth factor II gene expression during rat embryogenesis
Authors: Stylianopoulou Fotini , Efstratiadis Argiris , Herbert Joseph , Pintar John
Published: April 2021

The rat insulin-like growth factor II (IGF-II) gene, encoding a fetal somatomedin, expresses a family of transcripts in embryonic/fetal tissues, and also in the adult choroid plexus and the leptomeninges. We have localized IGF-II gene transcripts in sections of rat embryos of embryonic days 10–16 by performing in situ hybridization. These transcripts are present in the head mesenchyme, formed from both the mesoderm and the cephalic portion of the neural crest, and also in the majority of other tissues of mesodermal origin, predominantly those derived from the somites and the lateral mesoderm. Intense labelling was detected in muscle cells, and their precursors, throughout the examined stages, whereas in chondrocytes the initial high level of hybridization declined substantially prior to ossification. IGF-II gene transcripts are also present in derivatives of other germ layers, but in restricted sites. Thus, from the derivatives of the endoderm, only the liver and the bronchial epithelium yielded hybridization signals. Ectoderm-derived tissues, including the central and peripheral nervous system, were negative for hybridization, with the exception of the choroid plexus, the newly forming pituitary rudiment and, to a lesser extent, the auditory placode. The pattern of IGF-II gene expression during embryogenesis overlaps significantly with the reported distribution of immunohistochemically detected TGF-β1. A paracrine/autocrine role for IGF-II in the developmental process is discussed.
Tissue- and stage-specific control of homeotic and segmentation gene expression in Drosophila embryos by the polyhomeotic gene
Authors: Dura Jean-Maurice , Ingham Philip
Published: April 2021

The distributions of the products of the homeotic genes Sex combs reduced (Scr) and Ultrabithorax (Ubx) and of the segmentation genes, fushi tarazu (ftz), even skipped (eve) and engrailed (en) have been monitored in polyhomeotic (ph) mutant embryos. None of the genes monitored show abnormal expression at the blastoderm stage in the absence of zygotic ph expression. Both Scr and Ubx are ectopically expressed in the epidermis of ph embryos, confirming the earlier proposal, based on genetic analysis, that ph+ acts as a negative regulator of Antennapedia (ANT-C) and bithorax (BX-C) complex genes.

At the shortened germ band stage, en is also ectopically expressed, mainly in the anterior region of each segment. In contrast to these effects in the epidermis, the expression of en, Ubx, Scr and ftz is largely or completely suppressed in the central nervous system, whereas eve becomes ectopically expressed in most neurones.
Cycling cytoplasmic factors that promote mitosis in the cultured 2-cell mouse embryo
Authors: Pratt H. P. M. , Muggleton-Harris A. L.
Published: April 2021

A cytoplasmic component(s), previously shown to rescue the ‘blocked’ 2-cell mouse embryo in vitro, has been demonstrated to peak in activity during the transition between G2 and M phase and decline thereafter. The possible significance of this component(s) in the regulation of cleavage of the cultured
Complete sequence andin vitroexpression of a tissue-specific phosphatidylinositol-linked N-CAM isoform from skeletal muscle
Authors: Barton C. Howard , Dickson George , Gower Hilary J. , Rowett Lewis H. , Putt Wendy , Elsom Vicki , Moore Stephen E. , Goridis Christo , Walsh Frank S.
Published: April 2021

Neural cell adhesion molecules (N-CAMs) are a family of cell surface sialoglycoproteins encoded by a single copy gene. A full-length cDNA clone that encodes a nontransmembrane phosphatidylinositol (PI) linked N-CAM of Mr125×103 has been isolated from a human skeletal muscle cDNA library. The deduced protein sequence encodes a polypeptide of 761 amino acids and is highly homologous to the N-CAM isoform in brain of Mr120×103. The size difference between the 125×103Mr. skeletal muscle form and the 120× 103Mr N-CAM form from brain is accounted for by the insertion of a block of 37 amino acids called MSD1, in the extracellular domain of the muscle form. Transient expression of the human cDNA in COS cells results in cell surface N-CAM expression via a putative covalent attachment to PI-containing phospholipid. Linked in vitro transcription and translation experiments followed by immunoprecipitation with anti-N-CAM antibodies demonstrate that the full-length clone of 761 amino acid coding potential produces a core polypeptide of Mr110×103 which is processed by microsomal membranes to yield a 122× 103Mr species. Taken together, these results demonstrate that the cloned cDNA sequence encodes a lipid-linked, PI-specific phospholipase C releasable surface isoform of N-CAM with core glycopeptide molecular weight corresponding to the authentic muscle 125×103Mr N-CAM isoform. This is the first direct correlation of cDNA and deduced protein sequence with a known PI-linked N-CAM isoform from skeletal muscle.
The developmental potential of parthenogenetically derived cells in chimeric mouse embryos: implications for action of imprinted genes
Authors: Clarke Hugh J. , Varmuza Susannah , Prideaux Valerie R. , Rossant Janet
Published: April 2021

Parthenogenetic embryos of mice die shortly after implantation and characteristically contain poorly developed extraembryonic tissue. To investigate the basis of the abnormal development of parthenotes, we combined them with normal embryos to produce chimeras and examined the distribution of the parthenogenetically derived cells during preimplantation and early postimplantation development. The parthenogenetic embryos were derived from a transgenic mouse line bearing a large insert, which allowed these cells to be identified in histological sections using in situ hybridization. At the blastocyst stage, the parthenogenetic embryos contributed cells to the trophectoderm (TE) and inner cell mass (ICM) of chimeras. By 6·5 days, however, in almost every embryo, parthenogenetically derived cells were not detected in the extraembryonic trophoblast tissue descended from the TE. In contrast, parthenogenetically derived cells could contribute to all descendants of the ICM of 6·5 and 7·5-day chimeras, including the extraembryonic visceral and parietal endoderm. Quantitative analysis of the degree of chimerism in the embryonic ectoderm at 6·5–7·5 days indicated that parthenogenetically derived cells could contribute as extensively as normal cells. These results indicate that normal trophoblast development requires gene expression from the paternally inherited genome before 6·5 days of embryogenesis. Tissues of the ICM lineage, however, apparently can develop independently of the paternal genome at least to 7·5 days of embryogenesis. Comparison of these results with those of others suggests that the influence of imprinted genes is manifested at different times and in a variety of tissues during development.
Isolation and characterization of novel mutants of Arabidopsis thaliana defective in flower development
Authors: Komaki Masako K. , Okada Kiyotaka , Nishino Eisho , Shimura Yoshiro
Published: April 2021

We have isolated a number of mutants of Arabidopsis thaliana, a member of the mustard family, that have defects in flower development and morphogenesis. Of these, five mutants have been extensively characterized. Two mutants (Fl-40, Fl-48) lacking petals show homeotic conversion of sepals to carpels. One mutant (Fl-54) displays highly variable phenotypes, including several types of homeotic variations, loss or distorted positions of the floral organs as well as abnormal structures on the inflorescence. Two other mutants (Fl-82, Fl-89) show aberrant structures in the pistils.

Genetic analyses have revealed that these mutations are single and recessive, except for one mutant whose mutational loci still remain to be determined. These mutants may prove useful for the analysis of the genetic control of flower development and morphogenesis in the higher plant.
Two DIF-inducible, prestalk-specific mRNAs of Dictyostelium encode extracellular matrix proteins of the slug
Authors: Mcrobbie Stuart J. , Jermyn Keith A. , Duffy Karen , Blight Kenneth , Williams Jeffrey G.
Published: April 2021

The migratory slug of Dictyostelium discoideum is surrounded by, and continuously synthesizes, an extracellular protein-cellulose matrix known as the slime sheath which is deposited on the substratum as a trail marking the slug’s progress. We show that the stalk-specific proteins, ST310 and ST430, are exclusively located in the slime sheath and trail and that fusion genes, containing upstream sequences from the cognate genes, direct correct mRNA accumulation during development and correct localization of the fusion protein.

Immunoelectron microscopy shows the ST310 and ST430 proteins to be present throughout the entire thickness of the slime sheath and almost totally absent from the cells of the slug. The genes that encode the ST310 and ST430 polypeptides are inducible by DIF, a stalk-specific inducing agent, and the mRNAs are highly enriched in prestalk over prespore cells. The production of these extracellular proteins by prestalk cells suggests that, in a manner somewhat analogous to that of extracellular matrix proteins of higher eukaryotes, the anterior region of the slug may be responsible for the continuous deposition of a track, along which the slug cells migrate. In the mature culminant, the ST310, and possibly the ST430, protein form part of the stalk tube and stalk cell wall. Therefore, the results also show that there are proteins common to both slime trail and stalk tube, indicating a possible precursor-product relationship between these chemically similar integuments.
A cell-type-specific abnormality of cell proliferation in mutant (curly tail) mouse embryos developing spinal neural tube defects
Authors: Copp Andrew J. , Brook Frances A. , Roberts Heather J.
Published: April 2021

The mouse mutant curly tail (ct) provides a model system for studies of neurulation mechanisms. 60 % of ct/ct embryos develop spinal neural tube defects (NTD) as a result of delayed neurulation at the posterior neuropore whereas the remaining 40 % of embryos develop normally. In order to investigate the role of cell proliferation during mouse neurulation, cell cycle parameters were studied in curly tail embryos developing spinal NTD and in their normally developing litter-mates. Measurements were made of mitotic index, median length of S-phase and percent reduction of labelling index during a [3H]thymidine pulse-chase experiment. These independent measures of cell proliferation rate indicate a reduced rate of proliferation of gut endoderm and notochord cells in the neuropore region of embryos developing spinal NTD compared with normally developing controls. The incidence of cell death and the relative frequency of mitotic spindle orientations does not differ consistently between normal and abnormal embryos. These results suggest a mechanism of spinal NTD pathogenesis in curly tail embryos based on failure of normal cell proliferation in gut endoderm and notochord.
Prevention of spinal neural tube defects in the mouse embryo by growth retardation during neurulation
Authors: Copp Andrew J. , Crolla John A. , Brook Frances A.
Published: April 2021

Homozygous mutant curly tail mouse embryos developing spinal neural tube defects (NTD) exhibit a celltype-specific abnormality of cell proliferation that affects the gut endoderm and notochord but not the neuroepithelium. We suggested that spinal NTD in these embryos may result from the imbalance of cell proliferation rates between affected and unaffected cell types. In order to test this hypothesis, curly tail embryos were subjected to influences that retard growth in vivo and in vitro. The expectation was that growth of unaffected rapidly growing cell types would be reduced to a greater extent than affected slowly growing cell types, thus counteracting the genetically determined imbalance of cell proliferation rates and leading to normalization of spinal neurulation.

Food deprivation of pregnant females for 48 h prior to the stage of posterior neuropore closure reduced the overall incidence of spinal NTD and almost completely prevented open spina bifida, the most severe form of spinal NTD in curly tail mice. Analysis of embryos earlier in gestation showed that growth retardation acts by reducing the incidence of delayed neuropore closure. Culture of embryos at 40-5°C for 15-23 h from day 1(1 of gestation, like food deprivation in vivo, also produced growth retardation and led to normalization of posterior neuropore closure. Labelling of embryos in vitro with [3H]thymidine for 1 h at the end of the culture period showed that the labelling index is reduced to a greater extent in the neuroepithelium than in other cell types in growth-retarded embryos compared with controls cultured at 38°C. Moreover, the incidence of cell death is increased in the neuroepithelium to a greater extent than in other cell types. These results are consistent with the hypothesis that spinal NTD in curly tail embryos result from a genetically determined growth imbalance between neuroepithelium and gut endoderm/notochord.
Divergent axon collaterals in the regenerating goldfish optic tract: a fluorescence double-label study
Authors: Becker David L. , Cook Jeremy E.
Published: April 2021

In the normal goldfish, optic axons are distributed between the two arms (brachia) of each optic tract, in such a way that each axon enters the tectum close to its retinotopic termination site. We have shown previously that regenerating axons at first express little or no preference for their normal brachium. Later, however, a partial refinement of the brachial pathway takes place, implying that some axons must have sent out divergent collateral branches and then eliminated the least appropriate.

We have now studied the formation and subsequent loss of axon collaterals in regeneration using retro–gradely transported fluorescent dyes. We labelled the axons in the medial brachium with Fast Blue and those in the lateral brachium with Diamidino Yellow in a way that avoided cross–contamination. In normal fish, yellow–labelled ganglion cells dominated the dorsal retina and blue–labelled ganglion cells the ventral, with only a narrow zone of overlap. Double–labelled cells were not found.

In fish labelled early in regeneration, however, both dyes were spread over the entire retina in single– and double–labelled ganglion cells. As regeneration progressed, each dye again came to dominate its appropriate retinal region; but much less strongly, confirming previous results. At the same time, doublelabelled cells became harder to find. From 60 days after nerve cut onwards they were rare, and largely confined to the boundary zone between dorsal and ventral retina. Their distribution was consistent with our previous proposal that excess collaterals may be eliminated competitively. Since axons from the boundary zone terminate in a tectal strip equidistant from the two brachia, neither route would confer any clear competitive advantage over the other.
Sea urchin morphogenesis and cell–hyalin adhesion are perturbed by a monoclonal antibody specific for hyalin
Authors: Adelson David L. , Humphreys Tom
Published: April 2021

We have generated and characterized a monoclonal antibody (McA Tg-HYL) that recognizes sea urchin hyalin as evidenced by immunofluorescence staining of the hyaline layer (HL) and immunoblot staining of the hyalin protein band. On immunoblots of HL extracts only the hyalin protein reacted with McA Tg-HYL. Immunoprecipitates of radioactive proteins from embryos incubated with [3SS]methionine yielded radioactive hyalin and 190, 140 and 105×103Mr proteins associated with hyalin. McA Tg-HYL was generated against Tripneustes gratilla embryos but reacts with hyalin from the distantly related sea urchin species, Colobocentrotus atratus, Strongylocentrotus purpuradas, Arbacia punctulate, Lytechinus variegatus and Lytechinus pictus. Developing embryos of the abovementioned six species were treated with McA Tg-HYL and did not gastrulate or form arms. Observations of treated embryos revealed areas of separation of the hyaline layer from the underlying embryonic cells, suggesting that McA Tg-HYL was interfering with binding of the cells to the HL. Using the centrifugation-based adhesion assay of McClay et al. (Proc, natn. Acad. Sci. U.S.A. 78, 4975-4979, 1981), Fab’ fragments of McA Tg-HYL were found to inhibit cell-hyalin binding. McA Tg-HYL did not inhibit hyalin gelation in vitro or the reaggregation of dissociated blastula cells. We postulate that McA Tg-HYL recognizes an evolutionarily conserved hyalin domain involved in cell-hyalin binding and required for normal epithelial folding.
Axolotl pronephric duct cell migration is sensitive to phosphatidylinositol-specific phospholipase C
Authors: Zackson Saul L. , Steinberg Malcolm S.
Published: April 2021

On the basis of its distribution pattern in embryos of the axolotl (Ambystoma mexicanum), we recently identified alkaline phosphatase as a molecule potentially involved in guiding the migration of the pronephric duct. Alkaline phosphatase is a cell surface protein anchored to cell membranes via a covalent linkage to a phosphatidylinositol glycan (PI-G).

The enzyme phosphatidylinositol-specific phospholipase C (PIPLC) specifically releases from cell surfaces molecules anchored by the PI-G linkage. In order to test the possibility that a PI-G anchored protein is involved in directing pronephric duct cell migration, PIPLC was applied to axolotl embryos. The enzyme was introduced into embryos through the use of a novel slow-release bead material, hydrolysed polyacrylamide. PIPLC blocked pronephric duct cell migration without interfering with somite fissure formation, a concurrent, neighbouring morphogenetic cell rearrangement which occurs with little if any alkaline phosphatase present. In addition, alkaline phosphatase activity was markedly diminished in the vicinity of the implanted beads. These observations suggest that at least one protein anchored to the cell membrane by a PI-G linkage, possibly alkaline phosphatase, is involved in guiding or promoting pronephric duct cell migration.
Postnatal development of parthenogenetic ↔fertilized mouse aggregation chimeras
Authors: Paldi A. , Nagy A. , Markkula M. , Barna I. , Dezso L.
Published: April 2021

Chimeras were made from parthenogenetic and fertilized cleavage-stage mouse embryos. The perinatal mortality was high. The parthenogenetic contributions to different tissues at birth ranged from 0 to 50%. No selection of parthenogenetic cells was observed in the pigmentation of the coat, but this does not exclude that such selection could act in other tissues. The weight of chimeras at birth negatively correlated to the average contribution of the parthenogenetic part. The growth rate of chimeras was lower than that of nonchimeric animals.

The data presented demonstrate that, although parthenogenetic cells are not cell lethals and they can participate to some degree in normal development of most tissues, their extensive presence reduces the viability of chimeras and retards the postnatal development.
Novel patterns of homeotic protein accumulation in the head of theDrosophilaembryo
Authors: Mahaffey J. W. , Diederich R. J. , Kaufman T. C.
Published: April 2021

Antibodies that specifically recognize proteins encoded by the homeotic genes: Sex combs reduced, Deformed, labial and proboscipedia, were used to follow the distribution of these gene products during embryogenesis. The position of engrailed-expressing cells was used as a reference and staining conditions were established that could distinguish, among cells expressing engrailed, one of the homeotic proteins or both. Our observations demonstrate two important facts about establishing identity in the head segments. First, in contrast to the overlapping pattern of homeotic gene expression in the trunk segments, we observe a non-overlapping pattern in the head for those homeotic proteins required during embryogenesis. In contrast, the spatial accumulation of the protein product of the non-vital proboscipedia locus overlaps partially with the distribution of the Deformed and Sex combs reduced proteins in the maxillary and labial segments, respectively. Second, two of the proteins, Sex combs reduced and Deformed, have different dorsal and ventral patterns of accumulation. Dorsally, these proteins are expressed in segmental domains while, within the ventral region, a parasegmental register is observed. The boundary where this change in pattern occurs coincides with the junction between the ventral neurogenic region and the dorsal epidermis. After contraction of the germ band, when the nerve cord has completely separated from the epidermis, the parasegmental pattern is observed only within the ventral nerve cord while a segmental register is maintained throughout the epidermis.
Neural enhancer-like elements as specific cell markers in Drosophila
Authors: Ghysen Alain , O’Kane Ahir
Published: April 2021

We have analysed four strains of Drosophila melanogaster which each carry the transposon P[lac,ry+] at a unique genomic location. In one of the strains, P[lac, ry+]A37, all the peripheral neurones that we can identify express the P-lac fusion protein; in at least some cases, all the support cells associated to particular neurones are also labelled. Expression of the fusion protein can be detected in subepidermal cells of the body segments as early as 4–5 h of development, according to a precise and reproducible pattern. On the basis of genetic evidence, we propose that these cells are precursors of sense organs, implying that the development of the peripheral nervous system overlaps in time with the development of the central nervous system. In the other three strains, the fusion product is expressed in unique subsets of cells of the peripheral nervous system, as well as in some other tissues.
Bimodal and graded expression of theXenopushomeobox geneXhox3during embryonic development
Authors: Altaba A. Ruiz I , Melton D. A.
Published: April 2021

A Xenopus laevis homeobox gene, Xhox3, has been isolated using the homeobox of the Drosophila pair-rule gene even skipped as a hybridization probe. Xhox3 is first transcribed at the midblastula transition; RNA levels peak at the early neurula stage and decrease thereafter. During the early period of Xhox3 expression, the gastrula and neurula stages, transcripts are found in a graded fashion along the anteroposterior (A-P) axis in the mesoderm and are most concentrated at the posterior pole. In the late period of expression, the tailbud and tadpole stage, transcripts are concentrated at the two ends of the embryo: in the anterior nervous system and posterior tail bud. Analysis of Xhox3 expression in experimentally perturbed embryos shows that different A-P fates in the mesoderm are correlated with different levels of Xhox3 expression. Based on these results and those with other frog homeobox genes, we propose a role for homeobox genes in the patterning of the A-P embryonic axis.
The promoter region of theDrosophila α2-tubulin gene directs testicular and neural specific expression
Authors: Bo Jieying , Wensink Pieter C.
Published: April 2021

The temporal and spatial expression pattern of the Drosophila melanogaster α2-tubulin gene (α2) has been investigated by examining the expression of an α2-lacZ fusion gene. When this fusion gene is introduced into the germ line by P-element mediated transformation, expression is only detected in chordotonal organs and testes. Chordotonal organs, which are sensory organs of the peripheral nervous system, express the gene from late embryonic through adult stages in both males and females. Testicular expression occurs from larval through adult stages and is limited to germ-line cells, the primary and secondary spermatocytes and perhaps the early spermatids.
Developmental patterning of the carbohydrate antigen FC10.2 during early embryogenesis in the chick
Authors: Loveless Wendy , Bellairs Ruth , Thorpe Susan J. , Page Mark , Feizi Ten
Published: April 2021

An oligosaccharide antigen (FC10.2), formerly described only in mammalian cells and secreted glycoproteins, has been detected and found to display striking temporal and spatial patterning in the chick during early embryonic development. This antigen is expressed on type 1 chains, which are isomers of oligosaccharides of the poly-iV-acetyllactosamine series (type 2 chains). Immunoreactivities before and after neuraminidase treatment of serial sections of chick embryos during the first 17 stages of development indicate that the FC10.2 structure occurs predominantly in the sialylated form (S-FC10.2). The FC10.2 and S-FC10.2 antigens are prominent markers of the primordial germ cells, being strongly expressed by these cells from the pre-primitive streak stage onwards. S-FC10.2 is also a clear marker of the pronephric duct from its first appearance. Initially present over the entire apical surface of the ectoderm, antigenicity diminishes in an antero-posterior direction as neurulation proceeds. A unique pattern for a carbo hydrate antigen is displayed by cells of the primitive streak; antigenicity is lost with de-epithelialisation and ingression, but is regained in a pericellular distribution on the mesoderm cells that emerge from the primitive streak. Thereafter, successive changes in expression and distribution of FC10.2 and S-FC10.2 are features of mesodermal tissues, particularly during somitogenesis. These antigens are prominent components of the extracellular matrix around the notochord and sclerotome cells. They are also prominent posteriorly in the subecto-dermal region, ceasing abruptly at the lateral limits of the embryo proper. Although no absolute correlations can yet be made, several features of the distribution of these antigens suggest that they may be integral components of, or ligands for, cell adhesion molecules.
XY follicle cells in the ovaries of XO/XY and XO/XY/XYY mosaic mice
Authors: Palmer Stephen J. , Burgoyne Paul S.
Published: April 2021

XO/XY and XO/XY/XYY mosaic hermaphrodites were generated from crosses involving BALB/cWt males. The distribution of Y-bearing cells in the gonads of these mice was studied by in situ hybridisation using the Y-specific probe pY353B. XY cells were found to contribute to all cell lineages of the ovary including follicle cells. The proportion of XY follicle cells was not significantly different from the XY contribution to other gonadal or non-gonadal cell lineages. However, this proportion was consistently low, all the hermaphrodites having a low XY contribution to the animal as a whole.

Because the XO- and Y-bearing cell lineages are developmentally balanced, the XY follicle cells cannot have formed as a result of a ‘mismatch’ in which the Y-directed testis determination process is pre-empted by an early acting programme of ovarian development. These results are discussed with respect to the hypothesis that Tdy acts in the supporting cell lineage, the lineage from which Sertoli cells and follicle cells are believed to be derived.
Plasma membrane localization of the Toll protein in the syncytial Drosophila embryo: importance of transmembrane signaling for dorsal–ventral pattern formation
Authors: Hashimoto Carl , Gerttula Suzanne , Anderson Kathryn V.
Published: April 2021

Formation of the Drosophila embryo’s dorsal-ventral pattern requires the maternal product of the Toll gene. DNA sequence and genetic analyses together suggested that the Toll gene product is a transmembrane protein which communicates information from an extracyto-plasmic compartment to the cytoplasm. Using antibodies as probes, we show that the Toll protein is a 135 ×103Mr glycoprotein which is tightly associated with embryonic membranes. During the syncytial stage when dorsalventral polarity is established, the maternal Toll protein is associated with the plasma membrane around the entire embryo. During later embryonic stages, the Toll protein is expressed zygotically on many cell surfaces, possibly to promote cell adhesion. The plasma membrane localization of the Toll protein in the syncytial embryo suggests that transmembrane signaling from the extracellular perivitelline space to the cytoplasm is required for establishment of the embryonic dorsal-ventral pattern.