bluuebunny/crossref_metadata_2025 huggingface dataset:
Pax8, a murine paired box gene expressed in the developing excretory system and thyroid gland
Authors: Plachov Dimitrij , Chowdhury Kamal , Walther Claudia , Simon Dominique , Guenet Jean-Louis , Gruss Peter
Published: April 2021

Several mouse genes designated ‘Pax genes’ contain a highly conserved DNA sequence homologous to the paired box of Drosophila. Here we describe the isolation of Pax8, a novel paired box containing clone from an 8.5 day p.c. mouse embryo cDNA library. An open reading frame of 457 amino acids (aa) contains the 128 aa paired domain near the amino terminus. Another conserved region present in some other paired box genes, the octapeptide Tyr-Ser-Ile-Asn-Gly-Leu-Leu-Gly, is located 43 aa C-terminal to the paired domain. Using an interspecies backcross system, we have mapped the Pax8 gene within the proximal portion of mouse chromosome 2 in a close linkage to the surf locus. Several developmental mutations are located in this region. In situ hybridization was used to determine the pattern of Pax8 expression during mouse embryogenesis. Pax8 is expressed transiently between 11.5 and 12.5 days of gestation along the rostrocaudal axis extending from the myelencephalon throughout the length of the neural tube, predominantly in two parallel regions on either side of the basal plate. We also detected Pax8 expression in the developing thyroid gland beginning at 10.5 days of gestation, during the thyroid evagination. In the mesonephros and metanephros the expression of Pax8 was localized to the mesenchymal condensations, which are induced by the nephric duct and ureter, respectively. These condensations develop to functional units, the nephrons, of the kidney. These data are consistent with a role for Pax8 in the induction of kidney epithelium. The embryonic expression pattern of Pax8 is compared with that of Pax2, another recently described paired box gene expressed in the developing excretory system.
A new homeobox-containing gene, msh-2, is transiently expressed early during mesoderm formation of Drosophila
Authors: Bodmer Rolf , Jan Lily Y. , Jan Yuh Nung
Published: April 2021

Many homeobox-containing genes of Drosophila regulate pathways of differentiation. These proteins probably function as promoter- or enhancer-selective transcription factors. We have isolated a new homeobox-containing gene, msh-2, by means of the polymerase chain reactions (PCR) using redundant primers, msh-2 is specifically expressed in mesodermal primordia during a short time period early in development. It first appears at blastoderm stage just before the ventral invagination of the mesoderm and shortly after twist, a gene required for mesoderm formation, is expressed. During germband elongation all the mesodermal cells in the segmented part of the embryo express msh-2, but soon afterwards msh-2 becomes restricted to the dorsal mesoderm, which includes the primordia for the visceral musculature and the heart. Prior to muscle differentiation, msh-2 expression ceases, except for two rows of cells that will be included in the dorsal vessel. Embryos that are deficient for the chromosomal region, 93C-F, which includes the msh-2 gene, show normal mesoderm invagination and dorsal spreading. However, later in development no visceral muscle and dorsal vessel differentiation can be detected, but some skeletal muscles do form, albeit abnormally, msh-2 expression, except for a patch in the head, is dependent on twist function. On the other hand, snail, another mesoderm determinant, does not appear to be required for msh-2 initiation, but is necessary for the maintenance of msh-2 expression after germband elongation. H2.0, a homeobox-containing gene specifically expressed in visceral mesoderm, is not transcribed in the mesoderm in 93C-F deficiency embryos. These results suggest that msh-2 may have a regulatory function in myogenesis and may be required for visceral mesoderm differentiation, msh-2 may act immediately after or downstream of twist.
Cellular migration patterns in the developing mouse cerebral cortex
Authors: Austin Christopher P. , Cepko Constance L.
Published: April 2021

The migration patterns of embryonic mouse cortical cells were investigated using a replication-incompetent retrovirus vector (BAG). The lateral ventricles of embryonic day 12 mouse embryos were infected with BAG and brains were harvested 2, 3, 4 and 6 days after infection. The location and morphology of all infected cortical cells were recorded from serial sections of entire brains, which were then reconstructed in three dimensions. Examination of the distribution of labelled cells revealed that there were migration patterns characteristic of each medial-lateral domain of the cortex. In the medial and dorsal areas, migration was often radial, although tangential spread increased with survival time, in large part due to ramification of cells in the intermediate zone. In the dorsolateral and lateral areas of the cortex, radial migration was generally not observed. Rather, variable extents of tangential migration occurred, and often resulted in wide separation of cells in the cortical plate. Almost all of the cellular dispersion occurred in the intermediate zone, although a modest degree of dispersion also occurred within the cortical plate itself. Most dispersion occurred in the mediolateral plane, with relatively little dispersion along the anteroposterior axis. Though characteristic migration patterns could be defined, wide variability in the extents of radial migration and tangential separation of cells was seen. The patterns of migration paralleled the distribution of radial glial fibers in all areas, and are most likely a reflection of the role of this network in supporting the migration of cortical neurons. The extent and variability of cellular dispersion supports a lineageindependent mechanism of cortical column ontogenesis.
Masculinizing effect of testes on developing rat ovaries in organ culture
Authors: Charpentier Gilles , Magre Solange
Published: April 2021

Masculinizing effect of testes on developing rat ovaries was shown in vitro by culturing testes from 17.5-day-old fetuses in contact with female genital tracts from 14.5-day-old rat fetuses. The testes induced the differentiation of epithelial cells staining for cytokeratin in the ovarian blastema. These cells formed seminiferous cordlike structures delineated by a basement membrane, in a way that resembles early stages of testicular organogenesis. In addition to the morphological masculinization, functional masculinization was obtained since the ovaries produced the anti-Miillerian hormone as shown by bioassay and immunohistochemical procedures. Across a distance, testes from 17.5-day-old fetuses failed to induce masculinization. These results suggest that testes from 17.5-day-old fetuses produce a locally diffusible factor interfering with the development and the differentiation of the fetal ovaries. The possibility that the anti-Müllerian hormone secreted by the testes may be the factor involved is discussed comparing these results with those obtained with testes from different stages and with bibliographic data.
Expression of the N-myc proto-oncogene during the early development of Xenopus laevis
Authors: Vize Peter D. , Vaughan Ashley , Krieg Paul
Published: April 2021

The N-myc proto-oncogene is expressed in a wide range of tissues during mammalian embryogenesis. This observation, along with the oncogenic capacity of this gene, has led to the suggestion that N-myc plays an important role in early development. However, due to the complexity of the expression pattern and the difficulty of manipulating mammalian embryos, little progress has been made towards understanding the developmental function of this gene. To enable a more detailed analysis of the role of this gene in early development, a study of the Xenopus homologue of N-myc was undertaken. Xenopus N-myc cDNA clones were isolated from a neurula library using a murine N-myc probe. Analysis of the timing of expression of N-myc mRNA and of the distribution of N-myc protein during Xenopus development indicate that this gene may be playing an important role in the formation of a number of embryonic structures, including the nervous system. N-myc is initially expressed as a maternal RNA, but this mRNA is degraded by the gastrula stage of development. Zygotic expression does not commence until late neurula. Examination of the distribution of the N-myc protein by whole-mount immunohistochemistry indicates that the early embryonic expression occurs in the central nervous system, the neural crest, the somites and the epidermis. Later expression is mostly within the head and somites. Specific structures within the head that express the protein include the eye, otic vesicle, fore and hindbrain and a number of cranial nerves. The results demonstrate that while N-myc is expressed in the developing nervous system of Xenopus, the timing of expression indicates that it is unlikely to be involved in regulation of the very first stages of neurogenesis.
Proneural clusters: equivalence groups in the epithelium of Drosophila
Authors: Simpson Pat , Carteret Cathie
Published: April 2021

The segregation of neural precursors from epidermal cells during development of the nervous system of Drosophila relies on interactions between cells that are thought to be initially equivalent. During development of the adult peripheral nervous system, failure of the cellular interactions leads to the differentiation of a tuft of sensory bristles at the site where usually only one develops. It is thus thought that a group of cells at that site (a proneural cluster) has the potential to make a bristle but that in normal development only one cell will do so. The question addressed here is do these cells constitute an equivalence group (Kimble, J., Sulston, J. and White, J. (1979). In Cell Lineage, Stem Cells and Cell Determination (ed. N. Le Douarin). Inserm Symposium No. 10 pp. 59–68, Elsevier, Amsterdam)? Within clusters mutant for shaggy, where several cells of a cluster follow the neural fate and differentiate bristles, it is shown that these display identical neuronal specificity: stimulation of the bristles evoke the same leg cleaning response and backfilling of single neurons reveal similar axonal projections in the central nervous system. This provides direct experimental evidence that the cells of a proneural cluster are developmentally equivalent.
The development of handed asymmetry in aggregation chimeras of situs inversus mutant and wild-type mouse embryo
Authors: Brown Nigel A. , Mccarthy Afshan , Wolpert Lewis
Published: April 2021

Mutant iv/iv mice develop as if they have no sense of left and right, so the development of asymmetry is random: half normal, half as a mirror-image of normal, situs inversus. We have made aggregation chimeras of 8-cell stage iv/iv and +/+ embryos, transferred them into pseudopregnant mice, and examined their phenotype on day 10 of gestation. The contribution of mutant and wild-type cells to tissues of the embryo was estimated by strain-specific isozyme (GPI-1) analysis. We have also performed reciprocal embryo transfers, iv/iv blastocysts into +/+ mice, and vice versa. These transfers show that the development of handed asymmetry is determined by embryonic genotype, and is unaffected by the maternal environment (at least after day 3), or by the procedures of embryo collection, culture and transfer. Our observations on the development of 21 viable chimeric embryos show that neither iv/iv nor +/+ cells are dominant. All embryos (12) with less than 50 % contribution of iv/iv cells to the heart developed with normal situs. Of 9 embryos with greater than 50 % iv/iv cells, only 2 developed with inverted situs. These findings suggests that there was partial ‘rescue’ of embryos by some influence of normal over mutant cells. However, we cannot, statistically, exclude an alternative interpretation that cells are behaving autonomously. Interestingly, the embryos that developed with inverted situs were unique in having greater than two thirds contribution of iv/iv cells to both the heart and the visceral yolk-sac.
Division and differentiation during normal and liguleless-1 maize leaf development
Authors: Sylvester Anne W. , Cande W. Zacheus , Freeling Michael
Published: April 2021

The maize leaf is composed of a blade and a sheath, which are separated at the ligular region by a ligule and an auricle. Mutants homozygous for the recessive liguleless-1 (lgl) allele exhibit loss of normal ligule and auricle. The cellular events associated with development of these structures in both normal and liguleless plants are investigated with respect to the timing of cell division and differentiation. A new method is used to assess orientation of anticlinal division planes during development and to determine a division index based on recent epidermal cross-wall deposition. A normal leaf follows three stages of development: first is a preligule stage, in which the primordium is undifferentiated and dividing throughout its length. This stage ends when a row of cells in the preligule region divides more rapidly in both transverse and longitudinal anticlinal planes. During the second stage, ligule and auricle form, blade grows more rapidly than sheath, divisions in the blade become exclusively transverse in orientation, and differentiation begins. The third stage is marked by rapid increase in sheath length. The leaf does not have a distinct basal meristem. Instead, cell divisions are gradually restricted to the base of the leaf with localized sites of increased division at the preligule region. Divisions are not localized to the base of the sheath until near the end of development. The liguleless-1 homozygote shows no altération in this overall pattern of growth, but does show distinct alteration in the anticlinal division pattern in the preligule region. Two abnormal patterns are observed: either the increase in division rate at the preligule site is absent or it exhibits loss of all longitudinal divisions so that only transverse (or cell-file producing) divisions are present. This pattern is particularly apparent in developing adult leaves on older Igl plants, in which sporadic ligule vestiges form. From these and results previously published (Becraft et al. (1990)Devl Biol. 14), we conclude that the information carried by the Lgl+ gene product acts earlier in development than formation of the ligule proper. We hypothesize that Lgl+ may be effective at the stage when the blade-sheath boundary is first determined.
The distribution of plasmodesmata and its relationship to morphogenesis in fern gametophytes
Authors: Tilney Lewis G. , Cooke Todd J. , Connelly Patricia S. , Tilney Mary S.
Published: April 2021

Fern (Onoclea sensibilis) gametophytes when grown in the dark form a linear file of cells (one-dimensional) called a protonema. In the light two-dimensional growth occurs which results in a heart-shaped prothallus one cell thick. The objective of this paper is to relate the most common pattern of cell division observed in developing gametophytes to the formation of the plasmodesmatal network. Since the prothalli are only two dimensional, we can easily determine from thin sections the total number and the density (number per unit surface area) of plasmodesmata at each developmental stage. As the prothallus grows the number of plasmodesmata increases 50-fold in the apical or meristematic cell. This number eventually reaches a plateau even though the density continues to increase with each new cell division. What is particularly striking is that both the number and density of plasmodesmata between adjacent cells is precisely determined. Furthermore, the pattern of plasmodesmata distribution is predictable so that (1) we can identify the apical meristematic cells by their plasmodesmata number, or density, as well as by their size, shape and location, (2) we can predict, again from plasmodesmata number, the location of a future wall of the apical cell prior to its actual formation, (3) we can show that the density of plasmodesmata in the triangular apical cell of the prothallus (14 plasmodesmata μm-2) is comparable to those reported for secretory glands which are known to have high rates of plasmodesmatal transport and (4) we can show that once the plasmodesmata have been formed during division, no subsequent change in the number of plasmodesmata occurs following cell plate formation.
An in situ assessment of the routes and extents of colonisation of the mouse embryo by embryonic stem cells and their descendants
Authors: Lallemand Yvan , Brûlet Philippe
Published: April 2021

An embryonic stem (ES) cell line stably expressing lacZ under the control of an endogenous promoter has been isolated and used as a marker to follow the fate of ES cells injected into blastocysts and morulae, before midgestation. The results show a multisite pattern of blastocyst colonization by ES cells deposited into the blastocoel cavity and a low degree of mingling between ES cells and ICM cells. Furthermore, analysis of dispersal of ES cell descendants in postimplantation chimaeric embryos showed that colonization can be highly variable from one region of the embryo to another. In contrast, a high and reproducible degree of chimaerism was obtained when the ES cells were injected at the morula stage prior to ICM formation.
Blocking cell division does not remove the requirement for Polycomb function in Drosophila embryogenesis
Authors: Gould Alex P. , Lai Robert Y. K. , Green Michael J. , White Robert A. H.
Published: April 2021

The Polycomb (Pc) gene is required from the extended germ band stage onwards, to maintain spatially restricted patterns of homeotic gene expression. It has been thought to be involved in the ‘stable inheritance of the determined state’. In this paper, we have tested the notion that the Pc gene is required specifically during or after DNA replication to enable the stable transmission of states of gene activity. We found that arresting cell division using the string mutation or blocking DNA replication with aphidicolin failed to prevent ectopic expression of the homeotic gene Ultrabithorax in Pc mutants. Thus, even in the absence of DNA replication, Pc is required to maintain spatially restricted patterns of homeotic gene expression. The role of the Pc gene product in the stable repression of homeotic gene transcription is discussed.
Neonatal seminal vesicle mesenchyme induces a new morphological and functional phenotype in the epithelia of adult ureter and ductus deferens
Authors: Cunha Gerald R. , Young Peter , Higgins Stephen J. , Cooke Paul S.
Published: April 2021

Mesenchyme from neonatal mouse and rat seminal vesicles (SVM) was grown in association with postnatal (adult) epithelial cells from the ureter (URE) and ductus deferens (DDE) in chimeric tissue recombinants composed of mouse mesenchyme and rat epithelium or vice versa. Functional cytodifferentiation was examined in these SVM+URE and SVM+DDE tissue recombinants with antibodies against major androgen-dependent seminal-vesicle-specific secretory proteins. Adult DDE and URE were induced to express seminal cytodifferentiation and produced the complete spectrum of major seminal vesicle secretory (SVS) proteins. The SVS proteins produced were specific for the species that provided the epithelium. In the case of SVM+URE recombinants, the URE, which normally lacks androgen receptors (AR), expressed AR. These results demon strate that adult epithelial cells retain a developmental plasticity equivalent to their undifferentiated fetal counterparts and are capable of being reprogrammed to express a completely new morphological, biochemical and functional phenotype.
Microsurgically generated discontinuities provoke heritable changes in cellular handedness of a ciliate, Stylonychia mytilus
Authors: Shi Xinbai , Lu Li , Qiu Zijian , He Wei , Frankel Joseph
Published: April 2021

Stylonychia mytilus is a dorsoventrally flattened ciliate with compound ciliary structures arranged in a specific manner on the cell surface. In Mirror-image (MI) doublets of this ciliate, two nearly complete sets of ciliary structures are arrayed side-by-side, one in a normal or ‘right-handed’ (RH) arrangement, the other in a reversed or ‘left-handed’ (LH) arrangement. MI-doublets exist in two forms, one with the RH component on the right, the LH component on the left, and feeding structures near the center (‘buccal-adjoining MI-doublet’); the other with the RH component on the left, the LH component on the right, and feeding structures on the lateral edges (‘buccal-opposing MI-doublet’).

We describe an operation that can generate either type of MI-doublet. This operation interchanges large anterior and posterior regions of the cell, transposing the original posterior region anteriorly (P→A) and the original anterior region posteriorly (A—*P), while retaining the original anteroposterior polarity of each region. Two sets of new ciliary structures then are formed in Mirror-image arrangement, with the set in the P→A region oriented normally and the set in the A→P region undergoing a reversal of polarity along its anteroposterior axis. This sometimes creates end-to-end MI forms, but more commonly produces side-by-side MI-doublets through a folding together of the P→A and A→P regions. This folding occurs because one lateral edge of the cell had been removed during the operation; if the left edge was removed, the complex folds to the left and forms a buccal-adjoining MI-doublet, whereas if the right edge was removed, the complex folds to the right and forms a buccal-opposing MI-doublet. Both types can reorganize and later divide true-to-type, although the ‘buccal-opposing’ type is by far the more stable of the two.

The generation of Mirror-image forms is dependent on the prior abnormal juxtaposition of regions from opposite ends of the cell, and involves a coordinated respecification of large-scale organization. We interpret this response to be a consequence of intercalation of Missing intervening positional values in the zone of posterior–anterior abutment.
Expression of v-src induces aberrant development and twinning in chimaeric mice
Authors: Boulter Catherine A. , Aguzzi Adriano , Williams R. Lindsay , Wagner Erwin F. , Evans Martin J. , Beddington Rosa
Published: April 2021

The role of the proto-oncogene c-src in mouse development has been investigated by studying the consequences of expressing its viral homologue, v-src. Embryonic stem (ES) cell lines with differing levels of v-src tyrosine kinase activity have been used to generate chimaeric mice. Whereas a low level of v-src expression is compatible with embryogenesis, chimaeras derived from ES clones with high levels of v-src activity develop abnormally and die on the 8th–9th day of gestation. These abnormalities are characterized by the formation of twin or multiple embryos within the same Reichert’s membrane, and by the arrest of embryonic development at the late egg cylinder stage, accompanied by relative expansion of the visceral yolk sac (VYS) and hyperplasia of the VYS endoderm. These results demonstrate for the first time that deregulated expression of the src protooncogene product can induce developmental abnormalities during early embryogenesis.
Control of the expression of the bithorax complex genes abdominal-A and Abdominal-B by c/s-regulatory regions in Drosophila embryos
Authors: Sánchez-Herrero Ernesto
Published: April 2021

The abdominal-A (abd-A) and Abdominal-B (Abd-B) genes of the bithorax complex (BX-C) specify the identity of most of the Drosophila abdomen. Six different classes of infraabdominal (iab) mutations within the BX-C transform a subset of the parasegments affected by the lack of these two genes. It is thought that these mutations defíne parasegmental cw-regulatory regions that control the expression of abd-A and Abd-B. By staining embryos mutant for different iab mutations with anti-aiJ-A and anti-Abd-B antibodies I show here that the expression of Abd-B (and probably also abd-A) exhibit a parasegmental regulation. I have also studied the significance of the chromosomal order of parasegmental iab regulatory sequences, and the possible presence of chromosomal ‘boundaries’ between them, by looking at the expression of abd-A and Abd-B in embryos carrying the Uab1 and Mcp mutations. These data are discussed in the light of models of parasegmental-specific regulatory regions within the BX-C.
Single cell analysis of mesoderm formation in the Xenopus embryo
Authors: Godsave S. F. , Slack J. M. W.
Published: April 2021

We have examined the developmental specification of individual cells in the Xenopus blastula using a new in vitro culture system. Regional differences are apparent at the mid-blastula stage when animal hemisphere cells form only ectodermal cell types, while many clones from below the pigment boundary contain mesodermal cell types. A number of clones give rise to more than one differentiated cell type indicating that the initial steps of mesoderm induction are potentially reversible.

Animal hemisphere cells can be induced to form mesoderm by fibroblast growth factor (FGF). Different cell types predominate at different FGF concentrations and the neighbours in this sequence are also the pairs of cell types most usually associated in mixed clones derived from the marginal zone. We propose that the specification of individual cells depends upon both the concentration of inducing factor and on stochastic intracellular events.
Cephalic expression and molecular characterization of Xenopus En-2
Authors: Hemmati-Brivanlou Ali , Torre Jose R. de la , Holt Christine , Harland Richard M.
Published: April 2021

We have isolated and characterized cDNAs corresponding to the Xenopus En-2 gene. Comparison of amino acid sequences between the entire Xenopus En-2 and the Drosophila engrailed proteins confirms conservation of sequences inside as well as proximal to the homeobox and reveals a region of similarity towards the N terminus. Two transcripts encode the Xenopus En-2 protein. Both transcripts are regulated temporally in an identical fashion and are likely to be transcribed from two copies of the En-2 gene.

We have also analyzed the distribution of the protein in the head tissue and in the dissected brain of tailbud stage embryos. In addition to the main band of expression at the midbrain–hindbrain boundary, we show that the protein is expressed in three novel areas: the mandibular arch, the optic tectum and the region of anterior pituitary.
The mRNAs encoding acidic FGF, basic FGF and FGF receptor are coordinately downregulated during myogenic differentiation
Authors: Moore James W. , Dionne Craig , Jaye Michael , Swain Judith L.
Published: April 2021

Acidic and basic fibroblast growth factors (FGFs) are members of a family of proteins that exert pleiotropic effects in a range of cell types including skeletal myocytes. Previous studies demonstrate that exogenously supplied FGFs stimulate proliferation of myoblasts and inhibit their differentiation in culture, but little information is available concerning endogenous expression of FGFs by skeletal myocytes. In this study acidic and basic FGF mRNAs were found to be expressed in murine and rat skeletal muscle, and expression was demonstrated to vary with the tissue and species examined. Myogenic cell lines were then analyzed to determine if FGFs are expressed in myoblasts, and if so, whether expression is regulated during myogenic differentiation. Murine Sol 8 and rat L6 myoblasts were found to express acidic and basic FGF mRNAs, and the expression of both growth factors was downregulated at the transcriptional level during myogenic differentiation. A decrease in expression of the mouse homologue of the human FGF receptor paralleled the decrease in acidic and basic FGF mRNAs in Sol 8 cells, indicating that the decrease in FGF receptor abundance previously observed during myogenic differentiation is regulated at the mRNA level. The results of this study suggest that a coordinate decrease in endogenously produced acidic and basic FGFs and their cognate receptor may participate in the regulation of myogenic differentiation. Furthermore, the observation that expression of a myogenic determination gene, myogenin, increases as FGF transcripts decline, together with previous data demonstrating suppression of myogenin expression by FGF, suggest a mechanism whereby endogenously produced FGFs may exert their effect on differentiation.
Isolation and embryonic expression of an abdominal-A-like gene from the lepidopteran, Manduca sexta
Authors: Nagy Lisa M. , Booker Ronald , Riddiford Lynn M.
Published: April 2021

Using sequence homology to the Drosophila Antenna-pedia gene, we isolated a homeobox-containing gene from the lepidopteran, Manduca sexta. Sequence analysis and in situ hybridizations to tissue sections suggest that the Manduca gene encodes a lepidopteran homologue of the Drosophila Bithorax complex gene abdominal-A. The predicted amino acid sequence of a 76 amino acid region that includes the homeobox and the regions immediately flanking it are identical between the Manduca and Drosophila genes. Northern blots reveal that the Manduca abd-A gene is expressed first in the early embryo and continues to be expressed throughout later embryonic and larval stages. In situ hybridizations show that the posterior half of the first abdominal segment marks the anterior border of the Manduca abdA expression. This expression pattern demonstrates the conservation of parasegments as domains of gene activity in the lepidopteran embryo. The Manduca abd-A expression extends from the posterior half of the first abdominal segment through the tenth abdominal segment, a domain that is greater than that of the Drosophila abd-A expression, and reflects the difference in visible segment number between the two insects.
Cyclic changes in amphibian egg microvilli occur during the division cycle: implication of MPF
Authors: Aimar C.
Published: April 2021

The microvilli (MV) of Pleurodeles (amphibian) eggs were examined following fertilization and compared with those of artificially activated eggs and enucleated eggs using scanning and transmission electron microscopy. The MV pattern in fertilized eggs was found to undergo a cyclic transformation during the course of the first few division cycles. Similar changes also occurred in the MV of artificially activated eggs and enucleated eggs. The reorganization of the MV was sensitive to cycloheximide and cytochalasin B, but was unaffected by colchicine. Thus, this MV alteration requires protein synthesis and microfilaments but microtubules are not implicated in this process. In addition, the effects on the MV pattern of the maturation or mitosis promoting factor (MPF) were tested. Injection of MPF into eggs at different times during the first division cycle nearly always induced an elongation of the MV. This observation suggests that MPF could regulate either directly or indirectly, via a MPF-sensitive factor, the cyclic transformation of amphibian egg MV.
Developmental profile of glucose phosphate isomerase allozymes in parthenogenetic and tetrapioid mouse embryos
Authors: Petzoldt Ulrich
Published: April 2021

Glucose phosphate isomerase (GPI) allozymes were compared in eggs and embryos of the mouse strains C57BL/6-JHan (GPI-1BB) and 129/Sv (GPI-1AA) under different experimental conditions. The quantitative differences in eggs of the two strains disappeared by the blastocyst stage at day 4 to 5, both in fertilized and diploid parthenogenetic embryos. The degree of degradation of oocyte-coded enzyme molecules and the activation of the embryonic genome for GPI appeared to be equivalent in parthenogenetic embryos from heterozygous females when only one or other maternal allele type remained in the egg after meiosis. Also in tetrapioid embryos, generated by electrofusion of homozygous fertilized eggs from the two strains, both genomes seemed to be activated at the same time at day 4; here, however, the GPI-1BB allozyme remained predominant up to day 6.
Morphogenesis and regulated gene activity are independent of DNA replication in Xenopus embryos
Authors: Rollins Martha B. , Andrews Matthew T.
Published: April 2021

Xenopus embryos were transferred into media containing aphidicolin at late blastula, mid-gastrula, and early neurula stages. In each case, embryos continued to differentiate in the absence of DNA replication. When the inhibitor was added at late blastula, embryos continued to develop for about 8h. However, when aphidicolin was added at the early neurula stage, development could be seen for up to 40 h after addition. The influence of replication on embryonic gene activity was studied by RNA blot analysis. Of the genes we examined only histone gene expression was down regulated by the addition of aphidicolin. The expression of various embryo-specific genes was unaffected by the lack of DNA synthesis. Even after several hours of treatment with aphidicolin, replication-inhibited tailbud and tadpole stages showed the same levels of specific mRNAs as control embryos containing 4 –5 times more DNA. We conclude that morphogenesis and embryospecific gene activity are independent of both DNA replication and a precise amount of DNA per embryo.
Aldehyde dehydrogenase is a positional marker in the retina
Authors: McCaffery Peter , Tempst Paul , Lara Gustavo , Dräger Ursula C.
Published: April 2021

An asymmetrically distributed protein in the embryonic mouse retina was identified as an aldehyde dehydrogenase through protein microsequencing. It was characterized as a cytosolic isoform with basic isoelectric point and preference for aliphatic substrates, features that resemble those of the isoform AHD-2 which is known to oxidize retinaldehyde to retinoic acid. Immunohistochemistry with aldehyde dehydrogenase antisera showed strong labeling of the dorsal retina from the early eye vesicle stage into adulthood. In addition, optic axons originating from the dorsal retina were transiently labeled during their outgrowth phase. Whereas in the embryo the enzyme was expressed in undifferentiated cells and in neurons, in the retina of the adult mouse the asymmetrically distributed isoform was mainly expressed in Müller glia, with the number of labeled glial cells varying with retinal position.
The regulation of the cell cycle during Drosophila embryogenesis: the transition to polyteny
Authors: Smith Albert V. , Orr-Weaver Terry L.
Published: April 2021

The process of polytenization plays a crucial role in Drosophila development, and most of the larval tissues are polytene. By analyzing the pattern of DNA replication in embryos pulse-labeled with BrdU, we show that many larval tissues undergo a transition to begin becoming polytene late in embryogenesis. Our results demonstrate that in these larval tissues polyteny results from a modified cell cycle, the endo cell cycle, in which there is only an S (synthesis) phase and a G (gap) phase. A key regulator of the mitotic cell cycle, the product of the string gene (the Drosophila homologue of cdc25), is not required for the endo cell cycle. The developmental regulation of the endo cell cycle is striking in that tissue-specific domains undergo polytene DNA replication in a dynamic pattern at defined times in embryogenesis. During subsequent rounds of the endo cell cycle in late embryogenesis and first instar larval development, the domains are subdivided and the temporal control is not as rigid. The length of the G phase varies among different tissues. By quantifying DNA content, we show that during the early polytene S phases the genome is not fully duplicated.
Distribution and function of the lethal of scute gene product during early neurogenesis in Drosophila
Authors: Martín-Bermudo María D. , Martínez Carmen , Rodríguez Antonio , Jiménez Fernando
Published: April 2021

Genes of the achaete –cute complex (ASC) participate in the formation of the central nervous system in the Drosophila embryo. Previous genetic analyses have indicated that lethal of scute (l’sc) is the most important gene of the complex in that process. We have obtained antibodies against the 1’sc protein to study the expression of the gene during early neurogenesis. The protein is found in groups of embryonic neuroectodermal cells, analogous to the proneural clusters that precede the appearance of precursors of peripheral sensory organs in imaginai epithelia. The groups appear in different regions of the neuroectoderm, accompanying the three successive waves of neuroblast segregation. Most neuroblasts delaminate from these clusters and express position-specific levels of 1’sc protein. No significant differences have been found between the distribution of l’sc RNA and protein. Phenotypic analysis of a l’sc deficiency has shown that the gene is required for neuroblast commitment, although this requirement is less widespread than the domain of l’sc expression, suggesting a high degree of redundancy in the function of genes that participate in the process of neuroblast segregation. The ASC genes have been postulated to play a role in the control of NB identity, revealed by the generation of a defined lineage of identifiable neurons. However, our study in l’sc mutants of the expression of fushi tarazu, engrailed, and even-skipped, used as markers of neuronal identity, has not provided evidence to support this hypothesis.
The sisterless-b function of the Drosophila gene scute is restricted to the stage when the X:A ratio determines the activity of Sex-lethal
Authors: Torres Miguel , Sánchez Lucas
Published: April 2021

The gene scute (sc) has a dual function: the scute function which is involved in neurogenesis and the sisterless-b function which is involved in generating the X:A signal that determines the state of activity of Sxl, a gene that controls sex determination and dosage compensation. We show here that the lethal phase of sc- females is embryonic and caused by the lack of Sxl function. We also analyze the time in development when sc and Sxl interact by means of (a) determining the thermosensitive phase (TSP) of the interaction between Sxl and sc and (b) a chimeric gene in which sc is under the control of a heat-shock promoter (HSSC-3). Pulses of sc expression from the HSSC-3 activate Sxl only at a very specific and early stage in development, which coincides with the TSP of the interaction between sc and Sxl. It corresponds to the syncytial blastoderm stage and coincides with the time when the X:A signal regulates Sxl. At this stage sc undergoes a homogeneous transient expression in wild-type flies. We conclude that the sc expression at the syncytial blastoderm is responsible for its sisterless-b function. Since sc expression from the HSSC-3 fully suppresses the sisterless-b phenotype, we further conclude that the sisterless-b function is exclusively provided by the sc protein. Finally, we have analyzed, by in situ hybridization, the effect of sc and sis-a mutations on the embryonic transcription of Sxl. Our results support the view that the control of Sxl by the X:A signal occurs at the transcriptional level.
Cell polarity and microtubule organisation during mouse early embryogenesis
Authors: Maro Bernard , Gueth-Hallonet Catherine , Aghion Joël , Antony Claude
Published: April 2021

We have studied the distribution and the role of microtubules in the major developmental events occuring during early development of the mouse. These events are the setting up of asymmetries within blastomeres, the process of asymmetrical cell division and the changes in cellular organisation taking place during epithelial differentiation.
A PDGF receptor mutation in the mouse (Patch) perturbs the development of a non-neuronal subset of neural crest-derived cells
Authors: Morrison-Graham Kathleen , Schatteman Gina C. , Bork Tracie , Bowen-Pope Daniel F. , Weston James A.
Published: April 2021

The Patch (Ph) mutation in mice is a deletion of the gene encoding the platelet-derived growth factor receptor alpha subunit (PDGFR α). Patch is a recessive lethal recognized in heterozygotes by its effect on the pattern of neural crest-derived pigment cells, and in homozygous mutant embryos by visible defects in craniofacial structures. Since both pigment cells and craniofacial structures are derived from the neural crest, we have examined the differentiation of other crest cell-derived structures in Ph/Ph mutants to assess which crest cell populations are adversely affected by this mutation. Defects were found in many structures populated by non-neuronal derivatives of cranial crest cells including the thymus, the outflow tract of the heart, cornea, and teeth. In contrast, crest-derived neurons in both the head and trunk appeared normal.

The expression pattern of PDGFR α mRNA was determined in normal embryos and was compared with the defects present in Ph/Ph embryos. PDGFR α mRNA was expressed at high levels in the non-neuronal derivatives of the cranial neural crest but was not detected in the crest cell neuronal derivatives. These results suggest that functional PDGF α is required for the normal development of many non-neuronal crest-derived structures but not for the development of crest-derived neuronal structures.

Abnormal development of the non-neuronal crest cells in Ph/Ph embryos was also correlated with an increase in the diameter of the proteoglycan-containing granules within the crest cell migratory spaces. This change in matrix structure was observed both before and after crest cells had entered these spaces. Taken together, these observations suggest that functional PDGFR α can affect crest development both directly, by acting as a cell growth and/or survival stimulus for populations of non-neurogenic crest cells, and indirectly, by affecting the structure of the matrix environment through which such cells move.
The Drosophila orb gene is predicted to encode sex-specific germline RNA-binding proteins and has localized transcripts in ovaries and early embryos
Authors: Lantz Valerie , Ambrosio Linda , Schedl Paul
Published: April 2021

We report the identification of a new gene, orb, which appears to be expressed only in the gennline and encodes ovarian-and testis-specific transcripts. The predicted proteins contain two regions with similarity to the RRM family of RNA-binding proteins but differ at their amino termini. In testes, orb RNA accumulates in the primary spermatocytes and at the caudal ends of the spermatid bundles. In ovaries, orb transcripts display an unusual spatial pattern of accumulation in the oocyte. Preferen-tial accumulation in the oocyte of orb RNA is first detected in region 2 of the germanium and is dependent on Bicaudal-D and egalitarian. While in stage 7 egg chambers orb RNA is localized posteriorly in the oocyte, during stages 8-10 it is localized at the anterior of the oocyte, asymmetrically along the dorsal-ventral axis. In embryos the transcripts accumulate at the posterior end and are included in the pole cells. This pattern of localization and the similarity to RNA-binding proteins suggest that the orb gene product may mediate the localization of maternal RNAs during oogenesis and early embryogenesis.
Asymmetrical retinoic acid synthesis in the dorsoventral axis of the retina
Authors: Mccaffery Peter , Lee Mi-Ock , Wagner Michael A. , Sladek Norman E. , Dräger Ursula C.
Published: April 2021

An aldehyde dehydrogenase present at high levels in the dorsal retina of the embryonic and adult mouse was identified as the isoform AHD-2 known to oxidize retinaldehyde to retinoic acid. Comparative estimates of retinoic acid levels with a reporter cell line placed the retinas among the richest tissues in the entire body of the early embryo; levels in ventral retina, however, exceeded dorsal levels. Retinoic acid synthesis from retinaldehyde in the dorsal pathway was less effective than the ventral pathway at low substrate levels and more effective at high levels. The dorsal pathway was preferentially inhibited by disulfiram, while ventral synthesis was preferentially inhibited by p-hydroxymer-curibenzoate. When protein fractions separated by isoelectric focusing were analyzed for retinoic acid synthesizing capacity by a zymography-bioassay, most of the synthesis in dorsal retina was found to be mediated by AHD-2, and ventral synthesis was mediated by dehydrogenase activities distinct in charge from AHD-2. Postnatally, levels of highest retinoic acid synthesis shifted from ventral to dorsal retina. In the adult retina, the dorsal pathway persisted, but the preferential ventral pathway was no longer detectable. Our observations raise the possibility that retinoic acid plays a role in the determination and maintenance of the dorsoventral axis of the retina, and that the morphogenetically significant asymmetry here lies in the spatial arrangement of synthetic pathways.
PDGF receptors in the rat CNS: during late neurogenesis, PDGF alpha-receptor expression appears to be restricted to glial cells of the oligodendrocyte lineage
Authors: Pringle Nigel P. , Mudhar Hardeep S. , Collarini Ellen J. , Richardson William D.
Published: April 2021

Using in situ hybridization, we have visualized cells in the rat central nervous system (CNS) that contain mRNA encoding the platelet-derived growth factor alpha receptor (PDGF-αR). After embryonic day 16 (E16), PDGF-αR mRNA appears to be expressed by a subset of glial cells, but not by neurons. The temporal and spatial distribution of PDGF-αR+ cells, together with 125I-PDGF binding studies on subsets of glial cells in vitro, suggests that PDGF-αR may be expressed predominantly, or exclusively, by cells of the oligodendrocyte-type-2 astrocyte (O-2A) lineage. This conclusion is supported by the fact that the numbers of PDGF-αR+ cells in developing and adult optic nerves correlate well with independent estimates of the number of O-2A progenitor cells in the nerve at equivalent ages. Small numbers of PDGF-αR+ cells are present in the brain at E16, at which time they are found outside the subventricular germinal zones, suggesting that these cells do not express PDGF-αR until after, or shortly before they start to migrate away from the subventricular layer towards their final destinations. Reduced numbers of PDGF-αR+ cells persist in the adult CNS. PDGF-αR is also expressed strongly in the meningeal membranes and choroid plexus, and in the inner limiting membrane of the retina.
Hox-4 gene expression in mouse/chicken heterospecific grafts of signalling regions to limb buds reveals similarities in patterning mechanisms
Authors: Izpisúa-Belmonte J.-C. , Brown J. M. , Crawley A. , Duboule D. , Tickle C.
Published: April 2021

The products of Hox-4 genes appear to encode position in developing vertebrate limbs. In chick embryos, a number of different signalling regions when grafted to wing buds lead to duplicated digit patterns. We grafted tissue from the equivalent regions in mouse embryos to chick wing buds and assayed expression of Hox-4 genes in both the mouse cells in the grafts and in the chick cells in the responding limb bud using species specific probes. Tissue from the mouse limb polarizing region and anterior primitive streak respecify anterior chick limb bud cells to give posterior structures and lead to activation of all the genes in the complex. Mouse neural tube and genital tubercle grafts, which give much less extensive changes in pattern, do not activate 5’-located Hox-4 genes. Analysis of expression of Hox-4 genes in mouse cells in the grafted signalling regions reveals no relationship between expression of these genes and strength of their signalling activity. Endogenous signals in the chick limb bud activate Hox-4 genes in grafts of mouse anterior limb cells when placed posteriorly and in grafts of mouse anterior primitive streak tissue. The activation of the same gene network by different signalling regions points to a similarity in patterning mechanisms along the axes of the vertebrate body.