bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell shape changes during gastrulation in Drosophila
Authors: Leptin Maria , Grunewald Barbara 
Published: April 2021

Abstract
The first morphogenetic movement during Drosophila development is the invagination of the mesoderm, an event that folds a one-layered epithelium into a multilayered structure. In this paper, we describe the shape changes and behaviour of the cells participating in this process and show how mutations that change cell fate affect this behaviour.
We divide the formation of the mesodermal germ layer into two phases. During the first phase, the ventral epithelium folds into a tube by a series of concerted cell shape changes (ventral furrow formation). Based on the behaviour of cells in this phase, we conclude that the prospective mesoderm is not a homogeneous cell population, but consists of two subpopulations. Each subpopulation goes through a distinctive sequence of specific cell shape changes which together mediate the invagination of the ventral furrow. In the second phase, the invaginated tube of mesoderm loses its epithelial character, the mesoderm cells disperse, divide and then spread out along the ectoderm to form a single cell layer.
To test how ventral furrow formation depends on cell fates in the mesoderm and in neighbouring cells we alter these fates genetically using maternal and zygotic mutations. These experiments show that some of the aspects of cell behaviour specific for ventral furrow cells are part of an autonomous differentiation programme. The force driving the invagination is generated within the region of the ventral furrow, with the lateral and dorsal cell populations contributing little or none of the force. Two known zygotic genes that are required for the formation of the mesoderm, twist and snail, are expressed in ventral furrow cells, and the correct execution of cell shape changes in the mesoderm depends on both.
Finally, we show that the region where the ventral furrow forms is determined by the expression of mesoderm-specific genes, and not by mechanical or other epigenetic properties of the egg.
Microenvironment created by stromal cells is essential for a rapid expansion of erythroid cells in mouse fetal liver
Authors: Ohneda Osamu , Yanai Nobuaki , Obinata Masuo 
Published: April 2021

ABSTRACT
Mouse stromal cell lines (FLS lines), established from the livers of 13-day gestation mouse fetus, supported the proliferation and differentiation of the erythroid progenitor cells from mouse fetal livers and bone marrow in a semisolid medium in the presence of erythropoietin. A large erythroid colony of over 1000 benzidine-positive erythroid cells was developed from a single erythroid progenitor cell on the FLS cell layer after 4 days of culture. When in close contact with the layer, the erythroid progenitor cells divided rapidly with an average generation time of 9.6 h and mature erythroid cells, including enucleated erythrocytes, were produced. The present studies demonstrate that the microenvironment created by the stromal cells can support the rapid expansion of erythropoietic cell population in the fetal liver of mice.
DNA sequence-specific binding activity of the heat-shock transcription factor is heat-inducible before the midblastula transition of early Xenopus development
Authors: Ovsenek Nick , Heikkila John J. 
Published: April 2021

ABSTRACT
We have examined the activity of the Xenopus heat-shock transcription factor (HSF) in extracts from stressed and unstressed embryos at various stages of development using DNA mobility shift analysis. A specific interaction between HSF and a synthetic oligonucleotide corresponding to the proximal heat-shock element (HSE) of the Xenopus HSP70B gene was greatly enhanced in heat-shocked embryos compared to controls. HSF binding was inducible at all developmental stages examined including pre-midblastula transition (MBT) stages which are incapable of expressing HSP genes. In time-course experiments with both cleavage and neurula stage embryos, the activation of HSF binding was rapid and transient. Removal of cleavage and neurula stage embryos from heat stress resulted in a rapid loss of binding activity. The molecular mass of HSF, as determined by comparative gel electrophoresis of photoaffinity-labeled factor was 88X103 in both heat-shocked cleavage and neurula stage embryos. These experiments suggest that maternally derived HSF is stored in pre-MBT embryos in a heat-activatable form and may function in the regulation of heat-shock genes immediately after the MBT.
Phenotypic rescue of mutant brown melanocytes by a retrovirus carrying a wild-type tyrosinase-related protein gene
Authors: Bennett Dorothy C. , Huszar Dennis , Laipis Philip J. , Jaenisch Rudolf , Jackson Ian J. 
Published: April 2021

ABSTRACT
A mouse cDNA for the developmentally controlled, melanocyte-specific protein, tyrosinase-related protein 1 (TRP-1), was previously cloned and reported to show genetic linkage with the coat-colour locus brown (b) on mouse chromosome 4. The cDNA has been inserted into a retroviral vector derived from Moloney murine leukaemia virus, under the control of the human histone H4 promoter. This vector was used to infect melanocytes of the immortal line melan-b, which are homozygous for the b mutation and which display light brown pigmentation in culture. Infected cultures containing between 0.2 and 2 copies of provirus per cell displayed an altered phenotype: 20-50 % of cells now had the black to dark brown colour characteristic of cultured wild-type (Black, B/B) mouse melanocytes. Thus the TRP-1 gene complements the brown mutation. We conclude that TRP-1 is the product of the wild-type-b-locus.
Embryonic stem cells alone are able to support fetal development in the mouse
Authors: Nagy András , Gócza Elen , Diaz Elizabeth Merentes , Prideaux Valerie R. , Iványi Eszter , Markula Merja , Rossant Janet 
Published: April 2021

Abstract
The developmental potential of embryonic stem (ES) cells versus 3.5 day inner cell mass (ICM) was compared after aggregation with normal diploid embry os and with developmentally compromised tetraploid embryos. ES cells were capable of colonizing somatic tissues in diploid aggregation chimeras but less efficiently than ICMs of the same genotype. When ICM"-"tetraploid and IS-tetraploid chimeras were made, the newborns were almost all completely ICM-or ES-derived. as judged by GPI isozyme analysis, but tetraploid cells were found in the yolk sac endoderm and trophectoderm lineage. Investigation of ES contribution in 13.5 day ES-tetraploid chimeras by DNA in situ hy bridization confirmed the complete tetraploid origin of the placenta (except the fetal blood and blood vessels) and the yolk sac endoderm. However, the yolk sac mesoderm, amnion and fetus contained only ES-derived cells.
ES-derived newborns failed to survive after birth, although they had normal birthweight and anatomically they appeared normal. This phenomenon remains unexplained at the moment.
The present results prove that ES cells are able to support complete fetal development, resulting in ES-derived newborns, and suggest a useful route for studying the development of genetically manipulated ES cells in all fetal lineages.
Differential expression of laminin A and B chains during development of embryonic mouse organs
Authors: Klein Gerd , Ekblom Marja , Fecker Lothar , Timpl Rupert , Ekblom Peter 
Published: April 2021

Abstract
Laminin is a large glycoprotein of basement membranes. The best described laminin from a mouse tumor contains three polypeptide chains (A, Bl and B2), but there is recent evidence that some cell types produce, laminin isoforms lacking the A chain. We have here studied the occurrence of the isoforms during mouse organogenesis. In all tissues studied, the A chain mRNA and polypeptide were more weakly expressed than those of the B chains. Laminin A chain polypeptides showed a much more restricted tissue distribution than the B chains. Laminin A chain polypeptide was mainly detected in basement membranes of epithelial cells, suggesting that this chain is important for morphogenesis of epithelial sheets. Most endothelial basement membranes and all embryonic mesenchyme matrices studied seemed to lack the A chain even though they contained B chains. Several of the cells producing laminin devoid of A chain seem to produce other polypeptides that become complexed to the B chains. With an anti-laminin antiserum, which in immunblots reacts only with A and B polypeptide chains, additional polypeptides of 160 and 190×l03Mr were co-precipitated from all tissues studied. In developing heart, a polypeptide of 300×l03Mr was co-precipitated in addition. Our data suggest that these laminin-associated polypeptides are not formed by a differential splicing of the known A chain mRNA. Northern blotting of poly(A)+ RNA showed only 10 kb A chain transcripts but no truncated forms. We conclude that several cell types in the mouse embryo produce laminin variants that lack the 400×l03Mr A chain. Since a major cell binding site of laminin contains parts of the A chain, the variants should differ in biological function from laminin containing this A chain.
Retinoic acid modulation of the early development of the inner ear is associated with the control of c-fos expression
Authors: Represa Juan , Sanchez Alberto , Miner Cristina , Lewis John , Giraldez Fernando 
Published: April 2021

Abstract
The effects of retinoic acid (RA) on the early development of the inner ear were studied in vitro using isolated chick embryo vesicles. Low concentrations of RA (1–50 nM) inhibited vesicular growth in stage 18 otic vesicles that were made quiescent and then reactivated by either serum or bombesin. Growth inhibition was concentration-dependent and was paralleled by a reduction in the rate of DNA synthesis as measured by [3H]thymidine incorporation. Half-inhibition occurred between 1 and 10 nM RA, and the full effect at 20 nM. Retinoic acid, in the presence of serum, induced the precocious differentiation of (1) secretory epithelium, the tegmentum vasculosum and endolymphatic sac and (2) early sensory and supporting epithelia. These structures were positioned in their corresponding normal presumptive areas. The overall direction of growth was reversed by RA and the ratio of the internal to the external vesicular surface area increased with RA concentration. The expression of the nuclear protooncogene c-fos in the developing otic vesicle was transient and stage-dependent. High levels of c-fos mRNA were positively correlated with cell proliferation. Incubation of growth-arrested otic vesicles with bombesin plus insulin at concentrations that induced cell proliferation produced a strong induction of c-fos. This mitogen-induced expression was suppressed by 25 nM RA. The results suggest (1) a role for retinoic acid in controlling the early development of the inner ear and (2) that this control is effected through the regulation of the proto-oncogene c-fos.
Retinoic acid receptors and cellular retinoid binding proteins: I. A systematic study of their differential pattern of transcription during mouse organogenesis
Authors: Dollé Pascal , Ruberte Esther , Leroy Pierre , Morriss-Kay Gillian , Chambon Pierre 
Published: April 2021

Abstract
We report here the gene expression patterns, as revealed by in situ hybridisation, of the retinoic acid receptors alpha, beta and gamma (RAR-α, -β and -γ), and the cellular binding proteins for retinol and retinoic acid (CRBP, CRABP) in non-neural tissues of mouse embryos during the period of organogenesis. At all stages, RAR-α transcripts were almost ubiquitous, whereas the distribution of transcripts of the other four genes was distinctive in all systems. At early stages in the formation of an organ, the expression patterns were different in the epithelium, the adjacent mesenchyme, and in mesenchyme more distant from the epithelium, suggesting a role for RA and RA receptors in epithelial–mesenchymal tissue interactions. In the developing face, limb bud and genital tubercle, where large expanses of mesenchyme are present, differential patterns of expression were established before the onset of overt tissue differentiation, suggesting some significance for pattern formation in these regions. The distribution of RAR-β transcripts in tracheobronchial, intestinal and genital tract epithelia is consistent with the possibility that RAR-β plays a role in mediating retinoid effects on the differentiated stage of these epithelia. Possible developmental roles of RARs in relation to the expression patterns of other genes are discussed. CRBP expression domains showed a high degree of overlap with RAR-β and RAR-γ, and a mutual exclusivity with CRABP expression domains. Correlation of these expression patterns with the morphogenetic effects of vitamin A deficiency and retinoid excess lead us to propose that the function of CRBP is to store and release retinol where high levels of RA are required for specific morphogenetic processes, while CRABP serves to sequester RA in regions where normal developmental functions require RA levels to be low. Where both binding protein genes are expressed in a non-overlapping pattern within a large area of mesenchyme, a gradient of free RA may be created between them by release of retinol-derived RA from CRBP-expressing cells, with binding to CRABP enhancing the steepness of the decline in concentration distant to the source.
Nucleolar distribution of proteins B23 and nucleolin in mouse preimplantation embryos as visualized by immunoelectron microscopy
Authors: Biggiogera M. , Bürki K. , Kaufmann S. H. , Shaper J. H. , Gas N. , Amalric F. , Fakan S. 
Published: April 2021

Abstract
The ultrastructural distribution of proteins B23 and nucleolin in the nucleolus of mouse embryos from the zygote to the early blastocyst has been analyzed by means of specific antibodies and immunocytochemistry using colloidal gold complexes as markers. In parallel, silver staining of nucleoli was carried out on ultrathin sections. Our results show that the compact prenucleolar bodies at 1- and 2-cell stage as well as the compact residual fibrillar masses observed up to the morula stage, are labelled with the two antibodies. These masses, however, are not stained with silver up to the 4-cell stage. In well-developed nucleoli, the two antibodies co-localize in the dense fibrillar component (DFC) and the granular component (GC) while fibrillar centers (FCs) are devoid of label. On the contrary, silver staining occurs in the FCs and DFC but not in the GC. Our observations suggest that there is no direct relationship between the occurrence of silver staining and the distribution of protein B23 or nucleolin. Moreover, neither the localization of the two above proteins nor silver staining are unequivocally related to the nucleolar activity.
Developmental loss of laminin from the interstitial extracellular matrix correlates with decreased laminin gene expression
Authors: Kücherer-Ehret Andrea , Pottgiesser Jutta , Kreutzberg Georg W. , Thoenen Hans , Edgar David 
Published: April 2021

Abstract
The expression of the polypeptide subunits of the glycoprotein laminin in developing mouse tissues was analysed by immunoblots and Northern blots, and by immunohistochemistry at the ultrastructural level. In the neonate, almost all the laminin of the sciatic nerve was freely extractable and was located mainly in the mesenchymal interstitial extracellular matrix, rather than in basement membranes. During the first two postnatal weeks, the distribution of laminin shifted to assume the adult pattern, most being located in basement membranes and insoluble under physiological conditions. Analysis of laminin subunit expression showed that both the mRNA for the laminin B chains and the corresponding polypeptides are widely expressed in nerve and other tissues, the mRNA levels decreasing during the first two postnatal weeks as the amount of laminin in the tissue increased. In contrast, the A chain mRNA and polypeptide were undetectable in nerve at any age studied, although they were present in perinatal kidney and placenta. It is proposed that the large amount of soluble laminin present in the developing interstitial extracellular matrix is a consequence of the high levels of expression of laminin mRNA, the subsequent decrease in expression resulting in the adult distribution where most laminin is insoluble within the basement membrane.
Early C. elegans embryos are transcriptionally active
Authors: Schauer Irene E. , Wood William B. 
Published: April 2021

Abstract
We have developed a nucleotide incorporation assay for run-on transcription in C. elegans embryonic extracts as an approach to characterizing early transcription. The incorporation is primarily polymerase II-catalyzed RNA synthesis, producing transcripts of the expected size range for mRNAs. Incorporation is insensitive to inhibitors of reinitiation, indicating that the activity represents primarily elongation of nascent chains initiated prior to extract preparation. The transcripts produced appear to be unprocessed pre-mRNAs. Hy bridization of labeled transcripts from extracts of staged embryos to a set of cloned genes suggests that the specificity of the in vitro reaction accurately reflects developmentally regulated in vivo transcription. Com parative analyses of transcription in extracts from various stages indicate that pregastrulation embryos are active transcriptionally and that the level of transcrip tion per nucleus is approximately constant throughout embryogenesis. Furthermore, most embryonically ex pressed genes are already being transcribed in pregas trulation embryos. We also demonstrate that the labeled embryonic run-on transcripts can be used as probes to screen for sequences transcribed preferentially in pregastrulation embryos. There appears to be only a small set of such sequences, which could represent a previously unsuspected class of embryonically tran scribed genes important for early embryogenesis.
Expression of IGF-I and -II mRNA in the brain and craniofacial region of the rat fetus
Authors: Lievre C. Ayer-Le , Ståhlbom P.A. , Sara V. R. 
Published: April 2021

ABSTRACT
Insulin-like growth factors (IGF-I and -II) are present in the brain during development, with high levels of both being also found in the periphery particularly in the embryo. IGFs in the brain are believed to stimulate the proliferation of neuronal and glial precursors and their phenotypic differentiation. Using in situ hybridization, we have investigated the distribution of cells producing IGF-I and -II in the rat fetus during the second half of prenatal development with special emphasis on the peripheral and central nervous system. High levels of IGF-I mRNA were found in the olfactory bulb and in discrete neurons of the cranial sensory ganglia, notably in the trigeminal ganglion, as early as 13 days of gestation, in the pineal primordium of 18 day old fetuses, and in discrete groups of cells in the cochlear epithelium located laterally outside the forming spiral organ, in day 13 to 21 fetuses. High levels of IGF-II mRNA in the brain, besides the choroid plexus and the leptomeninges, were detected in hypothalamus, in the floor of the 3rd ventricle at all stages studied, in the pineal primordium at 18 days and in the pars intermedia of the pituitary or in the Rathke’s pouch epithelium from which it is derived, with progressive fading towards the end of the gestation. In the peripheral nervous system the IGF-II mRNA was only found in association with the vascular endothelia of the ganglia.
IGF-II mRNA in the nervous system was found in highly vascularized areas, meninges, blood vessels and choroid plexuses. It is thus associated with structures involved in the production of extracellular fluids and/or substrate transport and supply in the nervous tissues. A more specific role in the differentiation or fetal endocrine function should be considered for IGF-II in cells producing melatonin and melanocyte stimulating hormone (MSH) in the pineal and pituitary glands, respectively.
The presence of IGF-I mRNA in the nervous system could be associated with fiber outgrowth and synapto-genesis in the cases of olfactory bulb and developing iris. The role of IGF-I in restricted populations of cells of the cochlear epithelium and in the pineal gland is unclear and requires further investigations including a search for IGF-I receptors in possible target cells.
In the sensory ganglia, the presence of high levels of IGF-I mRNA eventually corresponds to the production, by post-translational processing, of the amino-terminal tripeptide of IGF-I, which might represent a neurotransmitter for these sensory neurons.
Differential expression of TGF β1, β2 and β3 genes during mouse embryogenesis
Authors: Schmid Peter , Cox David , Bilbe Graeme , Maier Rainer , Mcmaster Gary K. 
Published: April 2021

ABSTRACT
We have examined by Northern analysis and in situ hybridisation the expression of TGF β1 β2and β3 during mouse embryogenesis. TGF β1 is expressed predominantly in the mesodermal components of the embryo e.g. the hematopoietic cells of both fetal liver and the hemopoietic islands of the yolk sac, the mesenchymal tissues of several internal organs and in ossifying bone tissues. The strongest TGF β2 signals were found in early facial mesenchyme and in some endodermal and ectodermal epithelial cell layers e.g., lung and cochlea epithelia. TGF β3 was strongest in prevertebral tissue, in some mesothelia and in lung epithelia. All three isoforms were expressed in bone tissues but showed distinct patterns of expression both spatially and temporally. In the root sheath of the whisker follicle, TGF β1 β2 and β3 were expressed simultaneously. We discuss the implication of these results in regard to known regulatory elements of the TGF β genes and their receptors.
Embryonic gene expression patterns of TGF β1, β2 and β3 suggest different developmental functions in vivo
Authors: Millan Fergus A. , Denhez Fabienne , Kondaiah Paturu , Akhurst Rosemary J. 
Published: April 2021

ABSTRACT
We have compared the expression of the genes encoding transforming growth factors β1, β2 and β3 during mouse embryogenesis from 9.5 to 16.5 days p.c. using in situ hybridisation to cellular RNAs. Each gene has a different expression pattern, which gives some indication of possible biological function in vivo.
All three genes appear to be involved in chondro ossification, though each is expressed in a different cell type. Transcripts of each gene are also present in embryonic epithelia. Epithelial expression of TGF β1, β2 and β3 RNA is associated with regions of active morphogenesis involving epithelial-mesenchymal inter actions. In addition, widespread epithelial expression of TGF β2 RNA can be correlated with epithelial differentiation per se. The localisation of TGF β2 RNA in neuronal tissue might also be correlated with differentiation. Finally both TGF β1 and β2 transcripts are seen in regions actively undergoing cardiac septation and valve formation, suggesting some interaction of these growth factors in this developmental process.