An atlas of differential gene expression during early Xenopus embryogenesis

We have carried out a large-scale, semi-automated whole-mount in situ hybridization screen of 8369 cDNA clones in Xenopus laevis embryos. We confirm that differential gene expression is prevalent during embryogenesis since 24% of the clones are expressed non-ubiquitously and 8% are organ or cell type specific marker genes. Sequence analysis and clustering yielded 723 unique genes displaying a differential expression pattern. Of these, 18% were already described in Xenopus, 47% have homologs and 35% are lacking significant sequence similarity in databases. Many of them encode known developmental regulators. We classified 363 of the 723 genes for which a Gene Ontology annotation for molecular function could be attributed and found 'DNA binding' and 'enzyme' the most represented terms. The most common protein domains encoded in these embryonic, differentially expressed genes are the homeobox and RNA Recognition Motif (RRM). Fifty-nine putative orthologs of human disease genes, and 254 organ or cell specific marker genes were identified. Markers were found for nasal placode and archenteron roof, organs for which a specific marker was previously unavailable. Markers were also found for novel subdomains of various other organs. The tissues for which most markers were found are muscle and epidermis. Expression of cell cycle regulators fell in two classes, containing proliferation-promoting and anti-proliferative genes, respectively. We identified 66 new members of the BMP4, chromatin, endoplasmic reticulum, and karyopherin synexpression groups, thus providing a first glimpse of their probable cellular roles. Cluster analysis of tissues to measure tissue relatedness yielded some unorthodox affinities besides expectable lineage relationships. In conclusion, this study represents an atlas of gene expression patterns, which reveals embryonic regionalization, provides novel marker genes, and makes predictions about the functional role of unknown genes.     

Expression of the homeobox gene,Hox 2.1, during mouse embryogenesis

This article reviews recent studies on the expression of the homeobox gene, Hox 2.1, during mouse embryogenesis, using the technique of in situ hybridization. Differential hybridization of radiolabelled antisense versus sense strand RNA is first clearly detected in sections of 8.5 day post coitum (p.c.) early somite embryos. At 12.5 days p.c., higher levels of Hox 2.1 expression are seen in the spinal cord, extending into the base of the hind brain. Hybridization of antisense Hox 2.1 RNA is also seen in the spinal ganglia, in the nodose ganglia of the Xth cranial nerve (which contains derivatives of the neural crest arising from the posterior hind brain), and in the myenteric plexus. Mesodermal cells of certain visceral organs also express Hox 2.1 RNA, in particular the mesoderm of the lung, stomach and meso- and meta-nephric kidney. Comparison of the spatial domains of expression of mouse homeobox genes reveals a pattern consistent with the idea that they play a role in anteroposterior positional specification during embryogenesis.     

pag gene-like protein (ABP-25) of the Cynops embryo: regional distribution and gene expression during early embryogenesis

A maternal protein showing a unique distribution during early Cynops embryogenesis was screened by monoclonal antibody. The antigen protein, designated as ABP-25 (animal blastomere protein, molecular weight 25,000), was distributed uniformly in the uncleaved egg and concentrated into blastomeres of the animal half during cleavage. At the blastula stage, ABP-25 was definitely localized in cells of the animal half and a polarized distribution was observed within the cytoplasm. During gastrulation, immunohistochemical analysis indicated that the reactivity of the marginal zone (presumptive mesoderm) to the monoclonal antibody ABP-25 decreased after involution. At the end of gastrulation, a polarized distribution was still clearly observed in the ventral epidermis, but not in the neuroectoderm. Both Western and Northern blots indicated that the amount of antigen protein and the intensity of gene expresion were almost constant until the neurula stage. The deduced amino acid sequence of the ABP-25 cDNA showed a strong homology (84%) with that of the pag gene associated with cell proliferation.The nucleotide sequence data reported in this paper will appear in the GSDB, DDBJ, EMBL and NCBI nucleotide sequence databases with the accession number D37808     

SLAMseq resolves the kinetics of maternal and zygotic gene expression during early zebrafish embryogenesis

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