Thymosin beta10 mRNA expression during early postimplantation mouse development.

The beta-thymosins are a family of monomeric actin sequestering peptides that regulate actin dynamics within the cells. During embryogenesis the control of actin polymerization is essential in processes such as cell migration, angiogenesis and neurogenesis. Here we report that the levels of thymosin beta10 (Tbeta10) mRNA strongly increase during early postimplantation mouse embryogenesis as well as during in vitro P19 cell differentiation, indicating that this peptide plays an important role in early development. Moreover, analysis of the spatial distribution of Tbeta10 mRNA in 9.5-12.5 days postcoitum mouse embryos showed a remarkable presence of this transcript in mesenchymal structures as well as in the mantle layer of spinal cord. Interestingly, we observed differences in the distribution of the mRNAs encoding Tbeta10 and Tbeta4, another member of the beta-thymosin family, suggesting different roles for these peptides during mouse embryogenesis.

High levels of mouse thymosin beta4 mRNA in differentiating P19 embryonic cells and during development of cardiovascular tissues.

The self assembly of actin and the large number of actin-binding proteins are important in the establishment of cell shape and function during embryogenesis. Thymosin beta4 (Tbeta4) is a small acidic peptide that participates in the regulation of actin polymerization in mammalian cells. In the present work, we report the presence of the mRNA encoding for Tbeta4 in mouse embryonic stem cells and its induction in P1 9 embryonal cells stimulated to differentiate into ectodermal-like (neurons and glia) or mesodermal-like cells (cardiac and skeletal muscle). The induction of Tbeta4, mRNA in P19 cells was confirmed by in situ hybridization analysis of early mouse postimplantation embryos. Noteworthy, we observed an important hybridization signal in several areas of the embryo specially in blood vessels and in heart tissues, suggesting a role for this peptide in angiogenesis. In conclusion, the results presented here demonstrate the expression of Tbeta4 gene during early embryogenesis which immediately suggests an important role for this peptide in developmental processes requiring actin-based functions such as the formation of cardiovascular system.

The prothymosin alpha gene is specifically expressed in ectodermal and mesodermal regions during early postimplantation mouse embryogenesis.

Prothymosin alpha (ProT alpha) is a highly acidic nuclear protein, once believed to have an extracellular immunoregulatory role but more recently implicated in cell proliferation and/or differentiation. Several recent studies have revealed that ProT alpha mRNA is present during embryogenesis. However, these studies did not investigate the spatial distribution of ProT alpha mRNA in the embryo. Here we present a detailed study of the spatial distribution of ProT alpha mRNA during the early stages of postimplantation development (6.5-12.5 dpc) of the mouse. Three findings are of particular interest. First, ProT alpha mRNA levels increase during the early postimplantation stages (6.5-8.5 dpc) of mouse embryogenesis. Second, ProT alpha mRNA is not uniformly distributed in the mouse embryo, but is present in a spatially specific manner. Third, we have observed that the mouse ProT alpha gene is expressed almost exclusively in ectodermal and mesoderm-derived structures, and not in cells which give rise to the definitive endoderm.

Cloning and developmental expression of Grg, a mouse gene related to the groucho transcript of the Drosophila Enhancer of split complex.

Genes of the Enhancer of split complex are involved in neural-epidermal cell fate decisions during early embryogenesis in Drosophila. One of these genes, the product of the Enhancer of split m9/10 or groucho transcript, encodes a ubiquitous nuclear protein with homology at the carboxy-terminus to G-protein beta-subunits. Here we describe the cloning and RNA expression analysis of a mouse gene, designated Grg, that is homologous to just the amino-terminal region of the groucho product. Grg encodes a 197 amino acid protein that shares 53% amino acid identity with the corresponding region of the product of the Drosophila groucho gene. However, the mouse Grg protein does not contain the region homologous to G-protein beta-subunits. An analysis by in situ hybridization of the spatial and temporal localization of Grg RNA expression revealed that, while the initial pattern of Grg expression was quite restricted, by midgestation Grg RNA was ubiquitously expressed in the developing embryo. Widespread Grg RNA expression was maintained in adult mice. The implications of these results for the existence of separable functional domains of the Drosophila groucho product, and possible roles of the Grg gene during mouse development, are discussed.

Cloning, sequencing and expression of the mouse mammalian achaete-scute homolog 1 (MASH1).

We describe the cloning of a full length cDNA encoding the mouse mammalian achaete-scute homolog 1 (mouse MASH1). Using a ribonuclease protection assay to examine expression of this gene in cell lines, postimplantation embryos and adult tissues, expression was detected between days 10.5 and 16.5 of gestation and in adult brain. No expression was detected in other adult tissues or in most of the cell lines examined. However, differentiation of P19 embryonal carcinoma cells into neuronal cell types by exposure to retinoic acid resulted in the induction of MASH1 RNA expression.

Isolation of Sna, a mouse gene homologous to the Drosophila genes snail and escargot: its expression pattern suggests multiple roles during postimplantation development.

The Drosophila gene snail encodes a zinc-finger protein that is required zygotically for mesoderm formation. Snail acts as a transcriptional repressor during the period of mesoderm formation by preventing expression of mesectodermal and ectodermal genes in the mesoderm anlage. A Xenopus homolog (xsnail) of snail has been cloned and it too is expressed early in the mesodermal germ layer. We have isolated cDNA clones of a mouse gene (termed Sna) closely related to snail and xsnail and another Drosophila gene termed escargot that also encodes a zinc-finger protein. Sna encodes a 264 amino acid protein that contains four zinc fingers. Developmental RNA blot analysis showed that Sna transcripts are expressed throughout postimplantation development. Analysis of the spatial and temporal localization of Sna transcripts by in situ hybridization to both whole-mount and sectioned embryos revealed that, in the gastrulating embryo, Sna is expressed throughout the primitive streak and in the entire mesodermal germ layer. By 9.5 days post coitum (dpc) Sna is expressed at high levels in cephalic neural crest and limb bud mesenchyme. In fact, by 10.5 dpc Sna expression is observed in most mesenchymal cells, whether of neural crest or mesodermal origin. Later in gestation, high levels of Sna expression are observed in condensing cartilage and in the mesenchymal component of several tissues (lung, kidney, teeth and vibrissae) that undergo epithelial-mesenchymal inductive interactions during development. These results suggest multiple roles for the Sna gene in gastrulation and organogenesis during murine development.