Prothymosin α (ProTα) 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 ProTα mRNA is present during embryogenesis. However, these studies did not investigate the spatial distribution of ProTα mRNA in the embryo. Here we present a detailed study of the spatial distribution of ProTα mRNA during the early stages of postimplantation development (6.5–12.5 dpc) of the mouse. Three findings are of particular interest. First, ProTα mRNA levels increase during the early postimplantation stages (6.5–8.5 dpc) of mouse embryogenesis. Second, ProTα mRNA is not uniformly distributed in the mouse embryo, but is present in a spatially specific manner. Third, we have observed that the mouse ProTα gene is expressed almost exclusively in ectodermal and mesoderm-derived structures, and not in cells which give rise to the definitive endoderm.
