Systematic localization of oct‐3/4 to the gastrulating mouse conceptus suggests manifold roles in mammalian development

Oct-3/4 was localized to the mouse conceptus between the onset of gastrulation and 16-somite pairs (-s; approximately 6.5-9.25 days postcoitum, dpc). Results revealed Oct-3/4 in a continuum of morphologically distinct epiblast-derived embryonic and extraembryonic tissues. In the allantois, distal-to-proximal diminution in the Oct-3/4 domain over time and co-localization with Flk-1 in angioblasts accorded with a role in vascular differentiation and the presence of a stem cell reservoir. In addition, visceral endoderm exhibited a dynamic salt-and-pepper distribution, which, combined with previous results of fate mapping and gene expression, suggested that Oct-3/4 is involved in the genesis of definitive endoderm. By 8-s, Oct-3/4 was globally down regulated in all but putative primordial germ cells (PGCs) and some allantoic cell clusters. Taken together, Oct-3/4's expression profile suggests unexpected and potentially far more versatile roles in development than have been previously appreciated.