Three-dimensional immunohistochemical characterization of lineage commitment by localization of T and FOXA2 in porcine peri-implantation embryos.

Gene expression during gastrulation in porcine embryos has been sparsely studied, but there are indications that species-specific patterns exist. Here, we investigated the three-dimensional (3D) expression of the T-box transcription factor Brachyury (T) and the forkhead box transcription factor FOXA2 by immunocytochemistry in porcine peri-gastrulation embryos. The first T(+) cells were detected in posterior epiblast of ovoid blastocysts. Later T(+) FOXA2(-) cells were found in the posterior primitive streak (PS) and nascent mesoderm, T(+) FOXA2(+) cells in the anterior PS, probably identifying the organizer region, and T(-) FOXA2(+) cells anterior to this region. In embryos with a neural groove, T and FOXA2 were co-expressed in the node and notochord, FOXA2 was expressed in the floor plate and posteriorly T was expressed in the streak. In all developmental stages, FOXA2 was expressed in the entire hypoblast/definitive endoderm. We conclude that the expression pattern of T and FOXA2 is largely conserved between pig and mouse.