Mechanisms of embryonic and extra-embryonic tissue segregation in pre-implantation embryos

Abstract

The pre-implantation embryonic stage called blastocyst comprises of inner cell mass (ICM) tissue, which is a mosaic of epiblast (EPI) and primitive endoderm (PE) cells. Prior to uterine implantation, EPI and PE segregate into distinct tissue layers, which will give rise to the fetal body and extra-embryonic structures, respectively. Rhoassociated coiled-coil containing protein kinase (ROCK) is an enzyme responsible for a plethora of cellular functions, including cell migration and cell-to-cell adhesion. To investigate ROCK's role in EPI and PE segregation, blastocysts, prior to tissue segregation, were treated with ROCK inhibitor Y-27632 and immunostained for cell lineage-specific markers. Results showed EPI and PE cells remained intermingled, and ICM cells became loosely associated. Blastocysts treated with Fasudil, another ROCK inhibitor, showed similar results. This suggests that ROCK is required for segregation, possibly by mediating intercellular adhesion to maintain ICM morphology and differential cell adhesion to promote EPI and PE cell sorting.