Identification, subcellular localization, and functional comparison of novel Yap splicing isoforms in mouse embryonic stem cells.

Hippo signaling pathway is involved in many biological processes including the fate decision of embryonic stem cells (ESCs). Yes-associated protein (Yap) function as a key effector of Hippo pathway, but its role in ESCs is still controversial. So far, only two isoforms of Yap have been identified and they have both overlapping and distinct functions. Here, we identify six novel isoforms of mouse Yap, bringing the total number of isoforms to eight. According to the differences in the first exon, they are divided into two subtypes (a and b). Isoform-a and isoform-b exhibit different subcellular localizations. Moreover, isoform-a can fully reverse the impaired self-renewal phenotype induced by Yap knockout (KO). Upon overexpression, isoform-a moderately promotes mESCs self-renewal and markedly delays differentiation. On the contrary, no significant pro-self-renewal phenotype is observed when isoform-b overexpressed in wildtype (WT) mESCs or re-expressed in Yap KO cell lines. These finding not only help to clarify the role of Yap in mESCs, but also lay the foundation for advancing functional researches of Yap in other processes.