The Hippo pathway effector Taz is required for cell morphogenesis and fertilization in zebrafish

Abstract

Hippo signaling is a critical pathway integrating extrinsic and intrinsic mechanical cues to regulate organ size. Despite its essential role in organogenesis, little is known about its role in cell fate specification and differentiation. Here we unravel a novel and unexpected role of the Hippo pathway effector Taz (wwtr1) in controlling the size, shape and fate of a unique cell in the zebrafish ovary. We show that wwtr1 mutant females are infertile. In teleosts, fertilization occurs through the micropyle, a funnel-like opening in the chorion, formed by a unique, enlarged follicle cell, the micropylar cell (MC). We describe here for the first time the mechanism underlying the differentiation of the MC. Our genetic analyses show that Taz is essential for MC fate acquisition and subsequent micropyle formation in zebrafish. We identify Taz as the first bona fide MC marker and show that Taz is specifically and strongly enriched in the MC precursor. Altogether, we performed the first genetic and molecular characterization of the MC and propose that Taz is a key regulator of the MC fate.