Practice question

During mammalian preimplantation development Hippo pathway components MST1/2 and LATS1/2 regulate formation and patterning of blastula equivalent blastocyst. In inner apolar blastomeres active Hippo cascade phosphorylates LATS1/2 via MST1/2, leading to phosphorylated YAP cytoplasmic retention and inner cell mass fate. In outer polar cells Hippo off allows nuclear YAP-TEAD interaction inducing Cdx2-driven trophectoderm fate and blastocoel cavitation. Loss of MST/LATS disrupts outside-inside lineage allocation yielding defective blastocysts. These kinases are not involved in capacitation, acrosome reaction or direct zona digestion, but are fate switches enabling blastocyst morphogenesis and embryonic-abembryonic axis specification.