Poster Sessions

DEV-17

Aibing Wang

A. Wang, X. Ma, R.S. Adelstein

Nonmuscle Myosin Heavy Chain II-A Is Essential for Placental and Embryonic Development

To distinguish isoform-specific roles between nonmuscle myosin (NM) II-A and II-B and uncover novel functions of them, we expressed II-B at II-A locus using genetic replacement strategy. Our results show: first, normal homozygous Ab*/Ab* (II-B replacing II-A) embryos were found at embryonic day (E) 6.5 indicating that II-B can rescue the visceral endoderm abnormalities found in the II-A null mice at E6.5, allowing gastrulation and organogenesis to occur. It also demonstrates that the lethality of II-A null mice was not due to a specific role of NM II-A but due to a decrease in the total amount of NM II at this early stage. Second, Ab*/Ab* mice exhibit severe defects in placentation, which result in embryonic lethality at E9.5-10.5, indicating a unique function for NM II-A in normal placental development. Finally, the fetal vessels of mutant mice were found to fail in invading into the labyrinthine layer of the placenta, suggesting defects in cell migration, which are associated with abnormal actin organization and focal adhesion formation due to the absence of II-A. Taken together, our results indicate the importance of an isoform-specific function for NM II-A in placentation, and highlight the role of NM II-A in cell migration and adhesion.