FHOD1 regulates cytoplasmic actin-based spindle migration for mouse oocyte asymmetric cell division.

FHOD1 is a member of Diaphanous-related formins (DRFs) which belongs to the Formin family. Previous studies have shown that the DFRs might affect several cellular functions such as morphogenesis, cytokinesis, cell polarity, and embryonic differentiation. However, there is no evidence showing the functions of FHOD1 during oocyte meiosis. This study is aimed at exploring the roles of FHOD1 during the mammalian oocyte maturation. Immunofluorescent staining showed that FHOD1 was restricted to the nucleus in germinal vesicle (GV) stage of the oocytes, after the GV breakdown FHOD1 was primarily located at two poles of the spindle at both metaphases I and II stages. Knockdown of FHOD1 by siRNA injection did not affect polar body extrusion but generated the large polar bodies. In addition, we observed the spindle migration failure in metaphase I oocytes, with a large number of meiotic spindles anchoring in the center of cytoplasm. The expression level of cytoplasmic actin but not cortex actin was significantly reduced, indicating that FHOD1 regulates cytoplasmic actin distribution for the spindle movement. Furthermore, we found that the disruption of ROCK (the Rho-dependent protein kinase) with inhibitor Y-27632 caused the decreased FHOD1 protein expression. Therefore, our data indicate that FHOD1 is regulated by ROCK for cytoplasm actin assembly and spindle migration during mouse oocyte meiosis.

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