Involvement of microRNA-335-5p in cytoskeleton dynamics in mouse oocytes

MicroRNA is a short RNA molecule expressed in eukaryotic cells that is involved in multiple processes, including translational repression, target degradation and gene silencing. However, its specific role(s) in these processes remains largely unknown, especially in terms of germ cell development. The present study identified a microRNA, namely miR-335-5p, that is involved in mouse oocyte meiosis. MiR-335-5p was highly expressed in oocytes, but levels decreased markedly shortly after fertilisation. Microinjection of miR-335-5p or its inhibitor into oocytes resulted in a higher proportion of 2-cell-like MII oocytes and oocytes at the germinal vesicle breakdown and/or MI stage, indicating failure of asymmetric oocyte division. This may be due to regulation of actin because perturbation of miR-335-5p resulted in reduced expression of actin nucleator Daam1, a member of the Formin family. Moreover, injection of miR-335-5p or its inhibitor resulted in aberrant spindle morphology, namely an elongated spindle and multiple poles spindle. After injection of oocytes, levels of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) decreased, suggesting that miR-335-5p may regulate spindle formation via the mitogen-activated protein kinase pathway. Overexpression and inhibition of miR-335-5p had no effect on embryo development. Together, the results of the present study indicate that miR-335-5p is a novel regulator expressed in oocytes that is involved in cytoskeleton dynamics.