Mammalian oocytes undergo meiotic maturation prior to fertilization. The oocytes are arrested at the diplotene stage of the first meiotic prophase. Upon germinal vesicle breakdown, the oocytes resume meiosis, followed by microtubule assembly and chromatin segregation. The oocytes then complete the first meiotic division and become arrested at the metaphase stage of the second meiotic division, awaiting fertilization [1,2]. Mammalian oocytes are unique in their ability to undergo asymmetric cell division. Through asymmetric division, oocytes produce a smaller first polar body and a larger oocyte. This asymmetric division plays a crucial role in the correct segregation of the oocyte genome and the highly asymmetric distribution of cytoplasm. The larger oocyte is essential for storing maternal materials and supporting fertilization [3].

Actin filaments are key factors controlling asymmetric division in mouse oocytes. During oocyte maturation, two characteristic events occur in the reorganization of the actin cytoskeleton: the formation of an actin cap in the cortical region near the spindle and dynamic changes in the density of the cytoplasmic actin network [[4], [5], [6]]. The actin cytoskeleton is primarily composed of various actin-binding proteins. Myosins, which are actin-dependent motor proteins, have diverse functions, including the regulation of cytokinesis, cell motility, and cell polarity [5]. The microfilament skeleton also includes structural proteins such as radixin, which can form complexes with ezrin and moesin. These proteins are cytoskeletal components that may be important in linking actin to the plasma membrane [7,8]. Although some progress has been made in understanding the regulation of asymmetric division by the actin cytoskeleton, the mechanisms by which these microfilament proteins are regulated remain unclear.

DDX5 (DEAD-Box Helicase 5), also known as p68, is a protein belonging to the DEAD-box RNA helicase family. It functions as an ATP-dependent RNA helicase and plays critical roles in various biological processes, including transcriptional regulation, RNA splicing, and miRNA processing [9,10]. Recent studies have shown that DDX5 has important functions in the reproductive system. In the male mouse reproductive system, DDX5 is involved in spermatogenesis, acting as a transcriptional coactivator and interacting with the core reproductive transcription factor PLZF to regulate the expression of key genes and RNA metabolism, ensuring normal sperm development and function [11]. In zebrafish models, a deficiency in DDX5 results in mutants with small ovaries and female infertility [12]. Inhibition of DDX5 activity during the zygotic stage in mouse embryos leads to increased levels of γ-H2AX in both maternal and paternal pronuclei, affecting early embryonic genome activation [13]. Although these studies highlight the important roles of DDX5 in the reproductive system, and proteomic analyses reveal abundant expression of DDX5 in mouse and human oocytes [14], the specific function of DDX5 in mouse oocyte maturation remains unclear.

In this study, we demonstrate that DDX5 regulates cytokinesis during meiotic maturation in mouse oocytes. When oocytes resume meiosis, DDX5 protein exhibits partial colocalization with the spindle. Inhibition of DDX5 function results in a decreased rate of first polar body extrusion and abnormal cytokinesis in oocytes. RNA-seq experiments reveal that loss of DDX5 disrupts mRNA homeostasis in oocytes. IP-MS (Immunoprecipitation-Mass Spectrometry) experiments further demonstrate that DDX5 regulates cytokinesis by influencing the expression of microfilament-associated protein radixin. Our findings reveal that the RNA helicase DDX5 regulates oocyte cytokinesis by modulating the stability of microfilament-associated proteins radixin.