Ste20-like kinase (SLK) is involved in cell proliferation and migration in somatic cells.This study aims to explore SLK expression and function in mouse oocyte meiosis.Western blot, immunofluorescence, Co-immunoprecipitation, drug treatment, cRNA construct and in vitro transcription, microinjection of morpholino oilgo (MO) and cRNA were performed in oocytes. High and stable protein expression of SLK was detected in mouse oocyte meiosis, with dynamic distribution in the nucleus, chromosomes and spindle apparatus. SLK phosphorylation emerges around meiotic resumption and reaches a peak during metaphase I (MI) and metaphase II. SLK knockdown with MO or expression of kinase-dead SLK K63R dramatically delays meiotic resumption due to sequentially suppressed phosphorylation of Polo-like kinase 1 (Plk1) and cell division cycle 25C (CDC25C) and dephosphorylation of cyclin-dependent kinase 1 (CDK1). SLK depletion promotes ubiquitination-mediated degradation of paxillin, an antagonist to α-tubulin deacetylation, and thus destroys spindle assembly and chromosome alignment; these phenotypes can be substantially rescued by exogenous expression of SLK kinase active fragment. Additionally, exogenous SLK effectively promotes meiotic progression and spindle assembly in aging oocytes with reduced SLK. Collectively, this study reveals SLK is required for meiotic resumption and spindle assembly in mouse oocyte meiosis.
| INTRODUCTIONMammalian oocytes of high-developmental-competence are required for successful fertilization and subsequent embryo development, which initiates a new life. 1 Fully-grown oocytes are arrested at the diplotene stage of the first meiotic prophase, known as the germinal vesicle (GV) stage. 2 Following the ovulatory luteinizing hormone (LH) surge, the resumption of meiosis occurs with the signature of germinal vesicle breakdown (GVBD) followed by chromatin condensation. 3,4 During the prometaphase of meiosis I (Pro-MI), the acentrosomal spindle is assembled along with the congression of condensed chromosomes. 5 Upon all chromosomes are correctly aligned and stably attached by microtubules from spindle poles at metaphase I (MI), the meiotic cell cycle moves to anaphase I (AI), during which the homologous chromosomes are segregated, and the first polar body (PB1) is discharged. 6 The orderly meiotic progression is essential for the high-quality oocytes and, furthermore, female reproductive health. 1,7 The abnormal oocyte meiotic process leads to embryo aneuploidy, a significant cause of infertility, abortion and fetal deformity. 7 The fully-grown oocytes accumulate large quantities of mRNAs and proteins and stop de novo mRNA transcription at the GV stage, so the meiotic progression is regulated by a complex and cascading