ABSTRACT
Chromosome segregation requires the formation of a bipolar spindle. The timely bipolarization of the acentrosomal spindle during meiosis I in mouse oocytes depends on the antiparallel microtubule crosslinker Prc1. How Prc1 is regulated in oocytes remains poorly understood. In this study, we show that the kinase Cdk1 negatively regulates the spindle localization of Prc1 in mouse oocytes. The acute inhibition of Cdk1 activity led to excessive localization of Prc1 at the spindle and kinetochores, whereas the overactivation of Cdk1 had opposite effects. The overexpression of Prc1 carrying mutations at Cdk1-mediated phosphorylation sites increased its localization to the spindle, accelerated spindle bipolarization and caused spindle-checkpoint-dependent arrest at metaphase I. Overactivation of Cdk1 delayed spindle bipolarization, which was reversed by the overexpression of a phospho-mutant form but not the wild-type form of Prc1. These results suggest that Cdk1-mediated phosphorylation negatively regulates Prc1 localization to ensure the timely bipolarization of the acentrosomal spindle during meiosis I in mammalian oocytes.
Subject(s)
CDC2 Protein Kinase/metabolism , Microtubule-Associated Proteins/metabolism , Spindle Apparatus/metabolism , Animals , CDC2 Protein Kinase/genetics , Cell Cycle Proteins/metabolism , Chromosome Segregation , Female , Kinetochores/metabolism , Male , Metaphase , Mice , Mice, Inbred C57BL , Mice, Inbred DBA , Microtubules/metabolism , Oocytes/metabolism , Spindle Apparatus/geneticsABSTRACT
Acentrosomal meiosis in oocytes represents a gametogenic challenge, requiring spindle bipolarization without predefined bipolar cues. While much is known about the structures that promote acentrosomal microtubule nucleation, less is known about the structures that mediate spindle bipolarization in mammalian oocytes. Here, we show that in mouse oocytes, kinetochores are required for spindle bipolarization in meiosis I. This process is promoted by oocyte-specific, microtubule-independent enrichment of the antiparallel microtubule crosslinker Prc1 at kinetochores via the Ndc80 complex. In contrast, in meiosis II, cytoplasm that contains upregulated factors including Prc1 supports kinetochore-independent pathways for spindle bipolarization. The kinetochore-dependent mode of spindle bipolarization is required for meiosis I to prevent chromosome segregation errors. Human oocytes, where spindle bipolarization is reportedly error prone, exhibit no detectable kinetochore enrichment of Prc1. This study reveals an oocyte-specific function of kinetochores in acentrosomal spindle bipolarization in mice, and provides insights into the error-prone nature of human oocytes.
