Abstract
The microtubule-associated protein ASPM (abnormal spindle-like microcephaly-associated) plays an important role in spindle organization and cell division in mitosis and meiosis in lower animals, but its function in mouse oocyte meiosis has not been investigated. In this study, we characterized the localization and expression dynamics of ASPM during mouse oocyte meiotic maturation and analyzed the effects of the downregulation of ASPM expression on meiotic spindle assembly and meiotic progression. Immunofluorescence analysis showed that ASPM localized to the entire spindle at metaphase I (MI) and metaphase II (MII), colocalizing with the spindle microtubule protein acetylated tubulin (Ac-tubulin). In taxol-treated oocytes, ASPM colocalized with Ac-tubulin on the excessively polymerized microtubule fibers of enlarged spindles and the numerous asters in the cytoplasm. Nocodazole treatment induced the gradual disassembly of microtubule fibers, during which ASPM remained colocalized with the dynamic Ac-tubulin. The downregulation of ASPM expression by a gene-specific morpholino resulted in an abnormal meiotic spindle and inhibited meiotic progression; most of the treated oocytes were blocked in the MI stage with elongated meiotic spindles. Furthermore, coimmunoprecipitation combined with mass spectrometry and western blot analysis revealed that ASPM interacted with calmodulin in MI oocytes and that these proteins colocalized at the spindle. Our results provide strong evidence that ASPM plays a critical role in meiotic spindle assembly and meiotic progression in mouse oocytes.
Highlights
In mammals, meiosis is unique to germ cells and is critical for sexual reproduction [1]
When oocytes progressed to pro-metaphase I (MI) and MI, ASPM was concentrated at the total spindle apparatus; for MIIarrested oocytes, ASPM was concentrated at the spindle and the polar body (Figure 1B)
Throughout meiosis, Ac-tubulin coimmunostained with ASPM, suggesting that ASPM might play a role in spindle organization
Summary
Meiosis is unique to germ cells and is critical for sexual reproduction [1]. Each oogonium that initiates meiosis divides twice to form a single oocyte. Oocytes from all mammalian species are blocked in the ovary in prophase of meiosis I until meiosis resumes. During arrest, they contain a large centrally located nucleus called the germinal vesicle (GV). The oocyte is triggered to resume meiosis by gonadotropin stimulation or other factors. Spindle formation is followed by two consecutive asymmetric divisions, resulting in the formation of a large haploid oocyte and small polar bodies [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
