PtdIns(3,4,5)P3 is constitutively synthesized and required for spindle translocation during meiosis in mouse oocytes

Abstract

SummaryPrior to ovulation, mammalian oocytes complete their first meiotic division and arrest at metaphase II. During this marked asymmetric cell division, the meiotic spindle moves dramatically from the center of the oocyte to the cortex to facilitate segregation of half of its chromosomal content into the diminutive first polar body. Recent investigations have documented crucial roles for filamentous actin (Factin) in meiotic spindle translocation. However, the identity of the upstream regulators responsible for these carefully orchestrated movements has remained elusive. Utilizing fluorescently tagged probes and time-lapse confocal microscopy, we document that phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P 3 ] is constitutively synthesized with spatial and temporal dynamics similar to that of F-actin and Formin 2 (Fmn2). Blockage of PtdIns(3,4,5)P 3 synthesis by LY294002, a specific inhibitor of phosphoinositide 3-kinase (PI3K), disrupts cytoplasmic F-actin organization and meiotic spindle migration to the cortex. F-actin nucleator Fmn2 and Rho GTPase Cdc42 play roles in mediating the effect of PtdIns(3,4,5)P 3 on F-actin assembly. Moreover, the spatial and temporal dynamics of PtdIns(3,4,5)P 3 is impaired by depletion of MATER or Filia, two oocyte proteins encoded by maternal effect genes. Thus, PtdIns(3,4,5)P 3 is synthesized during meiotic maturation and acts upstream of Cdc42 and Fmn2, but downstream of MATER/Filia proteins to regulate the F-actin organization and spindle translocation to the cortex during mouse oocyte meiosis.

Specific deletion ofCdc42does not affect meiotic spindle organization/migration and homologous chromosome segregation but disrupts polarity establishment and cytokinesis in mouse oocytes

“…Cdc42 is also associated with the spindle's asymmetric position/rotation in many systems; however, Cdc42 is not necessary for this process (Figures 2B and 5B and Supplemental Movies S1B and S4B), although active Cdc42 moves to the cortex along with chromosomes (Figure 3A and Supplemental Movies S2A) during mouse oocyte maturation, which is also reported in two recent articles (Dehapiot et al. , 2013; Zheng et al. , 2013).…”

Phosphoinositides, Major Actors in Membrane Trafficking and Lipid Signaling Pathways

“…PtdIns(3,4,5) P 3 also promotes rearrangements of the actin cytoskeleton in response to growth factors via the activation of the Rho GTPase Cdc42 that mediates filamentous actin assembly. This dynamic assembly of actin plays an important role in the translocation of the meiotic spindle from the center of the oocyte to the cortex [97,134]. …”

Protein kinase Cδ (PKCδ) involved in the regulation of pAkt1 (Ser473) on the release of mouse oocytes from diplotene arrest

“…3 The occurrence of germinal vesicle break down (GVBD) initiates the event of asymmetry division. However, the mechanisms controlling oocyte maturation still need to be further explored.…”