Protein kinase C delta (PKCδ) interacts with microtubule organizing center (MTOC)-associated proteins and participates in meiotic spindle organization

Defects in meiotic spindle structure can lead to chromosome segregation errors and genomic instability. In this study the potential role of protein kinase C delta (PKCδ) on meiotic spindle organization was evaluated in mouse oocytes. PKCδ was previously shown to be phosphorylated during meiotic maturation and concentrate on the meiotic spindle during metaphases I and II. Currently we show that when phosphorylated on Threonine 505 (pPKCδThr505), within the activation loop of its C4 domain, PKCδ expression was restricted to the meiotic spindle poles and a few specific cytoplasmic foci. In addition, pPKCδThr505 co-localized with two key microtubule organizing center (MTOC)-associated proteins, pericentrin and γ-tubulin. An interaction between pPKCδThr505 and pericentrin as well as γ-tubulin was confirmed by co-immunoprecipitation analysis using both fetal fibroblast cells and oocytes. Notably, targeted knockdown of PKCδ expression in oocytes using short interfering RNAs effectively reduced pPKCδThr505 protein expression at MTOCs and leads to a significant (P < 0.05) disruption of meiotic spindle organization and chromosome alignment during MI and MII. Moreover, both γ-tubulin and pericentrin expression at MTOCs were decreased in pPKCδThr505-depleted oocytes. In sum, these results indicate that pPKCδThr505 interacts with MTOC-associated proteins and plays a role in meiotic spindle organization in mammalian oocytes.