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Introduction
Protein kinase C (PKC) is a multigene family of Ser/Thr kinases that is central to many signal transduction pathways (Hug & Sarre, 1993). The family is composed of 11 different isoforms that are subdivided into three groups based on sequence homology, as well as on activator and cofactor requirements. These groups include the conventional (PKC[alpha], [beta]I, [beta]II and [gamma]), novel (PKC[delta], [GREEK LUNATE EPSILON SYMBOL], [theta], [mu] and [eta]), and atypical (PKC[lambda]/[tau] and [zeta]) isoforms (Knopf et al., 1986; Osada et al., 1990; Selbie et al., 1993). Several studies have shown that mammalian oocytes are well equipped for PKC signalling and isoforms of all three subfamilies of PKCs have been identified at protein level in mouse (Luria et al., 2000; Quan et al., 2003), rat (Raz et al., 1998), pig (Fan et al., 2002) and human (Wu et al., 2006) oocytes. PKC isoforms were found to exist in mouse oocytes and early embryos, and their subcellular localization was in a stage-dependent fashion during oocyte maturation, activation and early embryonic mitosis (Gangeswaran & Jones, 1997; Luria et al. 2000; Pauken & Capco, 2000; Dehghani & Hahnel, 2005). Numerous investigators have proposed that PKC is involved in many biological processes during mouse oocyte meiosis, fertilization and early embryonic mitosis, including spindle organization and stabilization, polar-body extrusion, cortical granule exocytosis, oocyte activation, completion of the second meiosis and initiation of the first mitosis, nuclear remodeling, embryo compaction, and blastocyst formation as well (Luria et al., 2000; Viveiros et al., 2001, 2004; Fan et al., 2002; Avazeri et al., 2004; Page Baluch et al., 2004; Dehghani & Hahnel, 2005).
Advanced maternal age in mammals is associated with reduced fertility (Hassold & Chiu, 1985). The cause of this decline of fertility in older mammals has been the subject of many studies. Maternal age has been shown to affect oocyte quality and early development (Navot et al., 1991; Battaglia et al., 1996). Our previous study suggested that oocytes from 12-month-old mice showed a significantly higher rate of chromosome misalignment and premature chromatids than that from 6-8-week-old mice (Cui et al., 2005a). However, it is unknown whether PKC...