Effects of cumulus cells on rabbit oocyte in vitro maturation

Abstract

Cumulus cells (CCs) are of great importance in oocyte development and maturation in many species, but detailed influence of CCs has not been extensively examined, especially on rabbit. The present study was designed to investigate the effects of CCs and the elongation of in vitro maturation (IVM) time on rabbit oocyte nuclear and ooplasmic maturation and survival. Cumulus oocyte complexes (COCs) and naked oocytes (NOs) were recovered directly from rabbits super-ovulated with eCG. Corona-enclosed oocytes (COs) and denuded oocytes (DOs) were obtained from COCs after removing a part or whole of CCs. The oocytes were cultured in the following seven groups. (i) Cumulus cell enclosed oocytes (CEOs) were cultured alone (CEOs); (ii) COs were cultured alone (COs); (iii) DOs were cultured alone (DOs); (iv) NOs were cultured alone; (v) DOs were co-cultured with COCs [DOs(COCs)]; (vi) DOs were co-cultured with CCs [DOs(CCs)]; (vii) NOs were co-cultured with CCs [NOs(CCs)]. After the oocytes were cultured for 24 and 30 h, the nuclear maturation was evaluated by first polar body (PB1) extrusion while the ooplasmic maturation was evaluated by the cleavage rate after parthenogenetic activation. The results showed that the nuclear maturation rate of CEOs, COs, DOs(COCs) and DOs(CCs) after 24 h incubation were significantly different from each other (p < or = 0.05), the rate of DOs(CCs) was similar to that of DOs (p > or = 0.05). The cleavage rates in the first two groups were significantly higher than those of the others (p < 0.05). For oocytes cultured for 30 h, the nuclear maturation rates were significantly different for each culture model (p < 0.05). The cleavage rates in first two groups were significantly higher than those of others (p < 0.05). Both the nuclear and cleavage rates significantly increased when the culture time of DOs(COCs) was prolonged from 24 to 30 h. DOs(CCs) nuclear maturation was significantly improved when the culture time was prolonged from 24 to 30 h, but the ooplasmic maturation was not. Few NOs incubated with or without CCs accomplished nuclear maturation (approximately 2% both), even when the culture time was prolonged from 24 to 30 h. The oocyte degeneration rates were significantly different for each culture model after both 24 and 30 h incubation (p < or = 0.05). There was no significant difference in oocyte degeneration in the same groups between 24 and 30 h incubation (p > 0.05). The results suggest that rabbit CCs affect oocyte nuclear and ooplasmic maturation, and their survival. The prolongation of the culture time of rabbit oocyte from 24 to 30 h improves the nuclear and ooplasmic maturation differently in the present system. Rabbit oocytes free of CCs, especially NOs, show weak meiotic resumption potential and compromised viability, which cannot be improved by co-culture with dispersed CCs. The degeneration mostly happens at early time of IVM.

Live offspring from vitrified blastocysts derived from fresh and cryopreserved ovarian tissue grafts of adult mice

“…Cumulus cells are of critical importance for the final stages of oocyte nuclear and cytoplasmic maturation (Goud et al 1998, Moor et al 1998, because compounds such as amino acids and pyruvate enter the oocytes through the cumulus cell foot processes (Gilchrist et al 2004). With the decrease in the layers of cumulus cells surrounding rabbit oocytes, the maturation rates declined (Tao et al 2008). The presence of cumulus cells and corona cells also significantly improves the developmental potential of matured oocytes post-fertilization (Anderiesz & Trounson 1995).…”

“…Removal of cumulus cells before in vitro maturation (IVM) procedures reduces the developmental potential of oocytes of many species, including mouse (Anderiesz & Trounson 1995, Chang et al 2005, rabbit (Tao et al 2008), pig (Wongsrikeao et al 2005), cow (Chian et al 1994), and human (Johnson et al 2008). Cumulus cells are of critical importance for the final stages of oocyte nuclear and cytoplasmic maturation (Goud et al 1998, Moor et al 1998, because compounds such as amino acids and pyruvate enter the oocytes through the cumulus cell foot processes (Gilchrist et al 2004).…”

The effect of human cumulus cells on the maturation and developmental potential of immature oocytes in ICSI cycles

“…Based upon our observations that the nuclear maturation rates did not show significant difference between CCs denuded group and intact group, we suggest that this effect may be mediated by improved cytoplasmic maturation [42]. It has been shown that the cumulus cells are very important to complete oocyte cytoplasmic maturation in mouse, sheep, rats, cattle and pigs [11,36,37,40,43]. Many oocytes are mature in nucleus but immature in ooplasm after IVM.…”

“…Many oocytes are mature in nucleus but immature in ooplasm after IVM. As a consequence, this asynchronization could compromise on the developmental potential [37]. It has been demonstrated that cumulus cells co-culture starting at various IVF stages has no effect on fertilization and cleavage development but significantly improves rates of embryo development to morula or blastocyst stages [44].…”

“…Cumulus cells (CCs) are of great importance in oocyte maturation, fertilization and subsequent early embryonic development in many species both in vivo and in vitro [11,36,37,40,43], including in humans [14,16,17]. In vitro maturation followed by fertilization opens a new avenue to make full use of the immature oocytes derived from controlled ovarian stimulation cycles.…”