253. Calcium ionophore induction of marmoset oocyte activation

Abstract

The marmoset monkey (Callithrix jacchus) is a valuable model for developing assisted reproductive technologies in humans and endangered primate species. Calcium ionophore treatments have been used to induce parthenogenetic activation in a number of species, but the effectiveness of this reagent in initiating marmoset embryo development has not yet been reported. The aim of this study was to determine the developmental potential of in vitro matured (IVM) marmoset oocytes, following treatment with calcium ionophore. Immature oocytes from large (LA; >1.5 mm) and small (SA; 0.67–1.5 mm) antral follicles were isolated from the ovaries of FSH-primed animals and cultured in modified G2 medium for 26–30 h at 37.0°C in 6% CO₂ in air. Meiotically mature oocytes were sequentially incubated with 5 μM ionomycin for 5 min and 2 mM 6-dimethylaminopurine for 3 h and cultured in G1/G2 sequential medium at 37.0°C in 5% O₂, 6% CO₂, 89% N₂ for 10 days. Cumulus cell expansion associated with LA oocytes (n = 118) was greater than that of SA oocytes (n = 212), as determined using well established classification criteria (2.7 ± 0.1 v. 1.8 ± 0.2; P < 0.01). A greater proportion of LA oocytes completed meiosis to the metaphase-II stage compared with SA oocytes (85 ± 7% v. 63 ± 7%; P < 0.05). Pronuclear formation was induced at similar rates in mature oocytes of both groups, but the rate of cleavage was higher for LA oocytes compared with SA oocytes (93 ± 6% v. 66 ± 5%; P < 0.05). The number of cells per embryo was not different between the groups. This is the first study to demonstrate that calcium ionophore effectively induces parthenogenetic activation in IVM marmoset oocytes. However, the development of parthenotes was limited beyond the 8-cell stage. Further studies are needed to determine the cause of the developmental block.