Chronological and ultrastructural changes in camel (Camelus dromedarius) oocytes during in vitro maturation

Cumulus-oocyte complexes (COCs) were collected from non-pregnant camels at a local slaughterhouse by aspiration from antral follicles (2-6 mm). In Experiment I, camel COCs (n=304) were matured in vitro in Hams-F10, fixed at different time intervals (6, 12, 18, 24, 30, 36, 42, or 48 h) and stained with 1% aceto-orcein to assess nuclear changes in culture. A majority of the oocytes (81.5%) underwent germinal vesicle break down (GVBD) between 6 and 12h. Forty-eight percent of the oocytes were observed at the metaphase I (M I) stage by 18 h culture. The percentage of matured oocytes (M II stage) at 30 and 42 h were 66.5 and 71% respectively, which were significantly (p<0.05) different to that observed at 24 h (42.5%). In Experiment II, after different periods of culture (12, 24, 36, or 48 h), the COCs (n=26) were processed for transmission electron microscopy. Expansion of both the cumulus and corona radiate cells occurred between 12 and 24 h in the majority of oocytes concomitant with enlargement of the cumulus cell process endings (CCPEs) in the developed perivitelline space. After 12 h of culture disruption of the junctions between CCPEs and the oolemma was observed together with and breakdown of the GV. For 24-36 h of culture cortical granules had spread and aligned along the oolemma. Signs of degeneration in the cytoplasmic organelles of the oocytes were also observed from less than 36 h. After 48 h of culture, larger vesicles and lipid droplets had appeared in the central part of the oocytes and showed uneven distribution throughout the ooplasm. Predominantly non-penetrating CCPEs were also observed in four oocytes by 48 h. In conclusion, based on both light and electron microscopic evaluations, the optimal culture time for the development of competent Camelus dromedarius oocytes in vitro appears to be 30 h using Hams-F10 medium.