Dynamics of meiosis and protein kinase activities in bovine oocytes correlated to prolactin treatment and follicle size

Oocyte developmental competence depends on the size of the original follicl e and is affected by compounds like prolactin. We wished to investigate nuc lear and cytoplasmic maturation of bovine oocytes correlated to their origi n and response to prolactin treatment, by monitoring at frequent intervals meiotic configuration of chromosomes and activity of histone H1 and MAP-kin ase. Bovine ovaries were obtained from a slaughterhouse and oocytes were re covered by follicle isolation. Oocytes (n=1,397) with a compact cumulus wer e selected from small (2 to 3 mm) and large (4 to 5 mm in diameter) follicl es and cultured up to 28 h in TCM 199+20% bull serum with or without 50 ng/ mL bovine prolactin. Four groups of oocytes were formed: originating from s mall or large follicles, and treated or not treated with prolactin. At the scheduled time intervals for in vitro maturation, cumulus oocyte complexes from the 4 groups were randomly selected and the oocytes were analyzed for histone H1 and MAP-kinase, and for chromatin configuration. The first meiot ic division took longer to complete in oocytes from large follicles (P < 0. 01). Under the influence of prolactin the meiosis was prolonged in oocytes both from small and large follicles (P < 0.05). Histone H1 and MAP-kinases started to be activated at approximately the same time, around 6 h after be ginning maturation. But after this time, significantly lower levels of both kinase activities were found in oocytes treated with prolactin, especially those treated during Meiosis I (P < 0.05). Our results indicate a correlat ion of chromatin configuration and histone H1/MAP-kinase activities. <(c)> 2001 by Elsevier Science Inc.