Time-related effect of GnRH on histone H1 kinase activity in the goldfish follicle-enclosed oocyte

The level of cyclin B-associated cdc2 kinase, a component of maturation pro moting factor (MPF), is known to be high during metaphase of the meiotic ma turation of oocytes. The time-related action of gonadotropin-realising horm ones (GnRH) on histone H1 kinase activity (known to reflect cdc2 kinase act ivity) was investigated in vitro in follicle-enclosed goldfish oocytes. Ger minal vesicle breakdown (GVBD) and testosterone production were also invest igated in the same follicle-enclosed goldfish oocytes to determine the temp oral relationship between GnRH-induced histone H1 kinase activity and the r einitiation of meiosis and steroidogenesis. Treatments with gonadotropin (G TH) or GnRH stimulated the histone H1 kinase activity to the same maximum l evel. However, sGnRH- and cGnRH-II-induced histone H1 kinase activity were significantly higher compared with controls after 2 hours of treatment, whe reas the GTH-induced increase became significantly higher after 6-8 hours o f incubation. Overall, the results demonstrate a close temporal relationshi p between GVBD response and histone H1 kinase activity induced by GTH and s GnRH-cGnRH-II.