Inhibition of germinal vesicle breakdown in bovine oocytes by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB).

5,6-Dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) is an analog of the nucleoside adenosine that has been used to inhibit transcription in a variety of cell types. The present studies were designed to evaluate the ability of DRB to block germinal vesicle breakdown (GVBD) in bovine oocytes matured in vitro and to characterize culture conditions required for DRB-mediated arrest of meiosis. Administration of DRB (60-90 microM) at 2-3 h intervals during culture of COC blocked GVBD in approximately 70 percent of oocytes. The inhibitory effect of DRB was reversible and required the presence of cumulus cells. Treatment with DRB was associated with a 57% decrease in 3H-uridine incorporation into total COC RNA and a 90.8% decrease into mRNA but did not affect the incorporation of 3H-leucine into COC proteins. The ability of DRB to arrest meiosis was significantly compromised if supplemental gonadotropin preparations were absent from the maturation media. Gonadotropin-induced GVBD as well as cumulus cell expansion was blocked by treatment with DRB but not with adenosine. GVBD in cultured bovine COC was initially inhibited and then stimulated when supplemental gonadotropin preparations were included in the culture media. DRB treatment in the presence of gonadotropin supplementation blocked the stimulatory effect of gonadotropins on GVBD. In conclusion, DRB can be used to arrest GVBD in bovine COC in a specific and reversible manner. The data support the hypothesis that gene transcription is required for the stimulatory phase of gonadotropin-mediated GVBD in cultured bovine COC.