Studies on the Cumulus Expansion and Oocyte Maturation of Mouse Cumulus-Oocyte Complexes: Regulation of Intracellular cAMP Level

생쥐 난자-난구 복합체의 성숙과 분산에 관한 연구 : 세포내 cAMP의 조절

Cyclic AMP (cAMP) was known to play a key role in the regulation of cumulus expansion and oocyte maturation of mammalian cumulus-oocyte complexes (COC's) in vivo and in vitro. The present experiments were conducted to know how intracellular level of cAMP in these cells is controlled. Intracellular cAMP level was modulated by culturing mouse CGC's with an adenylate cyclase stimulator, forskolin, a phosphodiesterase inhibitor, 3-isobutyl-1-methyixanthine (IBMX), human chorionic gonadotrophin (HCG), or follicle stimulating hormone (FSH). The rate of cumulus expansion and germinal vesicle break-down (GVBD) was checked after culture and used as a biological end point. Forskolin in the medium began to stimulate the expansion of the complexes at 1 nM and induced maximum expansion (80~90%) at 0 1~10 $\mu$M. The expansion rate was reduced to 60% when forskolin concentration was increased to 100 $\mu$M. Oocyte GVBD occurred normally (75~82%) in the presence of 10 $\mu$M of forskolin, but partial suppression was appeared at 100 pM of the drug (40%). IBMX also stimulated the expansion from the concentration of 0.01 pM and induced full expansion (81~89%) between the concentration of 1-1000 $\mu$M. Meiotic resumption was occurred normally under 10 $\mu$M of IBMX, but suppressed drastically from the concentration of 100 $\mu$M. The minimum exposing time to hormone or drugs required to trigger cumulus expansion was two minutes with HCG, 15~30 minutes with FSH and fors kolin, and two hours with IBMX. The data presented here seemed to imply that intracellular cAMP level in cumulus cells is regulated by both adenylate cyclase and phosphodiesterase and cumulus expansion is induced by a peak of cAMP while meiotic arrest is maintained by continuous presence of cAMP.

생쥐 난자-난구 복합체를 인공배양하면서 adenylate cyclase의 촉진제인 forskilin과 phosphodiesterase의 저해제인 3-isobutyl-1-methylxanthine(IBMX)을 배양액에 첨가하여 이들이 난구세포의 분산과 난자의 성숙(핵붕괴)에 미치는 효과를 관찰한 결과 다음과 같았다. 1. Forskilin은 0.001$\mu$M에서 부터 난구세포의 분산을 유도하기 시작하여 (36%) 0.1-10$\mu$M 구간에서 최대의 분산율을 나타내었고 (80-90%) 100$\mu$M에서는 그 효과가 줄어들었다(60%). 이때 난자의 핵 붕괴는 10$\mu$M까지 정상으로 일어나다 (75-80%) 100$\mu$M에서 부분적으로 억제되기 시작하였다(40%). 2. IMBX는 0.01$\mu$M에서 부터 난구세포의 분산을 유도하기 시작하여 (30%) 1-1,000$\mu$M의 전 구간에서 최대의 분산율(81-89%)을 나타내었다. 난자들은 10$\mu$M의 농도까지 정상적으로 핵 붕괴를 일으키었으나(90% 이상) 100$\mu$M 이상에서 급격히 억제되었다(14%). 3. 난구세포의 분산을 유도하는데 필요한 최소의 자극기간을 조사해 본 결과 HCG는 2분, FSH와 forskilin은 15-30분, IBMX는 2시간이었다. 위 결과로 부터 생쥐 난구세포에서 cAMP의 농도를 높이는데 adenylate cyclase 와 phosphodiesterase의 두 효소가 모두 중요한 기여를 하며 난구세포는 단 기간에 생긴 cAMP의 peak로서 분산이 유도될 수 있으나 난자의 성숙억제 과정에서는 지속적인 cAMP의 존재가 필요하다는 것을 알았다.