Oocyte maturation involves compartmentalization and opposing changes of cAMP levels in follicular somatic and germ cells: Studies using selective phosphodiesterase inhibitors
Oocyte maturation involves compartmentalization and opposing changes of cAMP levels in follicular somatic and germ cells: Studies using selective phosphodiesterase inhibitors
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DOI：
10.1006/dbio.1996.0226
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发表时间：
1996-09-15
影响因子：
2.7
通讯作者：
Conti, M
中科院分区：
文献类型：
--
作者：
Tsafriri, A;Chun, SY;Conti, M
第二信使cAMP参与哺乳动物和两栖动物卵母细胞成熟的调节。尽管卵母细胞内cAMP水平的降低先于生殖泡破裂（GVBD），但促性腺激素诱导排卵和卵母细胞成熟与卵泡中cAMP的主要增加有关。在哺乳动物系统中，分离的卵母细胞在体外经历自发成熟，但该过程被磷酸二酯酶（PDE）抑制剂IBMX阻断，其增加卵母细胞内cAMP水平。相反，相同的抑制剂，当添加到培养的卵泡很短的时间，增加卵泡cAMP水平，随后由GVBD的诱导。为了解决这种PDE抑制剂对分离和卵泡封闭的卵母细胞成熟的矛盾作用，我们假设减数分裂成熟需要体细胞颗粒细胞和生殖细胞中cAMP水平的相反波动。这种相反的波动可能是由于卵泡体细胞和生殖细胞隔室中PDE的选择性表达和调节。为了检验这一假设，PDE活性在不同的滤泡细胞中使用类型特异性抑制剂进行操作。通过诱导GVBD来监测两个隔室中cAMP水平随后变化的影响。在分离的卵母细胞中，自发GVBD被两种3型PDE抑制剂（cGMP抑制：CGI-PDE）米力农和西洛酰胺阻断。相反，用4型PDE（cAMP特异性）抑制剂咯利普兰治疗无效。这些结果表明，卵母细胞表达3型PDE，但不表达4型PDE，并且卵母细胞内cAMP的增加抑制GVBD。这一假设得到了证实，在原位杂交研究与PDE 3和PDE 4探针。PDE 3B mRNA主要表达于卵母细胞，而PDE 4D主要表达于颗粒细胞。在培养的卵泡中，LH处理诱导卵母细胞成熟，但促性腺激素的作用被3型抑制剂阻断，但不被4型PDE抑制剂阻断。此外，用4型PDE抑制剂而不是3型PDE抑制剂处理模拟LH的作用并诱导卵母细胞成熟，推测是通过增加颗粒细胞中的cAMP水平。我们的研究结果表明PDE亚型4和3分别位于卵泡体细胞和生殖细胞。卵母细胞中PDE 3的优先抑制可能导致卵母细胞成熟延迟，而不影响体细胞中cAMP诱导的排卵过程。相反，选择性抑制颗粒细胞cAMP-PDE可增强促性腺激素诱导排卵和卵母细胞成熟。因此，除了公认的差异表达和调节腺苷酸环化酶在体细胞和生殖细胞的卵泡室，我们建议，选择性调节和表达的PDE可能参与调节cAMP水平和控制卵母细胞成熟的排卵前哺乳动物卵泡。(C)出版社：Academic Press，Inc.
The second messenger cAMP has been implicated in the regulation of mammalian and amphibian oocyte maturation. Although a a decrease in intraoocyte levels of cAMP precedes germinal vesicle breakdown (GVBD), the gonadotropin induction of ovulation and oocyte maturation is associated with major increases of cAMP in ovarian follicles. In the mammalian system, isolated oocytes undergo spontaneous maturation in vitro but this process is blocked by treatment with a phosphodiesterase (PDE) inhibitor, IBMX, which increases intraoocyte cAMP levels. In contrast, the same inhibitor, when added to cultured follicles for a brief time, increases follicle cAMP levels, followed by the induction of GVBD. To resolve the paradoxical actions of this PDE inhibitor on the maturation of isolated and follicle-enclosed oocytes, we hypothesized that meiotic maturation requires opposing fluctuations of cAMP levels in the somatic granulosa and germ cells. Such opposing fluctuations may result from selective expression and regulation of PDEs in the somatic and germ cell compartments of the follicle. To test this hypothesis, PDE activity was manipulated in different follicular cells using type-specific inhibitors. The impact of the ensuing changes in cAMP levels in the two compartments was monitored by the induction of GVBD. In isolated oocytes, spontaneous GVBD was blocked by two inhibitors of type 3 PDE (cGMP-inhibited: CGI-PDE), milrinone and cilostamide. In contrast, treatment with an inhibitor for type 4 PDE (cAMP-specific), rolipram, was ineffective. These findings suggest that the oocyte expresses type 3 but not type 4 PDE and that increases in intraoocyte cAMP suppress GVBD. This hypothesis was confirmed by in situ hybridization studies with PDE3 and PDE4 probes. PDE3B mRNA was concentrated in oocytes while PDE4D was mainly expressed in granulosa cells. In cultured follicles, LH treatment induced oocyte maturation but the gonadotropin action was blocked by inhibitors of type 3 but not the type 4 PDE inhibitors. Furthermore, treatment with the type 4, but not the type 3, PDE inhibitor mimics the action of LH and induces oocyte maturation, presumably by increasing cAMP levels in granulosa cells. Our findings indicate that PDE subtypes 4 and 3 are located in follicle somatic and germ cells, respectively. Preferential inhibition of PDE 3 in the oocyte may lead to a delay in oocyte maturation without affecting the cAMP-induced ovulatory process in the somatic cells. Conversely, selective suppression of granulosa cell cAMP-PDE may enhance the gonadotropin induction of ovulation and oocyte maturation. Thus, in addition to the well-recognized differential expression and regulation of adenylate cyclase in the somatic and germ cell compartments of the follicle, we suggest that selective regulation and expression of PDEs may be involved in the regulation of cAMP levels and control of oocyte maturation in the preovulatory mammalian follicle. (C) 1996 Academic Press, Inc.