Friday Harbor Laboratories, University of Washington, Friday Harbor, Washington, USA.
Mol Reprod Dev. 2011 Oct-Nov;78(10-11):726-33. doi: 10.1002/mrd.21349. Epub 2011 Jul 19.
Most mature ascidian oocytes undergo germinal vesicle breakdown (GVBD) when released by the ovary into sea water (SW). Acidic SW blocks this but they can be stimulated by raising the pH, increasing intracellular cAMP levels by cell permeant forms, inhibiting its breakdown or causing synthesis. Boltenia villosa oocytes undergo GVBD in response to these drugs. However, the cAMP receptor protein kinase A (PKA) does not appear to be involved, as oocytes are not affected by the kinase inhibitor H-89. Also, the PKA independent Epac agonist 8CPT-2Me-cAMP stimulates GVBD in acidic SW. GVBD is inhibited in calcium free sea water (CaFSW). The intracellular calcium chelator BAPTA-AM blocks GVBD at 10 µM. GVBD is also inhibited when the ryanodine receptors (RYR) are blocked by tetracaine or ruthenium red but not by the IP(3) inhibitor D-609. However, dimethylbenzanthracene (DMBA), a protein kinase activator, stimulates GVBD in BAPTA, tetracaine or ruthenium red blocked oocytes. The calmodulin kinase inhibitor KN-93 blocks GVBD at 10 µM. This and preceding papers support the hypothesis that the maturation inducing substance (MIS) produced by the follicle cells in response to increased pH causes activation of a G protein which triggers cAMP synthesis. The cAMP then activates an Epac molecule, which causes an increase in intracellular calcium from the endoplasmic reticulum ryanodine receptor. The increased intracellular calcium subsequently activates calmodulin kinase, which causes an increase in cdc25 phosphatase activity, activating MPF and the progression of the oocyte into meiosis.
大多数成熟的海鞘卵母细胞在从卵巢释放到海水中（SW）时会经历核膜破裂（GVBD）。酸性 SW 会阻止这种情况发生，但可以通过提高 pH 值、通过细胞渗透形式增加细胞内 cAMP 水平、抑制其分解或引起合成来刺激它们。绒毛海鞘卵母细胞会对这些药物产生 GVBD 反应。然而，cAMP 受体蛋白激酶 A（PKA）似乎并未参与，因为激酶抑制剂 H-89 不会影响卵母细胞。此外，PKA 非依赖性 Epac 激动剂 8CPT-2Me-cAMP 在酸性 SW 中刺激 GVBD。在无钙海水中（CaFSW），GVBD 受到抑制。细胞内钙螯合剂 BAPTA-AM 在 10μM 时阻断 GVBD。当 Ryanodine 受体（RYR）被四卡因或钌红阻断而不是被 IP（3）抑制剂 D-609 阻断时，GVBD 也会受到抑制。然而，蛋白激酶激活剂二苯并蒽（DMBA）在 BAPTA、四卡因或钌红阻断的卵母细胞中刺激 GVBD。钙调蛋白激酶抑制剂 KN-93 在 10μM 时阻断 GVBD。本研究及之前的研究支持了这样一种假设，即滤泡细胞在 pH 值升高时产生的成熟诱导物质（MIS）会激活 G 蛋白，从而触发 cAMP 合成。然后，cAMP 激活 Epac 分子，导致内质网 Ryanodine 受体的细胞内钙增加。随后增加的细胞内钙激活钙调蛋白激酶，导致 cdc25 磷酸酶活性增加，激活 MPF，促使卵母细胞进入减数分裂。
