Nature：一个涉及钙调神经磷酸酶的新通道

生物谷

September 20, 2007

从受精到卵中胞质Ca2+浓度增加（多细胞生物卵激发过程中的一个至关重要的事件）的通道已经明确确定了，但对其下游通道的研究却不是很多。现在，两个研究小组报告了这方面的研究。他们发现了一个新的涉及磷酸酶、钙调神经磷酸酶的通道。由钙诱导的钙调神经磷酸酶的激发，对于Xeonopus中胚胎发育的抑制是必不可少的，促使卵母细胞走出受精之后减数分裂的M-阶段中的细胞周期抑制时期。然后，第二波磷酸酶活动则充当进入有丝分裂的一个通道。

原始出处：

Nature 449, 336-340 (20 September 2007) | doi:10.1038/nature06121; Received 4 May 2007; Accepted 26 July 2007

Calcineurin is required to release Xenopus egg extracts from meiotic M phase

Satoru Mochida1 & Tim Hunt1

Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK

Correspondence to: Tim Hunt1 Correspondence and requests for materials should be addressed to T.H. (Email: tim.hunt@cancer.org.uk).

Fertilization induces a transient increase in cytoplasmic Ca2+ concentration in animal eggs that releases them from cell cycle arrest in the second meiotic metaphase1. In frog eggs, Ca2+ activates Ca2+/calmodulin-activated kinase, which inactivates cytostatic factor2, 3, 4, 5, allowing the anaphase-promoting factor to turn on and ubiquitinate cyclins and securin, which returns the cell cycle to interphase6. Here we show that the calcium-activated protein phosphatase calcineurin7 is also important in this process. Calcineurin is transiently activated after adding Ca2+ to egg extracts, and inhibitors of calcineurin such as cyclosporin A (ref. 8) delay the destruction of cyclins, the global dephosphorylation of M-phase-specific phosphoproteins and the re-formation of a fully functional nuclear envelope. We found that a second wave of phosphatase activity directed at mitotic phosphoproteins appears after the spike of calcineurin activity. This activity disappeared the next time the extract entered M phase and reappeared at the end of mitosis. We surmise that inhibition of this second phosphatase activity is important in allowing cells to enter mitosis, and, conversely, that its activation is required for a timely return to interphase. Calcineurin is required to break the deep cell cycle arrest imposed by the Mos-MAP (mitogen-activated protein) kinase pathway4, 5, 9, and we show that Fizzy/Cdc20, a key regulator of the anaphase-promoting factor6, is an excellent substrate for this phosphatase.