在細(xì)胞分裂過(guò)程中紡錘絲與著絲粒起初會(huì)以隨機(jī)方式相連接，使得前中期存在許多錯(cuò)誤的連接方式,。比如一個(gè)著絲粒同時(shí)受到來(lái)自相反方向的紡錘絲牽引,，這種現(xiàn)象被稱作merotelic連接。如果這些錯(cuò)誤的連接不被糾正,，將會(huì)導(dǎo)致著絲粒間的拉力異常,，引起染色體的不同步分離。因此,，真核生物采用了一種監(jiān)控機(jī)制來(lái)延遲染色體分離,，給糾正錯(cuò)誤連接方式留有充足時(shí)間，該機(jī)制被稱作紡錘體組裝監(jiān)控,。Bub1是一個(gè)絲氨酸/蘇氨酸蛋白激酶,，它是紡錘體組裝監(jiān)控機(jī)制中的上游蛋白，可以招集其它監(jiān)控蛋白定位到著絲粒上,。雖然Bub1的序列和功能在不同物種中比較保守,，可在植物界中至今仍未有相關(guān)報(bào)道。
中科院遺傳與發(fā)育生物學(xué)研究所程祝寬課題組利用圖位克隆的方法,，在水稻中克隆了植物中首個(gè)Bub1同源基因BRK1(Bub1-related kinase1),。brk1突變體營(yíng)養(yǎng)生長(zhǎng)正常，但在減數(shù)分裂后期I姊妹染色單體提前分離,，最終導(dǎo)致完全不育,。BRK1具有保守的TPR和激酶結(jié)構(gòu)域,，而缺失了GLEBS結(jié)構(gòu)域,。BRK1在減數(shù)分裂及有絲分裂過(guò)程中始終定位在著絲粒蛋白復(fù)合體的外層，與酵母及多細(xì)胞動(dòng)物相似,，BRK1對(duì)于著絲粒區(qū)域組蛋白H2A第134位蘇氨酸的磷酸化起重要作用,，并且調(diào)控shugoshin蛋白的著絲粒定位。在brk1突變體減數(shù)分裂中期I，錯(cuò)誤的merotelic連接方式不能被及時(shí)修正,，使得該時(shí)期同源染色體著絲粒間的拉力降低,，并引起紡錘體形態(tài)異常，最終導(dǎo)致后期I同源染色體分離的不同步,。在BRK1喪失功能的情況下,，著絲粒區(qū)域組蛋白H3第10位絲氨酸在終變期不能被磷酸化。H3第10位絲氨酸是Aurora B激酶的保守底物,，而Aurora B又直接參與微管和著絲粒錯(cuò)誤連接的糾正,。因此，推測(cè)BRK1通過(guò)調(diào)節(jié)中期I早期Aurora激酶的定位從而促進(jìn)錯(cuò)誤連接方式的糾正,。
該研究為探索植物紡錘體組裝監(jiān)控蛋白的功能開創(chuàng)了先例,，研究結(jié)果于12月15日在Plant Cell雜志上在線發(fā)表（DOI:10.1105/tpc.112.105874）。相關(guān)研究得到科技部和國(guó)家自然科學(xué)基金委項(xiàng)目的資助,。(生物谷Bioon.com)
DOI:10.1105/tpc.112.105874
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BRK1, a Bub1-Related Kinase, Is Essential for Generating Proper Tension between Homologous Kinetochores at Metaphase I of Rice Meiosis
Mo Wanga,1, Ding Tanga,1, Qiong Luob, Yi Jina, Yi Shena, Kejian Wanga and Zhukuan Chenga,2
Bub1 (for budding uninhibited by benzimidazole 1), one of the main spindle checkpoint kinases, acts as a kinetochore scaffold for assembling other checkpoint proteins. Here, we identify a plant Bub1-related kinase 1 (BRK1) in rice (Oryza sativa). The brk1 mutants are sterile due to the precocious separation of sister chromatids at the onset of anaphase I. The centromeric recruitment of SHUGOSHIN1 and phosphorylation of histone H2A at Thr-134 (H2A-pT134) depend on BRK1. Although the homologs can faithfully separate from each other at the end of meiosis I, the uncorrected merotelic attachment of paired sister kinetochores at the early stage of metaphase I in brk1 reduces the tension across homologous kinetochores, causes the metaphase I spindle to be aberrantly shaped, and subsequently affects the synchronicity of homolog separation at the onset of anaphase I. In addition, the phosphorylation of inner centromeric histone H3 at Ser-10 (H3-pS10) during diakinesis depends on BRK1. Therefore, we speculate that BRK1 may be required for normal localization of Aurora kinase before the onset of metaphase I, which is responsible for correcting the merotelic attachment. Glossary SAC spindle assembly checkpoint APC/C anaphase-promoting complex/cyclosome CPC chromosomal passenger complex RACE rapid amplification of cDNA ends RNAi RNA interference TPR tetratrichopeptide repeat FISH fluorescence in situ hybridization DAPI 4′,6-diamidino-2-phenylindole
