Biology Department, University of Massachusetts Amherst, Amherst, MA 01003, USA.
Development. 2010 Mar;137(6):953-61. doi: 10.1242/dev.041939. Epub 2010 Feb 11.
The caspase family protease, separase, is required at anaphase onset to cleave the cohesin complex, which joins sister chromatids. However, among eukaryotes, separases have acquired novel functions. Here, we show that Arabidopsis thaliana radially swollen 4 (rsw4), a temperature-sensitive mutant isolated previously on the basis of root swelling, harbors a mutation in At4g22970, the A. thaliana separase. Loss of separase function in rsw4 at the restrictive temperature is indicated by the widespread failure of replicated chromosomes to disjoin. Surprisingly, rsw4 has neither pronounced cell cycle arrest nor anomalous spindle formation, which occur in other eukaryotes upon loss of separase activity. However, rsw4 roots have disorganized cortical microtubules and accumulate the mitosis-specific cyclin, cyclin B1;1, excessive levels of which have been associated with altered microtubules and morphology. Cyclin B1;1 also accumulates in certain backgrounds in response to DNA damage, but we find no evidence for aberrant responses to DNA damage in rsw4. Our characterization of rsw4 leads us to hypothesize that plant separase, in addition to cleaving cohesin, regulates cyclin B1;1, with profound ramifications for morphogenesis.
半胱氨酸天冬氨酸蛋白酶家族的蛋白酶，分离酶，在后期起始时需要将姐妹染色单体连接的黏合蛋白复合物切割。然而，在真核生物中，分离酶已经获得了新的功能。在这里，我们表明拟南芥径向肿胀 4（rsw4），一个先前基于根肿胀分离的温度敏感突变体，携带 At4g22970 的突变，即拟南芥分离酶。rsw4 在限制温度下分离酶功能的丧失表明，复制染色体广泛未能分离。令人惊讶的是，rsw4 既没有明显的细胞周期停滞，也没有在其他真核生物中失去分离酶活性时出现的异常纺锤体形成。然而，rsw4 的根皮层微管排列紊乱，并积累有丝分裂特异性周期蛋白 cyclin B1;1，过多的 cyclin B1;1 与微管和形态的改变有关。cyclin B1;1 也会在某些背景下响应 DNA 损伤而积累，但我们没有发现 rsw4 对 DNA 损伤有异常反应的证据。我们对 rsw4 的表征使我们假设植物分离酶除了切割黏合蛋白外，还调节 cyclin B1;1，这对形态发生有深远的影响。
