Yamaguchi Yasuka L, Tanaka Satomi S, Yasuda Kunio, Matsui Yasuhisa, Tam Patrick P L
Embryology Unit, Children's Medical Research Institute, Locked Bag 23, Wentworthville, NSW, 2145, Australia.
Dev Biol. 2006 Sep 15;297(2):350-60. doi: 10.1016/j.ydbio.2006.04.465. Epub 2006 May 3.
Importin-mediated transport of cargoes is known to be a key mechanism for nucleo-cytoplasmic trafficking of molecules. Ipo13, which is a member of Importin-beta gene family, encodes two transcripts by utilizing different transcription start sites. In the mouse, the full-length transcript (L-Ipo13) is expressed in the primordial germ cells in the embryo and is later expressed predominantly at the pachytene phase of meiosis in both male and female germ cells. The shorter transcript (TS-Ipo13) is only expressed in the germ cells in the adult testis. Activity of L-Ipo13, but not TS-Ipo13, mediates the nuclear accumulation of ubiquitin-conjugating enzyme 9 (UBC9), a cargo of human IPO13. This finding is consistent with the progressive accumulation of UBC9 in the nucleus of the meiotic germ cells after the onset of L-Ipo13 expression. Following siRNA knockdown of IPO13 activity in the fetal ovary, fewer germ cells are found to progress to the late-pachytene stage of meiosis and nuclear accumulation of UBC9 is reduced. Our findings strongly implicate a stage-specific role of IPO13 in nuclear-cytoplasmic translocation of cargoes that accompanies meiotic differentiation of the mouse germ cells.
已知输入蛋白介导的货物运输是分子核质运输的关键机制。Ipo13是输入蛋白-β基因家族的成员，通过利用不同的转录起始位点编码两种转录本。在小鼠中，全长转录本（L-Ipo13）在胚胎的原始生殖细胞中表达，随后在雄性和雌性生殖细胞减数分裂的粗线期主要表达。较短的转录本（TS-Ipo13）仅在成年睾丸的生殖细胞中表达。L-Ipo13而非TS-Ipo13的活性介导了泛素结合酶9（UBC9，人IPO13的一种货物）的核积累。这一发现与L-Ipo13表达开始后UBC9在减数分裂生殖细胞核中的逐渐积累一致。在胎儿卵巢中敲低IPO13活性的siRNA后，发现进入减数分裂粗线期后期的生殖细胞减少，UBC9的核积累也减少。我们的发现强烈暗示了IPO13在小鼠生殖细胞减数分裂分化过程中货物核质转运中的阶段特异性作用。
