Spiller Cassy M, Wilhelm Dagmar, Jans David A, Bowles Josephine, Koopman Peter
Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia.
School of Biomedical Sciences, Monash University, Clayton, Victoria, Australia.
PLoS One. 2017 Jan 20;12(1):e0170576. doi: 10.1371/journal.pone.0170576. eCollection 2017.
Fetal germ cell development is tightly regulated by the somatic cell environment, and is characterised by cell cycle states that differ between XY and XX gonads. In the testis, gonocytes enter G1/G0 arrest from 12.5 days post coitum (dpc) in mice and maintain cell cycle arrest until after birth. Failure to correctly maintain G1/G0 arrest can result in loss of germ cells or, conversely, germ cell tumours. High mobility group box containing transcription factor 1 (HBP1) is a transcription factor that was previously identified in fetal male germ cells at the time of embryonic cell cycle arrest. In somatic cells, HBP1 is classified as a tumour suppressor protein, known to regulate proliferation and senescence. We therefore investigated the possible role of HBP1 in the initiation and maintenance of fetal germ cell G1/G0 arrest using the mouse model. We identified two splice variants of Hbp1, both of which are expressed in XY and XX fetal gonads, but only one of which is localised to the nucleus in in vitro assays. To investigate Hbp1 loss of function, we used embryonic stem (ES) cells carrying a Genetrap mutation for Hbp1 to generate mice lacking Hbp1 function. We found that Hbp1-genetrap mouse mutant germ cells proliferated correctly throughout development, and adult males were viable and fertile. Multiple Hbp1-LacZ reporter mouse lines were generated, unexpectedly revealing Hbp1 embryonic expression in hair follicles, eye and limbs. Lastly, in a model of defective germ cell G1/G0 arrest, the Rb1-knockout model, we found no evidence for Hbp1 mis-regulation, suggesting that the reported RB1-HBP1 interaction is not critical in the germline, despite co-expression.
胎儿生殖细胞的发育受到体细胞环境的严格调控，其特征是XY和XX性腺的细胞周期状态不同。在睾丸中，小鼠合子后12.5天（dpc）时生殖母细胞进入G1/G0期停滞，并维持细胞周期停滞直至出生后。未能正确维持G1/G0期停滞会导致生殖细胞丢失，或者相反，导致生殖细胞肿瘤。含高迁移率族框转录因子1（HBP1）是一种转录因子，先前在胚胎细胞周期停滞时的胎儿雄性生殖细胞中被鉴定出来。在体细胞中，HBP1被归类为一种肿瘤抑制蛋白，已知其可调节增殖和衰老。因此，我们使用小鼠模型研究了HBP1在胎儿生殖细胞G1/G0期停滞的起始和维持中的可能作用。我们鉴定出Hbp1的两种剪接变体，它们在XY和XX胎儿性腺中均有表达，但在体外实验中只有一种定位于细胞核。为了研究Hbp1的功能丧失，我们使用携带Hbp1基因陷阱突变的胚胎干细胞（ES细胞）来生成缺乏Hbp1功能的小鼠。我们发现Hbp1基因陷阱小鼠突变体的生殖细胞在整个发育过程中增殖正常，成年雄性小鼠存活且可育。我们生成了多个Hbp1-LacZ报告基因小鼠品系，意外地发现Hbp1在毛囊、眼睛和四肢中有胚胎表达。最后，在生殖细胞G1/G0期停滞缺陷的Rb1基因敲除模型中，我们没有发现Hbp1调控异常的证据，这表明尽管有共表达，但报道的RB1-HBP1相互作用在生殖系中并不关键。
