Centre for Reproduction and Development, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia.
PLoS One. 2013;8(1):e54606. doi: 10.1371/journal.pone.0054606. Epub 2013 Jan 16.
The developing testis provides an environment that nurtures germ cell development, ultimately ensuring spermatogenesis and fertility. Impacts on this environment are considered to underlie aberrant germ cell development and formation of germ cell tumour precursors. The signaling events involved in testis formation and male fetal germ cell development remain largely unknown. Analysis of knockout mice lacking single Tgfβ family members has indicated that Tgfβ's are not required for sex determination. However, due to functional redundancy, it is possible that additional functions for these ligands in gonad development remain to be discovered. Using FACS purified gonadal cells, in this study we show that the genes encoding Activin's, TGFβ's, Nodal and their respective receptors, are expressed in sex and cell type specific patterns suggesting particular roles in testis and germ cell development. Inhibition of signaling through the receptors ALK4, ALK5 and ALK7, and ALK5 alone, demonstrated that TGFβ signaling is required for testis cord formation during the critical testis-determining period. We also show that signaling through the Activin/NODAL receptors, ALK4 and ALK7 is required for promoting differentiation of male germ cells and their entry into mitotic arrest. Finally, our data demonstrate that Nodal is specifically expressed in male germ cells and expression of the key pluripotency gene, Nanog was significantly reduced when signaling through ALK4/5/7 was blocked. Our strategy of inhibiting multiple Activin/NODAL/TGFβ receptors reduces the functional redundancy between these signaling pathways, thereby revealing new and essential roles for TGFβ and Activin signaling during testis formation and male germ cell development.
发育中的睾丸为生殖细胞的发育提供了一个环境，最终确保了精子发生和生育能力。人们认为，对这种环境的影响是导致生殖细胞发育异常和形成生殖细胞瘤前体的原因。涉及睾丸形成和男性胎儿生殖细胞发育的信号事件在很大程度上仍不清楚。对缺乏单个 TGFβ 家族成员的敲除小鼠的分析表明，TGFβ 对于性别决定不是必需的。然而，由于功能冗余，这些配体在性腺发育中可能具有其他尚未发现的功能。在这项研究中，我们使用 FACS 纯化的性腺细胞表明，编码激活素、TGFβ、Nodal 及其各自受体的基因以性别和细胞类型特异性的模式表达，这表明它们在睾丸和生殖细胞发育中具有特定的作用。通过抑制受体 ALK4、ALK5 和 ALK7 以及 ALK5 的信号转导，我们证明 TGFβ 信号在睾丸决定期的关键时期对于睾丸索的形成是必需的。我们还表明，通过激活素/NODAL 受体 ALK4 和 ALK7 的信号转导对于促进雄性生殖细胞的分化及其进入有丝分裂阻滞是必需的。最后，我们的数据表明，Nodal 特异性地在雄性生殖细胞中表达，当阻断 ALK4/5/7 的信号转导时，关键多能性基因 Nanog 的表达显著降低。我们抑制多种激活素/NODAL/TGFβ 受体的策略降低了这些信号通路之间的功能冗余性，从而揭示了 TGFβ 和激活素信号在睾丸形成和雄性生殖细胞发育中的新的和必要的作用。
