Narula Anita, Kilen Signe, Ma Eva, Kroeger Jessica, Goldberg Erwin, Woodruff Teresa K
Department of Biochemistry, Northwestern University, Evanston, Illinois 60208, USA.
Am J Pathol. 2002 Nov;161(5):1723-34. doi: 10.1016/S0002-9440(10)64449-5.
Members of the transforming growth factor-beta (TGF-beta) superfamily play a variety of important roles in testicular development and function. The tumor suppressor gene, Smad4, is a common mediator of TGF-beta, activin, and bone morphogenetic protein-mediated signaling pathways. To investigate the role of the Smad4 gene during testicular development and function, transgenic mice were generated using a Flag-tagged Smad4 gene driven by 180-bp fragment of the Mullerian inhibiting substance upstream promoter sequence. Three Smad4 transgenic founders (A, B, and G) were detected by Southern blot analysis; line B showed the highest expression of the Smad4 transgene and was further studied. The fertility in F1 generation (B) and F2 generation (BB) of the Smad4 transgenic mice was not impaired. However, in the F3 generation (B2x) all animals were impacted by the overexpression of the Smad4 transgene and two kinds of phenotypes were observed. In one group animals were completely infertile, while in the other group animals were fertile and sired the normal number of pups/litter. These groups are designated as infertile and fertile in the text. Histological evaluation of the testes from the infertile group showed variable degrees of Leydig cell hyperplasia, apoptosis of germ cells, spermatogenic arrest, seminiferous tubule degeneration, and infertility. In the fertile group, there was no apparent change in the histology of the testis except for a slight increase in the number of Leydig cells. Serum follicle-stimulating hormone levels in the adult animals of both groups of Smad4 transgenic male mice were not significantly different from normal littermates; however, testosterone levels in both groups were significantly (P < 0.05) increased. These results suggest that overexpression of Smad4 leads to testicular abnormalities and infertility supporting the hypothesis that the TGF-beta signaling pathways are carefully orchestrated during testicular development. In the absence of normal levels of Smad4 testicular function is compromised.
转化生长因子-β（TGF-β）超家族成员在睾丸发育和功能中发挥着多种重要作用。肿瘤抑制基因Smad4是TGF-β、激活素和骨形态发生蛋白介导的信号通路的共同介质。为了研究Smad4基因在睾丸发育和功能中的作用，使用由苗勒氏管抑制物质上游启动子序列的180 bp片段驱动的Flag标记的Smad4基因生成了转基因小鼠。通过Southern印迹分析检测到三只Smad4转基因奠基鼠（A、B和G）；B系显示Smad4转基因的表达最高，并进一步进行了研究。Smad4转基因小鼠的F1代（B）和F2代（BB）的生育能力未受损。然而，在F3代（B2x）中，所有动物都受到Smad4转基因过表达的影响，并观察到两种表型。在一组中，动物完全不育，而在另一组中，动物可育并产仔数正常/窝。在本文中，这些组被指定为不育和可育。对不育组睾丸的组织学评估显示，存在不同程度的Leydig细胞增生、生殖细胞凋亡、生精停滞、曲细精管变性和不育。在可育组中，睾丸组织学除Leydig细胞数量略有增加外无明显变化。两组Smad4转基因雄性成年动物的血清促卵泡激素水平与正常同窝仔鼠无显著差异；然而，两组的睾酮水平均显著升高（P < 0.05）。这些结果表明，Smad4的过表达导致睾丸异常和不育，支持了TGF-β信号通路在睾丸发育过程中受到精心调控的假设。在缺乏正常水平的Smad4时，睾丸功能受损。
