Xia Yin, Sidis Yisrael, Schneyer Alan
Reproductive Endocrine Unit, BHX-5, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Mol Endocrinol. 2004 Apr;18(4):979-94. doi: 10.1210/me.2003-0364. Epub 2004 Jan 22.
Activin has numerous biological activities including regulation of follicular development, spermatogenesis, and steroidogenesis within the gonads. Activities of activin are regulated by follistatin (FST), an activin binding protein, and perhaps follistatin-like 3 (FSTL3; also known as FLRG and FSRP). FSTL3 is a recently described member of the FST family having an overall structure and activity profile similar to that of FST, including binding and neutralization of activin. FSTL3 is most highly expressed in the placenta and testis, whereas FST is highest in the ovary and kidney, suggesting that FSTL3 has biological actions that do not entirely overlap those of FST. To investigate the role of local FSTL3 as a potential regulator of activin action in gonad development and function, we examined FSTL3 expression in the mouse testis. FSTL3 protein was localized to Leydig cells, spermatagonia, and mature spermatids in normal male mice. We then created transgenic mice using a human FSTL3 cDNA driven by the mouse alpha-inhibin promoter. Three of five transgenic founders were fertile and were bred to establish lines. In the highest expressing line 3, transgene expression was largely restricted to gonads, with pituitary, adrenal, brain, and uterine expression being substantially lower. Gonad weights, sperm counts, and fertility were significantly reduced in transgenic males, and reduced litter size was evident in line 3 females. Within the testis, highest transgene expression was observed in Sertoli cells, and although most tubules showed evidence of normal spermatogenic development, degenerating tubules devoid of germ cells and Leydig cell hyperplasia were also evident in every line 3 animal examined. Ovaries from line 3 females contained fewer antral follicles and more apparent follicular atresia. Although circulating human FSTL3 levels were undetectable, FSH and LH levels in adult transgenic mice were not significantly different from wild-type animals. However, testosterone levels were significantly increased at d 21 and significantly reduced at d 60 compared with wild-type males. These results suggest that FSTL3 is likely to be a local regulator of activin action in gonadal development and gametogenesis and, further, that activin appears to have important actions in gonadal development and function that are critical for normal reproduction.
激活素具有多种生物学活性，包括调节性腺内的卵泡发育、精子发生和类固醇生成。激活素的活性受卵泡抑素（FST）调节，卵泡抑素是一种激活素结合蛋白，可能还受类卵泡抑素3（FSTL3；也称为FLRG和FSRP）调节。FSTL3是FST家族中最近被描述的成员，其整体结构和活性谱与FST相似，包括结合和中和激活素。FSTL3在胎盘和睾丸中表达最高，而FST在卵巢和肾脏中表达最高，这表明FSTL3具有一些与FST并不完全重叠的生物学作用。为了研究局部FSTL3作为激活素在性腺发育和功能中的潜在调节因子的作用，我们检测了FSTL3在小鼠睾丸中的表达。在正常雄性小鼠中，FSTL3蛋白定位于睾丸间质细胞、精原细胞和成熟精子细胞。然后，我们使用由小鼠α-抑制素启动子驱动的人FSTL3 cDNA创建了转基因小鼠。五只转基因奠基者中有三只可育，并进行了繁殖以建立品系。在表达最高的品系3中，转基因表达主要局限于性腺，垂体、肾上腺、脑和子宫的表达则低得多。转基因雄性小鼠的性腺重量、精子计数和生育力显著降低，品系3雌性小鼠的窝仔数明显减少。在睾丸内，在支持细胞中观察到最高的转基因表达，尽管大多数曲细精管显示出正常生精发育的迹象，但在每只检测的品系3动物中，也明显存在缺乏生殖细胞的退化曲细精管和睾丸间质细胞增生。品系3雌性小鼠的卵巢中窦状卵泡较少，卵泡闭锁更明显。尽管未检测到循环中的人FSTL3水平，但成年转基因小鼠的促卵泡生成素（FSH）和促黄体生成素（LH）水平与野生型动物无显著差异。然而，与野生型雄性相比，转基因雄性在第21天时睾酮水平显著升高，在第60天时显著降低。这些结果表明，FSTL3可能是性腺发育和配子发生中激活素作用的局部调节因子，此外，激活素在性腺发育和功能中似乎具有对正常生殖至关重要的重要作用。
