Chaves-Pozo E, Liarte S, Vargas-Chacoff L, García-López A, Mulero V, Meseguer J, Mancera J M, García-Ayala A
Department of Cell Biology, Faculty of Biology, University of Murcia, 30100 Murcia, Spain.
Biol Reprod. 2007 Jan;76(1):142-8. doi: 10.1095/biolreprod.106.056036. Epub 2006 Oct 18.
The testis is a tightly controlled dynamic tissue. In mammals, there is growing evidence that estrogen plays a role in the regulation of testicular functions. In teleosts, high levels of 17beta-estradiol (E2) in serum correlate with the end of spermatogenesis, spawning, and the initiation of postspawning stages when spermatogonia are the main cell types in the testis. Moreover, E2 modulates leukocyte functions in several teleost species. We hypothesized, therefore, that E2 would induce the infiltration of acidophilic granulocytes and cause a resumption of testicular cell proliferation in spermatogenically active gilthead seabream males. Several studies of this species have reported that supraphysiological doses of E2 are needed to induce histological and developmental changes in males. In fact, as gilthead seabream is a protandrous hermaphrodite teleost, long exposures (6-14 wk) to high doses of E2 result in feminization of the males. Taking all this into account, we sharply increased E2 levels during short times by i.p. injecting E2 diluted in coconut oil as the vehicle and sampled the fish after 7, 13, and 18 days to assess the effects that E2 had on spermatogenesis. It was observed that E2 levels in plasma increased, while 11-ketotestosterone (11-KT) and testosterone (T) levels remained unaltered. However, 11-KT and T levels strongly increased in control fish 18 days postinjection. The most relevant result of our study was that E2 accelerates the final events of spermatogenesis, inhibits the proliferation of spermatogonia in early stages, and induces some of the processes that usually occur during postspawning, such as the infiltration of acidophilic granulocytes and the apoptosis of primary spermatogonia. Strikingly, neither the shedding of spermatozoa nor an increase in the proliferative rate of spermatogonia stem cells was observed, probably because of the lack of other necessary stimuli, such as the increase in T levels that takes place during normal postspawning.
睾丸是一种受到严格调控的动态组织。在哺乳动物中，越来越多的证据表明雌激素在睾丸功能的调节中发挥作用。在硬骨鱼中，血清中高水平的17β - 雌二醇（E2）与精子发生的结束、产卵以及产卵后阶段的开始相关，此时精原细胞是睾丸中的主要细胞类型。此外，E2在几种硬骨鱼物种中调节白细胞功能。因此，我们推测E2会诱导嗜酸性粒细胞浸润，并导致精子发生活跃的金头鲷雄性睾丸细胞增殖恢复。对该物种的多项研究报告称，需要超生理剂量的E2才能诱导雄性的组织学和发育变化。事实上，由于金头鲷是一种雄性先熟的雌雄同体硬骨鱼，长时间（6 - 14周）暴露于高剂量的E2会导致雄性雌性化。考虑到所有这些因素，我们通过腹腔注射以椰子油为载体稀释的E2在短时间内大幅提高E2水平，并在7、13和18天后对鱼进行取样，以评估E2对精子发生的影响。观察到血浆中E2水平升高，而11 - 酮睾酮（11 - KT）和睾酮（T）水平保持不变。然而，注射后18天，对照鱼中的11 - KT和T水平大幅升高。我们研究中最相关的结果是，E2加速了精子发生的最终事件，抑制早期精原细胞的增殖，并诱导了一些通常在产卵后发生的过程，如嗜酸性粒细胞浸润和初级精原细胞凋亡。令人惊讶的是，未观察到精子脱落或精原干细胞增殖率增加，这可能是因为缺乏其他必要刺激，如正常产卵期间发生的T水平升高。
