Almeida Fernanda F L, Taranger Geir Lasse, Norberg Birgitta, Karlsen Orjan, Bogerd Jan, Schulz Rüdiger W
Faculty of Sciences, Department of Biology, Division of Endocrinology & Metabolism, Utrecht University, Utrecht, the Netherlands.
Biol Reprod. 2009 Apr;80(4):631-40. doi: 10.1095/biolreprod.108.071340. Epub 2008 Nov 26.
Precocious male puberty is a significant problem in Atlantic cod aquaculture. While photoperiod manipulation can inhibit testis growth, a detailed analysis of effects on spermatogenesis is missing. Starting July 1, 2004, prepubertal fish were exposed to different photoperiod regimens in indoor tanks for 17 mo. Testis histology, germ cell dynamics (proliferation and apoptosis), and plasma androgen levels were analyzed. In the natural light (NL) group, testis growth started in September 2004 and was completed in February 2005, when a 2-mo spawning period started. In the constant light (LL) group, none or very few spermatogenic cysts were recruited into spermatogenesis, and apoptotic germ cell loss was high. A change of photoperiod from NL to LL at winter solstice (December 21, 2004) resulted in premature (2 mo) completion of the reproductive cycle, while changing from LL to NL at winter solstice triggered faster than normal testis development. Plasma testosterone levels increased in the NL group from spermatogonial proliferation toward meiosis, while those of 11-ketotestosterone increased toward spermiogenesis and spermiation. Plasma androgen levels did not rise under LL conditions. Comparing fish with developing testes from all groups indicated that low androgen levels were associated with a high incidence of spermatogonial apoptosis; we also found that androgen receptor mRNA expression was most prominent in Sertoli cells in contact with growing spermatogonial clones. Our data show that an inhibitory photoperiod (LL) reduced or blocked differentiation of spermatogonia, increased apoptosis (particularly among proliferating spermatogonia), and was associated with reduced androgen levels, a situation possibly reflecting insufficient gonadotropic stimulation.
早熟雄性大西洋鳕鱼是大西洋鳕鱼水产养殖中的一个重大问题。虽然光周期调控可以抑制睾丸生长，但对精子发生影响的详细分析尚付阙如。从2004年7月1日起，将青春期前的鱼置于室内水箱中，使其暴露于不同的光周期方案下，持续17个月。对睾丸组织学、生殖细胞动态（增殖和凋亡）以及血浆雄激素水平进行了分析。在自然光（NL）组中，睾丸生长于2004年9月开始，并于2005年2月完成，随后开始为期2个月的产卵期。在持续光照（LL）组中，很少或几乎没有生精囊肿进入精子发生过程，且凋亡生殖细胞损失率很高。在冬至（2004年12月21日）将光周期从自然光改为持续光照，导致生殖周期提前（2个月）完成，而在冬至时从持续光照改为自然光则引发了比正常情况更快的睾丸发育。在自然光组中，血浆睾酮水平从精原细胞增殖阶段到减数分裂阶段升高，而11-酮睾酮水平在精子形成和精子释放阶段升高。在持续光照条件下，血浆雄激素水平没有升高。对所有组中睾丸正在发育的鱼进行比较表明，雄激素水平较低与生精细胞凋亡的高发生率相关；我们还发现雄激素受体mRNA表达在与生长中的精原细胞克隆接触的支持细胞中最为显著。我们的数据表明，抑制性光周期（持续光照）减少或阻断了精原细胞的分化，增加了凋亡（尤其是在增殖的精原细胞中），并与雄激素水平降低相关，这种情况可能反映了促性腺激素刺激不足。
