Department of Morphology, Institute of Biological Sciences, Federal University of Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, Minas Gerais, Brazil Reproductive Biology Group, Division Developmental Biology, Department of Biology, Faculty of Sciences, Utrecht University, Kruyt Building, Room W-606, Padualaan 8, NL-3584 CH Utrecht, The Netherlands Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway Institute of Marine Research, Matre Research Station, 5984 Matredal, Norway.
J Endocrinol. 2014 Feb 10;220(3):319-32. doi: 10.1530/JOE-13-0240. Print 2014 Mar.
The Atlantic salmon shows substantial life cycle plasticity, which also applies to the timing of puberty. While it is characterized by the activation of the brain-pituitary-gonad axis, many morphophysiological aspects of puberty and the influence of environmental conditions, such as water salinity, are not well understood in fish. Here, 12-month-old Atlantic salmon coming from an out-of-season smoltification regime in December were exposed to freshwater (FW) or seawater (SW) at 16 °C to stimulate puberty under a 24-h constant light (LL) or 12 h light:12 h darkness (LD) photoperiod. These four treatment groups (FWLL, SWLL, FWLD, and SWLD) were studied from January to March. Next to 11-ketotestosterone (11-KT) plasma levels, the expression of pituitary genes (gnrhr4, fshb, and lhb) and spermatogenesis was quantified. When spermatogonial proliferation started, fshb mRNA levels increased steeply and began to decrease when spermatogonial mitosis approached completion and most germ cells had reached meiotic or post-meiotic stages. Conversely, lhb mRNA levels increased progressively during spermatogenesis. Most males in all treatment groups matured, but exposure to SW resulted in the strongest stimulation of the onset of spermatogenesis and elevation of pituitary gnrhr4 and fshb mRNA levels. Later on, the LD photoperiod accelerated, irrespective of the salinity, the completion of spermatogenesis, associated with higher lhb mRNA and 11-KT plasma levels than in the LL groups. We find that both salinity and photoperiod modulated different aspects of spermatogenesis, and resulted in a differential activation of pituitary and testis functions; SW stimulating the onset and the shorter photoperiod the completion of spermatogenesis.
大西洋三文鱼表现出显著的生命周期可塑性，这也适用于青春期的时间。虽然它的特征是大脑-垂体-性腺轴的激活，但鱼类的青春期许多形态生理学方面以及环境条件（如盐度）的影响还不是很清楚。在这里，12 个月大的大西洋三文鱼来自于 12 月的非季节性化冰期，在 16°C 下暴露于淡水（FW）或海水（SW）中，在 24 小时恒定光照（LL）或 12 小时光照：12 小时黑暗（LD）光周期下刺激青春期。这四个处理组（FWLL、SWLL、FWLD 和 SWLD）从 1 月到 3 月进行研究。除了 11-酮睾酮（11-KT）的血浆水平外，还定量了垂体基因（gnrhr4、fshb 和 lhb）和精子发生的表达。当精原细胞增殖开始时，fshb mRNA 水平急剧增加，并在精原细胞有丝分裂接近完成且大多数生殖细胞达到减数分裂或减数分裂后期时开始下降。相反，lhb mRNA 水平在精子发生过程中逐渐增加。所有处理组的大多数雄性都成熟了，但暴露于 SW 导致精子发生的开始和垂体 gnrhr4 和 fshb mRNA 水平的升高受到最强的刺激。后来，LD 光周期加速了，而与盐度无关，完成了精子发生，并与更高的 lhb mRNA 和 11-KT 血浆水平相关，高于 LL 组。我们发现，盐度和光周期都调节了精子发生的不同方面，并导致了垂体和睾丸功能的不同激活；SW 刺激了精子发生的开始，而较短的光周期则完成了精子发生。
