Benedet Susana, Björnsson Björn Thrandur, Taranger Geir Lasse, Andersson Eva
Department of Zoology/Zoophysiology, University of Gothenburg, Gothenburg, Sweden.
Reprod Biol Endocrinol. 2008 Sep 15;6:42. doi: 10.1186/1477-7827-6-42.
Somatolactin (Sl) is a fish specific adenohypophyseal peptide hormone related to growth hormone (Gh). Some species, including salmonids, possess two forms: Sl alpha and Sl beta. The somatolactin receptor (slr) is closely related to the growth hormone receptor (ghr). Sl has been ascribed many physiological functions, including a role in sexual maturation. In order to clarify the role of Sl in the sexual maturation of female Atlantic salmon (Salmo salar), the full length cDNAs of slr, Sl alpha and Sl beta were cloned and their expression was studied throughout a seasonal reproductive cycle using real-time quantitative PCR (RTqPCR).
Atlantic salmon Sl alpha, Sl beta and slr cDNAs were cloned using a PCR approach. Gene expression of Sl alpha, SL beta and slr was studied using RTqPCR over a 17 month period encompassing pre-vitellogenesis, vitellogenesis, ovulation and post ovulation in salmon females. Histological examination of ovarian samples allowed for the classification according to the degree of follicle maturation into oil drop, primary, secondary or tertiary yolk stage.
The mature peptide sequences of Sl alpha, Sl beta and slr are highly similar to previously cloned salmonid forms and contained the typical motifs. Phylogenetic analysis of Atlantic salmon Sl alpha and Sl beta shows that these peptides group into the two Sl clades present in some fish species. The Atlantic salmon slr grouped with salmonid slr amongst so-called type I ghr. An increase in pituitary Sl alpha and Sl beta transcripts before and during spawning, with a decrease post-ovulation, and a constant expression level of ovarian slr were observed. There was also a transient increase in Sl alpha and Sl beta in May prior to transfer from seawater to fresh water and ensuing fasting.
The up-regulation of Sl alpha and Sl beta during vitellogenesis and spawning, with a subsequent decrease post-ovulation, supports a role for Sl during gonadal growth and spawning. Sl could also be involved in calcium/phosphate mobilization associated with vitellogenesis or have a role in energy homeostasis associated with lipolysis during fasting. The up-regulation of both Sl alpha and Sl beta prior to fasting and freshwater transfer, suggests a role for Sl linked to reproduction that may be independent of the maturation induced fasting.
生长催乳素（Sl）是一种鱼类特有的腺垂体肽激素，与生长激素（Gh）相关。包括鲑科鱼类在内的一些物种具有两种形式：Slα和Slβ。生长催乳素受体（slr）与生长激素受体（ghr）密切相关。Sl具有多种生理功能，包括在性成熟中发挥作用。为了阐明Sl在雌性大西洋鲑（Salmo salar）性成熟中的作用，克隆了slr、Slα和Slβ的全长cDNA，并使用实时定量PCR（RTqPCR）研究了它们在整个季节性繁殖周期中的表达。
采用PCR方法克隆大西洋鲑Slα、Slβ和slr的cDNA。使用RTqPCR在17个月的时间内研究了Slα、Slβ和slr的基因表达，该时间段涵盖了鲑鱼雌性的卵黄生成前期、卵黄生成期、排卵和排卵后。对卵巢样本进行组织学检查，以便根据卵泡成熟程度分为油滴、初级、次级或三级卵黄阶段。
Slα、Slβ和slr的成熟肽序列与先前克隆的鲑科鱼类形式高度相似，并包含典型基序。对大西洋鲑Slα和Slβ的系统发育分析表明，这些肽归入一些鱼类中存在的两个Sl进化枝。大西洋鲑slr在所谓的I型ghr中与鲑科鱼类slr归为一类。观察到垂体Slα和Slβ转录本在产卵前和产卵期间增加，排卵后减少，而卵巢slr的表达水平保持恒定。在从海水转移到淡水并随后禁食之前的5月，Slα和Slβ也有短暂增加。
在卵黄生成和产卵期间Slα和Slβ上调，随后排卵后减少，这支持了Sl在性腺生长和产卵过程中的作用。Sl也可能参与与卵黄生成相关的钙/磷酸盐动员，或在禁食期间与脂肪分解相关的能量稳态中发挥作用。在禁食和淡水转移之前Slα和Slβ均上调，表明Sl与繁殖相关的作用可能独立于成熟诱导的禁食。
