Hormonal Control of Chloride Cell Differentiation in Fish Gills

本研究的目的是阐明环境盐度变化对鱼鳃氯细胞分化的内分泌调控。过去两年取得的成果如下：1.利用针对虹鱼皮质醇受体激素结合区设计的引物，从罗非鱼肝脏mRNA中克隆出453bp的全长cDNA。Northern印迹分析表明，淡水鱼的受体信息比海水中的强。受体mRNA在受精后不久就已经存在于卵黄中，表明其在早期发育过程中对细胞和组织分化的重要性。鲑鱼鳃细丝中存在两种类型的氯化细胞。板层氯细胞主要存在于淡水鱼类中，并在海水适应过程中消失，这表明它们是淡水中离子吸收的场所。另一方面，在海水适应过程中形成了细丝氯细胞，i…更多地表明它们是海水中盐分排泄的场所。原位杂交检测发现，皮质醇受体基因在鲑鱼鱼苗的两种氯离子细胞中均有表达，表明皮质醇是调节氯离子细胞功能的重要因素之一；在未分化的细胞中也存在皮质醇受体，这也表明其参与了氯离子细胞的功能分化。利用哺乳动物催乳素受体胞外区和狭盐罗非鱼催乳素受体胞外区的引物，从罗非鱼肝组织中克隆了催乳素受体基因。竞争性聚合酶链式反应检测到受精后2天胚胎中存在该受体，且淡水中发育的胚胎的基因表达强于海水中发育的胚胎。越来越清楚的是，各种鱼类的卵黄中含有皮质醇和甲状腺激素等多种激素，可能会影响细胞和组织的分化。还需要进一步的研究，以确定催乳素和甲状腺激素是否特定地参与了鳃氯细胞的分化。较少

The aim of this study is to clarify endocrine control of differentiation of chloride cells in fish gills in response to the changes in environmental salinity. The results obtained during the past two years are as follows.1. A cDNA of 453 bp was cloned from liver mRNA of tilapia with primers designed for the hormone-binding domain of cortisol receptor of the rainbow trout. The receptor message by Northern blot analysis was stronger in fish in fresh water than in those in seawater. The receptor mRNA was already present in the yolk just after fertilization, indicating its importance in cell and tissue differentiation during the early development.2. Two types of chloride cells were identified in the gill filament of chum salmon. Lamellar chloride cells were mainly present in the fish in fresh water and disappeared during seawater adaptation, suggesting their role as a site for ion uptake in fresh water. On the other hand, filament chloride cells were developed during seawater adaptation, i … More ndicating their role as a site of salt excretion in seawater.3. Cortisol receptor gene expression, examined by in situ hybridization, were found in the two types of chloride cells in the chum salmon fry, indicating that cortisol is one of the important factors regulating chloride cell functions.Cortisol receptors were also present in undifferentiated cells, also suggesting its involvement in the functional differentiation of chloride cells.4. Prolactin receptor gene was cloned from the liver mRNA of tilapia with primers for the extracellular domain of the receptors of mammalian and stenohaline tilapia. Competitive PCR revealed the presence of the receptor in the embryos 2 days after fertilization, and the gene expression was stronger in the embryos developing in fresh water than those in seawater.5. It has becaome increasingly, clear that various hormones such as cortisol and thyroid hormones are contained in the yolk of various fish species, possibly affecting the cell and tissue differentiation. Further studies are called for to examine whether prolactin and thyroid hormones are involved specifically in the differentiation of the gill chloride cells. Less