Molecular and cellular diversity of aquaporin in a water-adaptation of the amphibians

我们从日本雨蛙腹侧皮肤中克隆了编码三种不同水通道蛋白（AQP-h1、AQP-h2和AQP-h3）的cDNA。AQP-h1 mRNA在多种组织中表达，AQP-h2在包括抗利尿剂依赖性组织在内的多种组织中表达，但AQP-h3 mRNA仅存在于腹侧皮肤中。免疫荧光研究表明，AQP-h3蛋白只定位于盆腔腹侧皮肤。在盆腔皮肤中，AQP-h3蛋白在颗粒层的上层更强烈，并且定位于颗粒细胞的顶侧和基底侧质膜。腹侧皮肤中的AQP-h3可能在树蛙的陆地适应中是必不可少的，但AQP-h2蛋白在成年腹侧皮肤中的颗粒细胞质膜中与AQP-h3相同的位点被检测到。在膀胱中，AQP-h2蛋白在颗粒细胞的胞浆中观察到。孵育成人腹侧皮肤与催产素增强AQP-h2和AQP-h3在皮肤中的顶端质膜的标记密度。两者合计，目前的数据表明，AQP-h3是一个内在的AQP在腹侧皮肤，它保持了高渗透性的水在腹侧皮肤与AQP-h2的调节下，催产素。在膀胱中，AQP-h2在水的重吸收中起关键作用。有趣的是，水通道蛋白-h2-和水通道蛋白-h3-样蛋白表达在腹侧皮肤的陆地青蛙日本蟾蜍和树适应青蛙日本雨蛙。另一方面，AQP-h3-like基因在所有蛙的腹侧皮肤中的表达被观察到，从水生物种到陆生动物，但没有AQP-h2-like蛋白在腹侧皮肤中的水生和半陆生适应的青蛙表达。

We cloned cDNAs encoding three distinct AQPs (AQP-h1,AQP-h2 and AQP-h3) from the ventral skin of the tree frog, Hyla japonica. AQP-h1 mRNA is expressed in a wide variety of tissues, and AQP-h2 in several tissues including anti-diuretic hormone-dependent tissues, but AQP-h3 mRNA exists only in the ventral skin. An immunofluorescence study showed that the AQP-h3 protein was only localized in the pelvic ventral skin. In the pelvic skin, AQP-h3 protein was more intense in the upper layer of the stratum granulosum, and was localized in both the apical and basolateral plasma membranes of the granular cells. AQP-h3 in the ventral skin may be essential in the land adaptation of the tree frog, but AQP-h2 protein was detected in the same sites as AQP-h3 in the plasma membrane of the granular cells in the adult ventral skin. In the urinary bladder, AQP-h2 protein was observed in the cytoplasm of the granular cells. Incubation of adult ventral skin with vasotocin enhanced the labeling density of both AQP-h2 and AQP-h3 in the apical plasma membrane in the skin. Taken together, the present data suggest that AQP-h3 is an intrinsic AQP in the ventral skin, and that it maintains a high permeability to water in the ventral skin in concert with AQP-h2 under the regulation of vasotocin. In the urinary bladder, AQP-h2 plays a pivotal role in the reabsorption of water. It is of interest that both AQP-h2-and AQP-h3-like proteins are expressed in the ventral skin of the terrestrial frog Bufo japonica and tree-adapted frog Hyla japonica. On the other hand, expression of AQP-h3-like gene in the ventral skins is observed in all the frogs from aquatic species to terrestrial dwellers, but no AQP-h2-like protein is expressed in the ventral skin in the aquatic and semi-terrestrial-adapted frogs.