University of British Columbia, Department of Zoology, 6270 University Blvd, Vancouver, BC, Canada V6T 1Z4.
Comp Biochem Physiol A Mol Integr Physiol. 2012 Apr;161(4):379-87. doi: 10.1016/j.cbpa.2011.12.008. Epub 2011 Dec 24.
Expression and function of the oligopeptide transporter PepT1 in response to changes in environmental salinity have received little study despite the important role that dipeptides play in piscine nutrition. We cloned and sequenced two novel full-length cDNAs that encode Fundulus heteroclitus PepT1-type oligopeptide transporters, and examined their expression and functional properties in freshwater- and seawater-acclimated fish and in response to fasting and re-feeding. Phylogenetic analysis of vertebrate SLC15A1 sequences confirms the presence of two PepT1 isoforms, named SLC15A1a and SLC15A1b, in fish. Similar to other vertebrate SLC15A1s, these isoforms have 12 transmembrane domains, and amino acids essential for PepT1 function are conserved. Expression analysis revealed novel environment-specific expression of the SLC15A1 isoforms in F. heteroclitus, with only SLC15A1b expressed in seawater-acclimated fish, and both isoforms expressed in freshwater-acclimated fish. Fasting and re-feeding induced changes in the expression of SLC15A1a and SLC15A1b mRNA. Short-term fasting resulted in up-regulation of PepT1 mRNA levels, while prolonged fasting resulted in down-regulation. The resumption of feeding resulted in up-regulation of PepT1 above pre-fasted levels. Experiments using the in vitro gut sac technique suggest that the PepT1 isoforms differ in functional characteristics. An increased luminal pH resulted in decreased intestinal dipeptide transport in freshwater-acclimated fish but suggested an increased dipeptide transport in seawater-acclimated fish. Overall, this is the first evidence of multiple isoforms of PepT1 in fish whose expression is environmentally dependent and results in functional differences in intestinal dipeptide transport.
尽管二肽在鱼类营养中起着重要作用，但有关环境盐度变化对寡肽转运蛋白 PepT1 表达和功能的研究却很少。我们克隆并测序了两种新型全长 cDNA，它们编码 Fundulus heteroclitus PepT1 型寡肽转运蛋白，并研究了它们在淡水和海水适应的鱼类中的表达和功能特性，以及在禁食和再喂养后的表达和功能特性。脊椎动物 SLC15A1 序列的系统发育分析证实了鱼类中存在两种 PepT1 同工型，分别命名为 SLC15A1a 和 SLC15A1b。与其他脊椎动物 SLC15A1 一样，这些同工型具有 12 个跨膜结构域，并且 PepT1 功能所必需的氨基酸是保守的。表达分析显示，在 F. heteroclitus 中，SLC15A1 同工型具有新颖的环境特异性表达，仅在海水适应的鱼类中表达 SLC15A1b，而在淡水适应的鱼类中则表达两种同工型。禁食和再喂养诱导 SLC15A1a 和 SLC15A1b mRNA 的表达变化。短期禁食导致 PepT1 mRNA 水平上调，而长期禁食导致 PepT1 mRNA 水平下调。恢复喂养导致 PepT1 的表达水平高于禁食前水平。使用离体肠囊技术的实验表明，PepT1 同工型在功能特性上存在差异。在淡水适应的鱼类中，肠腔 pH 值升高会导致二肽转运减少，但在海水适应的鱼类中，这可能会增加二肽的转运。总体而言，这是鱼类中 PepT1 同工型的第一个证据，其表达受环境影响，并导致肠道二肽转运的功能差异。
