Glucose and fructose play a central role in the metabolism and cellular homeostasis of organisms. Their absorption is co-mediated by two families of glucose transporters, Na+-coupled glucose co-transporters (SGLTs) and facilitative Na+-independent sugar carriers (GLUTs), in the intestine. However, limited information has been available on these transporters in fish. Therefore, we studied glut2, sglt1, and sglt4 genes in grass carp (Ctenopharyngodon idellus). The full-length cDNAs of glut2 was 2308 bp, with an open reading frame (ORF) of 503 amino acids (AAs). The full-length cDNAs of sglt1 was 2890 bp, with an ORF of 658 AAs. Additionally, the full-length cDNAs of sglt4 was 2090 bp, with an ORF encoding 659 AAs. The three deduced AA sequences showed high homology between grass carp and other cyprinid fish species. Based on homology modeling, three-dimensional models of GLUT2, SGLT1, and SGLT4 proteins were created and transmembrane domains were noted. glut2, sglt1, and sglt4 were abundantly expressed in the anterior and mid intestine. In particular, glut2 was markedly expressed in liver (P < 0.05). Additionally, the results indicated that different stocking densities (0.9 or 5.9 kg m-2) did not alter intestinal section-dependent expression patterns of the three transporter genes. However, high stocking density impacted segmental mRNA expression levels. This work demonstrated that mRNA expression of sugar transporter genes in the fish intestine was segment specific, and crowding stress may affect the activity of intestinal sugar transporters. These results provided new insights into the relationship between crowding stress and intestinal sugar transporters in fish.

中文翻译：

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草鱼中的糖转运蛋白基因（Ctenopharyngodon idellus）：分子克隆，表征和表达，以响应不同的放养密度。

葡萄糖和果糖在生物体的代谢和细胞稳态中起着重要作用。它们的吸收是由肠道中的两个葡萄糖转运蛋白家族共同介导的：Na +偶联的葡萄糖协同转运蛋白（SGLT）和促进性的Na +非依赖性糖转运蛋白（GLUT）。但是，关于这些鱼类运输工具的信息很少。因此，我们研究了草鱼（Ctenopharyngodon idellus）中的glut2，sglt1和sglt4基因。glut2的全长cDNA为2308 bp，具有503个氨基酸（AAs）的开放阅读框（ORF）。sglt1的全长cDNA为2890 bp，ORF为658 AAs。此外，sglt4的全长cDNA为2090 bp，ORF编码为659 AA。这三个推导的AA序列显示草鱼和其他鲤科鱼类之间的高度同源性。根据同源性建模，创建了GLUT2，SGLT1和SGLT4蛋白的三维模型，并记录了跨膜结构域。glut2，sglt1和sglt4在前肠和中肠中大量表达。特别是，glut2在肝脏中明显表达（P <0.05）。此外，结果表明，不同的放养密度（0.9或5.9 kg m-2）不会改变这三个转运蛋白基因的肠道切片依赖性表达模式。但是，高放养密度影响节段mRNA表达水平。这项工作表明鱼肠中糖转运蛋白基因的mRNA表达具有片段特异性，拥挤压力可能会影响肠糖转运蛋白的活性。这些结果提供了新的见解，在拥挤压力和鱼肠糖转运蛋白之间的关系。