Isolation, characterization and expression analysis of a hypoxia-responsive glucose transporter gene from the grass carp, Ctenopharyngodon idellus

Abstract

Glucose transporters (GLUTs) have been implicated in adaptive and survival responses to hypoxic stress in mammals. In fish, the expression and regulation of GLUT in relation to hypoxia remains unexplored. Here we describe the identification of a hypoxia-responsive glucose transporter gene (gcGLUT) and the corresponding full-length cDNA from the grass carp. The gene spans ≈ 11 kb of genomic sequence and consists of 12 exons and 11 introns, and an open reading frame (ORF) of 1599 bp encoding a polypeptide of 533 amino acids, with a predicted molecular mass of ≈ 57 kDa and a pI of 8.34. BLASTX analysis showed that the ORF shared high sequence identity with the GLUT1 (57-59%), GLUT3 (59-60%) and GLUT4 (55-59%) proteins from different vertebrates. Comparative analysis of GLUT genomic structures showed that the arrangement of exons and position of split codons are highly conserved amongst members of the class I GLUTs suggesting that these genes share a common ancestor. Phylogenetic analysis indicated that gcGLUT is most closely related to the GLUT3 proteins. Northern blot analysis showed that the 3.1-kb gcGLUT transcript was most abundantly expressed and responsive to hypoxia in kidney. Up-regulated expression by hypoxia was also evident in eye and gill, but differential patterns of expression were observed. Low expression levels detected in brain, heart, liver and muscle were not responsive to hypoxic stress.