Ovine glucose transporter-1 and -3: cDNA partial sequences and developmental gene expression in the placenta.

Transplacental glucose transfer utilizes specific glucose transporter (GLUT) proteins. cDNAs encoding ovine placental GLUT1 and GLUT3 genes were isolated, cloned and sequenced and then used to investigate their developmental regulation in ovine placenta. A cDNA of approximately 2.2 kb was isolated from a Clontech lambda gt10 ovine adult liver cDNA library using a 436-bp rat GLUT1 cDNA probe. Sequence data obtained from this clone (1600 bp) demonstrated 97 per cent homology to nucleotides 477-2079 of bovine GLUT1. The deduced amino acid sequence of the ovine cDNA presented 99 per cent identity to amino acid 103-493 of bovine GLUT1, and 97-98 per cent identity to corresponding regions in human and rat GLUT1 deduced amino acid sequences. Reverse transcription-PCR (RT-PCR) was used to isolate an ovine cDNA fragment from placental total RNA. Forward and reverse primers (16 mer) were designed to amplify a predicted 483-bp fragment between the second transmembrane-spanning domain (M2) and intracellular loop of GLUT3. The deduced 161 amino acid sequence of the ovine cDNA demonstrated 84 and 88 per cent identity with murine and human GLUT3. These cDNAs were used to investigate the ontogeny of placental oGLUT1 and oGLUT3 gene expression by Northern analysis. Total RNA was extracted from ovine placenta at gestational days 45, 60, 90, 120 and 138 (n=6 per time point). Ovine GLUT1 gene expression increased significantly from days 45 to 60 (P<0.05), peaked at around day 120 of gestation, then decreased to about two-thirds of maximal levels by day 138 of gestation (term 147 +/- 2). Ovine GLUT3 gene expression increased throughout gestation with significant increases from days 45 to 60, 60 to 120 and 120 to 138 (P<0.05). This study confirms the presence of both GLUT1 and GLUT3 genes in the ovine placenta and demonstrates ontogenic regulation of gene expression. The difference in temporal gene expression between oGLUT1 and oGLUT3 suggests distinct roles for each transporter during development. The nucleotide sequences reported in this paper have been submitted to the GenBank/EMBL Data Bank under accession numbers U89029 (oGLUT1) and U89030 (oGLUT3).