Molecular Cloning, Tissue Distribution and Ontogenetic Expression of the Amino Acid Transporter B(0,+) CDNA in the Small Intestine of Tibetan Suckling Piglets

The small intestine is the main absorption place of peptides and free amino acids in mammals. The amino acid transporter system b(0,+) mediates apical uptake of basic amino acids, especially lysine, arginine and cysteine. The aim of the current study was to clone Tibetan porcine amino acid transporter b(0,+)AT (SLC7A9) for comparing the sequences of Tibetan and common (Sus scrofa) pigs, and investigating the tissue distribution and ontogenetic expression in the small intestine of Tibetan suckling piglets. The Tibetan porcine SLC7A9 gene was first cloned from the porcine small intestine and found to encode the amino acid transporter b(0,+)AT. The entire open reading frame (ORF) of the SLC7A9 is 1464 bp and codes for 487 amino acid residues, with a higher degree of sequence similarity with common pig (99.59%) and horse counterparts (91.2%) than with monkey (89.5%) or human (88.7%). The deduced protein has 12 putative transmembrane domains. In this study, SLC7A9 mRNA was detected in brain, kidney, duodenum, jejunum, ileum, heart, liver, lung and muscle from Tibetan pigs at 7 and 21 days by PCR. We also investigated the age-dependent expression of b(0,+)AT in Tibetan suckling piglets in duodenum, anterior jejunum, posterior jejunum, ileum and kidney from day 1 to 35. The abundance of SLC7A9 mRNA in duodenum and jejunum was highest and lowest, respectively. Expression patterns were similar in duodenum and anterior jejunum, where the mRNA level was decreased before the suckling period and increased until day 35. Posterior jejunum expression was increasing steadily with age, except on day 7. The ileum has the highest expression at day 14 and became steady after day 28. The mRNA abundance in the kidney is opposite to duodenum, increasing until day 14 and reducing thereafter. Our results showed the pattern of b(0,+)AT expressed in small intestine of Tibetan pig and lay the foundation for in depth investigations of the regulation of b(0,+)AT in vivo.