Tissue- and Development-specific Expression of Proton-mediated Peptide Transporters in the Developing Chicken
PepT1, PepT2 and PHT1 are all members of the proton-coupled oligopeptide transporter family, which are important in the transport of amino acids in peptide form. PepT1 acts as a low affinity/high capacity transporter and PepT2 as a high affinity/low capacity transporter for di- and tri-peptides. PHT1 transports di- and tri-peptides as well as histidine. The objective of this study was to profile PepT1, PepT2 and PHT1 mRNA expression in the proventriculus, duodenum, jejunum, ileum, ceca, large intestine, brain, heart, bursa of Fabricius, lung, kidney, and liver in layer chicks on embryonic days 18 and 20 and days 1, 3, 7, 10, and 14 post-hatch. Absolute quantification real-time PCR was used to measure gene expression. PepT1 expression was greatest in the duodenum, jejunum and ileum. Over time, PepT1 expression increased in the duodenum, jejunum, ileum and large intestine and decreased in the ceca. PepT2 expression was greatest in the brain, aiding in neuropeptide homeostasis, and the kidney, aiding in the reabsorption of substrates. Over time, PepT2 expression increased in the bursa of Fabricius and decreased in the proventriculus, duodenum, jejunum and liver. In the small intestine during embryogenesis, PepT2 may function to transport di- and tri-peptides prior to the induction of PepT1. PHT1 expression was expressed in all tissues analyzed. Over time, PHT1 expression increased in the jejunum, large intestine, brain and liver and decreased in the proventriculus. The uptake of peptides in the developing chick is regulated by peptide transporters that are expressed in a tissue- and development-specific manner.