Molecular Cloning and Functional Characterization of a Turkey Intestinal Peptide Transporter (tPepT1), and Developmental Regulation of PepT1 Expression in Turkey and Broiler Embryos
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A cDNA clone encoding a turkey intestinal peptide transporter, tPepT1, was isolated from a turkey small intestinal cDNA library by screening with our chicken PepT1 (cPepT1) cDNA probe. The tPepT1 cDNA is 2,921-bp long and encodes a 79.4 kDa protein of 714 amino acids (AA) with 12 predicted transmembrane domains. The isoelectric point (pI) of tPepT1 is 5.9, which is much lower than that of PepT1 cloned from chicken (pI = 7.5) and other species. The AA sequence of tPepT1 is 94.3% identical to cPepT1 and ~ 60% identical to PepT1 from rat, sheep, rabbit, and human. Using a two-electrode voltage-clamp technique in Xenopus oocytes expressing tPepT1, Gly-Sar transport was pH dependent, but independent of Na+ and K+. For the dipeptides Gly-Sar and Met-Met, the evoked inward currents indicated that the transporter was saturable and had a high affinity for these substrates. However, transport of the tetrapeptide, Met-Gly-Met-Met, exhibited a possible substrate inhibition. To study developmental regulation of PepT1 in broiler and turkey embryos, 12 Nicholas turkey or Cobb x Cobb broiler embryos (six males and six females) were sampled daily from 5 d before hatch to the day of hatch (d 0). The abundance of PepT1 mRNA in the small intestine was quantified densitometrically from northern blots after hybridization with full-length cPepT1 and tPepT1 cDNA as probes. There was a quadratic increase (P < 0.001) in PepT1 mRNA abundance with age in turkey and broiler embryos. The relative increase in abundance of PepT1 mRNA in intestinal tissue from 5 d before hatch to d 0 was much less in the turkey than in the broiler (3.2-fold vs 14-fold). The dramatic increase in PepT1 mRNA abundance indicates a developmental regulation of the PepT1 gene and that there may be a crucial role for PepT1 in the neonatal chick and poult.
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