The mRNA expression of amino acid transporters, aminopeptidase N, and the di- and tri-peptide transporter PepT1 in the embryo of the domesticated chicken (Gallus gallus) shows developmental regulation.

The mRNA expression profile for 10 amino acid transporters, the di-and tri- peptide transporter (PepT1), and aminopeptidase N (APN) during chick embryogenesis was determined. Fertilized eggs were sampled at d 9, 11, 15, 17, 19, and 20 of incubation. Three to 4 embryos were sampled at each time period. At d 9 and 11, the entire intestine was collected due to its undifferentiated appearance. The ceca, duodenum, midgut, and liver were sampled at d 15, 17, 19, and 20. Gene expression was measured using absolute quantitation quantitative reverse-transcription PCR. In the liver, all genes except for PepT1 were expressed at most time points. At d 9, only the expression of Na⁺-independent cationic amino acid transporter 1, Na⁺-independent cationic amino acid transporter 2, and excitatory amino acid transporter 3 was detectable in the intestine, but by d 11, all genes associated with transporters of the basolateral surface were expressed, and at higher levels than genes associated with brush border transporters. By d 15, all of the genes tested were expressed in the duodenum, midgut, and ceca at high levels that remained relatively constant until d 20. Statistical analysis shows that at d 15, 17, 19, and 20 there is a significant interaction between the 2 main effects (days of incubation and region of the gut); therefore, it is likely that gene expression in different regions of the gut is dependent on the age of the embryo. At d 9 and 11, the gut may not function in amino acid uptake from the lumen and possibly relies on other structures such as the yolk sac. As the gut matures and protein becomes available in the lumen, amino acid transporters become highly expressed in all parts of the intestine. The data suggest that by d 15 of embryo development the gut may be capable of amino acid absorption.