Expression of nutrient transporters and digestive enzymes in the yolk sac membrane and intestine of the embryonic chick

Chicks derive nutrients from the yolk during incubation and transition to intestinal absorption of nutrients posthatch. The objective of this study was to determine the expression profiles of nutrient transporters and digestive enzymes during incubation in the yolk sac membrane (YSM) and embryonic intestine of Leghorn and Cobb chicks from 22-30 wk and 45–50 wk breeder flocks. Transporters and digestive enzymes examined included the peptide transporter PepT1, the glutamate/aspartate (EAAT3), cationic (CAT-1) and neutral (B^oAT) amino acid transporters, the fructose (GLUT5) and glucose (SGLT1) transporters, aminopeptidase N (APN) and sucrase-isomaltase (SI). Expression was assessed by real-time PCR in YSM at embryonic (e) d 11, 13, 15, 17, 19, 20, and 21 and intestine at e15, e17, e19, e20, and e21. Gene expression in the YSM increased from e11 to e21 (EAAT3, SGLT1), increased from e11, peaked between e13 and e19 and then decreased to e21 (APN, B^oAT, PepT1, CAT1, GLUT5), or was barely detectable (SI).   Gene expression in the intestine increased from e15 to e21 (APN, B^oAT, PepT1, EAAT3, SGLT1), decreased from e15 to e21 (CAT1, GLUT5) or remained steady (SI). CAT1 and GLUT5 were expressed greater in Cobb than Leghorn, whereas EAAT3 was expressed greater in Leghorn than Cobb.  APN, B^oAT, and CAT1 were expressed greater in embryos from young flocks than old flocks. These results demonstrate that the YSM expresses many of the digestive enzymes and nutrient transporters typically associated with the intestine and that these genes show tissue- and development-specific patterns of expression.