The chick embryo yolk sac membrane expresses nutrient transporter and digestive enzyme genes

The yolk sac membrane plays a major role in the transport of nutrients from the yolk contents to the chick embryo. We examined whether the yolk sac membrane expresses genes for nutrient digestion, enzymes, and nutrient transporters. We evaluated relative mRNA abundance of the digestive enzymes aminopeptidase N (APN) and sucrase-isomaltase (SI); the nutrient transporters oligopeptide transporter Pept1, cationic amino acid transporter CAT1, and sodium glucose transporter SGLT1; and the micronutrient transporters type IIb sodium phosphate cotransporter NPT2b, calcium transporter TRPV6, and zinc transporter ZnT-1 from embryonic d 11 (11E) to 21E (day of hatch) by real-time reverse-transcription PCR. The yolk sac membrane expressed all the examined genes, which exhibited several patterns of expression. Relative abundance of APN mRNA increased in the yolk sac membrane from 11E to 17E and decreased from 17E to 20E. Expression of PepT1 increased from 11E to 15E and decreased from 15E to 20E. In contrast, CAT1 expression decreased from 11E to 13E and increased from 15E to 17E. Expression of SGLT1 increased between 15E and 20E and decreased substantially between 20E and 21E. Expression of NPT2b increased during incubation and exhibited the highest relative expression of all the examined genes, particularly on 20E to 21E. Expression of TRPV6 decreased from 11E to 13E and increased substantially from 15E to 19E. No significant difference was found between the sampled days for ZnT-1 or SI expression, with the latter exhibiting the lowest relative expression of all the genes studied. These results present the first documentation of nutrient transporter and digestive enzyme gene-expression patterns in the yolk sac membrane, and provide a basis for future research on the capacity of the yolk sac membrane for nutrient digestion and transport.