Expression of Nutrient Transporters and Host Defense Peptides in the Intestine and Yolk Sac of Chickens

In chickens, the yolk sac and small intestine are two important organs responsible for the digestion and absorption of nutrients during the embryonic and posthatch periods, respectively. The small intestine also plays an important role in gut immunity. We have previously determined the development- and tissue-specific expression profiles for a number of amino acid, peptide, and sugar transporters as well as a host defense peptide using qPCR. To identify specific cells that express these genes, we used the RNAscope method for in situ hybridization. The objective of this study was to profile the spatial transcriptional patterns of the peptide transporter PepT1 in the yolk sac and small intestine from embryonic and posthatch broilers. In yolk sac endodermal cells, expression of PepT1 mRNA was barely detectable at e11, increased from e11 to e13, e15 and e17, and then decreased from e17 to day of hatch (DOH). This is identical to the profile we previously reported using qPCR. In the small intestine there was a rapid increase in expression of PepT1 mRNA in the enterocytes from e19 to DOH, with expression relatively constant from D1 to D7. We have also identified stem cells in the crypts that express mRNA for olfactomedin 4. In another study, the mRNA expression of the host defense peptide liver expressed antimicrobial peptide 2 (LEAP2) was also localized to the enterocytes lining the villi. In summary, we have identified absorptive and secretory cells in the villi as well as stem cells in the crypt using in situ hybridization.