ABSTRACT: Mature small intestines have crypts populated by stem cells which produce replacement cells to maintain the absorptive villus surface area. The embryonic crypt is rudimentary and cells along the villi are capable of proliferation. By 7 d post-hatch the crypts are developed and are the primary sites of proliferation. Research characterizing the proliferative expansion of the small intestine during the peri-hatch period is lacking. The objective of this study was to profile the changes of genes that are markers of stem cells and proliferation: Olfactomedin 4 (Olfm4), Leucine-rich repeat containing G protein-coupled receptor 5 (Lgr5), and marker of proliferation Ki67 from embryonic day 17 to 7 d post-hatch using quantitative PCR and in situ hybridization (ISH). The expression of the stem cell marker genes differed. Olfm4 mRNA increased while Lgr5 mRNA decreased post-hatch. Ki67 mRNA decreased post-hatch in the duodenum and was generally the greatest in the ileum. The ISH was consistent with the quantitative PCR results. Olfm4 mRNA was only seen in the crypts and increased with morphological development of the crypts. In contrast Lgr5 mRNA was expressed in the crypt and the villi in the embryonic periods but became restricted to the intestinal crypt during the post-hatch period. Ki67 mRNA was expressed throughout the intestine pre-hatch, but then expression became restricted to the crypt and the center of the villi. The ontogeny of Olfm4, Lgr5, and Ki67 expressing cells show that proliferation in the peri-hatch intestine changes from along the entire villi to being restricted within the crypts.
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