EXPRESSION OF DIFFERENTIATED FUNCTIONS IN THE DEVELOPING PORCINE SMALL-INTESTINE

Heterologous cDNA clones were used as hybridization probes to define t he temporal expression of intestinal functions during fetal and postna tal development in the pig. Northern hybridization analysis revealed t he presence of the mRNAs for the cellular retinol binding protein CRBP II, for the digestive enzyme aminopeptidase N, and for the microvilla r proteins villin and ezrin in the small intestine of both weaned and 40-day fetal pigs. The presence of these mRNAs suggests that at the en d of the first third of gestation the pig fetal intestine is already e xhibiting some characteristics of a differentiated epithelium. The mRN As for the two fatty acid-binding proteins I-FABP and L-FAPB, both inv olved in the metabolism of long chain fatty acids, were detected only in the intestinal mRNA extracted from weaned animals while that for th e cellular retinol-binding protein CRBP I was expressed only in the fe tal tissue. The temporal limits of expression of intestinal genes in t he pig epithelium seem therefore more easily defined than in other exp erimental animals with shorter times of fetal development. To isolate pig genes expressed at different developmental stages during intestina l epithelial cell differentiation, a cDNA library was constructed from poly(A) + RNA extracted from mature pig intestine. This library was e mployed in the isolation of clones encoding CRBP II and L-FABP. The nu cleotide sequence of the two pig cDNA clones was determined, and the s equences of the deduced proteins compared with their homologues from o ther species. The results of this analysis showed that the two pig clo nes share a high level of homology with human and rat homologues both at the DNA and at the protein level.