COMPARATIVE-ANALYSIS OF NEUTRAL ENDOPEPTIDASE (NEP) AND VILLIN GENE-EXPRESSION DURING MOUSE EMBRYOGENESIS AND ENTEROCYTE MATURATION

Neutral endopeptidase (Endopeptidase 24.11; NEP; neprilysin), an integ ral membrane protein, and villin, a major microvillar cytoskeletal act in-binding protein, are both typically associated with brush border ep ithelia. In this study, cRNA probes were hybridized in situ to investi gate the expression of NEP and villin genes in embryo and adult mouse enterocytes. During development, villin mRNAs were easily detected in the immature digestive tract well before establishment of the brush bo rder. In 17-day-old embryos, a transient elevation of villin mRNA occu rred just prior to a dramatic increase in microvilli length and densit y. NEP only appeared by day 17 as the embryonic gut began to become fu nctional. It therefore appears that the onset of transcription of spec ialized cytoskeletal proteins from the brush border preceded that of i ntrinsic membrane-bound enzyme from microvilli. In the adult intestina l fold, both mRNAs were expressed along the whole length of the villus with maximal expression at its base. In contrast, both proteins were uniformly expressed along the whole crypt-villus axis. Quantitative an alysis revealed an asymmetric intracellular distribution of both mRNAs that were differentially polarized in the apical cytosplasm of entero cytes.