EXPRESSION OF LACTASE-PHLORHIZIN HYDROLASE IN SHEEP IS REGULATED AT THE RNA LEVEL

Lactase-phlorizin hydrolase (LPH) is expressed on the intestinal brush border and is responsible for the hydrolysis of lactose, the chief su gar in mammalian milk. The enzymic activity of LPH peaks soon after bi rth in most mammals and declines to much lower levels before adolescen ce. The molecular basis of this pattern of expression has not been cle arly established. We have measured relative amounts of LPH mRNA in int estine from sheep with ages across a developmental spectrum, including third trimester fetal lambs, newborn lambs and adult sheep. LPH mRNA levels in the jejunum decline similar to 50-fold between infancy and a dulthood, in parallel with the reduction in both lactase specific acti vity and immunologically reactive lactase protein expression in sheep jejunum. LPH mRNA is present in high concentration in the duodenum of newborn lambs, but steadily declines by day 34 and is dramatically red uced in adults. Because the changes in LPH mRNA: protein, and enzymic activity are generally parallel, we conclude that the developmental re gulation of LPH in sheep is probably mediated primarily at the mRNA le vel.