In vitro translation of RNA to lactase during postnatal development of rat intestine.

mRNA levels encoding lactase were detected by Northern blot analysis using two different probes in developing rat intestine. Probe I and probe II corresponding to second half of prolactase gene showed a 6.8 kb mRNA transcript in 7, 14, 21 and 30 day old rat intestine. There was no change in quantity of lactase mRNA detected using probe II, but hybridization with probe I showed a progressive decrease in mRNA transcript encoding lactase with age. At day 7 and 14 of postnatal development, the lactase mRNA was quite high, but it reduced upon weaning. The in vitro translation products of RNA detected by Western blot analysis using brush border lactase antibodies showed several isoforms of lactase antigen with molecular weight ranging from 100-220 kDa. Analysed at days 7 and 30 of postnatal development, lactase isoforms of molecular weight 130 kDa and 220 kDa were similar to those found in purified brush border membranes. The translation of RNA to 220 kDa lactase protein was high in 7 and 14 day old pups, but it was markedly reduced in 30 day old animals. These findings support the contention that translation of mRNA to lactase is impaired in weaned animals, which may also be responsible for the maturational decline in lactase activity in adult rat intestine.