CRYPTDIN GENE-EXPRESSION IN DEVELOPING MOUSE SMALL-INTESTINE

In rodents, the four intestinal epithelial cell lineages differentiate and become morphologically distinct during the first 2-3 postnatal wk . In studies reported here, reverse transcriptase-polymerase chain rea ction (RT-PCR)-based assays detected Paneth cell defensin mRNAs in int estinal RNA from 1-day-old (P1) mice before crypt formation and matura tion of the epithelium. Analysis of these defensin-coding RT-PCR produ cts from P1 mice showed that 69% of clones sequenced coded for cryptdi n-6, suggesting that it is the most abundant enteric defensin mRNA in the newborn. Paneth cell mRNAs, including cryptdins-4 and -5, lysozyme , matrilysin, and defensin-related sequences, also were detected in RN A from P1 mouse intestine. Unlike adult mice, where only Paneth cells are immunopositive for cryptdin, cryptdin-containing cells were distri buted throughout the newborn intestinal epithelium and not in associat ion with rudimentary crypts. Cryptdin immunoreactivity in the P1 mouse intestine was specific for intracellular granule contents, and immuno fluorescent detection of cryptdins on mucosal surfaces suggested that the peptides are released into the intestinal lumen in P1 mice. Defens in secretion may contribute to innate immunity of the neonatal intesti ne before the presence of distinguishable Paneth cells.