A FAMILY OF DEFENSIN-LIKE GENES CODES FOR DIVERSE CYSTEINE-RICH PEPTIDES IN MOUSE PANETH CELLS

Cryptdins constitute a diverse population of defensins in Paneth cells of intestinal crypts. In mice, certain intestinal mRNAs, termed ''CRS 1C'' and ''CRS4C,'' are considered to be cryptdin-related sequences, b ecause their prepro-coding sequences are 94% identical to those of cry ptdin-1 mRNA; however, their predicted products, which are cationic, c ysteine-rich peptides, are not defensins (A. J. Ouellette and J. C. Lu aldi, J. Biol. Chem. 265: 9831-9837, 1990). Here we describe several m ouse small intestinal mRNAs and genes that code for CRS4C prepropeptid es. The 10-kDa deduced CRS4C proteins consist of a prepro sequence, po tential monobasic or dibasic peptide cleavage sites, a predicted 3.7-k Da peptide that contains 7 [C]-[X]-[Y] repeats, and a C(N/K)CNPK carbo xyl-terminal consensus sequence. In situ hybridization experiments sho wed that CRS4C mRNAs are found in Paneth cells of adult small bowel. T he CRS4C genes closely resemble cryptdin genes, having a two-exon stru cture with highly conserved transcription start sites, intron-exon jun ctions, and a single intron of approximate to 550 bp. Like the cryptdi n genes, exon 1 of CRS4C genes consists of 5' untranslated sequences ( UTS) and the prepro-coding region, and exon 2 codes for the predicted mature peptide and 3' UTS. Despite the similarity of first exons in CR S4C and cryptdin genes, their introns exhibit very little homology, an d their second exons code for unrelated peptides. Analysis of introns suggests that the ancestral cryptdin and CRS4C genes may have diverged from a common ancestor in the distant past and expanded only recently . We speculate that the cryptdin/ CRS genes evolved so that prepro reg ions encoded by exon 1 were conserved to allow the varied peptides cod ed by exon 2 to be directed into Paneth cell secretory granules. (C) 1 994 Academic Press,Inc.