Peptide Localization and Gene Structure of Cryptdin 4, a Differentially Expressed Mouse Paneth Cell α-Defensin

Abstract

ABSTRACT Paneth cells in crypts of the small intestine express antimicrobial peptides, including α-defensins, termed cryptdins in mice. Of the known Paneth cell α-defensins, the cryptdin 4 gene is unique, because it is inactive in the duodenum and expressed at maximal levels in the distal small bowel (D. Darmoul and A. J. Ouellette, Am. J. Physiol. 271:G68–G74, 1996). With a cryptdin 4-specific antibody, immunohistochemical staining of ileal Paneth cells was strong and specific for cytoplasmic granules, demonstrating that this microbicidal peptide is a secretory product of Paneth cells in the distal small intestine. Consistent with the pattern of cryptdin 4 mRNA distribution along the length of the gut, the cryptdin 4 peptide was not detected in duodenum. Structurally, the cryptdin 4 gene resembles other Paneth cell α-defensin genes. Its two exons, transcriptional start site, intron, splice sites, and 3′ flanking sequences are characteristic of the highly conserved mouse α-defensin genes. However, in the region upstream of the transcriptional initiation site, the cryptdin 4 gene contains a repeated 130-bp element that is unique to this α-defensin gene. Every independent cryptdin 4 genomic clone examined carries the repeated element, which contains putative recognition sequences for TF-IID-EIIA, cMyc-RS-1, and IgHC.2/CuE1.1; the repeat proximal to the start of transcription replaces DNA at the corresponding position in other mouse α-defensin genes. We speculate that this unique duplicated element may have a cis -acting regulatory role in the positional specificity of cryptdin 4 gene expression.