Developmental regulation of a gene that encodes a cysteine-rich intestinal protein and maps near the murine immunoglobulin heavy chain locus.

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Abstract
Mouse and rat small intestinal cDNA libraries were screened for recombinants derived from mRNAs whose concentration changed during the transition from suckling to weaning. cDNAs transcribed from a 570-nucleotide-long mRNA were isolated. Dot blot hybridization analyses of RNA recovered at various stages of rat gastrointestinal ontogeny indicated that the concentration of this mRNA begins to increase during the mid-suckling period, reaching a peak during weaning. There is considerable variation in the relative amount of this mRNA in adult tissues, with highest levels encountered in the rat small intestine and colon. Its concentration in duodenum, jejunum, and ileum is approximately the same. It is more concentrated in villi than in crypts. The rat mRNA encodes a 77 amino acid, 8.55-kDa polypeptide that has seven cysteine residues. This cysteine-rich intestinal protein (named CRIP) has two internal repeated sequence blocks. Computer-assisted comparisons of CRIP to proteins of known function disclosed that it is homologous to certain ferredoxins. Southern blot analyses revealed that sequences homologous to the rat gene are present in sea squirt, fish, bird, and human DNA, indicating that this gene is highly conserved and that related proteins may be present in many if not all vertebrates. Recombinant inbred mouse strains were utilized to show that the CRIP gene is closely linked to the immunoglobulin heavy chain constant region locus, Igh-c, on chromosome 12. CRIP mRNA is a molecular marker for the suckling-to-weaning transition of rodent intestinal development. The cloned cDNA may be a useful probe for identifying factors that regulate intestinal development during this period.