CHICKEN BETA-DEFENSINS AND DEFENSIN GENE CLUSTER

¹ Department of Poultry Science, Texas A & M University, College Station, TX 77843

² Department of Computer Science, Texas A & M University, College Station, TX 77843

³ Department of Animal Science, Texas A & M University, College Station, TX 77843

The defensins comprise a large family of antimicrobial peptides that play an important role in first-line host defense of plants and animals. Defensins are encoded in gene clusters in humans, mice, and rats. Currently, three chicken beta-defensins have been reported and no alpha- and theta-defensins are found in birds yet. Using bioinfomatic tools, six novel beta-defensin genes were identified from the chicken EST and genome sequence databases. The number of amino acid residues of the propeptides ranges from 60-68 with a typical motif of 6 cysteines (C-X6-C-X4-C-X9-C-X6-CC). Local assembly of the defensin genes revealed that the coding sequences were located in two exons with one encoding a leader sequence and the other the cysteine motif similar to what have been found in mammals. Sequences from the chicken EST and genomic sequences indicate that there are alternative spicing sites for one gene. The results of PCR screening of a chicken radiation hybrid panel demonstrated that these genes were tightly linked in a gene cluster. The expression of these genes was tissue-specific except gallinacin 1 that was expressed in all tissues tested. All identified defensins were expressed in the lung and spleen. In conclusion, the data of present study together with the genetic information of mammalian defensins indicate that the beta-defensin gene cluster originated before the divergence of the birds and mammals.