Identification, evolution, and regulation of expression of Guinea pig trappin with an unusually long transglutaminase substrate domain

Trappins are found in human, bovine, hippopotamus, and members of the pig family, but not in rat and mouse. To clarify the evolution of the trappin genes and the functional significance of their products, we isolated the trappin gene in guinea pig, a species belonging to a rodent family distinct from rat and mouse. Guinea pig trappin was confirmed to encode the same domain structure as trappin, consisting of a signal sequence, an extra large transglutaminase substrate domain, and a whey acidic protein motif. Northern blot analysis and in situ hybridization histochemistry as well as immunohistochemistry demonstrated that guinea pig trappin is expressed solely in the secretory epithelium of the seminal vesicle and that its expression is androgen-dependent. We confirmed that guinea pig trappin is cross-linked by prostate transglutaminase and that the whey acidic protein motif derived from guinea pig trappin has an inhibitory activity against leukocyte elastase. Genome sequence analysis showed that guinea pig trappin belongs to the family of REST (rapidly evolving seminal vesicle transcribed) genes.