Molecular remodeling of members of the relaxin family during primate evolution

Employing comparative analysis of the cDNA-coding sequences of the unique preprorelaxin of the Afro-lorisiform Galago crassicaudatus and the Malagasy lemur Varecia variegata and the relaxin-like factor (RLF) of G. crassicaudatus, we demonstrated distinct differences in the dynamics of molecular remodeling of both hormones during primate evolution. The lorisiform and lemuriform preprorelaxin sequences encoded identical hormones, providing the first endocrinological evidence for the monophyletic origin of all Strepsirrhini. Structural analysis revealed the lemuriform members of the relaxin family to be potentially bioactive single-gene products. In contrast to the "two-prong" relaxin receptor-binding motif (RELVR) present within the B-domains of other primate relaxins, strepsirrhine relaxin contained a unique "three-prong" motif (RRLIR) with highest sequence homology to the receptor-binding motif of the evolutionarily much older skate relaxin. In contrast to relaxin, the RLF molecule was highly conserved during primate evolution and contained within its B-domain the putative relaxin receptor-binding motif and a pentameric sequence implicated in binding to specific RLF receptors. Mutually exclusive expression of strepsirrhine preprorelaxin and RLF were observed in the fetal villous trophoblast cells of the strepsirrhine placenta and postpubertal testicular Leydig cells, respectively, reflecting distinct functional roles for both hormones within the reproductive tract of Strepsirrhini.