Marsupial relaxin: complementary deoxyribonucleic acid sequence and gene expression in the female and male tammar...

The nucleotide and derived amino acid sequences of tammar preprorelaxin were established by combined reverse transcriptase polymerase chain reaction and 3'- and 5'-rapid amplification of cDNA ends methods, using RNA from the corpus luteum of late pregnancy as template. Relaxin gene expression was then investigated in tissues at various stages of the 26-day pregnancy and in adult males. The full-length tammar relaxin preprohormone is 579 base pairs. The derived amino acid sequence contains a probable signal peptide of 26 amino acids, a B-domain of 31 amino acids, a C-domain of 111 amino acids, and an A-domain of 24 amino acids, with sequence homologies of 49%, 38%, 47%, and 47%, respectively, to dogfish, pig, and both human relaxins, for the combined A- and B-domains of the functional peptides. The conserved amino acid residues in the B-domain confirm a region shown to be essential for binding of the peptide to its receptor. A relaxin gene is expressed in several other tissues of pregnant tammars including the placenta, follicle, and hypothalamus. Northern analysis showed a 1-kilobase relaxin transcript in the corpus luteum and placenta. Using RNase protection assays, relaxin gene expression in the corpus luteum was greater in early and mid pregnancy, reduced at term, and absent postpartum. These data demonstrate relaxin biosynthesis in both the corpus luteum and placenta in this marsupial and suggest that a relaxin physiology has been conserved during mammalian evolution.