Ruminant relaxin in the pregnant one-humped camel (Camelus dromedarius)

We have determined the cDNA sequence of preprorelaxin in the pregnant one-h umped camel by employing reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Camel preprorelaxin consisted of 600 b ase pairs (bp) encoding a protein of 199 amino acids (aa) with a signal pep tide of 25 aa (75 bp), a B domain of 28 aa (84 bp), a C domain of 121 aa (3 66 bp), and an A domain of 24 aa (72 bp). The N terminus of the C domain of camel prorelaxin contained the unique proline-rich repetitive sequence (-R PAP)(3)-(-K/RPAL-)(2), and within the B domain the classical -GRELVR- recep tor binding motif was found. Camel preprorelaxin showed highest homology wi th porcine (74.6%) and equine (65.4%) relaxin. The ovary and the uteroplace ntal unit were a dual source of relaxin in the pregnant dromedary. Within t he ovary, weak expression of relaxin was detected in large luteal cells of the mature corpus luteum. In the ovarian follicles, immunoreactive relaxin, but not relaxin mRNA, was detected in the granulosa and theca interna cell layer. Beginning at around Day 93 of gestation and coinciding with increas ing interdigitation of the fetal villus with the underlying maternal endome trium, uterine luminal epithelial cells in the uteroplacental tissue expres sed relaxin. Weak expression of immunoreactive relaxin, but not relaxin mRN A, was observed in villous trophoblast cells. Pseudostratified trophoblast cells at the base of the placental villi and multinucleate giant cells did not express relaxin.