Nucleic acid sequence of feline preprorelaxin and its localization within the feline placental

The cat placenta is known to secrete large amounts of relaxin. We employed uteroplacental tissue at approximately Day 35 of gestation to determine the nucleic acid sequence of feline preprorelaxin using reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Feline pre prorelaxin cDNA was found to consist of 540 base pairs encoding a protein o f 180 amino acids (aa). We identified a signal peptide of 25 aa, a B domain of 33 aa, a C domain of 98 aa, and an A domain of 24 aa. The putative rece ptor binding region in the N'-terminal part of the B domain contained one s ubstitution from the classical GRELVR motif (L-->F). Feline preprorelaxin s hared highest homology with porcine and equine preprorelaxin, Northern anal ysis revealed a specific 1-kilobase transcript present in total RNA of feli ne uteroplacental tissue but not of liver tissue. Nonradioactive in situ hy bridization was used to localize relaxin mRNA, and immunohistochemistry was used to localize the relaxin hormone and cytokeratin, in tissues of the fe te-maternal interface recovered from two queens at Day 35 of gestation. Spe cific hybridization signals for relaxin mRNA were exclusively detected in c ells located in the lamellar placental labyrinth but were absent from other placental and non-placental uterine parts. The cells expressing relaxin mR NA also displayed immunoreactivity for cytokeratin and were, therefore, ide ntified as trophoblast cells. Immunoreactive relaxin colocalized in those p lacental areas expressing relaxin mRNA. Trophoblast cells located at the vi llous chorioallantoic tips invading the endometrium and extravillous tropho blast cells in the junctional placental zone were devoid of relaxin.