T. Klonisch et al., Nucleic acid sequence of feline preprorelaxin and its localization within the feline placental, BIOL REPROD, 60(2), 1999, pp. 305-311
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.