Abstract
BackgroundThe prolactin-related proteins (PRPs) are non-classical placental-specific members of the prolactin/growth hormone family. Among ruminants, they are expressed in the cotyledonary villi of cattle and goat. We investigated placental PRP in sheep in order to gain a comprehensive understanding of the function and evolution of these molecules. We also examined the sequence properties, expression and lactogenic activation of the cloned genes.ResultsWe cloned two novel ovine PRPs, named oPRP1 and oPRP2. oPRP2 had a typical PRP sequence similar to bovine PRP1 (bPRP1). oPRP1 had a short sequence identical with bovine or caprine type PRP but the reading frame was shifted. Both oPRPs were expressed in trophoblast giant binucleate cells (BNC) as in cattle and goat. oPRP1 expression declined from the early to the middle stage of gestation. In contrast, oPRP2 expression remained constant throughout the gestation period. oPRP2 was translated to form a mature protein in a mammalian cell expression system. Western blotting showed a molecular mass of 35 kDa for the FLAG-tag fusion oPRP2 protein. This recombinant protein and bPRP1 were bioassayed using Nb2 lymphoma cells; it was confirmed that neither ruminant PRP had lactogenic activity because the Nb2 lymphoma cells did not proliferate.ConclusionWe have identified two novel PRPs, oPRP1 and oPRP2, in ovine placenta. Both these ovine PRPs were localized and quantitatively expressed in BNC. Absence of lactogenic activity was confirmed for the oPRP2 molecule. It is anticipated that novel and known ruminant PRPs have common functions, except for lactogenic activity.
Highlights
The prolactin-related proteins (PRPs) are non-classical placental-specific members of the prolactin/growth hormone family
Results ovine prolactin-related protein-1 (oPRP1) and oPRP2 nucleotide sequences and deduced amino acid sequences Full-length oPRP1 and oPRP2 were cloned from the ovine placentome on day 95 of gestation. oPRP1 was 893 nucleotides long with a 540-nts protein coding sequence region (CDS); oPRP2 had a 947-nts full-length sequence and a 717-nts CDS
The sequence region in which oPRP1 mRNA is defective compared to other PRP mRNAs is shown in Fig. 1 along with the sequences of oPRP2, cPRP1 and bovine PRP1 (bPRP1). oPRP1 has a shorter sequence, lacking 52 bp from the CDS regions of other PRP sequences
Summary
The prolactin-related proteins (PRPs) are non-classical placental-specific members of the prolactin/growth hormone family. Among ruminants, they are expressed in the cotyledonary villi of cattle and goat. Prolactin-related proteins (PRPs) are non-classical members of the prolactin (PRL)/growth hormone (GH) family that have been found in bovine, caprine, murine and rat placenta. The purposes of the present study are (i) to explore a bPRP homolog gene in ovine placenta, (ii) to investigate the localized and quantitative expression of oPRP and (iii) to examine the possible biological activity of oPRP, because comparison among ruminant PRP structures and/or expression may provide clues to understanding PRP function
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