Caprine pregnancy-associated glycoproteins (PAG): Their cloning, expression, and evolutionary relationship to other PAG

Pregnancy-associated glycoproteins (PAG) are structurally related to aspart ic proteinases and belong to an extensive, vapidly evolving family of recen tly duplicated genes expressed in the placentas of artiodactyl species. The aim of the present study was to clone PAG from the goat, study their tempo ral and cell-specific expression, and determine their phylogenetic relation ship to PAG from other species. RT-PCR was used to generate PAG cDNA from p ooled placental RNA obtained between days 45 and 115 of pregnancy. A total of 11 cDNA, which differed by >5% from each other, were selected for comple te bidirectional sequencing from 60 clones analyzed. A group of nine (caPAG 1, caPAG3-7(var), caPAG9-11), which displayed >80% sequence identity with e ach other, were expressed after day 45 of pregnancy and were localized to t rophoblast binucleate cells. These PAG demonstrated an unusually high ratio of nonsynonymous (amino acid changing) to synonymous nucleotide difference s. CaPAG2, by contrast, was detectable only in early pregnancy (days 18 and 19) and expressed throughout trophectoderm. It was of more ancient origin than the PAG1 group, but more recent than caPAG8. The latter was expressed at all stages examined (days 18 to 115). The data confirm that many PAG gen es, with different patterns of temporal and spatial expression, are transcr ibed in the placenta of the goat. The data also suggest that the recently d uplicated PAG genes are being selected for rapid diversification of functio n. (C) 2000 Wiley-Liss, Inc.