Pregnancy‐associated endometrial expression of antileukoproteinase gene is correlated with epitheliochorial placentation

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Abstract
Uterine expression of the mRNA encoding antileukoproteinase (ALP) is highest in pig uterus during mid‐ to late pregnancy, suggesting a stage of pregnancy‐dependent role for this elastase/cathepsin G protease inhibitor in feto‐maternal interactions. To examine a potential relationship between uterine synthesis of ALP and the type of placentation in mammalian species, the expression of ALP mRNA and/or protein in pregnant mares, cows, rats, and mice was evaluated. Genomic DNA and mRNA hybridization analyses were performed using a porcine ALP cDNA as probe. The concentration of ALP protein in reproductive tissues was determined by RIA using a polyclonal antibody raised against a synthetic peoptide (ALP 16P) corresponding to amino acid residues 21–36 of the porcine ALP protein. A single ALP mRNA transcript of approximately 0.8 kb in length was detected in equine and bovine uterine tissues. The relative abundance of ALP mRNA in equine endometrium increased between days 125–170 (mid‐pregnancy), and then decreased by day 215 of pregnancy. Similarly, the steady state levels of ALP mRNA in bovine endometrium and myometrium were higher during mid‐ to late than during early pregnancy. The levels of ALP mRNA in bovine fetal cotyledon were low and did not change significantly with stage of pregnancy. No hybridization was detected to pregnant rat endometrial tissues, although high stringency Southern blot analysis of porcine, bovine, and rat genomic DNAs using porcine ALP cDNA as probe predicted a high degree of nucleotide sequence homology in their respective ALP genes. In pregnant cows, concentrations of ALP protein were higher in maternal endometrium and myometrium than in fetal cotyledon. Tissue ALP content in bovine uterus increased between days 17–89, and then decreased by day 248 of pregnancy. In contrast, no ALP protein was detected in cytosolic extracts prepared from endometrium of pregnant rats and mice. THe demonstrated synthesis of ALP mRNA and/or protein in the endometrium of the mare and the cow similar to that of the pig, but not in the endometrium of the rat and mouse, during pregnancy indicates a potential correlation between endometrial ALP expression and epitheliochorial type of placentation in mammalian species.

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