Cloning and characterization of platelet-activating factor receptor gene in domestic animals

In the present study, the coding sequence of platelet-activating factor receptor (PAFr) gene was found to be 1029 by long in pig, goat and cow. The deduced amino acid sequence of the PAFr contains 7 putative transmembrane domains, characteristic of a member of G-protein coupled receptors. The porcine PAFr gene was mapped to SSC6q26-27. Alternative splicing produced two different transcripts of the gene. Transcript 1 directed by promoter 1 was detected in various tissues including white blood cells (WBC), and transcript 2 directed by promoter 2 was observed in the same tissues but not in WBC. The presence of three steroid hormone-binding sites in promoter 1 was suggested. In addition, the sequence of PAFr cDNA was preliminarily studied in the sheep and dog and the organization of bovine PAFr gene was also examined.; Temporal expression of PAFr and estrogen receptor α (ER) genes was studied in porcine endometrial tissues and embryos on days 10, 12, 14, 16 and 18. The temporal expression of PAFr and ER genes in non-pregnant tissues was affected by cyclicity, suggesting a synergistic role of PAF and estradiol-17β (E₂) in regulation of estrous cycle events. The temporal expression of the PAFr gene in pregnant endometrial (P > 0.05) and embryonic (P < 0.05) tissues increased from day 10 to day 16. The temporal expression of ER genes in pregnant endometrial tissues decreased from day 10 to day 18 (P < 0.05). In addition, ER expression was detectable in 20–60% of embryonic tissue samples with decreasing ER levels from day 10 to day 18. In combination with previously obtained data on PAF and E₂ concentrations in uterine luminal fluids (ULF) and tissues, the present results indicated that the increasing PAFr transcripts were associated positively with increasing levels of PAF. This suggests important roles for PAF in establishment of pregnancy. ER transcripts in both pregnant tissues and embryos and E₂ in ULF decreased correspondingly from day 13 to day 16. Both PAFr and PAF increased in tissues and embryos from day 12 to day 16. These results suggest that over the course of implantation the importance of PAF becomes increasingly greater than E₂.