EXPRESSION OF TROPHOBLASTIC INTERFERON GENES IN SHEEP AND CATTLE

The trophoblastic interferons ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1, respectively) have been implicated as mediators of maternal recognition of pregnancy in sheep and cattle. The objective of this study was to describe the onset and duration of gene expression for oTP-1 and bTP-1 in preimplantation ovine and bovine conceptuses by in situ hybridization and Northern analysis. Sections from paraffin-embedded ovine conceptuses, collected on Days 10, 11, 12, 13, and 15 of gestation (n = 1, 3, 3, 2, 2), and bovine conceptuses, collected on Days 12/13, 15/16, and 19 (n = 2, 4, 5), were hybridized to specific [35S]-labeled cDNA probes. Two different probes, one encompassing bases 442-918 and representing both coding and 3'-untranslated regions, and a second 3'-specific probe (bases 650-912) were used to detect oTP-1 mRNA. At all stages examined, oTP-1 mRNA was confirmed to trophectoderm of ovine conceptuses. Consistent with earlier studies, expression increased markedly at Day 13. oTP-1 mRNA was detected at low levels in seven of seven ovine conceptuses prior to Day 13 when the longer probe was employed. With the 3'-specific probe, however, oTP-1 mRNA was detected in only one of the seven ovine conceptuses prior to Day 13. Thus, although low amounts of oTP-1 mRNA may be present in ovine conceptuses prior to Day 13, massive induction of this mRNA occurs on Day 13 coincident with the initiation of maternal recognition of pregnancy. bTP-1 mRNA, detected with a coding plus 3'-noncoding region probe (bases 236-913), was confined to the trophectoderm and present in all conceptuses from Days 12/13-19. Maximal expression was noted at Day 15/16. These results were confirmed by Northern blotting of RNA extracted from bovine conceptuses on Days 15, 17, 19, 21, 23, and 25 of gestation. bTP-1 mRNA was detected on all days examined. Taken together, these data demonstrate that bTP-1 mRNA is present in conceptuses as early as Day 12 of pregnancy, with a marked increase in expression occurring on Day 15/16 of pregnancy and continuing through at least Day 25. The increase in expression of bTP-1 mRNA on Day 15/16 occurs coincident with elongation of the blastocyst and maternal recognition of pregnancy in this species.