Cloning and structural analysis of two distinct families of ovine interferon-alpha genes encoding functional class II and trophoblast (oTP) alpha-interferons.

Ovine trophoblast protein (oTP) is a polypeptide secreted by ovine trophectoderm from day 11 to 21, which plays a key role in maternal recognition of pregnancy. Structural analyses established that oTP shares extensive homology with class II alpha-interferon (IFN-alpha II) subfamily. Previous screening of an ovine genomic DNA library probed with an oTP cDNA incidently resulted in the isolation of a functional IFN-alpha II gene and two relevant pseudogenes, as shown by sequence analysis and study of expression in eukaryotic COS cells. The expected oTP gene together with a cognate pseudogene was successfully isolated from the series of clones selected from another genomic library probed with the oTP cDNA, using two specific oligonucleotides, each one complementary to a region of oTP cDNA with little homology with the IFN-alpha II gene and related pseudogenes. Southern blotting of ovine genomic DNA indicated the existence of at least five trophoblast IFN-alpha genes or pseudogenes. Nucleotide sequence comparisons showed that the oTP gene exhibits a higher homology (90%) with bovine trophoblast IFN gene (Stewart et al. (1990) J. Mol. Endocrinol. 4, 275-282) than with oIFN-alpha II gene (70%), thus providing evidence that embryonic IFNs constitute a distinct subfamily of IFN-alpha s.