Identification of the expressed forms of ovine interferon-tau in the periimplantation conceptus: sequence relationships and comparative biological activities.

Interferon-tau (IFN-τ) is secreted from trophectoderm of periimplantation ruminant conceptuses and is a critical component of pregnancy recognition. Multiple genes encode IFN-τ. The objectives of this study were to identify expressed forms of ovine IFN-τ and to compare their biological activities. Sequences analyzed after cloning 36 reverse transcription-polymerase chain reaction products of ovine conceptus RNA provided seven new cDNA that were similar in sequence to previously cloned forms (p3, p6, and p8 cDNA). Phylogenetic analysis of amino acid sequence for all new and previously reported forms showed that ovine IFN-τ forms can be divided into three main groups. Equivalent amounts of mRNA for p3, p6, and p8 forms were detected in conceptuses following RNase protection. Recombinant p3 and p8 protein had similar antiviral activity on ovine and bovine cells whereas p6 protein was less active. The p3 form was the most potent of the three in its ability to extend estrous cycle length in nonpregnant ewes. In summary, there appeared to be three main groups of ovine IFN-τ, each containing several variant forms. Antiviral activity was not particularly well correlated with ability to prevent luteolysis, suggesting that distinct intracellular mechanisms are used to exert the various actions of IFN-τ.