Polymorphic forms of expressed bovine interferon-tau genes: relative transcript abundance during early placental development, promoter sequences of genes and biological activity of protein products.

Multiple interferon (IFN)-tau genes exist in cattle, but it has remained unclear how many are expressed, the extent of their variation, and whether different genes exhibit similar patterns of expression and code for proteins with similar biological activities. A total of 118 complementary DNA (cDNA) were bi-directionally sequenced from reverse-transcribed bovine (bo) conceptus RNA over the period from blastocyst formation until day 25 of pregnancy. Fourteen different cDNAs, encoding eight different IFN-tau, were confirmed unique. All showed high sequence conservation (>98% nucleotide identity; >96% amino acid identity). The cDNA fell into three, recently evolved, phylogenetic groups (tau1, 2, and 3). Mean concentrations of IFN-tau messenger RNA were greater at day 17 and day 19 than at day 14 and day 25, with different genes showing comparable expression patterns, although there appeared to be a major bias in expression of two genes (for boIFN-tau1c and tau3a) in blastocysts. Genes representing members of the three boIFN-tau groups were cloned. Their promoter regions were conserved over regions considered important for transcriptional activation. Recombinant protein generated in Escherichia coli from representative genes in the three groups had similar but not identical antiviral activities. In summary, many IFN-tau genes, which are probably under similar transcriptional control, are expressed in bovine trophoblast during the peri-implantation period of development.

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

Interferon-tau (IFN-tau) is secreted from trophectoderm of periimplantation ruminant conceptuses and is a critical component of pregnancy recognition. Multiple genes encode IFN-tau. The objectives of this study were to identify expressed forms of ovine IFN-tau 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-tau 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-tau, 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-tau.