An antiluteolytic substance secreted by the ovine conceptus and primarily responsible for maternal recognition of pregnancy is ovine trophoblast protein-1 (oTP-1), a new type I interferon (IFN). The objectives of this research were 1) to investigate whether multiple, distinct genes encode oTP-1 and other type I IFNs in the ovine genome and 2) to examine expression of oTP-1 and other IFN mRNAs during conceptus development. Genes for type I IFNs were isolated from a subgenomic library constructed from Day 25 (Day 0 = estrus) ovine conceptus high-molecular-weight DNA. Six clones were isolated and nucleotide-sequenced from -1000 to +900 (bases relative to cap site). Comparisons of inferred amino acid sequences demonstrated that four clones were distinct oTP-1 genes and that two clones, defined as o9 and o12, were related type 1 IFNs (deduced aa homology of o9 and o12 to oTP-1 was 71% and 54%, respectively). The presence of mRNAs encoded by oTP-1 and type I IFN genes was examined quantitatively via reverse transcription-polymerase chain reaction (RT-PCR) analysis of total cellular RNA (tcRNA) extracted from Day 13-45 concepti. Total cellular RNA obtained from Day 75 placenta and adult lymphocytes was also analyzed by RT-PCR, coupled with Southern blot hybridization of the PCR reaction products with specific DNA probes. PCR products were sequenced in order to confirm primer specificity, and mRNAs corresponding to two of the four oTP-1 genes and to both related IFN clones (o9 and o12) were identified. Furthermore, quantitation of the PCR products revealed that of the two oTP-1 genes examined, one was highly expressed on Days 13-20 and transcripts were weakly detectable on Days 30 and 45. In contrast, the other oTP-1 gene examined was weakly expressed on Days 13-20 only. Densitometric analysis of hybridization signals revealed that IFN o9 mRNA was detected in Day 75 placenta but only weakly detected in conceptus (Days 13-45) and adult lymphocytes. IFN o12 mRNA was abundant in lymphocytes relative to the other tissues examined. Collectively, these results demonstrate the existence of distinct oTP-1 and related type I IFN genes. The data suggest that these genes display differential, tissue-specific expression and developmental regulation during pregnancy.