Organization of the murine and human interleukin-7 receptor genes: two mRNAs generated by differential splicing and presence of a type I-interferon-inducible promoter.

To better understand the regulation of interleukin-7 receptor (IL-7R) expression, we have pursued a detailed analysis of the structure of the murine and human IL-7R genes. The genes consist of eight exons, the sizes of which are conserved in mouse and human cells, spread out over 24 kbp (murine) and 19 kbp (human). A differential splicing event results in an mRNA encoding a secreted form of the human IL-7R gene. Primer extension and S1 nuclease analysis show a single transcriptional start site for the murine IL-7R gene. The 5'-flanking region of the murine IL-7R gene contains TATA- and CAAT-like sequences. The promoter region also contains a functional interferon regulatory element, to which the interferon-induced nuclear factors IRF-1 and IRF-2 are capable of binding and which is able to confer interferon-inducible expression on a heterologous gene. There are also potential binding sites for the transcription factors AP-1 and AP-2 as well as multiple glucocorticoid response elements. A fusion gene containing 2.5 kb of murine IL-7R 5' regulatory sequence linked to the bacterial chloramphenicol acetyltransferase gene directed expression of chloramphenicol acetyltransferase activity in murine pre-B-cell line 70Z/3 but not in the mouse fibroblast cell line NIH 3T3. Comparison of the murine and human IL-7R exon/intron boundaries with those of other hematopoietin receptor superfamily members whose exon/intron boundaries are also known reveals a conserved evolutionary structure.