The proximal promoter governs germ cell-specific expression of the mouse glutathione transferase mGstm5 gene

To explain the tissue-selective expression patterns of a distinct subclass of glutathione S-transferase (GST), transgenic mice expressing EGFP under control of a 2 kb promoter sequence in the 5'-flanking region of the mGstm5 gene were produced. The intent of the study was to establish whether the promoter itself or whether posttranscriptional mechanisms, particularly at the levels of mRNA translation and stability or protein targeting, based on unique properties of mGSTM5, determine the restricted expression pattern. Indeed, the transgene expression was limited to testis as the reporter was not detected in somatic tissues such as brain, kidney or liver, indicating that the mGstm5 proximal promoter is sufficient to target testis-specific expression of the gene. EGFP expression was also more restricted vis-a-vis the natural mGstm5 gene and exclusively found in germ but not in somatic cells. Real-time quantitative PCR (qPCR) data were consistent with alternate transcription start sites in which the promoter region of the natural mGstm5 gene in somatic cells is part of exon 1 of the germ cell transcript. Thus, the primary transcription start site for mGstm5 is upstream of a TATA box in testis and downstream of this motif in somatic cells. The 5' flanking sequence of the mGstm5 gene imparts germ cell-specific transcription.