Selective activation of testis-specific genes in cultured rat spermatogenic cells

During mammalian spermatogenesis the isozyme pattern of a glycolytic enzyme, phosphoglycerate kinase (PGK; ATP: 3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3), changes from the somatic-type PGK-1 to the testis-specific PGK-2, and this change has been suggested to involve transcription switch. We have isolated genomic DNA fragments which code for the mouse PGK isozymes and determined the transcription start site of each gene. The results demonstrate that transcriptions of the two PGK genes are initiated at multiple sites under the control of TATA box-lacking promoters. The putative promoter regions of the two genes contain several distinct sequences known as the CCAAT box and the GC box which possibly bind CCAAT-binding proteins and Sp1, respectively. We next developed a culture system in which spermatogenic gene expression is partly reproduced. When spermatogenic cells of 20-day-old rats were cultured, transcripts from PGK-2 and another spermatogenic gene PRPS3 became detectable, while expression of other non-spermatogenic genes did not significantly change during culture. These results suggest that two spermatogenic genes PGK-2 and PRPS3 were activated in culture according to a developmental program of spermatogenesis. Thus, this culture system may be useful for studying the molecular mechanism underlying mammalian spermatogenic gene expression.