Developmental and cell type-specific regulation of core promoter transcription factors in germ cells of frogs and mice.

This article reports on the comparative cell type-specific expression profiles of selected core promoter-associated transcription factors during gametogenesis and embryogenesis in frogs and mice. In frogs we tested TBP, TRF2/TLF, TRF3, TFIIAalphabeta, and ALF, as well as variant forms of TAFs 4, 5, and 6. Four of these factors, TRF3, TAF4L, TAF5L, and the previously-characterized ALF gene, are preferentially expressed in testis and ovary. In mice we tested TBP, TRF2/TLF, TRF3, TFIIAalphabeta, and ALF. The results showed that while ALF was present in testis and ovary, as expected, TRF3 could only be detected in the ovary. RT-PCR experiments using RNAs from microdissected ovary tissue, together with in situ hybridization analysis, showed that TRF3 and ALF genes are specifically expressed in oocytes in both adult and prepubertal animals, whereas, their somatic counterparts, TBP and TFIIAalphabeta, are present in oocytes and in surrounding somatic cells of the follicle. Furthermore, both mice and frogs displayed a reduction in TRF3 and ALF transcript levels around the time of fertilization. In mice, transcripts from these genes could again be detected at low levels in embryonic reproductive tissues, but only reached maximal levels in adult animals. Finally, the results of protein-DNA interaction assays show that all combinations of core promoter complexes can be formed in vitro using recombinant TBP, TRF3, TFIIA, and ALF, including a TRF3-ALF complex. Overall, the diverse gene regulatory patterns observed here and in earlier reports indicate precise control over which transcription factor complexes can be formed in vivo during gametogenesis and early embryogenesis.