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Background  Mammalian spermatogenesis involves formation of haploid cells from the male germline and then a complex morphological transformation to generate motile sperm. Focusing on meiotic prophase, some tissue-specific transcription factors are known (A-MYB) or suspected (RFX2) to play important roles in modulating gene expression in pachytene spermatocytes. The current work was initiated to identify both downstream and upstream regulatory connections for  Rfx2 .    Results  Searches of pachytene up-regulated genes identified high affinity RFX binding sites (X boxes) in promoter regions of several new genes:  Adam5 ,  Pdcl2 , and  Spag6 . We confirmed a strong promoter-region X-box for  Alf , a germ cell-specific variant of general transcription factor TFIIA. Using  Alf  as an example of a target gene, we showed that its promoter is stimulated by RFX2 in transfected cells and used ChIP analysis to show that the promoter is occupied by RFX2 in vivo. Turning to upstream regulation of the  Rfx2  promoter, we identified a cluster of three binding sites (MBS) for the MYB family of transcription factors. Because testis is one of the few sites of  A-myb  expression, and because spermatogenesis arrests in pachytene in  A-myb  knockout mice, the MBS cluster implicates  Rfx2  as an  A-myb  target. Electrophoretic gel-shift, ChIP, and co-transfection assays all support a role for these MYB sites in  Rfx2  expression. Further,  Rfx2  expression was virtually eliminated in  A-myb  knockout testes. Immunohistology on testis sections showed that A-MYB expression is up-regulated only after pachytene spermatocytes have clearly moved away from the tubule wall, which correlates with onset of RFX2 expression, whereas B-MYB expression, by contrast, is prevalent only in earlier spermatocytes and spermatogonia.    Conclusion  With an expanding list of likely target genes, RFX2 is potentially an important transcriptional regulator in pachytene spermatocytes.  Rfx2  itself is a good candidate to be regulated by A-MYB, which is essential for meiotic progression. If  Alf  is a genuine RFX2 target, then  A-myb ,  Rfx2 , and  Alf  may form part of a transcriptional network that is vital for completion of meiosis and preparation for post-meiotic differentiation.

RFX2 is a candidate downstream amplifier of A-MYB regulation in mouse spermatogenesis