Tissue-specific TAFs counteract Polycomb to turn on terminal differentiation.

Polycomb transcriptional silencing machinery is implicated in the maintenance of precursor fates, but how this repression is reversed to allow cell differentiation is unknown. Here we show that testis-specific TAF (TBP-associated factor) homologs required for terminal differentiation of male germ cells may activate target gene expression in part by counteracting repression by Polycomb. Chromatin immunoprecipitation revealed that testis TAFs bind to target promoters, reduce Polycomb binding, and promote local accumulation of H3K4me3, a mark of Trithorax action.

Testis-specific TAF homologs collaborate to control a tissue-specific transcription program.

Alternate forms of the PolII transcription initiation machinery have been proposed to play a role in selective activation of cell-type-specific gene expression programs during cellular differentiation. The cannonball (can) gene of Drosophila encodes a homolog of a TBP-associated factor (dTAF5) protein expressed only in spermatocytes, where it is required for normal transcription of genes required for spermatid differentiation. We show that Drosophila primary spermatocytes also express four additional tissue-specific TAFs: nht (homolog of dTAF4), mia (homolog of dTAF6), sa (homolog of dTAF8) and rye (homolog of dTAF12).

Germ-line specific variants of components of the mitochondrial outer membrane import machinery in Drosophila.

A search of the Drosophila genome for genes encoding components of the mitochondrial translocase of outer membrane (TOM) complex revealed duplication of genes encoding homologues of Tom20 and Tom40. Tom20 and Tom40 were represented by two differentially expressed homologues in the Drosophila genome. While dtom20 and dtom40 appeared to be expressed ubiquitously, the second variants, called tomboy20 and tomboy40, were expressed only in the male germ-line.

Regulation of transcription of meiotic cell cycle and terminal differentiation genes by the testis-specific Zn-finger protein matotopetli.

A robust developmentally regulated and cell type specific transcriptional programme is activated in primary spermatocytes in preparation for differentiation of the male gametes during spermatogenesis. Work in Drosophila is beginning to reveal the genetic networks that regulate this gene expression. The Drosophila aly-class meiotic arrest loci are essential for activation of transcription of many differentiation-specific genes, as well as several genes important for meiotic cell cycle progression, thus linking meiotic cell cycle progression to cellular differentiation during spermatogenesis.

Differential expression of the Drosophila mitofusin genes fuzzy onions (fzo) and dmfn.

Mitofusins comprise a family of evolutionarily conserved, nuclear encoded mitochondrial guanosine triphoshatases that control mitochondrial fusion and morphology. The fuzzy onions (fzo) and Drosophila mitofusin (dmfn) genes, which encode the only Mitofusin homologs in Drosophila are differentially expressed during development. Dmfn-mRNA was widely expressed during embryogenesis accumulating in the mesoderm and endoderm during gut development, during oogenesis with transcripts maternally deposited into the early embryo and in the male germ line, where dmfn-mRNA was expressed in spermatogonia, spermatocytes and early spermatids.