Exploring the reciprocity between pioneer factors and development.

Development is regulated by coordinated changes in gene expression. Control of these changes in expression is largely governed by the binding of transcription factors to specific regulatory elements. However, the packaging of DNA into chromatin prevents the binding of many transcription factors.

The interaction between the Dbf4 ortholog Chiffon and Gcn5 is conserved in Dipteran insect species.

Chiffon is the sole Drosophila ortholog of Dbf4, the regulatory subunit for the cell-cycle kinase Cdc7 that initiates DNA replication. In Drosophila, the chiffon gene encodes two polypeptides with independent activities. Chiffon-A contains the conserved Dbf4 motifs and interacts with Cdc7 to form the Dbf4-dependent Kinase (DDK) complex, which is essential for a specialized form of DNA replication.

Chiffon triggers global histone H3 acetylation and expression of developmental genes in Drosophila embryos.

The histone acetyltransferase Gcn5 is critical for gene expression and development. In Drosophila, Gcn5 is part of four complexes (SAGA, ATAC, CHAT and ADA) that are essential for fly viability and have key roles in regulating gene expression. Here, we show that although the SAGA, ADA and CHAT complexes play redundant roles in embryonic gene expression, the insect-specific CHAT complex uniquely regulates expression of a subset of developmental genes.

The Dbf4 ortholog Chiffon forms a complex with Gcn5 that is necessary for histone acetylation and viability.

Metazoans contain two homologs of the Gcn5-binding protein Ada2, Ada2a and Ada2b, which nucleate formation of the ATAC and SAGA complexes, respectively. In , there are two splice isoforms of Ada2b: Ada2b-PA and Ada2b-PB. Here, we show that only the Ada2b-PB isoform is in SAGA; in contrast, Ada2b-PA associates with Gcn5, Ada3, Sgf29 and Chiffon, forming the Chiffon histone acetyltransferase (CHAT) complex.