Histone H3 lysine 4 dimethylation signals the transcriptional competence of the adiponectin promoter in preadipocytes.

Adipogenesis is regulated by a coordinated cascade of sequence-specific transcription factors and coregulators with chromatin-modifying activities that are between them responsible for the establishment of the gene expression pattern of mature adipocytes. Here we examine the histone H3 post-translational modifications occurring at the promoters of key adipogenic genes during adipocyte differentiation. We show that the promoters of apM1, glut4, gpd1, and leptin are enriched in dimethylated histone H3 Lys4 (H3-K4) in 3T3-L1 fibroblasts, where none of these genes are yet expressed. A detailed study of the apM1 locus shows that H3-K4 dimethylation is restricted to the promoter region in undifferentiated cells and associates with RNA polymerase II (pol II) loading. The beginning of apM1 transcription at the early stages of adipogenesis coincides with promoter H3 hyperacetylation and H3-K4 trimethylation. At the coding region, H3 acetylation and dimethylation, as well as pol II binding, are found in cells at later stages of differentiation, when apM1 transcription reaches its maximal peak. This same pattern of histone modifications is detected in mouse primary preadipocytes and adipocytes but not in a related fibroblast cell line that is not committed to an adipocyte fate. Inhibition of H3-K4 methylation by treatment of 3T3-L1 cells with methylthioadenosine results in decreased apM1 gene expression as well as decreased adipogenesis. Taken together, our data indicate that H3-K4 dimethylation and pol II binding to the promoter of key adipogenic genes are distinguishing marks of cells that have undergone determination to a preadipocyte stage.