DSP1, an HMG-like protein, is involved in the regulation of homeotic genes

The Drosophila dsp1 gene, which encodes an HMG-like protein, was originally identified in a screen for corepressors of Dorsal. Here we report that los s of dsp1 function causes homeotic transformations resembling those associa ted with loss of function in the homeotic genes Sex combs,reduced (Scr), Ul trabithorax (Ubx), and Abdominal-B. The expression pattern of Scr is altere d in dsp1 mutant imaginal discs, indicating that dsp1 is required for norma l expression of this gene. Genetic interaction studies reveal that a null a llele of dsp1 enhances trithorax-group gene (trx-G) mutations and partially suppresses Polycomb-group gene (Pc-G) mutations. On the contrary, overexpr ession of dsp1 induces an enhancement of the transformation of wings into h alteres and of the extra sex comb phenotype of Pc. In addition, dsp1 male m utants exhibit a mild transformation of A4 into A5. Comparison of the chrom atin structure at the Mcp locus in wild-type and dsp1 mutant embryos reveal s that the 300-bp DNase I hypersensitive region is absent in a dsp1 mutant context. We propose that DSP1 protein is a chromatin remodeling factor, act ing as a trx-G or a Pc-G protein depending on the considered function.