The H3K79me3 methyl-transferase Grappa is involved in the establishment and thermal plasticity of abdominal pigmentation in Drosophila melanogaster females.

Temperature sensitivity of abdominal pigmentation in Drosophila melanogaster females allows to investigate the mechanisms underlying phenotypic plasticity. Thermal plasticity of pigmentation is due to modulation of tan and yellow expression, encoding pigmentation enzymes. Furthermore, modulation of tan expression by temperature is correlated to the variation of the active histone mark H3K4me3 on its promoter. Here, we test the role of the DotCom complex, which methylates H3K79, another active mark, in establishment and plasticity of pigmentation. We show that several components of the DotCom complex are involved in the establishment of abdominal pigmentation. In particular, Grappa, the catalytic unit of this complex, plays opposite roles on pigmentation at distinct developmental stages. Indeed, its down-regulation from larval L2 to L3 stages increases female adult pigmentation, whereas its down-regulation during the second half of the pupal stage decreases adult pigmentation. These opposite effects are correlated to the regulation of distinct pigmentation genes by Grappa: yellow repression for the early role and tan activation for the late one. Lastly, reaction norms measuring pigmentation along temperature in mutants for subunits of the DotCom complex reveal that this complex is not only involved in the establishment of female abdominal pigmentation but also in its plasticity.