Gibert Jean-Michel, Mouchel-Vielh Emmanuèle, De Castro Sandra, Peronnet Frédérique
Sorbonne Universités, Université Pierre et Marie Curie (UPMC), CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire de Biologie du Développement, Equipe "Contrôle épigénétique de l'homéostasie et de la plasticité du développement", Paris, France.
PLoS Genet. 2016 Aug 10;12(8):e1006218. doi: 10.1371/journal.pgen.1006218. eCollection 2016 Aug.
Phenotypic plasticity is the ability of a given genotype to produce different phenotypes in response to distinct environmental conditions. Phenotypic plasticity can be adaptive. Furthermore, it is thought to facilitate evolution. Although phenotypic plasticity is a widespread phenomenon, its molecular mechanisms are only beginning to be unravelled. Environmental conditions can affect gene expression through modification of chromatin structure, mainly via histone modifications, nucleosome remodelling or DNA methylation, suggesting that phenotypic plasticity might partly be due to chromatin plasticity. As a model of phenotypic plasticity, we study abdominal pigmentation of Drosophila melanogaster females, which is temperature sensitive. Abdominal pigmentation is indeed darker in females grown at 18°C than at 29°C. This phenomenon is thought to be adaptive as the dark pigmentation produced at lower temperature increases body temperature. We show here that temperature modulates the expression of tan (t), a pigmentation gene involved in melanin production. t is expressed 7 times more at 18°C than at 29°C in female abdominal epidermis. Genetic experiments show that modulation of t expression by temperature is essential for female abdominal pigmentation plasticity. Temperature modulates the activity of an enhancer of t without modifying compaction of its chromatin or level of the active histone mark H3K27ac. By contrast, the active mark H3K4me3 on the t promoter is strongly modulated by temperature. The H3K4 methyl-transferase involved in this process is likely Trithorax, as we show that it regulates t expression and the H3K4me3 level on the t promoter and also participates in female pigmentation and its plasticity. Interestingly, t was previously shown to be involved in inter-individual variation of female abdominal pigmentation in Drosophila melanogaster, and in abdominal pigmentation divergence between Drosophila species. Sensitivity of t expression to environmental conditions might therefore give more substrate for selection, explaining why this gene has frequently been involved in evolution of pigmentation.
表型可塑性是指给定基因型在不同环境条件下产生不同表型的能力。表型可塑性可以是适应性的。此外，人们认为它有助于进化。尽管表型可塑性是一种普遍现象，但其分子机制才刚刚开始被揭示。环境条件可通过染色质结构的修饰，主要是通过组蛋白修饰、核小体重塑或DNA甲基化来影响基因表达，这表明表型可塑性可能部分归因于染色质可塑性。作为表型可塑性的一个模型，我们研究了温度敏感的黑腹果蝇雌性腹部色素沉着。在18°C下生长的雌性果蝇腹部色素沉着确实比在29°C下生长的雌性果蝇更深。这种现象被认为是适应性的，因为在较低温度下产生的深色色素会提高体温。我们在此表明，温度调节tan（t）的表达，tan是一种参与黑色素生成的色素沉着基因。在雌性腹部表皮中，t在18°C时的表达量是29°C时的7倍。遗传实验表明，温度对t表达的调节对于雌性腹部色素沉着可塑性至关重要。温度调节t增强子的活性，而不改变其染色质的紧实度或活性组蛋白标记H3K27ac的水平。相比之下，t启动子上的活性标记H3K4me3受到温度的强烈调节。参与这一过程的H3K4甲基转移酶可能是三胸复合物，因为我们表明它调节t的表达以及t启动子上的H3K4me3水平，并且还参与雌性色素沉着及其可塑性。有趣的是，之前已表明t参与黑腹果蝇雌性腹部色素沉着的个体间差异以及果蝇物种间腹部色素沉着的差异。因此，t表达对环境条件的敏感性可能为选择提供更多底物，解释了为什么该基因经常参与色素沉着的进化。
