The effect ofJIL-1on position-effect variegation is proportional to the total amount of heterochromatin in the genome

Abstract

In this study we have taken advantage of recent whole genome sequencing studies that have determined the DNA content in the heterochromatic regions of each Drosophila chromosome to directly correlate the effect on position-effect variegation of a pericentric insertion reporter line, 118E-10 with the total amount of heterochromatic DNA. Heterochromatic DNA levels were manipulated by adding or subtracting a Y chromosome as well as by the difference in the amount of pericentric heterochromatin between the X and Y chromosome. The results showed a direct, linear relationship between the amount of heterochromatic DNA in the genome and the expression of the w marker gene in the 118E-10 pericentric reporter line and that increasing amounts of heterochromatic DNA resulted in increasing amounts of pigment/gene activity. In Drosophila heterochromatic spreading and gene silencing is counteracted by H3S10 phosphorylation by the JIL-1 kinase, and we further demonstrate that the haplo-enhancer effect of JIL-1 is proportional to the amount of total heterochomatin, suggesting that JIL-1's activity is dynamically modulated to achieve a more or less constant balance depending on the levels of heterochromatic factors present.

Histone H3S10 phosphorylation by the JIL-1 kinase in pericentric heterochromatin and on the fourth chromosome creates a composite H3S10phK9me2 epigenetic mark

“…This was further supported by the finding that under these conditions euchromatic H3S10ph labeling by the occluded antibodies was abolished. These findings are consistent with the model that JIL-1 kinase activity under normal conditions antagonizes Su(var)3-9 activity by keeping H3K9 dimethylation levels low relative to H3S10 phosphorylation levels at actively transcribed interband regions on the chromosome arms (Ebert et al, 2004; Zhang et al, 2006; Deng et al, 2007; Wang et al, 2011b; Girton et al, 2013). However, it also implies the existence of a different mechanism for regulating the interactions between kinase and methyltransferase activity in the context of pericentric heterochromatin and the 4th chromosome that instead of competition promotes creation of the double mark.…”

“…It has been proposed that the epigenetic H3S10ph mark functions to counteract heterochromatization by participating in a dynamic balance between factors promoting repression and activation of gene expression (Ebert et al, 2004; Zhang et al, 2006; Deng et al, 2007; Wang et al, 2011b; Girton et al, 2013). In this model JIL-1 kinase activity antagonizes Su(var)3-9 activity, keeping H3K9 dimethylation levels low relative to H3S10 phosphorylation levels at actively transcribed interband regions.…”

H2Av facilitates H3S10 phosphorylation but is not required for heat shock-induced chromatin decondensation or transcriptional elongation

“…Notably, H3K9me2 marking also changed and was inversely correlated with expression level: genes showing decreased expression in the JIL-1 mutant were found to have acquired the H3K9me2 mark, whereas genes showing increased expression had either no or reduced levels of H3K9me2 marking as compared with wild type. These results are consistent with a model whereby the H3S10ph mark itself is not essential for gene transcription but rather that gene expression levels are modulated by the levels of the H3K9me2 mark independently of the state of the H3S10ph mark (Wang et al, 2011a(Wang et al, ,b, 2012Girton et al, 2013;Cai et al, 2014). Thus, H3S10 phosphorylation acts indirectly to maintain active transcription by counteracting H3K9 dimethylation and gene silencing.…”