Date of Award
Doctor of Philosophy
Biochemistry, Biophysics and Molecular Biology
Molecular, Cellular and Developmental Biology
Kristen M. Johansen
Epigenetic processes, such as histone modifications, play essential roles in regulating chromatin structure and gene expression. In Drosophila JIL-1 tandem kinase has been identified as a major regulator of chromatin structure and gene expression. It has been demonstrated that JIL-1 is responsible for histone H3 serine 10 (H3S10) phosphorylation at interphase, which counteracts gene silencing marker histone H3 lysine 9 (H3K9) dimethylation. In addition, JIL- 1 localizes specifically to euchromatic interband regions, and a reduction in JIL-1 levels lead to a global disruption of chromatin morphology.
JIL-1 can be divided into four domains, including an NH2- terminal domain (NTD), two kinase domains (KDI and KDII), and a COOH-terminal domain (CTD). Functions of all four domains have been characterized. The NTD is essential for JIL-1 kinase activity; a truncated JIL-1 protein without the NTD fails to phosphorylate H3S10 despite its proper localization on the chromosome and the presence of both kinase domains. Both kinase domains are required for JIL-1's kinase activity and have equal importance. The CTD is sufficient for JIL's localization to chromosome, but not required for kinase activity.
Furthermore, to explore the mechanisms of JIL-1 mediated histone modification and its interplay with other histone markers, we have conducted a genome-wide study of relationships between JIL-1 mediated H3S10 phosphorylation and H3K9 dimethylation in binding profiles and gene expression. Utilizing ChIP-seq, we show that the H3S10 phosphorylation marker is localized predominantly to active genes, whereas the silencing H3K9 dimethylation marker is enriched at inactive genes. Additionally, studying the transcription profile using RNA-seq reveals functions of JIL-1 in maintaining a balance between active and inactive transcribed genes, where down-regulation of genes in the JIL-1 mutant is associated with elevated levels of H3K9 dimethylation, whereas up-regulation of genes is correlated with loss of H3K9 dimethylation. These results support a model where gene expression levels are regulated by H3K9 dimethylation independent of the state of H3S10 phosphorylation, which in turn functions to indirectly maintain active transcription by counteracting H3K9 dimethylation.
Li, Yeran, "Regulation of gene expression and chromatin structure by JIL-1 mediated histone H3 serine10 phosphorylation in Drosophila" (2015). Graduate Theses and Dissertations. 14368.