Professor
Regulation of nuclear organization and function
Recent advances in probing the nucleus have made it clear that nuclear organization is far more complex and ordered than had earlier been appreciated and that it plays a major role in cell function including gene expression and cell division. Our research is directed towards identifying the molecules defining such nuclear organization, as well as the signal transduction pathways regulating cell cycle-specific changes. Using Drosophila as a model system, a combination of molecular and genetic approaches are being used to analyze genes involved in these processes.
The following projects are done in collaboration with Dr. Jorgen Johansen.
PROJECT 1: Regulation of Chromatin Structure and gene expression.
The long term objective of my laboratory is to gain a molecular understanding of epigenetic processes that regulate chromatin structure and gene expression. Towards this end we have identified a novel tandem kinase in Drosophila, JIL-1, that localizes specifically to the gene-active interband regions of the larval polytene chromosomes, phosphorylates histone H3S10, and is enriched almost two-fold on the transcriptionally hyperactive male larval polytene X chromosome. In JIL-1 hypomorphs orderly interband regions of polytene chromosomes are disrupted and the chromosome arms highly condensed. Position effect variegation (PEV) in Drosophila has served as a major paradigm for the identification and genetic analysis of evolutionarily conserved determinants of epigenetic regulation of chromatin structure and gene silencing and we provide evidence that loss-of-function alleles of the JIL-1 histone H3S10 kinase can act either as suppressors or enhancers of PEV depending on the chromatin environment of the reporter locus. These effects on PEV were correlated with the spreading of the major heterochromatin markers dmH3K9 and HP1 to ectopic locations on the chromosome arms with the most pronounced upregulation found on the male and female X chromosomes. Based on these findings we propose a model where JIL-1 kinase activity and phosphorylation of histone H3S10 at interphase functions to antagonize heterochromatization by regulating a dynamic balance between factors promoting repression and activation of gene expression.
Gene silencing is a critical developmental process relevant to many human health problems that include cancer. Furthermore, JIL-1 is the Drosophila homolog of the mammalian MSK1 kinase which also functions as a regulator of chromatin structure by phosphorylating the histone H3S10 residue. At present the mammalian studies have been directed towards analyzing histone phosphorylation in the context of immediate early gene transcription. However, our results suggest that the concept of histone phosphorylation should be expanded to be considered in the context of the regulation of gene silencing as well. Thus, our studies will serve to provide general insights into the molecular mechanisms of how kinase activity modulates chromatin structure and gene regulation that are directly relevant to humans.
This Research is funded by the National Institutes of Health.
PROJECT 2: Cell and molecular biology of spindle function during mitosis.
The long-term objective of this study is to test the hypothesis that nuclear derived proteins form a spindle matrix during mitosis that is distinct from the microtubule spindle apparatus and that this structure is involved in normal chromosome segregation as well as in spindle function. The concept of a spindle matrix has long been proposed based on theoretical considerations of the requirements for force production to help organize and stabilize the microtubule spindle during mitosis. However, molecular evidence corroborating its existence and function has been elusive. In Drosophila we have recently identified four nuclear proteins, Skeletor, Chromator, Megator, and EAST that interact with each other and that redistribute during prophase forming a fusiform spindle structure that persists in the absence of polymerized tubulin. Two of these proteins, Skeletor and Chromator, are localized to chromosomes during interphase whereas the other two, Megator and EAST, occupy the intranuclear space surrounding the chromosomes. RNAi and mutational analysis suggests that these genes are essential and that they affect spindle function and chromosome segregation. Future studies will examine the role of these proteins and the spindle matrix in microtubule spindle formation.
This research is funded by the National Science Foundation.
