ABSTRACT
Drosophila melanogaster animal model and tissue culture cells have been widely used for studies of nuclear structure and processes as well as for chromatin structure and expression. This system has been used also for studies of the properties of karyoskeletal proteins and the role of chromatin proteins and sequences in chromatin structure maintenance and regulation upon heat shock induction. We previously reported that lamin Dm and topoisomerase II bind in vivo both DNA and RNA and the properties of both proteins have been modulated by specific phosphorylation on particular sites. Here we report the results of the part of the project focused on the demonstration of the role of lamins and Top2 in the regulation of gene expression and chromatin organization upon heat shock induction and recovery. We demonstrated that heat shock significantly induced specific phosphorylation of lamin Dm at least on S25. Lam and Top2 were relocated and changed properties including solubility. Both proteins interact with each other directly and indirectly and binding was significantly increased by HS. Relocation of Lam and Top2 was associated with the relocation of chromatin as detected in polyploidy third instar larvae nuclei. In vivo, photocrosslinking and IP studies indicated a significant increase in binding to chromatin and nucleic acids upon HS induction. The highest binding affinity showed a soluble fraction of lamin Dm and topoisomerase II while the lowest was the insoluble fraction (nuclear matrix fraction). All the detected changes in properties and location of proteins returned to “normal” after recovery from heat shock. Based on this data and available interactome data for lamin Dm and Top2 as well as RNAse and CHhIPseq (manuscript in preparation) we believe that both proteins play essential roles in the proper response of fly cells to HS by participation in chromatin remodelling, rearrangement of protein complexes and proper gene expression regulation.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵& ryszard.rzepecki{at}uwr.edu.pl