Chromatin structure and nuclear remodeling.

Nuclear architecture is remodeled during interphase in response to changes in gene activity as well as to changing structural and functional requirements during cell division. Using the monoclonal antibody mAb2A, we have identified two proteins that appear to play important roles in these processes: JIL-1 is a tandem serine-threonine kinase implicated in the regulation of chromatin structure, whereas Skeletor is a novel protein participating in structural nuclear remodeling during the cell cycle. Antibody staining and live imaging of JIL-1-GFP transgenic flies show that JIL-1 localizes to the gene-rich interband regions of larval polytene chromosomes and is upregulated almost twofold on the hypertranscribed male X chromosome compared with autosomes. We propose that JIL-1 may play a role in transcriptional control potentially by regulating chromatin structure. The other mAb2A antigen, Skeletor, is distributed in a nuclear meshwork pattern that can be observed in stereo pair images to reorganize during the cell cycle to form a spindle-like structure at prometaphase that is distinct from the microtubule spindle apparatus. Taking advantage of the powerful molecular and genetic approaches offered in Drosophila, the study of these two proteins promises to yield new insight into what defines nuclear architecture at the molecular level and how its remodeling is regulated.