CHD1 is a conserved chromatin remodeling factor that localizes to active genes 
and functions in nucleosome assembly and positioning as well as histone 
turnover. Mouse CHD1 is required for the maintenance of stem cell pluripotency 
while human CHD1 may function as a tumor suppressor. To investigate the action 
of CHD1 on higher order chromatin structure in differentiated cells, we examined 
the consequences of loss of CHD1 and over-expression of CHD1 on polytene 
chromosomes from salivary glands of third instar Drosophila melanogaster larvae. 
We observed that chromosome structure is sensitive to the amount of this 
remodeler. Loss of CHD1 resulted in alterations of chromosome structure and an 
increase in the heterochromatin protein HP1a, while over-expression of CHD1 
disrupted higher order chromatin structure and caused a decrease in levels of 
HP1a. Over-expression of an ATPase inactive form of CHD1 did not result in 
severe chromosomal defects, suggesting that the ATPase activity is required for 
this in vivo phenotype. Interestingly, changes in CHD1 protein levels did not 
correlate with changes in the levels of the euchromatin mark H3K4me3 or 
elongating RNA Polymerase II. Thus, while CHD1 is localized to transcriptionally 
active regions of the genome, it can function to alter the levels of HP1a, 
perhaps through changes in methylation of H3K9.