BACKGROUND: Heterochromatin protein 1 (HP1) family proteins have a 
well-characterized role in heterochromatin packaging and gene regulation. Their 
function in organismal development, however, is less well understood. Here we 
used genome-wide expression profiling to assess novel functions of the 
Caenorhabditis elegans HP1 homolog HPL-2 at specific developmental stages.
RESULTS: We show that HPL-2 regulates the expression of germline genes, 
extracellular matrix components and genes involved in lipid metabolism. 
Comparison of our expression data with HPL-2 ChIP-on-chip profiles reveals that 
a significant number of genes up- and down-regulated in the absence of HPL-2 are 
bound by HPL-2. Germline genes are specifically up-regulated in hpl-2 mutants, 
consistent with the function of HPL-2 as a repressor of ectopic germ cell fate. 
In addition, microarray results and phenotypic analysis suggest that HPL-2 
regulates the dauer developmental decision, a striking example of phenotypic 
plasticity in which environmental conditions determine developmental fate. HPL-2 
acts in dauer at least partly through modulation of daf-2/IIS and TGF-β 
signaling pathways, major determinants of the dauer program. hpl-2 mutants also 
show increased longevity and altered lipid metabolism, hallmarks of the 
long-lived, stress resistant dauers.
CONCLUSIONS: Our results suggest that the worm HP1 homologue HPL-2 may 
coordinately regulate dauer diapause, longevity and lipid metabolism, three 
processes dependent on developmental input and environmental conditions. Our 
findings are of general interest as a paradigm of how chromatin factors can both 
stabilize development by buffering environmental variation, and guide the 
organism through remodeling events that require plasticity of cell fate 
regulation.