CHL-1 provides an essential function affecting cell proliferation and chromosome stability in Caenorhabditis elegans

A family of helicases that are important in maintaining genome stability is the iron-sulfur group. Members of this family include DOG-1/FANCJ, RTEL1, XPD and Chl1p/DDX11. In Caenorhabitis elegans, the predicted gene M03C11.2 has orthology to the CHL1 (Chromosome loss 1) gene in Saccharomyces cerevisiae and DDX11 (DEAD/H box polypeptide 11) in humans. In this paper, we show that the chl-1 gene in C. elegans is required for normal development and fertility. Mutants have lineage-independent cell proliferation defects that result in a Stu (sterile uncoordinated) phenotype, characterized by gonadal abnormalities and a reduced number of D motor neurons and seam cells. A chromosome stability defect is present in the germ cells, where an abnormal number of DAPI-staining chromosomes appear in diakinesis. CHL-1 function is required for the integrity of poly-guanine/poly-cytosine DNA in the absence of DOG-1/FANCJ: the loss of CHL-1 alone does not result in the deletion of G-tracts, but it does increase the number of deletions observed in the dog-1; chl-1 double mutant, indicating a role for CHL-1 during replication and repair. In addition, we observed that cohesin defects increased the number of deletions in the absence of DOG-1/FANCJ. Our results demonstrate a role for CHL-1 in cell proliferation and maintaining normal chromosome numbers, and implicate CHL-1 in chromosome stability and repair of unresolved secondary structures during replication.