The involvement of FANCM, FANCI, and checkpoint proteins in the interstrand DNA crosslink repair pathway is conserved in C. elegans

Fanconi anemia (FA) patients are specifically defective in the repair of interstrand DNA crosslinks (ICLs), a complex process involving at least 13 FA proteins and other repair/checkpoint proteins. Of the 13 FA proteins, FANCD1/BRCA2, FANCD2, and FANCJ were previously found to be functionally conserved in C. elegans. We have also identified C. elegans homologs of FANCM and FANCI, and determined their epistatic relationships with homologs of FANCD2, checkpoint proteins, and RAD51 upon DNA crosslinking. The counterparts of FANCM, FANCI, and three checkpoint proteins (RPA, ATR and CHK1) are required for focus formation and ubiquitination associated with FANCD2 in C. elegans. However, C. elegans FANCM affects neither RPA focus formation nor CHK1 phosphorylation induced by ICLs, unlike the reported role of human FANCM, which influences ATR-CHK1 signaling at stalled replication forks. Although focus formation by both FANCD2 and RAD51 requires ATR-CHK1 signaling, FANCD2 and RAD51 acted independently in the formation of their respective foci. Thus, the FANCD2 activation pathway involving FANCM, FANCI, and the checkpoint proteins is conserved in C. elegans but with distinct differences.