Chromosome organization by Structural Maintenance of Chromosomes complexes in C. elegans.

Genome folding is a key regulator of transcription, chromosome segregation, and genome stability. In Caenorhabditis elegans, chromatin folding strategies have diverged from those observed in mammals or flies, resulting in the absence of visible topologically associating domains (TADs) on autosomes. Here, condensin I, rather than cohesin, serves as the primary long-range loop extruder, while distinct cohesin isoforms specialize in mitotic cohesion and loop extrusion, forming enhancer-associated 'fountains' that modulate neuronal gene expression. On the X chromosome, dosage compensation depends on the dosage compensation complex, which incorporates a specialized condensin IDC to establish TADs, regulate chromatin states, and repress transcription. These multilayered mechanisms illustrate the evolutionary versatility of 3D genome organization and its intimate links to development, physiology, and lifespan, positioning C. elegans as a powerful model for dissecting structural maintenance of chromosomes-mediated genome regulation.