eLife Assessment:
Mutations in a variety of intermediate filament proteins and their regulators lead to abnormal development, reduced lifetime, and increased stress sensitivity. This manuscript rigorously demonstrates that such defects result from inappropriate assembly of intermediate filament networks, as mutations in a central intermediate filament protein prevent assembly of both the normal network and these inappropriate assemblages and largely rescue most of the defects. This has important implications for our understanding of the assembly of intermediate filament structures and for understanding and potentially treating diseases resulting from mutations in intermediate filament protein genes.