Generation of a C. elegans tdp-1 null allele and humanized TARDBP containing human disease-variants.

Abstract

Clinical variants of TARDBP are associated with frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS) and other degenerative diseases. The predicted C. elegans ortholog of TARDBP is encoded by tdp-1 , but functional orthology has not been demonstrated in vivo. We undertook CRISPR/Cas9-based genome editing of the tdp-1 locus to create a complete loss of function allele; all tdp-1 exons and introns were deleted, creating tdp-1(tgx58) , which resulted in neurodegeneration after oxidative stress. Next, we undertook CRISPR-based genome editing to replace tdp-1 exons with human TARDBP coding sequences, creating humanized ( hTARDBP ) C. elegans expressing TDP-43 . Based on the efficiency of this genome editing, we suggest that iterative genome editing of the tdp-1 target locus using linked coCRISPR markers, like dpy-10 , would be a more efficient strategy for sequential assembly of the large engineered transgenes. hTARDBP decreased the neurodegeneration defect of tdp-1(tgx58) , demonstrating functional cross-species orthology. To develop C. elegans models of FTD and ALS, we inserted five different patient TARDBP variants in the C. elegans hTARDBP locus. Only one clinical variant increased stress-induced neurodegeneration; other variants caused inconsistent or negligible defects under these conditions. Combined, this work yielded an unambiguous null allele for tdp-1 , a validated, humanized hTARDBP, and multiple ALS/FTD patient-associated variant models that can be used for future studies.