Ttc30a affects tubulin modifications in a model for ciliary chondrodysplasia with polycystic kidney disease

Abstract

Significance Cilia are tubulin-based cellular appendages, and their dysfunction has been linked to a variety of genetic diseases. Ciliary chondrodysplasia is one such condition that can co-occur with cystic kidney disease and other organ manifestations. We modeled skeletal ciliopathies by mutating two established disease genes in Xenopus tropicalis frogs. Bioinformatic analysis identified ttc30a as a ciliopathy network component, and targeting it replicated skeletal malformations and renal cysts as seen in patients and the amphibian models. A loss of Ttc30a affected cilia by altering posttranslational tubulin modifications. Our findings identify TTC30A/B as a component of ciliary segmentation essential for cartilage differentiation and renal tubulogenesis. These findings may lead to novel therapeutic targets in treating ciliary skeletopathies and cystic kidney disease. Skeletal ciliopathies (e.g., Jeune syndrome, short rib polydactyly syndrome, and Sensenbrenner syndrome) are frequently associated with nephronophthisis-like cystic kidney disease and other organ manifestations. Despite recent progress in genetic mapping of causative loci, a common molecular mechanism of cartilage defects and cystic kidneys has remained elusive. Targeting two ciliary chondrodysplasia loci (ift80 and ift172) by CRISPR/Cas9 mutagenesis, we established models for skeletal ciliopathies in Xenopus tropicalis. Froglets exhibited severe limb deformities, polydactyly, and cystic kidneys, closely matching the phenotype of affected patients. A data mining–based in silico screen found ttc30a to be related to known skeletal ciliopathy genes. CRISPR/Cas9 targeting replicated limb malformations and renal cysts identical to the models of established disease genes. Loss of Ttc30a impaired embryonic renal excretion and ciliogenesis because of altered posttranslational tubulin acetylation, glycylation, and defective axoneme compartmentalization. Ttc30a/b transcripts are enriched in chondrocytes and osteocytes of single-cell RNA-sequenced embryonic mouse limbs. We identify TTC30A/B as an essential node in the network of ciliary chondrodysplasia and nephronophthisis-like disease proteins and suggest that tubulin modifications and cilia segmentation contribute to skeletal and renal ciliopathy manifestations of ciliopathies in a cell type–specific manner. These findings have implications for potential therapeutic strategies.