The ARPKD Protein DZIP1L Regulates Ciliary Protein Entry by Modulating the Architecture and Function of Ciliary Transition Fibers.

Serving as the cell's sensory antennae, primary cilia are linked to numerous human genetic diseases when they malfunction. DZIP1L, identified as one of the genetic causes of human autosomal recessive polycystic kidney disease (ARPKD), is an evolutionarily conserved ciliary basal body protein. Although it has been reported that DZIP1L is involved in the ciliary entry of PKD proteins, the underlying mechanism remains elusive. Here, an uncharacterized role of DZIP1L is reported in modulating the architecture and function of transition fibers (TFs), striking ciliary base structures essential for selective cilia gating. Using C. elegans as a model, C01G5.7 (hereafter termed DZIP-1) is identified as the sole homolog of DZIP1L, which specifically localizes to TFs. While DZIP-1 or ANKR-26 (the ortholog of ANKRD26) deficiency shows subtle impact on TFs, co-depletion of DZIP-1 and ANKR-26 disrupts TF assembly and cilia gating for soluble and membrane proteins, including the ortholog of ADPKD protein polycystin-2. Notably, the synergistic role for DZIP1L and ANKRD26 in the formation and function of TFs is highly conserved in mammalian cilia. Hence, the findings illuminate an evolutionarily conserved role of DZIP1L in TFs architecture and function, highlighting TFs as a vital part of the ciliary gate implicated in ciliopathies ARPKD.