ABSTRACT
Primary cilia have specific proteins on their membrane to fulfill their sensory functions. Preservation of the specific protein composition of cilia relies on the barrier function of the transition zone (TZ) located at the ciliary base. Defects in cilia and the TZ cause ciliopathies, which have diverse clinical manifestations, including Meckel syndrome (MKS). Many of the proteins mutated in individuals with MKS are known to constitute the MKS module of the TZ. Although TXNDC15 (also known as MKS14) is a thioredoxin-related transmembrane protein that is localized mainly in the endoplasmic reticulum (ER) and is mutated in individuals with MKS, its role at the TZ or within cilia has not been characterized. Here, we show that TXNDC15-knockout cells have defects in MKS module assembly and in ciliary membrane protein localization. These defects in TXNDC15-knockout cells were not rescued by exogenous expression of any of the TXNDC15 constructs with MKS variations in the thioredoxin domain. Furthermore, TXNDC15 with mutations of two cysteine residues within the thioredoxin domain failed to rescue defects in TXNDC15-knockout cells, suggesting that TXNDC15 controls the TZ integrity from outside the TZ via its thioredoxin domain.
Footnotes
Author contributions
Conceptualization: S.C., H.-W.S., K.N., Y.K.; Methodology: H.-W.S.; Formal analysis: S.Y., T.F.; Investigation: S.Y., T.F.; Writing - original draft: K.N.; Writing - review & editing: S.C., H.-W.S., K.N., Y.K.; Supervision: H.-W.S., K.N., Y.K.; Project administration: K.N.; Funding acquisition: K.N., Y.K.
Funding
This work was supported in part by grants from the Japan Society for the Promotion of Science (grant numbers 20H04904 and 24K02022 to K.N., and 21H02427 and 22H05539 to Y.K.), and from the Takeda Science Foundation to Y.K.
Data availability
All relevant data can be found within the article and its supplementary information.
