IFT56 regulates vertebrate developmental patterning by maintaining IFTB complex integrity and ciliary microtubule architecture

Abstract

Cilia are key regulators of animal development and depend on intraflagellar transport (IFT) proteins for their formation and function, yet the roles of individual IFT proteins remain unclear. We examined the Ift56 hop mouse mutant and reveal novel insight into the function of IFT56, a poorly understood IFTB protein. Ift56 hop mice have normal cilia distribution but display defective cilia structure, including abnormal positioning and number of ciliary microtubule doublets. We show that Ift56 hop cilia are unable to accumulate Gli proteins efficiently, resulting in developmental patterning defects in Shh signaling-dependent tissues such as the limb and neural tube. Strikingly, core IFTB proteins are unable to accumulate normally within Ift56 hop cilia, including IFT88, IFT81 and IFT27, which are crucial for key processes such as tubulin transport and Shh signaling. IFT56 is required specifically for the IFTB complex, as IFTA components and proteins that rely on IFTA function are unaffected in Ift56 hop cilia. These studies define a distinct and novel role for IFT56 in IFTB complex integrity that is crucial for cilia structure and function and, ultimately, animal development.

Cell type‐specific regulation of ciliary transition zone assembly in vertebrates

“…Furthermore, cilia length was not altered in the absence of Nphp4 (Fig E). To test whether these in vitro data are transferable to the in vivo situation, we used embryonic limb buds which are a well‐established in vivo model for investigating functional mechanisms in regard to cilia research (Goetz & Anderson, ; Bimonte et al , ; Emechebe et al , ; Xin et al , ). In Nphp4 −/− embryonic limb bud cilia, the TZ amount of Rpgrip1l and Cep290 was unchanged, while the amount of Nphp1 and Invs at the TZ was decreased (Fig F–I) confirming the data obtained in MEFs.…”

Biallelic Mutations in Tetratricopeptide Repeat Domain 26 (Intraflagellar Transport 56) Cause Severe Biliary Ciliopathy in Humans

“…(23) Indeed, unlike most other IFT-B proteins, its deficiency does not abrogate ciliogenesis in mouse mutants (see below). (24) Several animal models have been published that further highlight the requirement for TTC26 in ciliary physiology. In Chlamydomonas, deficiency of TTC26 results in a constellation of short flagella with impaired motility.…”

“…( and colleagues similarly showed dysregulated SHH signaling in hop but proposed a different mechanism involving reduced ciliary Gli2/3. (24) They further showed that Ift56 hop neural tube cilia show educed sensitivity to SHH signaling and that the mice developed preaxial polydactyly because of impaired Gli3R function, thus providing a mechanistic insight into at least part of the hop phenotype. (24) Our results suggest that TTC26 deficiency causes a ciliopathy phenotype that is primarily characterized by severe neonatal cholestasis with frequent involvement of the digits and kidneys.…”

“…(24) They further showed that Ift56 hop neural tube cilia show educed sensitivity to SHH signaling and that the mice developed preaxial polydactyly because of impaired Gli3R function, thus providing a mechanistic insight into at least part of the hop phenotype. (24) Our results suggest that TTC26 deficiency causes a ciliopathy phenotype that is primarily characterized by severe neonatal cholestasis with frequent involvement of the digits and kidneys. Primary cilia in cholangiocytes serve as chemo-, osmo-, and mechanosensors and play an important role in cholangiocyte proliferation.…”

Mechanobiology of limb musculoskeletal development

“…It is well established that hedgehog signaling is coordinated by primary cilia, and gene mutations of primary cilia components frequently recapitulate phenotypes associated with dysfunctional hedgehog signaling. [123][124][125] Examples in musculoskeletal development include endochondral ossification in long bone growth (regulated by Ihh) and digit patterning (regulated by Shh). Conditional mutants for cilia components IFT88 or KIF3a in limb mesenchyme result in phenotypes associated with abnormal hedgehog signaling, including shortened limb skeletons and polydactyly.…”