Chlamydomonas ARMC2/PF27 is an obligate cargo adapter for intraflagellar transport of radial spokes

Abstract

Intraflagellar transport (IFT) carries proteins into flagella but how IFT trains interact with the large number of diverse proteins required to assemble flagella remains largely unknown. Here, we show that IFT of radial spokes in Chlamydomonas requires ARMC2/PF27, a conserved armadillo repeat protein associated with male infertility and reduced lung function. Chlamydomonas ARMC2 was highly enriched in growing flagella and tagged ARMC2 and the spoke protein RSP3 comigrated on anterograde trains. In contrast, a cargo and an adapter of inner and outer dynein arms moved independently of ARMC2, indicating that unrelated cargoes distribute stochastically onto the IFT trains. After concomitant unloading at the flagellar tip, RSP3 attached to the axoneme whereas ARMC2 diffused back to the cell body. In armc2/pf27 mutants, IFT of radial spokes was abolished and the presence of radial spokes was limited to the proximal region of flagella. We conclude that ARMC2 is a cargo adapter required for IFT of radial spokes to ensure their assembly along flagella. ARMC2 belongs to a growing class of cargo-specific adapters that enable flagellar transport of preassembled axonemal substructures by IFT.

Biochemically validated structural model of the 15‐subunit intraflagellar transport complex IFT‐B

“…IFT trains carry a variety of cargo into cilia including tubulin, radial spokes, and axonemal motility complexes like outer‐ and inner dynein arms (ODAs and IDAs; Lechtreck et al , 2022). In Chlamydomonas , ODAs are imported into cilia by IFT46 via the cargo adaptor protein ODA16 (Ahmed & Mitchell, 2005; Hou et al , 2007).…”

Ordered deployment of distinct ciliary beating machines in growing axonemes of vertebrate multiciliated cells

“…It will be interesting, then, to determine if IFT or diffusion accounts for the rapid deployment of MIPs into axonemes. Similarly, radial spokes are known cargoes of IFT (Lechtreck et al, 2022; Qin et al, 2004), yet they deploy at rates similar to that of the growing axonemes, raising the possibility that -like tubulin-they may also undergo substantial diffusive movement during axoneme growth.…”

Oligogenic heterozygous inheritance of sperm abnormalities in mouse

“…These head defects can actually be explained by the molecular function of the genes studied: CFAP43 is involved in intra-manchette transport ( Yu et al, 2021 ) and it has been previously shown through the study of several genes such as Azh ( Mendoza-Lujambio et al, 2002 ), Clip170 ( Akhmanova et al, 2005 ), Rim-bp3 ( Zhou et al, 2009 ), or Azil ( Hall et al, 2013 ), that manchette modifications impact the head shape of the sperm. The implication of ARMC2 in intraflagellar transport has also recently been shown ( Lechtreck et al, 2022 ) and several previous reports associated sperm head malformations with IFT genes, like IFT20 ( Zhang et al, 2016 ), IFT25 ( Liu et al, 2017 ), IFT27 ( Zhang et al, 2017 ), or IFT88 ( San Agustin et al, 2015 ). Finally, CCDC146 was described as a centriolar proteins ( Firat-Karalar et al, 2014 ) and other centriolar proteins are known to induce sperm head defects ( Hwang et al, 2021 ).…”