Title:
|
A role for giantin in primary ciliogenesis through control of the localisation of the cytoplasmic dynein-2 intermediate chains
|
Properly assembled primary cilia play fundamental roles in the development and function
of nearly all cells. The cilium is assembled by extension of a microtubule bundle, the
axoneme from the mother centriole ensheathed by a specialised membrane, the ciliary
membrane which is continuous with the plasma membrane. Intraflagellar transport (IFT)
traffics ciliary components along the length of the nascent cilium and is required for the
assembly, maintenance and function of the cilium. The microtubule motor, cytoplasmic
dynein-2 mediates retrograde IFT from the axoneme tip to base and has been shown to be
necessary for cilia assembly. Vital cilia machinery constituents localise to the centrosome.
The Golgi is positioned adjacent to the centrosome in most cells and both organelles
polarise towards the apical plasma membrane during ciliogenesis. Furthermore, some
Golgi-localised proteins have been shown to execute cilia-related functions. Here, the
transmembrane Golgi protein giantin (GOLG81) is shown to be required for cilia formation.
Giantin is not required for the RABll-RABIN8-RAB8 pathway that is implicated in the early
stages of ciliary membrane formation. Instead, giantin depletion caused mislocalisation of
the intermediate chains of dynein-2, WDR34 and WDR60. Highly effective suppression of
giantin, WDR34 or WDR60 in cells completely inhibited primary cilia formation; while,
partial depletion of giantin, WDR34 or WDR60 permitted the assembly of cilia, albeit of
abnormally increased lengths. These data implicate giantin in ciliogenesis through control
of dynein-2 localisation.
Unlike the cytoplasmic dynein-l complex, existing knowledge of cytoplasmic dynein-2
composition is limited. This work details the subunit composition of the human cytoplasmic
dynein-2 motor complex. WDR34 and WDR60 are genuine dynein-2 intermediate chains
and associate with the known heavy (DYNC2Hl) and light intermediate (LlC3) chains of
dynein-2. Dynein-2 possesses all the' known dynein-l light chains in addition to exclusive
possession of the light chain, TCTEX-2. The only dynein-l accessory factor found to be
shared by dynein-2 was NUDCD3, whose depletion resulted in mislocalisation of WDR34,
failure of cilia assembly and assembly of abnormally long cilia in partial knockdowns. No
interactions were found between dynein-2 and dynactin, LlSl, NUDE/NUDEL or BICD2.
NUDCD3, thus, presents a common avenue for regulating dynein-l and dynein-2 functions,
indicating a functional interplay between the two motors. This novel biochemical
characterisation of the human cytoplasmic dynein-2 complex could potentially advance
research into 1FT and dynein-2 function in ciliopathies
|