TheTalpid3gene (KIAA0586) encodes a centrosomal protein that is essential for primary cilia formation

Abstract

The chicken talpid3 mutant, with polydactyly and defects in other embryonic regions that depend on hedgehog (Hh) signalling(e.g. the neural tube), has a mutation in KIAA0568. Similar phenotypes are seen in mice and in human syndromes with mutations in genes that encode centrosomal or intraflagella transport proteins. Such mutations lead to defects in primary cilia, sites where Hh signalling occurs. Here, we show that cells of talpid3 mutant embryos lack primary cilia and that primary cilia can be rescued with constructs encoding Talpid3. talpid3 mutant embryos also develop polycystic kidneys,consistent with widespread failure of ciliogenesis. Ultrastructural studies of talpid3 mutant neural tube show that basal bodies mature but fail to dock with the apical cell membrane, are misorientated and almost completely lack ciliary axonemes. We also detected marked changes in actin organisation in talpid3 mutant cells, which may explain misorientation of basal bodies. KIAA0586 was identified in the human centrosomal proteome and, using an antibody against chicken Talpid3, we detected Talpid3 in the centrosome of wild-type chicken cells but not in mutant cells. Cloning and bioinformatic analysis of the Talpid3 homolog from the sea anemone Nematostella vectensis identified a highly conserved region in the Talpid3 protein, including a predicted coiled-coil domain. We show that this region is required to rescue primary cilia formation and neural tube patterning in talpid3 mutant embryos, and is sufficient for centrosomal localisation. Thus, Talpid3 is one of a growing number of centrosomal proteins that affect both ciliogenesis and Hh signalling.

Dampened Hedgehog signaling but normal Wnt signaling in zebrafish without cilia

“…These results address a long-standing enigma in the field by providing the first genetic evidence that cilia function in Hh signaling is conserved from zebrafish to mouse. Together with recent reports that link cilia to Hh signaling in Xenopus and chick (Davey et al, 2006;Park et al, 2006;Yin et al, 2009), our results indicate that the ciliary requirement for Hh signaling is conserved in the entire vertebrate lineage.…”

Hedgehog signalling

“…This primitive organelle was first implicated in Hh signalling through the isolation of mouse mutations disrupting primary ciliogenesis that have phenotypes indicative of aberrant Hh signalling (Huangfu et al, 2003). Subsequent analyses in chick and fish revealed a universal involvement of the PC in Hh signalling across vertebrates (Huang and Schier, 2009;Yin et al, 2009). The central role of the PC in transduction of the Hh signal is reflected in the dynamic localisation of the various Hh pathway components to this organelle.…”

“…Accordingly, loss of the PC also disrupts the PKA-dependent proteolytic cleavage of Gli factors as well as their activation. Consequently, animals mutant for genes that encode proteins involved in the formation or maintenance of the PC, such as the centriolar Talpid3 protein (Yin et al, 2009) and intraflagellar transport (IFT) proteins (Goetz and Anderson, 2010), display both gain and loss of Hh function phenotypes, reflecting the differing contributions of Gli-mediated repression and activation to the specification of different organs.…”

Far from solved: A perspective on what we know about early mechanisms of left–right asymmetry

“…Even though monociliated cells are present at the node (Essner et al, 2002), they are not confined to this area, they are short and immotile, and they are found on endodermal cells, not mesodermal cells (Gros et al, 2009). Additionally, the Talpid3 mutant chick lacks cilia (Yin et al, 2009) yet has normal LR asymmetry (Cheryll Tickle, personal communication), further indicating that cilia are not required to establish laterality in the chick.…”