Abstract
BackgroundIn vertebrates, rootletin is the major structural component of the ciliary rootlet and is also part of the tether linking the centrioles of the centrosome. Various functions have been ascribed to the rootlet, including maintenance of ciliary integrity through anchoring and facilitation of transport to the cilium or at the base of the cilium. In Drosophila, Rootletin function has not been explored.ResultsIn the Drosophila embryo, Rootletin is expressed exclusively in cell lineages of type I sensory neurons, the only somatic cells bearing a cilium. Expression is strongest in mechanosensory chordotonal neurons. Knock-down of Rootletin results in loss of ciliary rootlet in these neurons and severe disruption of their sensory function. However, the sensory cilium appears largely normal in structure and in localisation of proteins suggesting no strong defect in ciliogenesis. No evidence was found for a defect in cell division.ConclusionsThe role of Rootletin as a component of the ciliary rootlet is conserved in Drosophila. In contrast, lack of a general role in cell division is consistent with lack of centriole tethering during the centrosome cycle in Drosophila. Although our evidence is consistent with an anchoring role for the rootlet, severe loss of mechanosensory function of chordotonal (Ch) neurons upon Rootletin knock-down may suggest a direct role for the rootlet in the mechanotransduction mechanism itself.
Highlights
In vertebrates, rootletin is the major structural component of the ciliary rootlet and is part of the tether linking the centrioles of the centrosome
In situ hybridisation of embryos shows that Rootletin mRNA is not expressed ubiquitously but in a dynamic pattern corresponding exclusively to the developing sensory neuron lineages (Fig. 1)
Expression begins at stage 12 in a pattern that suggests it is expressed in the precursors and progeny cells of type I sensory lineages of all sensory modalities, including olfactory, external sensory (ES—mechanosensory and gustatory) and Ch neurons (Fig. 1b)
Summary
Rootletin is the major structural component of the ciliary rootlet and is part of the tether linking the centrioles of the centrosome. Various functions have been ascribed to the rootlet, including maintenance of ciliary integrity through anchoring and facilitation of transport to the cilium or at the base of the cilium. The ciliary rootlet has long been known from transmission electron microscopy studies as the striated fibrous structure extending from the cilium basal body towards the cell nucleus [1]. Mammalian photoreceptors have a large rootlet at the base of a connecting cilium that links to the large photoreceptive outer segment [2, 3]. Mice lacking rootletin only exhibit a prominent ciliary phenotype in photoreceptors [6], which are cells with high rootletin expression levels and a robust rootlet [2, 3]. It is notable that cells with less prominent rootlets did not show this phenotype
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