PLoS One. Jing, X. Development Cambridge, England. Zhang, Y. Journal of visualized experiments : JoVE. Kitambi, S. Mechanisms of Development.
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Omori, Y. Liu, T. Li, G. Tsujikawa, M.
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Otteson, D. Molecular Vision. Methods Cell Biol.. The International journal of developmental biology. Bang, P. Journal of Neuroscience Methods. Wei, X. Nature Genetics. Doerre, G. The Journal of comparative neurology. The Journal of neuroscience : the official journal of the Society for Neuroscience. Trends in neurosciences. Link, B. In Vertebrate Eye Development, E. Fini, ed. Marlow, F. It is two-headed with two HCs and three ICs.
This is corroborated by male infertility of Dic61B mutants Fatima, These are not well characterized in metazoans, but many RS proteins of Chlamydomonas have orthologs in Drosophila Table 3. Six single-headed dynein variants are thought to exist in Chlamydomonas and humans a—e, g , as classified by their HC and IC constituents. Interestingly, however, this analysis also revealed that the antennal transcript includes an extra penultimate bp exon compared to testis and not annotated in the Drosophila genome Figure 2B.
Drosophila has orthologs of both genes CG and l 2 41Ab and each is expressed in Ch neurons and testes Table 3.
Fifty years of microtubule sliding in cilia
Tektins appear to be required for IDA assembly on, or attachment to, the microtubule doublets, but it is not clear whether they also have other functions in both motile and non-motile cilia Tanaka et al. Drosophila has four tektin genes, all of which are expressed in testes and enriched in Ch neurons.
Knockdown shows that these tektins have some function in fertility, but Ch neuron phenotypes are not observed, perhaps due to redundancy or compensation Table 5. In Chlamydomonas it has at least 11 subunits and helps to maintain axonemal alignment and resistance to sliding Bower et al. In Drosophila , orthologs of most human N-DRC subunits can be identified, and many are expressed in both Ch neurons and testis Table 3. Surprisingly homologs of some components that might be considered core subunits are expressed exclusively in Ch neurons or in testes, suggesting cell-type specific variations in N-DRC Table 3.
Consistent with this, knockdown of CG only affects Ch neuron function Table 5. As noted by Jerber et al.
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Consistent with this, the Drosophila ortholog CG is exclusively expressed in Ch neurons Table 4. A cohort of some 11 proteins, largely identified through characterization of PCD mutations, are required for the cytoplasmic pre-assembly of axonemal dynein complexes Mitchison and Valente, Despite the cell-type-specific differences in motors, these orthologs are highly expressed in both testes and Ch neurons Table 4 ; Figures 3R—T , and have clear defects in both cell types upon knock-down Table 5. This gene is highly expressed in Ch neurons and testes, consistent with a specific role in dynein assembly Table 4 ; Figure 3R.
It is not strongly enriched in Ch neurons either, with RNA in situ hybridization revealing widespread expression, but somewhat elevated in Ch neurons Figure 3S. It seems likely that nop17l is not dedicated solely to dynein assembly in Drosophila. We found in general that the entire ciliary motility apparatus is highly conserved in Drosophila Figure 4A.
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This suggests that despite the restricted distribution and function of its motile cilia, Drosophila has great potential as a genetic model for metazoan motile cilia biology. Indeed, the fact that only two cell types have motile cilia can be turned to advantage: it aids gene discovery and characterization, and it also provides a simple model system for exploring how diversity of motile cilium structure and function might be explained by cell-type-specific differences in ciliary motility machinery. For the dynein motor complexes, all expected metazoan outer and inner dynein subtypes are represented in the Drosophila genome except for the IDA d subtype containing the DNAH1 HC in humans.
Single-headed IDAs work in pairs dyads. Our analysis has revealed interesting differences between the two motile ciliated cell types. ODA motor differences presumably reflect the different functions of ciliary motility between the two cell types. In sperm, the motors must generate substantial force at a relatively low frequency for movement.
In Ch neuron cilia, motors are required for the highly specialized process of auditory mechanotransduction, putatively for active mechanical amplification and probably also for sensory adaptation. However, the Ch cilium motors must potentially respond with high temporal resolution e.
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Here we found that knockdown of either HC results in defective proprioception, consistent with defective Ch neuron mechanotransduction. In Chlamydomonas this dynein is thought to be important for regulating the size and shape of the axonemal bend, but clearly this motor function is dispensable in Ch neuron cilia.
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Some cell type differences in motility proteins can be ascribed to their requirement for IFT during ciliogenesis, and therefore are not expressed in IFT-independent sperm. This may reflect the different docking requirements of the different ODA motors in each cell type, or the need to interact with IFT machinery in Ch neuron ciliogenesis.
Interestingly, we find some differences in expression of N-DRC subunits between cell types: for example, the DRC2 homolog, CG appears to be expressed and required only in Ch neurons. Whether this reflects cell type differences in N-DRC function or transport remains to be determined. N-DRC structure and function is only beginning to be understood in Chlamydomonas Porter, , and is very poorly known in other organisms. We suggest that Drosophila will be a useful model for exploring the possibility of cell type-specific differences in N-DRC.
Conversely, the observation that dynein pre-assembly factor DNAAF homologs are all required in both motile ciliated cell types corroborates the view that they are required for cytoplasmic pre-assembly of motors rather than for their IFT-dependent trafficking. One caveat of this suggestion is that Ch neurons apparently do not express a homolog of IC, which is required for assembly of the IC subcomplex in Chlamydomonas. However, there is evidence that IC also binds tubulin directly Hendrickson et al. Further investigation would require showing that these proteins indeed localize to the Ch cilium.
In Chlamydomonas the molecular mechanism of how dynein motor activity is regulated is very uncertain Porter, Overall, Ch neuron cilia may provide a useful model for future analysis of this regulatory axis, and excitingly this may provide insight into the molecular mechanism of mechanosensory amplification and frequency selectivity in these neurons.
The disease PCD results from the mutation of any one of at least 40 different human genes encoding diverse components of the ciliary motility machinery Mitchison and Valente, The high retention of ciliary motility genes in Drosophila is reflected in the fact that the majority of PCD-causative genes have functional Drosophila homologs Table 6. This suggests that despite its specialized motile ciliated cell types, Drosophila will continue to be a useful metazoan model for PCD studies. As shown here, genetically supplied RNAi knockdown in developing sensory neurons driven by scaGal4 and spermatocytes driven by BamGal4 is quite efficient for validating the function of ciliary motility genes in Drosophila.
RNAi analysis appears particularly effective in showing the function of genes expected to have a major effect on motility DNAAFs, molecular ruler, etc.