A Migrating Ciliary Gate Compartmentalizes the Site of Axoneme Assembly in Drosophila Spermatids

Abstract

SUMMARY Background In most cells, the cilium is formed within a compartment separated from the cytoplasm. Entry into the ciliary compartment is regulated by a specialized gate located at the base of the cilium in a region known as the transition zone. The transition zone is closely associated with multiple structures of the ciliary base including the centriole, axoneme, and ciliary membrane. However, the contribution of these structures to the ciliary gate remains unclear. Results Here, we report that in Drosophila spermatids, a conserved module of transition zone proteins mutated in Meckel-Gruber Syndrome (MKS) including Cep290, Mks1, B9d1, and B9d2 comprise a ciliary gate that continuously migrates away from the centriole to compartmentalize the growing axoneme tip. We show that Cep290 is essential for transition zone composition, compartmentalization of the axoneme tip, and axoneme integrity, and find that MKS proteins also delimit a centriole-independent compartment in mouse spermatids. Conclusion Our findings demonstrate that the ciliary gate can migrate away from the base of the cilium, thereby functioning independently of the centriole and of a static interaction with the axoneme to compartmentalize the site of axoneme assembly.

Drosophila Hook-Related Protein (Girdin) Is Essential for Sensory Dendrite Formation

“…We recorded MRCs and TEPs from bristles in homozygote and hemizygote mecA 101 and found that they lack MRCs, but are able to maintain normal TEPs (Figure 1 C-E). The severity of the MRC is similar to that of asterless mecD , oseg2 mecE , and cep290 mecH mutants that lack functional sensory cilia (Avidor-Reiss et al 2004;Blachon et al 2008;Basiri et al 2014), suggesting that mecA 101 flies have severe defects in the function or formation of the mechanosensory neuron.…”

“…In addition, the cell bodies of those sensory neurons that lack dendrites are often clustered together ( Figure 1F). The mechanosensory organ defects displayed by mecA 101 are more severe than those observed in mutations that specifically affect components of the sensory cilium; in such mutations the dendrite extends to the base of the socket, and absence or clustering of neuronal cell bodies is not observed (Avidor-Reiss et al 2004;Blachon et al 2008;Basiri et al 2014). However, the mecA phenotype resembles that of nompA, which also often fails to innervate the bristle base.…”

“…In addition, the dendrites of these ciliated sensory neurons are composed of an inner segment that terminates in a sensory cilium composed of a connecting cilium and an outer segment on the other end ( Figure 1A) (Thurm 1965;Kernan et al 1994;Keil 1997). Second, mutations affecting the connecting cilium, such as cep290 (den Hollander et al 2006;Cideciyan et al 2007;Basiri et al 2014), and sensory cilium, such as intraflagellar transport (IFT) proteins, have a similar effect in both human photoreceptor and Drosophila sensory function (Avidor-Reiss et al 2004;Crouse et al 2014). Third, the connecting cilium of both D. melanogaster mechanosensory neurons and human photoreceptors is uniquely long and serves as the connection between two bulky compartments: the inner and outer segments, which display much greater width and volume compared to the transition zone itself (Malicki and Avidor-Reiss 2014).…”

“…The cilium at the tip of a mechanosensory dendrite is formed using the typical protein machinery essential for ciliogenesis including centriolar, connecting cilium, and IFT proteins (Avidor-Reiss et al 2004;Martinez-Campos et al 2004;Rodrigues-Martins et al 2007;Blachon et al 2008Blachon et al , 2009Basiri et al 2014). The tip of the mechanosensory cilium associates with two cuticular structures: the bristle and the socket ( Figure 1A), each of which is formed by a unique support cell.…”

Methods to Study Centrosomes and Cilia in Drosophila

“…Note: This table is not an exhaustive list of all centrosome and cilia components mapped. Due to space constrain, only references for mutants and/or markers for each gene are mentioned in the list [15,16,19,21,31,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. Also, for more information about the genes visit www.flybase.org.…”