Unique properties of Drosophila spermatocyte primary cilia

Abstract

SummaryThe primary cilium is an essential organelle required for animal development and adult homeostasis that is found on most animal cells. The primary cilium contains a microtubule-based axoneme cytoskeleton that typically grows from the mother centriole in G0/G1 phase of the cell cycle as a membrane-bound compartment that protrudes from the cell surface. A unique system of bidirectional transport, intraflagellar transport (IFT), maintains the structure and function of cilia. While the axoneme is dynamic, growing and shrinking at its tip, at the same time it is very stable to the effects of microtubule-targeting drugs. The primary cilia found on Drosophila spermatocytes diverge from the general rules of primary cilium biology in several respects. Among these unique attributes, spermatocyte cilia assemble from all four centrioles in an IFT-independent manner in G2 phase, and persist continuously through two cell divisions. Here, we show that Drosophila spermatocyte primary cilia are extremely sensitive to microtubule-targeting drugs, unlike their mammalian counterparts. Spermatocyte cilia and their axonemes fail to assemble or be maintained upon nocodazole treatment, while centriole replication appears unperturbed. On the other hand, paclitaxel (Taxol), a microtubule-stabilizing drug, disrupted transition zone assembly and anchoring to the plasma membrane while causing spermatocyte primary cilia to grow extensively long during the assembly/elongation phase, but did not overtly affect the centrioles. However, once assembled to their mature length, spermatocyte cilia appeared unaffected by Taxol. The effects of these drugs on axoneme dynamics further demonstrate that spermatocyte primary cilia are endowed with unique assembly properties.

Transition Zone Migration: A Mechanism for Cytoplasmic Ciliogenesis and Postaxonemal Centriole Elongation

“…Simultaneously, the ciliary axoneme slowly begins to grow from the distal end of the centriole to provide a platform for transition zone assembly. This modest axoneme growth occurs throughout most of the spermatocyte differentiation program and does not extend beyond the region defined by transition zone markers at the level of light microscopy (Basiri et al, 2014; Riparbelli et al, 2013; Tates, 1971). …”

“…Within the ciliary cap compartment distal to the transition zone, axonemal microtubules are extended via patterned tubulin polymerization, the template for which was originally established in the centriole (Riparbelli et al, 2013). As the transition zone migrates, it leaves behind bare axonemal microtubules assembled in the appropriate architecture.…”

Aurora A inhibition by MNL8054 promotes centriole elongation during Drosophila male meiosis

“…In the presence of nocodazole, a microtubule destabilizer, the axonemes of CLRs failed to assemble, whereas Taxol, a stabilizer, leads to unusually long centrioles and axonemes. 48 These findings implicate the requirement of factors that control the dynamics of the transition from centriolar triplet microtubules to the axonemal doublets of the CLRs.…”

“…Given that Aurora A accumulates at the centrosomes in most of organisms, 21,[40][41][42][43][44][45][46][47][48][49][50][51][52][53] including Drosophila, 54 it is tempting to speculate that this kinase might also regulate the dynamics of the centriole microtubules. Suppression of Aurora-A by small interfering RNA causes an incorrect separation of the centriole pairs in cultured cells, indicating that Aurora-A is essential for the proper execution of this process.…”

Targeting Toxoplasma Tubules: Tubulin, Microtubules, and Associated Proteins in a Human Pathogen

“…IFT machinery is essential for construction of most axonemes. However, a few organisms assemble axonemes in the cell cytoplasm rather than at the cell periphery (63). For example, Drosophila lack a morphologically distinct transition zone and genes for IFT components.…”