Biology subjects

Hatzopoulos, G.

Publications and source records attributed to Hatzopoulos, G..

3 recordsLinked to original sources

bioRxiv2025

C. elegans SAS-1 ensures centriole integrity and ciliary function, and operates with SSNA-1

Centrioles are microtubule-based organelles critical for signaling, motility and division. The microtubule-binding protein SAS-1 is homologous to the human ciliopathy component C2CD3 and contributes to centriole integrity in C. elegans, but how this function is exerted is incompletely understood. Here, through the generation of a null allele and analysis with U-Ex-STED, we establish that SAS-1 is dispensable for the onset of centriole assembly, but essential for organelle integrity during oogenesis, spermatogenesis and in the early embryo. Additionally, we uncover that SAS-1 is present at the transition zone of sensory neurons, where it contributes in a partially redundant manner to ciliary function. Furthermore, we investigate the relationship between SAS-1 and the C. elegans Sjogren Syndrome Nuclear Antigen 1 protein SSNA-1, establishing that SSNA-1 localizes next to the SAS-1 C-terminus in the centriole architecture. Moreover, through molecular epistasis experiments with null alleles of both components, we reveal that SAS-1 is essential for SSNA-1 localization to centrioles during oogenesis and to the transition zone during ciliogenesis. Moreover, using a heterologous human cell assay, we establish that SAS-1 recruits SSNA-1 to microtubules. Overall, our findings help clarify how SAS-1, together with SSNA-1, ensures centriole integrity and reveals that it contributes to cilium function.

cell biology↗

bioRxiv2022

Tubulin engineering by semisynthesis reveals that polyglutamylation directs detyrosination

Microtubules, a critical component of the cytoskeleton, carry combinations of post-translational modifications (PTMs), which are critical for the regulation of key cellular processes. Long-lived microtubules, in neurons particularly, exhibit both detyrosination of -tubulin as well as polyglutamylation. Dysregulation of these PTMs results in disease, including developmental defects and neurodegeneration. Despite their importance, the mechanisms governing the emergence of such PTM patterns are not well understood, mostly because tools to dissect the function and regulation of tubulin PTMs have been lacking. Here, we report a chemical method to produce fully functional tubulin carrying precisely defined PTMs within its C-terminal tail. Using a sortase- and intein-mediated tandem transamidation strategy, we ligate synthetic -tubulin tails, which are site-specifically glutamylated to specific extents, to recombinant human tubulin heterodimers. Using microtubules reconstituted with such designer tubulins, we show that polyglutamylation of -tubulin promotes its detyrosination by enhancing the activity of the tubulin tyrosine carboxypeptidase vasohibin/SVBP in a manner dependent on the length of polyglutamyl chains. Moreover, modulating polyglutamylation levels in cells results in corresponding changes in detyrosination. Together, using synthetic chemistry to produce tubulins carrying defined PTMs, we can directly link the detyrosination cycle to polyglutamylation, connecting two key regulatory systems that control tubulin function.

biochemistry↗

bioRxiv2020

Novel features of centriole polarity and cartwheel stacking revealed by cryo-tomography

Centrioles are polarized microtubule-based organelles that seed the formation of cilia, and which assemble from a cartwheel containing stacked ring oligomers of SAS-6 proteins. A cryo-tomography map of centrioles from the termite flagellate Trichonympha spp. was obtained previously, but higher resolution analysis is likely to reveal novel features. Using sub-tomogram averaging (STA) in T. spp. and Trichonympha agilis, we delineate the architecture of centriolar microtubules, pinhead and A-C-linker. Moreover, we report [~]25 [A] resolution maps of the central cartwheel, revealing notably polarized cartwheel inner densities (CID). Furthermore, STA of centrioles from the distant flagellate Teranympha mirabilis uncovers similar cartwheel architecture and a distinct filamentous CID. Fitting the CrSAS-6 crystal structure into the flagellate maps and analyzing cartwheels generated in vitro indicates that SAS-6 rings can directly stack onto one another in two alternating configurations: with a slight rotational offset and in register. Overall, improved STA maps in three flagellates enabled us to unravel novel architectural features, including of centriole polarity and cartwheel stacking, thus setting the stage for an accelerated elucidation of underlying assembly mechanisms.

cell biology↗