Biology subjects

Mikeladze-Dvali, T.

Publications and source records attributed to Mikeladze-Dvali, T..

5 recordsLinked to original sources

bioRxiv2024

PCMD-1 stabilizes the PCM scaffold and facilitates centriole separation

Centrosomes are highly dynamic organelles, and maintaining their stability is crucial for spindle pole integrity and bipolar spindle formation. Centrosomes consist of a pair of centrioles surrounded by the pericentriolar material (PCM). In Caenorhabditis elegans, interactions between the PCM scaffold protein SPD-5 and the regulatory kinase PLK-1 are essential for PCM formation and disassembly. However, how PCM stability is established and maintained remains an open question. Here, we address this question by analyzing the function of PCMD-1, a protein that predominantly localizes to centrioles. Mutations in the predicted PLK-1 binding sites of PCMD-1 result in a reduction of centrosomal PLK-1 and PCMD-1 levels, leading to severe distortion of the PCM scaffold. The disorganization of the PCM is already evident during its formation and results in the assembly of a structurally unstable mitotic centrosome, which is unable to resist the microtubule pulling forces exerted on the spindle pole. As a consequence of a weakened PCM scaffold, the pulling forces are not effectively relayed to the entrapped centriole pair, resulting in delayed centriole separation in late anaphase. Together, these findings show that PCMD-1, which predominantly localizes to centrioles and tethers the PCM scaffold to them, is essential for stabilizing the entire PCM scaffold and ensuring timely centriole separation during PCM disassembly. We propose a model in which PCMD-1 initiates the ordered assembly of the PCM scaffold by biasing the PCM core to a certain intrinsic order around the centrioles. This intrinsic order acts as a seed that propagates throughout the surrounding micron-scale PCM scaffold, providing the necessary strength and structural integrity for the centrosome.

cell biology↗

bioRxiv2023

Spatially distinct inputs modulate the amount of active Mitotic-phase GAP to locally restrict RhoA signaling for successful cell division

At the end of mitosis a contractile ring consisting of filamentous actin (F-actin) assembles at the cell equator and ring constriction equally partitions the cellular content. Inhibitory and stimulatory signaling cascades spatially limit RhoA activity to a narrow central zone to promote F-actin polymerization only at the cell equator. While the stimulatory signal is well-characterized, the mechanisms by which inhibitory signals restrict active RhoA to a narrow equatorial zone and prevent improper RhoA activity at the cell poles are not known. Here, we identify two regulatory inputs that control the activation and cortical targeting of the Mitotic-phase GTPase activating protein (MP-GAP) for RhoA which limits RhoA activity both at the cell poles and at the cell equator. We show that at cell poles, MP-GAP is a direct phosphorylation target of spindle-pole associated Aurora A kinase. We identify three Aurora A target residues in a region of MP-GAP that binds directly to its catalytic GAP domain suggesting the Aurora A phosphorylation releases MP-GAP autoinhibition. We show that phosphorylation of these sites is required to keep RhoA activity low at the cell poles. At the cell equator, F-actin facilitates MP-GAP enrichment, which opposes RhoA GEF activity and thereby accelerates RhoA flux through the GTPase cycle for the formation of a narrow equatorial zone of active RhoA. Thus, the amount of active MP-GAP is modulated by two distinct regulatory inputs that function in spatially restricted locations: Aurora A phosphorylation relieves MP-GAP autoinhibition to limit RhoA activity at the cell poles, while F-actin polymerization promotes MP-GAP targeting to prevent distribution of active RhoA in a broad zone at the cell equator. By determining the mechanism of spatially confining RhoA activity at the equator and the cell poles during cytokinesis, our work has broad implications to how Rho activity zones are formed and maintained during cytokinesis and how defects in their formation impact animal development and disease.

cell biology↗

bioRxiv2023

Centriole elimination during C. elegans oogenesis initiates with loss of the central tube protein SAS-1

Centrioles are lost during oogenesis in most metazoans, ensuring that the zygote is endowed with the correct number of two centrioles, which are paternally contributed. How centriole architecture is dismantled during oogenesis is not understood. Here, we analyze with unprecedent detail the ultrastructural and molecular changes during oogenesis centriole elimination in C. elegans. Centriole elimination begins with loss of the so-called central tube and organelle widening, followed by microtubule disassembly. The resulting cluster of centriolar proteins then disappears gradually, usually moving in a microtubule- and dynein-dependent manner to the plasma membrane. Moreover, we find that neither Polo-like kinases nor the PCM, which modulate oogenesis centriole elimination in Drosophila, do so in C. elegans. Furthermore, we demonstrate that the central tube protein SAS-1 normally departs first from the organelle, which loses integrity earlier in sas-1 mutants. Overall, our work provides novel mechanistic insights regarding the fundamental process of oogenesis centriole elimination.

cell biology↗

bioRxiv2022

Anillin forms linear structures and facilitates furrow ingression after septin and formin depletion

During cytokinesis a contractile ring consisting of unbranched filamentous actin (F-actin) and myosin II filaments assembles and constricts at the cell equator. Unbranched F-actin is de novo generated by formin and without formin cleavage furrow ingression fails. In C. elegans depletion of septin restores cleavage furrow ingression in formin (CYK-1) mutants. How the cleavage furrow ingresses without a detectable unbranched F-actin ring is not known. We report, that in this setting anillin (ANI-1) is essential for furrow ingression and forms a meshwork of linear structures, which circumferentially align around the cell equator. Although equatorial ANI-1 recruitment is facilitated by septins, the formation of linear ANI-1 structures is septin independent. Analysis of ANI-1 deletion mutants reveals that its disordered linker region is required for linear structure formation and furrow ingression. We also found that myosin II (NMY-2) decorates linear ANI-1 structures and promotes their circumferential alignment. NMY-2 also interacts with various lipids and forms membrane localized clusters in absence of F-actin and anillin binding. This suggests that NMY-2 represents an independent link between the F-actin / ANI-1 network and the plasma membrane. Collectively, our data reveals a compensatory mechanism, mediated by ANI-1 linear structures and membrane-bound NMY-2, that promotes furrow formation and ingression when formins are depleted and therefore unbranched F-actin polymerization is compromised.

cell biology↗

bioRxiv2020

PCMD-1 bridges the centrioles and the PCM scaffold in C. elegans

Correct cell division relies on the formation of a bipolar spindle. In animal cells, microtubule nucleation at the spindle poles is facilitated by the pericentriolar material (PCM), which assembles around a pair of centrioles. Although centrioles are essential for PCM assembly, proteins that anchor the PCM to the centrioles are less known. Here we investigate the molecular function of PCMD-1 in bridging the PCM and the centrioles in Caenorhabditis elegans. We demonstrate that centrosomal recruitment of PCMD-1 is dependent on the outer centriolar protein SAS-7. While the most C-terminal part of PCMD-1 is sufficient to target it to the centrosome, the coiled-coil domain promotes its accumulation by facilitating self-interaction. We reveal that PCMD-1 is bridging the centrioles and PCM scaffold through protein-protein interactions with the PCM scaffold protein SPD-5, the mitotic kinase PLK-1 and the centriolar protein SAS-4. Using an ectopic translocation assay, we show that PCMD-1 is able to selectively recruit downstream PCM scaffold components to an ectopic location in the cell, indicating that PCMD-1 is sufficient to anchor the PCM scaffold proteins to the centrioles. Our work suggests that PCMD-1 is an essential functional bridge between the centrioles and the PCM.

cell biology↗