Biology subjects

Roll-Mecak, A.

Publications and source records attributed to Roll-Mecak, A..

8 recordsLinked to original sources

bioRxiv2026

Tubulin autoregulation mediator TTC5 regulates neuronal morphology and migration

Microtubule dynamics regulation is critical for neuronal development, yet how neurons regulate tubulin levels remains poorly understood. Tetratricopeptide repeat domain 5 (TTC5) mediates the co-translational degradation of tubulin transcripts in response to excess soluble tubulin, a.k.a. "tubulin autoregulation", and TTC5 mutations are associated with cerebral atrophy, speech and motor impairment. Despite clinical relevance, the role of TTC5 and tubulin autoregulation in neurons has not been established. Using human induced pluripotent stem cells (iPSCs)-derived cortical-like neurons, we demonstrate that tubulin autoregulation is active in neurons and fully TTC5-dependent. Loss of TTC5 function suppresses microtubule polymerization and impairs axonal outgrowth and arborization, while enhancing cellular motility. These phenotypes recapitulate in vivo where TTC5 loss in mouse cerebral cortex projection neurons disrupts axon and dendrite arborization and drives aberrant hypermigration. Patient disease mutants phenocopy this motility dysregulation, directly linking TTC5 dysfunction to clinically relevant neurological deficits. Together, our findings establish tubulin autoregulation and its mediators as essential regulators of neuronal morphogenesis and connectivity and provides a mechanistic framework for understanding TTC5-associated neurodevelopmental disease.

Cell Biology↗

bioRxiv2025

A system for high-throughput axonal imaging of induced pluripotent stem cell-derived human i3Neurons

Neurons have long, thin axons and branched dendritic processes which rely on an extensive microtubule network that functions as a cellular scaffold and substrate for cargo transport. Microtubule defects are a defining pathological feature of neurological disorders. The highly arborized, long, polarized neuronal processes pose challenges for imaging-based assays. Available methods use either dispersed cultures, which are inefficient for compartment-specific analyses, or microfluidic chambers, which allow clear separation of somatodendritic and axonal compartments but are expensive and difficult to maintain. Here, we introduce an "i3Neurosphere" culture model of induced pluripotent stem cell (iPSC)-derived human cortical i3Neurons that enables high-throughput imaging of hundreds of axons without specialized equipment. We characterize neurite outgrowth, polarization, microtubule dynamics, and motility of diverse cargo, providing a reference for future work on microtubule processes in this system. The high-throughput compartment-specific imaging we present, combined with facile genetic engineering in i3Neurons provides a powerful tool to study human neurons. SIGNIFICANCE STATEMENTHuman neurons are difficult to study due to limited access to tissue and technical challenges in existing in vitro models of axonal transport. We developed i3Neurospheres, a simple and scalable 3D culture system of human iPSC-derived neurons that enables high-throughput imaging of axonal outgrowth, microtubule dynamics, and intracellular transport. This platform provides an accessible, reproducible method for investigating neuronal function and disease mechanisms, offering broad utility for neuroscience research and preclinical drug screening.

neuroscience↗

bioRxiv2024

Multi-camera Simultaneous Total Internal Reflection and Interference Reflection Microscopy

Interference Reflection Microscopy (IRM) is an optical technique that relies on the interference between the reflected light from an incident beam as it passes through materials of different refractive indices. This technique has been successfully used to image microtubules, biologically important biofilaments with a diameter of 25 nm. However, it is often desirable to image both the microtubule and microtubule interacting proteins simultaneously. Here we present a simple modification to a standard multi-color total internal reflection fluorescence (TIRF) microscope that enables simultaneous high-speed IRM and single molecule TIRF imaging. Our design utilizes a camera for each channel (IRM and TIRF) allowing independent optimization of camera parameters for the two different modalities. We illustrate its application by imaging unlabeled microtubules and GFP-labeled end-binding protein EB1 which forms comets on the tips of polymerizing microtubules. Our design is easily implemented, and with minimal cost, making it accessible to any laboratory with an existing fluorescence microscope.

biophysics↗

bioRxiv2024

The TTLL10 polyglycylase is stimulated by tubulin glutamylation and inhibited by polyglycylation

Microtubules in cells have complex and developmentally stereotyped posttranslational modifications that support diverse processes such as cell division, ciliary growth and axonal specification. Glycylation, the addition of glycines, singly (monoglycylation) or in chains (polyglycylation), is primarily found on axonemal microtubules where it functions in cilia maintenance and motility. It is catalyzed by three enzymes in the tubulin tyrosine ligase-like family, TTLL3, 8 and 10. We show that TTLL8 monoglycylates both - and {beta}-tubulin, unlike TTLL3 which prefers {beta}-tubulin. Microscopy and mass spectrometry show that TTLL10 requires monoglycylation for high affinity microtubule binding and elongates polyglycine chains only from pre-existing glycine branches. Surprisingly, tubulin polyglycylation inhibits TTLL10 recruitment to microtubules proportional with the number of posttranslationally added glycines, suggesting an autonomous mechanism for polyglycine chain length control. In contrast, tubulin glutamylation, which developmentally precedes polyglycylation in cilia, increases TTLL10 recruitment to microtubules, suggesting a mechanism for sequential deposition of tubulin modifications on axonemes. Our work sheds light on how the tubulin code is written by establishing the substrate preference and regulation of TTLL glycylases and provides a minimal system for generating differentially glycylated microtubules for in vitro analyses of the tubulin code.

biochemistry↗

bioRxiv2023

Cryo-EM structures of human α1B/βI+βIVb microtubules shed light on isoform specific assembly

Microtubules are dynamic polymers assembled from {beta}-tubulin dimers. Mammals have multiple and {beta}-tubulin isoforms. Despite a high degree of conservation, microtubules assembled from different tubulin isoforms have unique dynamic properties. How isoform sequence variation affects polymerization interfaces and nucleotide dependent conformational changes in microtubules is still not well understood. Here we report 2.9[A] resolution cryo-EM structures of human 1B/{beta}I+{beta}IVb microtubules in the GDP state, and a GTP-like state, bound to GMPCPP. Our structures show that, similar to microtubules assembled from other mammalian isoforms, transition from the GTP to the GDP states in 1B/{beta}I+{beta}IVb microtubules results in strengthening of the longitudinal interface and an overall compaction of the axial dimer repeat distance in the lattice. Interestingly, we find that -tail residues link longitudinally adjacent tubulin dimers through interactions with two conserved arginine residues in {beta}-tubulin that are mutated in human disease. Comparative analysis of tubulin isoforms shows minimal isoform-specific effects at the longitudinal interface or the -tubulin lateral interface, but a high concentration of sequence variability in the second shell of residues away from the {beta}-tubulin lateral interface which can modulate polymerization interfaces and thus impact microtubule dynamics.

biophysics↗

bioRxiv2023

Nonequilibrium bending fluctuations reveal microtubule mechanics in-vivo and their regulation by glutamylation

Cells can be described as active composite materials. The mechanical properties of cells are controlled by complex polymer networks and are dynamically tuned for diverse cellular processes driven by force-generating motor proteins. Microtubules are the most rigid protein polymers in the cytoskeleton, and their material properties have been measured in vitro by active bending or by analyzing thermal bending fluctuations. Microtubule mechanics in living cells are extremely difficult to probe directly, while fluctuations are difficult to interpret because they are generated by active forces in a surrounding cytoplasm with poorly understood material properties. Here we introduce a method to measure the elastic properties of microtubules in living cells by making use of motor-generated forces that drive bending fluctuations. Bending dynamics are governed by three main factors: microtubule material properties, cytoskeletal active forces, and the response characteristics of the surrounding cytoplasm. We show theoretically that, when one factor can be independently determined, the other two can be derived from observed fluctuations. Using this method we discovered that polyglutamylation, a post-translational modification enriched on microtubule arrays that need to withstand large mechanical forces such as those in axons or cilia, increases microtubule stiffness in living cells. Our work provides a theoretical and experimental framework to study microtubule mechanics and their regulation by tubulin modifications and microtubule effectors in complex cellular environments. The approach can be extended to other large aspect ratio cellular structures such as the endoplasmic reticulum or the mitochondrial network.

biophysics↗

bioRxiv2020

Structural basis for polyglutamate chain initiation and elongation by TTLL family enzymes

Glutamylation, introduced by TTLL enzymes, is the most abundant modification of brain tubulin. Essential effector proteins read the tubulin glutamylation pattern, and its misregulation causes neurodegeneration. TTLL glutamylases posttranslationally add glutamates to internal glutamates in tubulin C-terminal tails (branch initiation, through an isopeptide bond), and additional glutamates can extend these (elongation). TTLLs are thought to specialize for initiation or elongation, but the mechanistic basis for regioselectivity is unknown. We present cocrystal structures of murine TTLL6 bound to tetrahedral intermediate analogs that delineate key active-site residues that make this an elongase. We show that TTLL4 is exclusively an initiase, and through combined structural and phylogenetic analyses, engineer TTLL6 into a branch-initiating enzyme. TTLL glycylases add glycines posttranslationally to internal glutamates, and we find that the same active-site residues discriminate between initiase and elongase glycylases. These active-site specializations of TTLL glutamylases and glycylases ultimately yield the chemical complexity of cellular microtubules.

biochemistry↗

bioRxiv2019

Structural determinants of microtubule minus end preference in CAMSAP CKK domains

CAMSAP/Patronins regulate microtubule minus-end dynamics. Their end specificity is mediated by their CKK domains, which we proposed recognise specific tubulin conformations found at minus ends. To critically test this idea, we compared the human CAMSAP1 CKK domain (HsCKK) with a CKK domain from Naegleria gruberi (NgCKK), which has lost minus-end specificity. Near-atomic cryo-electron microscopy structures of HsCKK- and NgCKK-microtubule complexes show that these CKK domains share the same protein fold, bind at the intradimer interprotofilament tubulin junction, but exhibit subtly different footprints on microtubules. Whereas NgCKK binding does not alter the microtubule architecture, HsCKK remodels its microtubule interaction site and changes the underlying polymer structure because the tubulin lattice conformation is not optimal for its binding. NMR experiments show that HsCKK is remarkably rigid, supporting this remodelling ability. Thus, in contrast to many MAPs, CKK domains can differentiate subtly specific tubulin conformations to enable microtubule minus-end recognition.

biophysics↗