Ciliopathy patient variants reveal organelle-specific functions for TUBB4B in axonemal microtubules
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ABSTRACT: Tubulin, one of the most abundant cytoskeletal building blocks, exhibits extensive isotype diversity in humans. Displaying high similarity, whether these distinct isotypes form cell-type and context specific microtubule structures is poorly understood. Studying a cohort of 11 patients with the motile ciliopathy primary ciliary dyskinesia as well as mouse mutants, we report mutations in the TUBB4B isotype specifically perturb centriole and cilium biogenesis. We demonstrate that distinct TUBB4B mutations differentially affect microtubule dynamics and cilia formation in a dominant negative manner. Finally, structure-function studies reveal that different TUBB4B mutations disrupt distinct tubulin interfaces allowing clear stratification of patients into three classes of ciliopathic disease. These findings illustrate that specific tubulin isotypes have unique and non-redundant subcellular functions and establishes the missing link between human tubulinopathies and ciliopathies.
Project description:Microtubules are ancient and highly conserved polymers composed of alpha and beta tubulin heterodimers. Their dynamic remodelling drives diverse cellular processes from organelle trafficking and chromosome segregation to templating more stable structures like those of centrioles and ciliary axonemes. While organisms like Chlamydomonas reinhardtii only have a single - and -tubulin gene, TUBB4B, is one of 10 human -tubulin isotypes which can pair with one of the 9 isotypes of -tubulin. Whether this diversification permits discrete transcriptional units for cell type specific expression, or whether additional functional differences exist between isotypes remains unclear. Here, using human disease genetics, we reveal three distinct classes of ciliopathic disease in human patients carrying de novo mutations in TUBB4B. Using structure-function studies, we demonstrate these mutations differentially affect microtubule dynamics and cilia formation in a dominant negative manner. Importantly, using patient-modelled mutant as well as knockout Tubb4b mice we establish a necessary and non-redundant function for TUBB4B in building centrioles and axonemes of multiciliated cells. Our results suggest that a functional difference in TUBB4B is required to support the unique microtubule architecture in motile ciliated cells. It places primary ciliary dyskinesia and the ciliopathies more broadly into an expanding phenotypic and clinical spectrum of human tubulinopathies.
Project description:We establish a necessary and non-redundant function for TUBB4B in building centrioles and axonemes of multiciliated cells placing ciliopathies more broadly into human tubulinopathies.
Project description:Among hematopoietic cells, osteoclasts (Oc) and immature dendritic cells (Dc) are closely related myeloid cells with distinct functions; Oc participate skeleton maintenance while Dc sample the environment for foreign antigens. Such specificities rely on profound modifications of gene and protein expression during Oc and Dc differentiation. We provide global proteomic and transcriptomic analyses of primary mouse Oc and Dc, based on original SILAC and RNAseq data. We established specific signatures for Oc and Dc including genes and proteins of unknown functions. In particular, we showed that Oc and Dc have the same α and β tubulin isotypes repertoire but that Oc express much more β tubulin isotype Tubb6. In both mouse and human Oc, we demonstrate that elevated expression of Tubb6 in Oc is necessary for correct podosomes organization and thus for the structure of the sealing zone, which sustains the bone resorption apparatus. Hence, lowering Tubb6 expression hindered Oc resorption activity. Overall, we highlight here potential new regulators of Oc and Dc biology and illustrate the functional importance of the tubulin isotype repertoire in the biology of differentiated cells.
Project description:Among hematopoietic cells, osteoclasts (Oc) and immature dendritic cells (Dc) are closely related myeloid cells with distinct functions; Oc participate skeleton maintenance while Dc sample the environment for foreign antigens. Such specificities rely on profound modifications of gene and protein expression during Oc and Dc differentiation. We provide global proteomic and transcriptomic analyses of primary mouse Oc and Dc, based on original SILAC and RNAseq data. We established specific signatures for Oc and Dc including genes and proteins of unknown functions. In particular, we showed that Oc and Dc have the same alpha and beta tubulin isotypes repertoire but that Oc express much more beta tubulin isotype Tubb6 (also known as Tubulin beta class V). In both mouse and human Oc, we demonstrate that elevated expression of Tubb6 in Oc is necessary for correct podosomes organization and thus for the structure of the sealing zone, which sustains the bone resorption apparatus. Hence, lowering Tubb6 expression hindered Oc resorption activity. Overall, we highlight here potential new regulators of Oc and Dc biology and illustrate the functional importance of the tubulin isotype repertoire in the biology of differentiated cells.
Project description:Oral-facial-digital syndromes (OFD) are a heterogeneous group of congenital disorders characterized by malformations of the face and oral cavity, and digit anomalies. To date, mutations in 12 ciliary-related genes have been identified to cause several OFD types suggesting OFDs constitute a subgroup of developmental ciliopathies. Through homozygosity mapping and exome sequencing performed on two families with variable OFD type 2, we identified distinct germline mutations in INTS13, a subunit of the Integrator Complex. This 14-component complex associates with RNAPII and can cleave nascent RNA to modulate gene expression. We determined that INTS13 utilizes a discrete domain within its C-terminus to bind the Integrator cleavage module, which is disrupted by the identified germline INTS13 mutations. Depletion of INTS13 disrupts ciliogenesis in human cultured cells and causes dysregulation of a broad collection of ciliary genes. Accordingly, its knockdown in Xenopus embryos lead to motile cilia anomalies. Altogether, we show that mutations in INTS13 cause an autosomal recessive ciliopathy, which reveal key interactions within Integrator components.
Project description:In this study we identify SUMO isotype-specific non covalent binders. The different isotypes include SUMO1, SUMO2 and a 3xSUMO2 chain.
Project description:A proliferated and post-translationally modified microtubule network underlies cellular growth in cardiac hypertrophy and contributes to contractile dysfunction in heart failure. Yet how the heart achieves this modified network is poorly understood. Determining how the “tubulin code” – the permutations of tubulin isoforms and post-translational modifications - is rewritten upon cardiac stress may provide new targets to modulate cardiac remodeling. Further, while tubulin can autoregulate its own expression, it is unknown if autoregulation is operant in the heart or tuned in response to stress. Here we use heart failure patient samples and murine models of cardiac remodeling to interrogate transcriptional, autoregulatory, and post-translational mechanisms that contribute to microtubule network remodeling at different stages of heart disease. We find that autoregulation is operant across tubulin isoforms in the heart and leads to an apparent disconnect in tubulin mRNA and protein levels in heart failure. We also find that within 4 hours of a hypertrophic stimulus and prior to cardiac growth, microtubule detyrosination is rapidly induced to help stabilize the network. This occurs concomitant with rapid transcriptional and autoregulatory activation of specific tubulin isoforms and microtubule motors. Upon continued hypertrophic stimulation, there is an increase in post-translationally modified microtubule tracks and anterograde motors to support cardiac growth, while total tubulin content increases through progressive transcriptional and autoregulatory induction of tubulin isoforms. Our work provides a new model for how the tubulin code is rapidly rewritten to establish a proliferated, stable microtubule network that drives cardiac remodeling, and provides the first evidence of tunable tubulin autoregulation during pathological progression.
Project description:A proliferated and post-translationally modified microtubule network underlies cellular growth in cardiac hypertrophy and contributes to contractile dysfunction in heart failure. Yet how the heart achieves this modified network is poorly understood. Determining how the “tubulin code” – the permutations of tubulin isoforms and post-translational modifications - is rewritten upon cardiac stress may provide new targets to modulate cardiac remodeling. Further, while tubulin can autoregulate its own expression, it is unknown if autoregulation is operant in the heart or tuned in response to stress. Here we use heart failure patient samples and murine models of cardiac remodeling to interrogate transcriptional, autoregulatory, and post-translational mechanisms that contribute to microtubule network remodeling at different stages of heart disease. We find that autoregulation is operant across tubulin isoforms in the heart and leads to an apparent disconnect in tubulin mRNA and protein levels in heart failure. We also find that within 4 hours of a hypertrophic stimulus and prior to cardiac growth, microtubule detyrosination is rapidly induced to help stabilize the network. This occurs concomitant with rapid transcriptional and autoregulatory activation of specific tubulin isoforms and microtubule motors. Upon continued hypertrophic stimulation, there is an increase in post-translationally modified microtubule tracks and anterograde motors to support cardiac growth, while total tubulin content increases through progressive transcriptional and autoregulatory induction of tubulin isoforms. Our work provides a new model for how the tubulin code is rapidly rewritten to establish a proliferated, stable microtubule network that drives cardiac remodeling, and provides the first evidence of tunable tubulin autoregulation during pathological progression.
Project description:A proliferated and post-translationally modified microtubule network underlies cellular growth in cardiac hypertrophy and contributes to contractile dysfunction in heart failure. Yet how the heart achieves this modified network is poorly understood. Determining how the “tubulin code” – the permutations of tubulin isoforms and post-translational modifications - is rewritten upon cardiac stress may provide new targets to modulate cardiac remodeling. Further, while tubulin can autoregulate its own expression, it is unknown if autoregulation is operant in the heart or tuned in response to stress. Here we use heart failure patient samples and murine models of cardiac remodeling to interrogate transcriptional, autoregulatory, and post-translational mechanisms that contribute to microtubule network remodeling at different stages of heart disease. We find that autoregulation is operant across tubulin isoforms in the heart and leads to an apparent disconnect in tubulin mRNA and protein levels in heart failure. We also find that within 4 hours of a hypertrophic stimulus and prior to cardiac growth, microtubule detyrosination is rapidly induced to help stabilize the network. This occurs concomitant with rapid transcriptional and autoregulatory activation of specific tubulin isoforms and microtubule motors. Upon continued hypertrophic stimulation, there is an increase in post-translationally modified microtubule tracks and anterograde motors to support cardiac growth, while total tubulin content increases through progressive transcriptional and autoregulatory induction of tubulin isoforms. Our work provides a new model for how the tubulin code is rapidly rewritten to establish a proliferated, stable microtubule network that drives cardiac remodeling, and provides the first evidence of tunable tubulin autoregulation during pathological progression.