Reversible detyrosination of α-tubulin is crucial to microtubule dynamics and functions, and defects have been implicated in cancer, brain disorganization, and cardiomyopathies. The identity of the ...tubulin tyrosine carboxypeptidase (TCP) responsible for detyrosination has remained unclear. We used chemical proteomics with a potent irreversible inhibitor to show that the major brain TCP is a complex of vasohibin-1 (VASH1) with the small vasohibin binding protein (SVBP). VASH1 and its homolog VASH2, when complexed with SVBP, exhibited robust and specific Tyr/Phe carboxypeptidase activity on microtubules. Knockdown of vasohibins or SVBP and/or inhibitor addition in cultured neurons reduced detyrosinated α-tubulin levels and caused severe differentiation defects. Furthermore, knockdown of vasohibins disrupted neuronal migration in developing mouse neocortex. Thus, vasohibin/SVBP complexes represent long-sought TCP enzymes.
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BFBNIB, NMLJ, NUK, ODKLJ, PNG, SAZU, UL, UM, UPUK
Morphometry characterization is an important procedure in describing neuronal cultures and identifying phenotypic differences. This task usually requires labor-intensive measurements and the ...classification of numerous neurites from large numbers of neurons in culture. To automate these measurements, we wrote AutoNeuriteJ, an imageJ/Fiji plugin that measures and classifies neurites from a very large number of neurons. We showed that AutoNeuriteJ is able to detect variations of neuritic growth induced by several compounds known to affect the neuronal growth. In these experiments measurement of more than 5000 mouse neurons per conditions was obtained within a few hours. Moreover, by analyzing mouse neurons deficient for the microtubule associated protein 6 (MAP6) and wild type neurons we illustrate that AutoNeuriteJ is capable to detect subtle phenotypic difference in axonal length. Overall the use of AutoNeuriteJ will provide rapid, unbiased and accurate measurement of neuron morphologies.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The balance of contralateral and ipsilateral retinogeniculate projections is critical for binocular vision, but the transcriptional programs regulating this process remain ill defined. Here we show ...that the Pou class homeobox protein POU3F1 is expressed in nascent mouse contralateral retinal ganglion cells (cRGCs) but not ipsilateral RGCs (iRGCs). Upon Pou3f1 inactivation, the proportion of cRGCs is reduced in favor of iRGCs, leading to abnormal projection ratios at the optic chiasm. Conversely, misexpression of Pou3f1 in progenitors increases the production of cRGCs. Using CUT&RUN and RNA sequencing in gain- and loss-of-function assays, we demonstrate that POU3F1 regulates expression of several key members of the cRGC gene regulatory network. Finally, we report that POU3F1 is sufficient to induce RGC-like cell production, even in late-stage retinal progenitors of Atoh7 knockout mice. This work uncovers POU3F1 as a regulator of the cRGC transcriptional program, opening possibilities for optic nerve regenerative therapies.
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•POU3F1 is expressed in postmitotic RGC precursors but downregulated in most mature RGCs•Pou3f1 loss increases production of ipsilateral RGCs at the expense of contralateral RGCs•POU3F1 represses ipsilateral determinants and activates contralateral determinants•POU3F1 promotes RGC-like cell production when misexpressed in late progenitors
Fries et al. demonstrate that POU3F1 is expressed in postmitotic retinal ganglion cell (RGC) precursors, where it represses Atoh7 and the ipsilateral determinant Zic2, while promoting expression of several contralateral determinants, leading to the generation of contralateral RGCs. This work uncovers a developmental regulator of cells involved in binocular vision.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Vasohibins are tubulin tyrosine carboxypeptidases that are important in neuron physiology. We examined the crystal structures of human vasohibin 1 and 2 in complex with small vasohibin-binding ...protein (SVBP) in the absence and presence of different inhibitors and a C-terminal α-tubulin peptide. In combination with functional data, we propose that SVBP acts as an activator of vasohibins. An extended groove and a distinctive surface residue patch of vasohibins define the specific determinants for recognizing and cleaving the C-terminal tyrosine of α-tubulin and for binding microtubules, respectively. The vasohibin-SVBP interaction and the ability of the enzyme complex to associate with microtubules regulate axon specification of neurons. Our results define the structural basis of tubulin detyrosination by vasohibins and show the relevance of this process for neuronal development. Our findings offer a unique platform for developing drugs against human conditions with abnormal tubulin tyrosination levels, such as cancer, heart defects and possibly brain disorders.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The development and function of the central nervous system rely on the microtubule (MT) and actin cytoskeletons and their respective effectors. Although the structural role of the cytoskeleton has ...long been acknowledged in neuronal morphology and activity, it was recently recognized to play the role of a signaling platform. Following this recognition, research into Microtubule Associated Proteins (MAPs) diversified. Indeed, historically, structural MAPs—including MAP1B, MAP2, Tau, and MAP6 (also known as STOP);—were identified and described as MT-binding and -stabilizing proteins. Extensive data obtained over the last 20 years indicated that these structural MAPs could also contribute to a variety of other molecular roles. Among multi-role MAPs, MAP6 provides a striking example illustrating the diverse molecular and cellular properties of MAPs and showing how their functional versatility contributes to the central nervous system. In this review, in addition to MAP6’s effect on microtubules, we describe its impact on the actin cytoskeleton, on neuroreceptor homeostasis, and its involvement in signaling pathways governing neuron development and maturation. We also discuss its roles in synaptic plasticity, brain connectivity, and cognitive abilities, as well as the potential relationships between the integrated brain functions of MAP6 and its molecular activities. In parallel, the Collapsin Response Mediator Proteins (CRMPs) are presented as examples of how other proteins, not initially identified as MAPs, fall into the broader MAP family. These proteins bind MTs as well as exhibiting molecular and cellular properties very similar to MAP6. Finally, we briefly summarize the multiple similarities between other classical structural MAPs and MAP6 or CRMPs.In summary, this review revisits the molecular properties and the cellular and neuronal roles of the classical MAPs, broadening our definition of what constitutes a MAP.
Neurodevelopmental axonal pathfinding plays a central role in correct brain wiring and subsequent cognitive abilities. Within the growth cone, various intracellular effectors transduce axonal ...guidance signals by remodeling the cytoskeleton. Semaphorin-3E (Sema3E) is a guidance cue implicated in development of the fornix, a neuronal tract connecting the hippocampus to the hypothalamus. Microtubule-associated protein 6 (MAP6) has been shown to be involved in the Sema3E growth-promoting signaling pathway. In this study, we identified the collapsin response mediator protein 4 (CRMP4) as a MAP6 partner and a crucial effector in Sema3E growth-promoting activity. CRMP4-KO mice displayed abnormal fornix development reminiscent of that observed in Sema3E-KO mice. CRMP4 was shown to interact with the Sema3E tripartite receptor complex within detergent-
membrane (DRM) domains, and DRM domain integrity was required to transduce Sema3E signaling through the Akt/GSK3 pathway. Finally, we showed that the cytoskeleton-binding domain of CRMP4 is required for Sema3E's growth-promoting activity, suggesting that CRMP4 plays a role at the interface between Sema3E receptors, located in DRM domains, and the cytoskeleton network. As the fornix is affected in many psychiatric diseases, such as schizophrenia, our results provide new insights to better understand the neurodevelopmental components of these diseases.
In the central nervous system, microtubule-associated protein 6 (MAP6) is expressed at high levels and is crucial for cognitive abilities. The large spectrum of social and cognitive impairments ...observed in MAP6-KO mice are reminiscent of the symptoms observed in psychiatric diseases, such as schizophrenia, and respond positively to long-term treatment with antipsychotics. MAP6-KO mice have therefore been proposed to be a useful animal model for these diseases. Here, we explored the brain anatomy in MAP6-KO mice using high spatial resolution 3D MRI, including a volumetric T
method to image brain structures, and Diffusion Tensor Imaging (DTI) for white matter fiber tractography. 3D DTI imaging of neuronal tracts was validated by comparing results to optical images of cleared brains. Changes to brain architecture included reduced volume of the cerebellum and the thalamus and altered size, integrity and spatial orientation of some neuronal tracks such as the anterior commissure, the mammillary tract, the corpus callosum, the corticospinal tract, the fasciculus retroflexus and the fornix. Our results provide information on the neuroanatomical defects behind the neurological phenotype displayed in the MAP6-KO mice model and especially highlight a severe damage of the corticospinal tract with defasciculation at the location of the pontine nuclei.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Structural microtubule associated proteins (MAPs) stabilize microtubules, a property that was thought to be essential for development, maintenance and function of neuronal circuits. However, deletion ...of the structural MAPs in mice does not lead to major neurodevelopment defects. Here we demonstrate a role for MAP6 in brain wiring that is independent of microtubule binding. We find that MAP6 deletion disrupts brain connectivity and is associated with a lack of post-commissural fornix fibres. MAP6 contributes to fornix development by regulating axonal elongation induced by Semaphorin 3E. We show that MAP6 acts downstream of receptor activation through a mechanism that requires a proline-rich domain distinct from its microtubule-stabilizing domains. We also show that MAP6 directly binds to SH3 domain proteins known to be involved in neurite extension and semaphorin function. We conclude that MAP6 is critical to interface guidance molecules with intracellular signalling effectors during the development of cerebral axon tracts.
Etude de l'implication de CRMP4, un partenaire de MAP6, dans la voie de signalisation sémaphorine 3E.Pendant le développement embryonnaire, les neurones établissent des milliards de connexions. Ces ...connexions ne sont pas aléatoires, mais précisément orientées, dirigées par des molécules de guidage situées dans l’environnement cellulaire. Le branchement inapproprié de ces neurones a de graves conséquences sur les fonctions sensorielles, motrices et cognitives du système nerveux, aboutissant à des pathologies neurologiques et psychiatriques telle que la schizophrénie. Ainsi la mutation de certaines protéines impliquées dans le guidage de ces connexions, comme MAP6 ou CRMP4, peut entraîner des perturbations conduisant à des prédispositions pour le développement de telles pathologies. En effet l'absence de MAP6 (souris KO MAP6) conduit à l'altération de nombreuse connections neuronales associé a différents troubles comportementaux réminiscent avec des symptômes schizoïdes. Parmi les faisceaux d'axones affectés on remarque la disparition du fornix, un faisceau neuronal connu pour son implication dans la schizophrénie. Cette disparition est en partie causée, en l'absence de MAP6, par l'abolition de la signalisation induite par la molécule de guidage sémaphorine 3E (Sema3E). Dans ce projet de thèse, le lien entre MAP6 et CRMP4 dans cette voie de signalisation Sema3E à pu être établi. De plus, l'impact de l'absence de la protéine CRMP4 sur la formation du fornix a pu être caractérisé par l'étude neuroanatomique des souris KO CRMP4. Nous avons par ailleurs pu mettre en évidence de nouvelles altérations causée par l'absence de MAP6. Dans son ensemble ce travail approfondit les connaissances des défauts des connectivités des souris KO MAP6 et identifie CRMP4 comme un nouvel acteur de la signalisation Sema3E et de la formation du fornix.
Study of the involvement of the MAP6 partners, CRMP4, in the semaphorin 3E signaling pathway.During embryonic development, neurons establish billion of connections between them. Those connections are not random. On the contrary, they are precisely targeted thanks to the driving by cellular environment guidance cues. A wrong branching of those neurons can lead to dramatic impairment of sensory, motor and cognitive function of the central nervous system resulting in neurologic or psychiatric disorders such as Schizophrenia. Thus, mutation of proteins implicated on neurons guidance like MAP6 or CRMP4 can lead to susceptibility for those kind of pathology occurrence. In fact, MAP6 deletion ( MAP6 KO mice) leads to diverse neuronal connectivity alterations associated to schizophrenia-like behavior disorders. Among axonal tracts affected we notice the absence of the fornix known for its implication on Schizophrenia. In MAP6 KO mice, this fornix disruption is partly due to the loss of semaphorin 3E (Sema3E) dependant signaling pathway. This project shows the involvement of CRMP4, a partner of MAP6, in the Sema3E signaling pathway. Furthermore, it characterized the impact of the CRMP4 deletion (CRMP4 KO) on fornix formation. Finally, neuroanatomical studies allowed us to identify unknown alteration of MAP6 KO mice connectivity alteration.
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