ABSTRACT
Lissencephaly is a neurodevelopmental disorder characterized by a loss of brain surface convolutions caused by genetic variants that disrupt neuronal migration. However, the genetic origins of the disorder remain unidentified in nearly one-fifth of people with lissencephaly. Using whole-exome sequencing, we identified a de novo BAIAP2 variant, p.Arg29Trp, in an individual with lissencephaly with a posterior more severe than anterior (P>A) gradient, implicating BAIAP2 as a potential lissencephaly gene. Spatial transcriptome analysis in the developing mouse cortex revealed that Baiap2 is expressed in the cortical plate and intermediate zone in an anterior low to posterior high gradient. We next used in utero electroporation to explore the effects of the Baiap2 variant in the developing mouse cortex. We found that Baiap2 knockdown caused abnormalities in neuronal migration, morphogenesis and differentiation. Expression of the p.Arg29Trp variant failed to rescue the migration defect, suggesting a loss-of-function effect. Mechanistically, the variant interfered with the ability of BAIAP2 to localize to the cell membrane. These results suggest that the functions of BAIAP2 in the cytoskeleton, cell morphogenesis and migration are important for cortical development and for the pathogenesis of lissencephaly in humans.
Subject(s)
Lissencephaly , Animals , Humans , Mice , Brain/metabolism , Cell Movement/genetics , Cytoskeleton/metabolism , Lissencephaly/genetics , Lissencephaly/metabolism , Microtubule-Associated Proteins/genetics , Microtubule-Associated Proteins/metabolismABSTRACT
The development of the cerebral cortex involves a series of dynamic events, including cell proliferation and migration, which rely on the motor protein dynein and its regulators NDE1 and NDEL1. While the loss of function in NDE1 leads to microcephaly-related malformations of cortical development (MCDs), NDEL1 variants have not been detected in MCD patients. Here, we identified two patients with pachygyria, with or without subcortical band heterotopia (SBH), carrying the same de novo somatic mosaic NDEL1 variant, p.Arg105Pro (p.R105P). Through single-cell RNA sequencing and spatial transcriptomic analysis, we observed complementary expression of Nde1/NDE1 and Ndel1/NDEL1 in neural progenitors and post-mitotic neurons, respectively. Ndel1 knockdown by in utero electroporation resulted in impaired neuronal migration, a phenotype that could not be rescued by p.R105P. Remarkably, p.R105P expression alone strongly disrupted neuronal migration, increased the length of the leading process, and impaired nucleus-centrosome coupling, suggesting a failure in nucleokinesis. Mechanistically, p.R105P disrupted NDEL1 binding to the dynein regulator LIS1. This study identifies the first lissencephaly-associated NDEL1 variant and sheds light on the distinct roles of NDE1 and NDEL1 in nucleokinesis and MCD pathogenesis.
Subject(s)
Lissencephaly , Humans , Lissencephaly/genetics , Cell Movement/genetics , Cell Proliferation , Cerebral Cortex , Dyneins/genetics , Carrier Proteins , Microtubule-Associated Proteins/geneticsABSTRACT
Huntington's disease (HD) is a hereditary neurodegenerative disorder characterized by involuntary movements, cognitive deficits, and psychiatric symptoms. Currently, there is no cure, and only limited treatments are available to manage the symptoms and to slow down the disease's progression. The molecular and cellular mechanisms of HD's pathogenesis are complex, involving immune cell activation, altered protein turnover, and disturbance in brain energy homeostasis. Microglia have been known to play a dual role in HD, contributing to neurodegeneration through inflammation but also enacting neuroprotective effects by clearing mHTT aggregates. However, little is known about the contribution of microglial metabolism to HD progression. This study explores the impact of a microglial metabolite transporter, equilibrative nucleoside transporter 3 (ENT3), in HD. Known as a lysosomal membrane transporter protein, ENT3 is highly enriched in microglia, with its expression correlated with HD severity. Using the R6/2 ENT3-/- mouse model, we found that the deletion of ENT3 increases microglia numbers yet worsens HD progression, leading to mHTT accumulation, cell death, and disturbed energy metabolism. These results suggest that the delicate balance between microglial metabolism and function is crucial for maintaining brain homeostasis and that ENT3 has a protective role in ameliorating neurodegenerative processes.
Subject(s)
Disease Models, Animal , Disease Progression , Huntington Disease , Microglia , Nucleoside Transport Proteins , Animals , Humans , Male , Mice , Brain/metabolism , Huntingtin Protein/metabolism , Huntingtin Protein/genetics , Huntington Disease/metabolism , Huntington Disease/genetics , Mice, Inbred C57BL , Mice, Knockout , Microglia/metabolism , Nucleoside Transport Proteins/metabolism , Nucleoside Transport Proteins/geneticsABSTRACT
During the development of mammalian brains, pyramidal neurons in the cerebral cortex form highly organized six layers with different functions. These neurons undergo developmental processes such as axon extension, dendrite outgrowth, and synapse formation. A proper integration of the neuronal connectivity through dynamic changes of dendritic branches and spines is required for learning and memory. Disruption of these crucial developmental processes is associated with many neurodevelopmental and neurodegenerative disorders. To investigate the complex dendritic architecture, several useful staining tools and genetic methods to label neurons have been well established. Monitoring the dynamics of dendritic spine in a single neuron is still a challenging task. Here, we provide a methodology that combines in vivo two-photon brain imaging and in utero electroporation, which sparsely labels cortical neurons with fluorescent proteins. This protocol may help elucidate the dynamics of microstructure and neural complexity in living rodents under normal and disease conditions.
Subject(s)
Neurons , Animals , Mice , Neurons/cytology , Neurons/metabolism , Electroporation/methods , Microscopy, Fluorescence, Multiphoton/methods , Dendritic Spines/metabolism , Dendritic Spines/ultrastructure , Pyramidal Cells/metabolism , Pyramidal Cells/cytology , Female , Cerebral Cortex/cytology , Dendrites/metabolismABSTRACT
Development of the cerebellum requires precise regulation of granule neuron progenitor (GNP) proliferation. Although it is known that primary cilia are necessary to support GNP proliferation, the exact molecular mechanism governing primary cilia dynamics within GNPs remains elusive. Here, we establish the pivotal roles for the centrosomal kinase TTBK2 (Tau tubulin kinase-2) and the E3 ubiquitin ligase HUWE1 in GNP proliferation. We show that TTBK2 is highly expressed in proliferating GNPs under Sonic Hedgehog (SHH) signaling, coinciding with active GNP proliferation and the presence of primary cilia. TTBK2 stabilizes primary cilia by inhibiting their disassembly, thereby promoting GNP proliferation in response to SHH. Mechanistically, we identify HUWE1 as a novel centrosomal E3 ligase that facilitates primary cilia disassembly by targeting TTBK2 degradation. Disassembly of primary cilia serves as a trigger for GNP differentiation, allowing their migration from the external granule layer (EGL) of the cerebellum to the internal granule layer (IGL) for subsequent maturation. Moreover, we have established a link between TTBK2 and SHH-type medulloblastoma (SHH-MB), a tumor characterized by uncontrolled GNP proliferation. TTBK2 depletion inhibits SHH-MB proliferation, indicating that TTBK2 may be a potential therapeutic target for this cancer type. In summary, our findings reveal the mechanism governing cerebellar development and highlight a potential anti-cancer strategy for SHH-MB.