Apical complex protein Pals1 is required to maintain cerebellar progenitor cells in a proliferative state
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ABSTRACT: Through their biased localization and function within the cell, polarity complex proteins are necessary to establish the cellular asymmetry required for tissue organization. Well-characterized germinal zones, mitogenic signals, and cell types make the cerebellum an excellent model for addressing the critical function of polarity complex proteins in the generation and organization of neural tissues. Deleting apical polarity complex protein Pals1 in the developing cerebellum results in a remarkably undersized cerebellum with disrupted layers in poorly formed folia and strikingly reduced granule cell production. We demonstrate that Pals1 is not only essential for cerebellum organogenesis, but also for preventing premature differentiation and thus maintaining progenitor pools in cerebellar germinal zones, including cerebellar granule neuron precursors (CGNP) in the external granule layer (EGL). In the Pals1 mutants, expression of genes that regulate cell cycle were diminished, correlating with the loss of proliferating population of germinal zones. Furthermore, enhanced Shh signaling through activated Smoothened (Smo) cannot overcome impaired cerebellar cell generation, arguing for an epistatic role of Pals1 in proliferation capacity. Our study identifies Pals1 as a new intrinsic factor that regulates the generation of cerebellar cells and Pals1 deficiency as a potential inhibitor of overactive mitogenic signaling.
Project description:Through their biased localization and function within the cell, polarity complex proteins are necessary to establish the cellular asymmetry required for tissue organization. Well-characterized germinal zones, mitogenic signals, and cell types make the cerebellum an excellent model for addressing the critical function of polarity complex proteins in the generation and organization of neural tissues. Deleting apical polarity complex protein Pals1 in the developing cerebellum results in a remarkably undersized cerebellum with disrupted layers in poorly formed folia and strikingly reduced granule cell production. We demonstrate that Pals1 is not only essential for cerebellum organogenesis, but also for preventing premature differentiation and thus maintaining progenitor pools in cerebellar germinal zones, including cerebellar granule neuron precursors (CGNP) in the external granule layer (EGL). In the Pals1 mutants, expression of genes that regulate cell cycle were diminished, correlating with the loss of proliferating population of germinal zones. Furthermore, enhanced Shh signaling through activated Smoothened (Smo) cannot overcome impaired cerebellar cell generation, arguing for an epistatic role of Pals1 in proliferation capacity. Our study identifies Pals1 as a new intrinsic factor that regulates the generation of cerebellar cells and Pals1 deficiency as a potential inhibitor of overactive mitogenic signaling. Two groups of samples are included: mRNA obtained from 4 WT and 4 CKO animals at E17.5. hGFAP-Cre mice was used to delete Pals1 from most cerebellar neurons and glia (termed Pals1 CKO). Pals1fl/fl and hGFAP-Cre (Zhuo et al., 2001) were bred for generation of CKO.
Project description:Cerebellar development requires regulated proliferation of cerebellar granule neuron progenitors (CGNPs). Inadequate CGNP proliferation causes cerebellar hypoplasia while excessive CGNP proliferation can cause medulloblastoma, the most common malignant pediatric brain tumor. Although Sonic Hedgehog (SHH) signaling is known to activate CGNP proliferation, the mechanisms down-regulating proliferation are less defined. We investigated CGNP regulation by GSK-3, which down-regulates proliferation in the forebrain, gut and breast by suppressing mitogenic WNT signaling. In striking contrast, we found that co-deleting Gsk-3α and Gsk-3β blocked CGNP proliferation, causing severe cerebellar hypoplasia. Transcriptomic analysis showed activated WNT signaling and up-regulated Cdkn1a in Gsk-3-deleted CGNPs. These data show that a GSK-3/WNT axis modulates the developmental proliferation of CGNPs and the pathologic growth of SHH-driven medulloblastoma. The requirement for GSK-3 in SHH-driven proliferation suggests that GSK-3 may be targeted for SHH-driven medulloblastoma therapy. In this experiment, we dissociated cells from whole cerebella collected from postnatal day 1 (P1) mice with the indicated genotypes.
Project description:During cerebellar development, the main portion of the cerebellar plate neuroepithelium (NE) gives birth to Purkinje cells and interneurons, while the germinal zone at its dorsal edge, called the rhombic lip (RL), generates granule cells and cerebellar nuclei neurons. However, it remains elusive how these components work together to generate the intricate structure of the cerebellar anlage. In this study, we found that a polarized cerebellar anlage structure self-organizes in three-dimensional (3D) human ES cell (hESC) culture. This NE is capable of differentiating into electrophysiologically functional Purkinje cells. The addition of FGF19 promotes spontaneous generation of dorsoventrally polarized NE structures containing cerebellar and basal plates. Furthermore, further addition of SDF1 promoted the generation of stratified cerebellar plate NE with RL-like germinal zones self-forming at the edge. Thus, hESC-derived cerebellar progenitors exhibit substantial self-organizing potential for generating a polarized structure reminiscent of the early human cerebellar anlage at the first trimester. Examination of mRNA profile in two different treated human ES cells .
Project description:During cerebellar development, the main portion of the cerebellar plate neuroepithelium (NE) gives birth to Purkinje cells and interneurons, while the germinal zone at its dorsal edge, called the rhombic lip (RL), generates granule cells and cerebellar nuclei neurons. However, it remains elusive how these components work together to generate the intricate structure of the cerebellar anlage. In this study, we found that a polarized cerebellar anlage structure self-organizes in three-dimensional (3D) human ES cell (hESC) culture. This NE is capable of differentiating into electrophysiologically functional Purkinje cells. The addition of FGF19 promotes spontaneous generation of dorsoventrally polarized NE structures containing cerebellar and basal plates. Furthermore, further addition of SDF1 promoted the generation of stratified cerebellar plate NE with RL-like germinal zones self-forming at the edge. Thus, hESC-derived cerebellar progenitors exhibit substantial self-organizing potential for generating a polarized structure reminiscent of the early human cerebellar anlage at the first trimester.
Project description:Origins of the brain tumor, medulloblastoma, from stem cells or restricted pro-genitor cells are unclear. To investigate this, we activated oncogenic Hedgehog signaling in multipotent and lineage-restricted CNS progenitors. We observed that normal unipo-tent cerebellar granule neuron precursors (CGNP) derive from hGFAP+ and Olig2+ rhombic lip progenitors. Hedgehog activation in a spectrum of early and late stage CNS progenitors generated similar medulloblastomas, but not other brain cancers, indicating that acquisition of CGNP identity is essential for tumorigenesis. We show in human and mouse medulloblastoma that cells expressing the glia-associated markers Gfap and Olig2 are neoplastic and that they retain features of embryonic-type granule lineage progenitors. Thus, oncogenic Hedgehog signaling promotes medulloblastoma from lineage-restricted granule cell progenitors. Gene expression profiling of cerebellar tumors generated from various early and late stage CNS progenitor cells. Experiment Overall Design: Group comparisons with biological replicates
Project description:Neurons within the cerebellum form temporal-spatial connections through the cerebellum, and the entire brain. Organoid models provide an opportunity to model the early differentiation of the developing human cerebellum, which is difficult to study in vivo, and affords the opportunity to study neurodegenerative and neurodevelopmental diseases of the cerebellum. Previous cerebellar organoid models focused on early neuron generation and single cell activity. Here, we modify previous protocols to generate more mature cerebellar organoids that allow for the establishment of several classes of mature neurons during cerebellar differentiation and development, including the establishment of neural networks during whole organoid maturation. This will provide a means to study the generation of several more mature cerebellar cell types, including Purkinje cells, granule cells, interneurons expression as well as neuronal communication for biomedical, clinical, and pharmaceutical application.
Project description:Origins of the brain tumor, medulloblastoma, from stem cells or restricted pro-genitor cells are unclear. To investigate this, we activated oncogenic Hedgehog signaling in multipotent and lineage-restricted CNS progenitors. We observed that normal unipo-tent cerebellar granule neuron precursors (CGNP) derive from hGFAP+ and Olig2+ rhombic lip progenitors. Hedgehog activation in a spectrum of early and late stage CNS progenitors generated similar medulloblastomas, but not other brain cancers, indicating that acquisition of CGNP identity is essential for tumorigenesis. We show in human and mouse medulloblastoma that cells expressing the glia-associated markers Gfap and Olig2 are neoplastic and that they retain features of embryonic-type granule lineage progenitors. Thus, oncogenic Hedgehog signaling promotes medulloblastoma from lineage-restricted granule cell progenitors. Gene expression profiling of cerebellar tumors generated from various early and late stage CNS progenitor cells.
Project description:Govek et al. demonstrate conditional loss of Cdc42 in cerebellar granule cell progenitors (GCPs) perturbs GCP polarity and impairs axon patterning, glial-guided migration, and cerebellar foliation. Phospho-proteomic analysis identified polarity and cytoskeletal proteins as affected targets in Cdc42 deficient GCPs.
Project description:It is generally believed that cerebellar granule neurons originate exclusively from granule neuron precursors (GNPs) in the external germinal layer (EGL). Here we identify a rare population of neuronal progenitors in the developing cerebellum that expresses Nestin. Although Nestin is widely considered a marker for multipotent stem cells, these Nestin-expressing progenitors (NEPs) are committed to the granule neuron lineage. Unlike conventional GNPs, which reside in the outer EGL and proliferate extensively, NEPs reside in the deep part of the EGL and are quiescent. Expression profiling reveals that NEPs are distinct from GNPs, and in particular, express markedly reduced levels of genes associated with DNA repair. Consistent with this, upon aberrant activation of Sonic hedgehog (Shh) signaling, NEPs exhibit more severe genomic instability and give rise to tumors more efficiently than GNPs. These studies identify a novel progenitor for cerebellar granule neurons and a novel cell of origin for medulloblastoma.
Project description:The cerebellum is a brain structure involved in motor and cognitive functions. The development of the cerebellar cortex (the external part of the cerebellum) is under the control of numerous factors. Among these factors, neuropeptides including PACAP or somatostatin modulate the survival, migration and/or differentiation of cerebellar granule cells. Interestingly, such peptides contributing to cerebellar ontogenesis usually exhibit a specific transient expression profile with a low abundance at birth, a high expression level during the developmental processes, which take place within the first two postnatal weeks in rodents, and a gradual decline toward adulthood. Thus, to identify new peptides transiently expressed in the cerebellum during development, rat cerebella were sampled from birth to adulthood, and analyzed by a semi-quantitative peptidomic approach. A total of 33 peptides were found to be expressed in the cerebellum. Among these 33 peptides, 8 had a clear differential expression pattern during development, 4 of them i.e. cerebellin 2, nociceptin, somatostatin and VGF [353-372], exhibiting a high expression level during the first two postnatal weeks followed by a significative decrease at adulthood. A focus by a genomic approach on nociceptin, confirmed that the precursor mRNA is transiently expressed during the first week of life in granule neurons within the internal granule cell layer of the cerebellum, and showed that the nociceptin receptor is also actively expressed between P8 and P16 by the same neurons. Finally, functional studies revealed a new role for nociceptin, acting as a neurotrophic peptide able to promote the survival and differentiation of developing cerebellar granule neurons.