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, maternal granule cell progenitors (GCPs) divide to produce not only postmitotic granule cells (GCs) but also sister GCPs. However, molecular machinery to proportionally produce distinct sister cell types from seemingly uniform GCPs is still elusive. Here we report Notch signaling makes a difference among GCPs, leading to their proportional differentiation.
Project description:The two vertebrate Gsk-3 isoforms, Gsk-3a and Gsk-3b, are encoded by distinct genetic loci and exhibit mostly redundant function in murine embryonic stem cells (ESCs). Here we report that deletion of both Gsk-3a and Gsk-3b in mouse ESCs results in significant changes in gene expression. In contrast, deletion of either Gsk-3a or Gsk-3b individually had little effect on gene expression. These data support the notion that Gsk-3 isoforms are functionally redundant in embryonic stem cells. In addition, we did not find the expected upregulation of known Wnt target genes. Our data suggests that Gsk-3-meidated regulation of gene expression in embryonic stem cells is complex, and likely involves affects on numerous signaling pathways. The study was designed to examine the changes in gene expression between wild-type, Gsk-3a-/-, Gsk-3b-/-, and Gsk-3a-/-;Gsk-3b-/- mouse embryonic stem cells.
Project description:Microcephaly and medulloblastoma result from mutations that compromise genomic stability. We report that Atr, which is mutated in the microcephalic disorder Seckel syndrome, is required to maintain chromosomal integrity during postnatal cerebellar neurogenesis. Atr deletion in cerebellar granule neuron progenitors (CGNPs) induced proliferation-associated DNA damage, p53 activation, apoptosis, and cerebellar hypoplasia. Co-deletions of either Bax and Bak or p53 prevented apoptosis in Atr-deleted CGNPs, but failed to fully rescue cerebellar growth. Atr-deficient CGNPs showed impaired cell cycle checkpoint function and continued to proliferate, accumulating chromosomal abnormalities. RNA-Seq demonstrated that the transcriptional response to Atr-deficient proliferation was p53-driven. Acute Atr inhibition in vivo by nanoparticle-formulated VE-822 reproduced the disruptions seen with Atr deletion. Our data show that p53-driven apoptosis and senescence, and non-apoptotic cell death redundantly limit growth in Atr-deficient progenitors. These overlapping mechanisms that suppress growth in Atr-disrupted CGNPs may be exploited for treatment of CGNP-derived medulloblastoma using Atr inhibition.
Project description:We set out to ascertain whether it was possible to use PSCs (pluripotent stem cells) to generate a mix of neuronal cell types resembling those in the cerebellum, most notably Purkinje and granule cells. Several groups have previously demonstrated generation of cerebellar-like neuronal cells from murine ESCs (embryonic stem cells), and more recently the Erceg group achieved similar success using human PSCs. Using principles from these studies we successfully induced expression of mid–hindbrain markers EN1 & GBX2 and later MATH1 (a transcription factor which marks rhombic lip/granule cell progenitors) in a mixed neuronal population derived from hPSCs. Further, we show that it is possible to expand these progenitors to produce spontaneously active neuronal cells with morphological similarities to neuronal cells at specific stages of cerebellar development. Based on morphology, electrophysiology, immunohistochemistry and transcriptomic analysis we demonstrate that these cells express behavior, markers and molecular signatures consistent with distinct epochs of cerebellar development spanning from the late embryonic to early postnatal periods. This study describes an in vitro model that provides insight into the early events that drive the formation of the human cerebellum with support from a high-resolution survey of the trancriptomic landscape, including expression of non-coding RNAs and specific transcript isoforms. The generated datasets and accompanying characterization are a valuable resource for researchers to formulate and test hypotheses regarding the molecular players that are involved in the formation of the cerebellum
Project description:Microcephaly and medulloblastoma result from mutations that compromise genomic stability. We report that Atr, which is mutated in the microcephalic disorder Seckel syndrome, is required to maintain chromosomal integrity during postnatal cerebellar neurogenesis. Atr deletion in cerebellar granule neuron progenitors (CGNPs) induced proliferation-associated DNA damage, p53 activation, apoptosis, and cerebellar hypoplasia. Co-deletions of either Bax and Bak or p53 prevented apoptosis in Atr-deleted CGNPs, but failed to fully rescue cerebellar growth. Atr-deficient CGNPs showed impaired cell cycle checkpoint function and continued to proliferate, accumulating chromosomal abnormalities. RNA-Seq demonstrated that the transcriptional response to Atr-deficient proliferation was p53-driven. Acute Atr inhibition in vivo by nanoparticle-formulated VE-822 reproduced the disruptions seen with Atr deletion. Our data show that p53-driven apoptosis and senescence, and non-apoptotic cell death redundantly limit growth in Atr-deficient progenitors. These overlapping mechanisms that suppress growth in Atr-disrupted CGNPs may be exploited for treatment of CGNP-derived medulloblastoma using Atr inhibition.
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:The two vertebrate Gsk-3 isoforms, Gsk-3a and Gsk-3b, are encoded by distinct genetic loci and exhibit mostly redundant function in murine embryonic stem cells (ESCs). Here we report that deletion of both Gsk-3a and Gsk-3b in mouse ESCs results in significant changes in gene expression. In contrast, deletion of either Gsk-3a or Gsk-3b individually had little effect on gene expression. These data support the notion that Gsk-3 isoforms are functionally redundant in embryonic stem cells. In addition, we did not find the expected upregulation of known Wnt target genes. Our data suggests that Gsk-3-meidated regulation of gene expression in embryonic stem cells is complex, and likely involves affects on numerous signaling pathways.