Transcriptional control of differentiation in cerebellar granule neurons and medulloblastoma

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Cerebellar granule neurons (GN), the most numerous neurons in the brain (~5 x 1010 in humans) mediate critical steps in motor control and motor learning. They arise from symmetric division of progenitors known as granule neuron precursor cells (GNPs). GNP terminal differentiation involves cell cycle exit, extension of processes, nuclear migration, and synapse formation with mossy fibers and Purkinje cells. Much remains to be learned about how gene regulation underlies neurogenesis steps like migration or neurite extension during GNP differentiation. Increasing, our understanding of GNP differentiation could have important therapeutic importance for children with brain tumors. Medulloblastoma is the most common malignant brain tumor in children and the SHH subtype of medulloblastoma arises from the cerebellar GN lineage. If we can identify what regulates differentiation in GNPs these processes could be targeted to induce differentiation of medulloblastoma cell. We have combined gene transcription data over the course of GN differentiation with measures of chromatin features such as histone marks, DNA methylation and DNA accessibility in proliferating GNPs. Of the genes that increase as GNPs terminally differentiate, more than half the genes are marked by H3K27me3 near their promoters, implying repression by the protein complex PRC2. Genetic inactivation of Ezh2, which encodes the enzyme that catalyzes formation of H3K27me3, resulted in GNPs leaving the external granule cell layer prematurely. while not affecting cell cycle exit. Ezh2 the catalytic methyltransferase of the repressive PRC2 complex shows the most substantial transcriptional decrease of the genes that are known to directly or indirectly effect H3K27me3. A normal role of Ezh2 is therefore to restrain GNP radial migration. Shh medulloblastoma tumors arise from cells within the GN lineage. Mice, which are heterozygous for Ptch1 will develop spontaneous medulloblastoma. In medulloblastoma cells from Ptch1+/- mice, ¾ of the H3K27me3 marked GN differentiation genes are persistently marked with H3K27me3 and the majority did not show an increase in transcription in MB compared to the dividing GNPs. In human SHH subtype medulloblastoma, the EZH2 transcript varies, with low EZH2 transcript being associated with higher expression of the differentiation genes and better survival. PRC2 mediated repression of differentiation genes seen in GNPs is ongoing in medulloblastoma. As with GNPs, Ezh2 inhibition in actively dividing Ptch1+/-MB cells did not induce differentiation. Combining a cell cycle inhibitor with the Ezh2 inhibitor, did allow differentiation of the tumor cells as measured by morphology and gene expression markers. Thus Ezh2 delays transcription of a set of differentiation genes in GNPs which, when depressed in MB cause differentiation preventing re-entry into cell cycle.


Type of resource text
Form electronic resource; remote; computer; online resource
Extent 1 online resource.
Place California
Place [Stanford, California]
Publisher [Stanford University]
Copyright date 2018; ©2018
Publication date 2018; 2018
Issuance monographic
Language English


Author Purzner, James
Degree supervisor Fuller, Margaret T, 1951-
Thesis advisor Fuller, Margaret T, 1951-
Thesis advisor Crabtree, Gerald R
Thesis advisor Meyer, Tobias
Thesis advisor Wysocka, Joanna, Ph. D
Degree committee member Crabtree, Gerald R
Degree committee member Meyer, Tobias
Degree committee member Wysocka, Joanna, Ph. D
Associated with Stanford University, Department of Developmental Biology.


Genre Theses
Genre Text

Bibliographic information

Statement of responsibility James Purzner.
Note Submitted to the Department of Developmental Biology.
Thesis Thesis Ph.D. Stanford University 2018.
Location electronic resource

Access conditions

© 2018 by James G Purzner
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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