Dataset Information

MiR-34a is dispensable for normal development but its loss accelerates medulloblastoma formation

ABSTRACT: Previous studies have evaluated the role of miRNAs in the initiation and progression of cancer. MiR-34a was found to be downregulated in several tumors, including medulloblastoma. We here analysed the function of miR-34a in vivo by targeted transgenesis to generate mice with constitutive deletion of the miR-34a gene, which resulted in the absence of mir-34a in all analysed tissues. Nevertheless, these mice were viable and fertile. A comprehensive standardized phenotypic analysis including more than 300 single parameters performed by the German Mouse Clinic revealed no apparent phenotype. Analysis of miR-34a expression in human medulloblastomas and medulloblastoma cell lines revealed significant downregulation as compared to human cerebellum. Re-expression of mir-34a in human medulloblastoma cells in vitro reduced cell viability, cell proliferation and induced apoptosis. Among the targets downregulated by miR-34a in human medulloblastoma cells were NMYC and SIRT1. Activation of the Shh pathway by targeted overexpression of SmoA1 causes medulloblastoma in mice, which is dependent on the presence and upregulation of NMYC. Analysis of miR-34a in ND2:SmoA1-derived medulloblastomas revealed significant suppression of miR-34a compared to normal cerebellum. Crossbreeding these mice with miR-34a knockout mice significantly accelerated medulloblastoma growth in mice deficient for miR-34a. Interestingly, NMYC and SIRT1 were highly expressed in medulloblastomas derived from these mice. We here demonstrate that miR-34a is dispensable for normal development, but that its loss accelerates medulloblastoma. Strategies aiming to re-express miR-34a in tumors could therefore represent an efficient therapy option.

ORGANISM(S): Mus musculus

PROVIDER: GSE40511 | GEO | 2014/09/22

SECONDARY ACCESSION(S): PRJNA174321

REPOSITORIES: GEO

ACCESS DATA

Dataset's files

Source:

			Action	DRS
		Other

Items per page:

1 - 1 of 1

Similar Datasets

Project description:Previous studies have evaluated the role of miRNAs in the initiation and progression of cancer. MiR-34a was found to be downregulated in several tumors, including medulloblastoma. We here analysed the function of miR-34a in vivo by targeted transgenesis to generate mice with constitutive deletion of the miR-34a gene, which resulted in the absence of mir-34a in all analysed tissues. Nevertheless, these mice were viable and fertile. A comprehensive standardized phenotypic analysis including more than 300 single parameters performed by the German Mouse Clinic revealed no apparent phenotype. Analysis of miR-34a expression in human medulloblastomas and medulloblastoma cell lines revealed significant downregulation as compared to human cerebellum. Re-expression of mir-34a in human medulloblastoma cells in vitro reduced cell viability, cell proliferation and induced apoptosis. Among the targets downregulated by miR-34a in human medulloblastoma cells were NMYC and SIRT1. Activation of the Shh pathway by targeted overexpression of SmoA1 causes medulloblastoma in mice, which is dependent on the presence and upregulation of NMYC. Analysis of miR-34a in ND2:SmoA1-derived medulloblastomas revealed significant suppression of miR-34a compared to normal cerebellum. Crossbreeding these mice with miR-34a knockout mice significantly accelerated medulloblastoma growth in mice deficient for miR-34a. Interestingly, NMYC and SIRT1 were highly expressed in medulloblastomas derived from these mice. We here demonstrate that miR-34a is dispensable for normal development, but that its loss accelerates medulloblastoma. Strategies aiming to re-express miR-34a in tumors could therefore represent an efficient therapy option. For genome-wide expression analysis total RNA from brain and thymus of three or four male miR34a and four control mice was isolated using RNeasy Midi kit (Qiagen, Hilden, Germany). The cDNA microarrays were generated, hybridized and analysed as described (Horsch et al 2009). Two chip hybridizations were performed with total RNA for each individual mutant mouse against a reference RNA pool of the same organ.

Project description:Deregulated developmental processes in the cerebellum cause medulloblastoma, the most common malignant tumor of the central nervous system. About 20-30% of cases are caused by mutations increasing the activity of the Sonic hedgehog (Shh) pathway, a critical mitogen in cerebellar development. The proto-oncogene Smoothened is a key transducer of the Shh pathway. Activating mutations in Smoothened that lead to constitutive activity of the Shh pathway have been identified in human medulloblastoma. To understand the molecular and cellular effects of Smoothened variants in normal development and medulloblastoma genesis, we generated the SmoA2 transgenic mouse model which expresses the transgene exclusively in granule neuron precursors. In this study, we demonstrate how two point mutations in a single molecule can produce starkly different phenotypes as seen in comparison to our previous model, ND2:SmoA1. The SmoA2 mice have severe aberrations in cerebellar development whereas the SmoA1 mice are largely normal during development. Medulloblastomas in the SmoA2 mice develop in the dysplastic cerebellar milieu. Intriguingly, despite disruptions in the stereotypic organization of the cerebellum, the SmoA2 mice do not exhibit any overt abnormalities in motor coordination. The differences in the global transcriptional profiles downstream of SmoA1 and SmoA2 further demonstrate the distinctiveness of the two oncogenic Smoothened mutations. The SmoA2 model serves as a unique spatiotemporal tool to investigate the functional significance of the reiterative cerebellar circuitry as well as to further understand Shh pathway mechanics in cerebellar development and oncogenesis. We previously generated a SmoA1 transgenic mouse medulloblastoma model, which expresses the SmoA1 transgene driven by the GNP-specific fragment of the promoter of ND2 transcription factor leading to constitutively active Shh signaling exclusively in the cerebellum. In this study, we characterize the ND2:SmoA2 transgenic mouse model with a similarly designed transgene expressing the SmoA2 mutation. To assess transcriptional changes downstream of SmoA1 and SmoA2, we evaluated global gene expression profiles of P5 SmoA1, SmoA2 and Wt age-matched cerebella. We chose this specific developmental stage because (1) the phenotypes of SmoA1 and SmoA2 are robust and distinct at P5; (2) at P5 GNPs undergo proliferation, migration and differentiation and therefore expression profiling could capture key differences in multiple processes.

Project description:Medulloblastoma encompasses a collection of clinically and molecularly diverse tumor subtypes that together comprise the most common malignant childhood brain tumor. These tumors are thought to arise within the cerebellum, with approximately 25% originating from granule neuron precursor cells (GNPCs) following aberrant activation of the Sonic Hedgehog pathway (hereafter, SHH-subtype). The pathological processes that drive heterogeneity among the other medulloblastoma subtypes are not known, hindering the development of much needed new therapies. Here, we provide evidence that a discrete subtype of medulloblastoma that contains activating mutations in the WNT pathway effector CTNNB1 (hereafter, WNT-subtype), arises outside the cerebellum from cells of the dorsal brainstem. We found that genes marking human WNT-subtype medulloblastomas are more frequently expressed in the lower rhombic lip (LRL) and embryonic dorsal brainstem than in the upper rhombic lip (URL) and developing cerebellum. Magnetic resonance imaging (MRI) and intra-operative reports showed that human WNT-subtype tumors infiltrate the dorsal brainstem, while SHH-subtype tumors are located within the cerebellar hemispheres. Activating mutations in Ctnnb1 had little impact on progenitor cell populations in the cerebellum, but caused the abnormal accumulation of cells on the embryonic dorsal brainstem that included aberrantly proliferating Zic1+ precursor cells. These lesions persisted in all mutant adult mice and in 15% of cases in which Tp53 was concurrently deleted, progressed to form medulloblastomas that recapitulated the anatomy and gene expression profiles of human WNT-subtype medulloblastoma. We provide the first evidence that subtypes of medulloblastoma have distinct cellular origins. Our data provide an explanation for the marked molecular and clinical differences between SHH and WNT-subtype medulloblastomas and have profound implications for future research and treatment of this important childhood cancer. A total of 16 samples are analyzed, repsresenting 4 experimental groups: Ctnnb1 medulloblastoma (3 samples); Ptch1 medulloblastoma (6 samples); embryonic dorsal brainstem (4 samples); and postnatal granule neuron precursor cells (3 samples). Every sample was prepared from a different mouse.

Dataset Information

MiR-34a is dispensable for normal development but its loss accelerates medulloblastoma formation

Dataset's files

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets