1. The Aryl Hydrocarbon Receptor and Cerebellar Granule Cell Neurogenesis: Implications for Development and Medulloblastoma Pathogenesis
- Author
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Dever, Daniel Patrick, Opanashuk, Lisa A., Dever, Daniel Patrick, and Opanashuk, Lisa A.
- Abstract
Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Environmental Medicine, 2014., The aryl hydrocarbon receptor (AhR) is a ligand-activated member of the basic-helixloop- helix (bHLH)/PER-ARNT-SIM transcription factor superfamily that mediates 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) toxicity. Increasing evidence suggests that AhR endogenously influences the development of many tissues, including the central nervous system (CNS). Previous data from our laboratory demonstrated that inappropriate and/or sustained AhR activation by TCDD disrupted cerebellar granule neuron precursor (GNP) proliferation and differentiation, whereas AhR deletion produced abnormal GNP maturation. These observations led to the hypothesis that the AhR endogenously controls GNP proliferation and/or differentiation in a cell autonomous manner. To test this hypothesis, GNP-specific AhR deletion mice (AhR CKO) were generated utilizing the Cre-LoxP conditional knockout strategy. GNPs in AhR CKO exclusively expressed Cre recombinase in the developing cerebellum, which excised AhR alleles and subsequently produced marked decreases in protein expression. Selective AhR deletion was associated with reduced GNP proliferation as demonstrated by a reduction of cells in the S (BrdU) and G2/M (pH3) phases in vivo, as well as diminished DNA synthesis (3H-thymidine) in vitro. Moreover, total granule neurons, at PND21 and PND60, were diminished in AhR CKO cerebella. These observations suggest that AhR maintains GNPs in their cycling state to regulate final granule cell numbers. Interestingly, abnormal proliferating GNPs are thought to give rise to medulloblastoma (MB), which is a devastating primary pediatric cerebellar tumor. Because loss of AhR expression reduced GNP proliferation, additional studies tested the hypothesis that AhR promotes the growth of human MB cells. Therefore, a stable AhR knockdown MB (DAOY) cell line (AhR shRNA) was produced, which exhibited a 70% reduction in AhR protein levels. Compared to wild type DAOY cells, AhR shRNA DAOY cells displayed an impaired G1 to S
- Published
- 2014