Epigenetic regulators Rbbp4 and Hdac1 are overexpressed in a zebrafish model of RB1 embryonal brain tumor, and are required for neural progenitor survival and proliferation

Abstract

<p>In this study, we used comparative genomics and developmental genetics to identify epigenetic regulators driving oncogenesis in a zebrafish <em>retinoblastoma 1</em> (<em>rb1</em>) somatic-targeting model of RB1 mutant embryonal brain tumors. Zebrafish <em>rb1</em> brain tumors caused by TALEN or CRISPR targeting are histologically similar to human central nervous system primitive neuroectodermal tumors (CNS-PNETs). Like the human oligoneural <em>OLIG2+/SOX10+</em> CNS-PNET subtype, zebrafish <em>rb1</em> tumors show elevated expression of neural progenitor transcription factors <em>olig2</em>, <em>sox10</em>, <em>sox8b</em> and the receptor tyrosine kinase <em>erbb3a</em> oncogene. Comparison of <em>rb1</em> tumor and <em>rb1/rb1</em> germline mutant larval transcriptomes shows that the altered oligoneural precursor signature is specific to tumor tissue<strong>.</strong> More than 170 chromatin regulators were differentially expressed in <em>rb1</em> tumors, including overexpression of chromatin remodeler components <em>histone deacetylase 1</em> (<em>hdac1</em>) and <em>retinoblastoma binding protein 4</em>(<em>rbbp4</em>). Germline mutant analysis confirms that zebrafish <em>rb1</em>, <em>rbbp4</em> and <em>hdac1</em> are required during brain development. <em>rb1</em> is necessary for neural precursor cell cycle exit and terminal differentiation, <em>rbbp4</em> is required for survival of postmitotic precursors, and <em>hdac1</em> maintains proliferation of the neural stem cell/progenitor pool. We present an <em>in vivo</em> assay using somatic CRISPR targeting plus live imaging of histone-H2A.F/Z-GFP fusion protein in developing larval brain to rapidly test the role of chromatin remodelers in neural stem and progenitor cells. Our somatic assay recapitulates germline mutant phenotypes and reveals a dynamic view of their roles in neural cell populations. Our study provides new insight into the epigenetic processes that might drive pathogenesis in RB1 brain tumors, and identifies Rbbp4 and its associated chromatin remodeling complexes as potential target pathways to induce apoptosis in RB1 mutant brain cancer cells.</p>