RNA-seq analysis of gene regulation by miR-34a and expression changes induced by DNA damage in zebrafish

Li-Fraumeni syndrome (LFS) is a disorder due to inherited mutations in the TP53 gene resulting in an increased risk of developing several types of cancer. MicroRNA miR-34a has been implicated downstream of p53 on the basis of being a direct transcriptional target and, when over-expressed, having pro-apoptotic phenotypes in cell lines. Moreover, miR-34a has been shown to be a modifier gene in the context of LFS, since its epigenetic silencing increases the likelihood of tumour development in patients with mutant TP53. However, the in vivo consequences of miR-34 loss are still unclear. For example, mice lacking all three (a,b,c) miR-34 homologs show no detectable abnormalities in p53 responses. The relative expression of different miR-34 genes in zebrafish was studied using qRT-PCR with specific assays. The miR-34a, miR-34b and miR-34c display unique onset of developmental expression and expression levels, with miR-34a being the most abundant and constant in expression. All of the miR-34 genes also showed clear induction by p53 when DNA-damaging treatments are performed. Using CRISPR-Cas9 technology, we generated a zebrafish miR-34a deletion mutant to further investigate the roles of miR-34a on its own and its association with the p53 pathway. Predictably, a miR-34a deletion mutant demonstrated absence of miR-34a, though without miR-34b and miR-34c compensation beyond baseline expression levels. Mutants survive to adulthood, show no overt phenotypes and have normal apoptotic responses to DNA-damaging irradiation or camptothecin treatments. To further explore the effects of miR-34a, we performed gene expression profiling using RNA-seq of wild-type and miR-34a deletion mutant zebrafish embryos at 28 hpf with or without treatment with a DNA-damaging drug camptothecin. The results of this RNA-seq experiments showed that the loss of miR-34a does not strongly affect induction of genes by DNA-damage. However, the overall pattern of gene expression is significantly different as shown by Principal Component Analysis and there is a group of about 100 genes which are differentially expressed due to loss of miR-34a. The dataset we present in this submission was used to reach these conclusions. Zebrafish embryos at 24 hpf of wild-type and miR-34a-/- genotypes were dechorionated and the control (DMSO) or 1 uM camptothecin treatment for 4 hours was performed followed by RNA extraction from all samples.