The transcription factor IIH (TFIIH) is a complex of ten proteins essential for the transcription of protein-coding genes and for DNA nucleotide excision repair (NER). Two of the core proteins, XPB/ERCC3 and XPD/ERCC2, exhibit 3′–5′ DNA helicase activity and contribute to the unwinding of DNA during RNA Pol2-mediated transcription and NER.
Through an ENU mutagenesis screen, we identified a zebrafish mutant, sycorax, with a single point mutation in gtf2h4, which encodes the TFIIH p52 protein that directly interacts with XPB. Loss of p52 expression during sycorax development results in a dysplastic intestinal epithelium comprising multi-layered, unpolarised cells, with a greater proportion of cells in S phase, compared to wild-type.
To study the impact of p52 depletion on transcription, RNA-seq was performed on individual, micro-dissected intestines from wild-type and sycorax larvae. Using locally developed software for differential expression and gene set enrichment analysis (Subread, edgeR, ROAST), we found that the intestine-specific transcriptome in sycorax contains 759 and 731 up-regulated and down-regulated genes, respectively. Interestingly, a significant upregulation of genes participating in mRNA splicing, transcription elongation and RNA processing components was identified, while genes that participate in metabolic and digestive functions were downregulated, indicative of impaired intestinal epithelial cell differentiation. These phenotypic and gene expression features are reminiscent of cancer cells.
As yet, the specific role of p52 has not been determined. Our zebrafish mutant provides an excellent in vivo model with which to study the function of p52 in the TFIIH complex during organogenesis, and to determine whether dysregulation of this role is relevant to cancer.