A single high-zinc activation enhancer can control two genes oriented head-to-head inC. elegans

Abstract

Enhancers play critical roles in gene expression, but a full understanding of their complex functions has yet to be defined. The cellular response to excess zinc levels inC. elegansrequires the HIZR-1 transcription factor, which binds the high‑zinc activation (HZA) enhancer in the promoters of multiple target genes. Cadmium hijacks the excess zinc response by binding and activating HIZR-1. By analyzing the genome-wide transcriptional response to excess zinc and cadmium, we identified two positions in the genome where head-to-head oriented genes are both induced by metals. In both examples, a single predicted HZA enhancer is positioned between the two translational start sites. We hypothesized that a single enhancer can control both head-to-head genes, an arrangement that has not been extensively characterized. To test this hypothesis, we used CRISPR genome editing to precisely delete the HZAmTenhancer positioned betweenmtl‑2andT08G5.1, and the HZAcFenhancer positioned betweencdr‑1andF35E8.10. In both examples, deleting the enhancer caused both head-to-head genes to lose metal-activated transcription, whereas the induction of more distant genes was not strongly affected. These studies rigorously document that a single HZA enhancer can control two head-to-head genes, advancing our understanding of the diverse functions of enhancers.