Knockdown of a Zebrafish Aryl Hydrocarbon Receptor Repressor (AHRRa) Affects Expression of Genes Related to Photoreceptor

The aryl hydrocarbon receptor repressor (AHRR) is a tran-scriptional repressor of aryl hydrocarbon receptor (AHR) and hypoxia-inducible factor (HIF) and is regulated by an AHR-dependent mechanism. Zebrafish (Danio rerio) possess two AHRR paralogs; AHRRa regulates constitutive AHR signaling during de-velopment, whereas AHRRb regulates polyaromatic hydrocarbon-induced gene expression. However, little is known about the en-dogenous roles and targets of AHRRs. The objective of this study was to elucidate the role of AHRRs during zebrafish develop-ment using a loss-of-function approach followed by gene expression analysis. Zebrafish embryos were microinjected with morpholino oligonucleotides against AHRRa or AHRRb to knockdown AHRR protein expression. At 72 h postfertilization (hpf), microarray anal-ysis revealed that the expression of 279 and 116 genes was altered by knockdown of AHRRa and AHRRb, respectively. In AHRRa