aip Mutant Zebrafish Display Morphological and Transcriptional Changes Associated with Stress-Induced Hematopoiesis

The Aryl Hydrocarbon Receptor (AHR) is a versatile receptor that binds various compounds, triggering downstream transcriptional changes involved in the regulation of xenobiotic metabolism and cell fate. The Ahr Interacting Protein (AIP), also known as XAP2 and ARA9, is a molecular chaperone essential for the cytosolic retention and stabilization of the AHR. Past studies, and AIP-linked human pathologies, suggest an alternative developmental role of the AIP apart from the AHR and canonical xenobiotic response. A null mutation of the AIP in zebrafish larvae (designated as aip^wh86) resulted in craniofacial malformations, failure to inflate the swim bladder, and an enlarged and darkened liver, emerging at 5-6 days post-fertilization (dpf). Histopathological analysis at 5 dpf suggested no histological differences in the homozygous (HMZ) mutant compared to the wild type (WT). Whole-larvae RNA sequencing at 6 and 7 dpf showed significant dysregulation of key transcripts in the mutant larvae compared to WT, with pathway analysis revealing alterations in embryonic hematopoiesis and cardiac development. RT-qPCR validation showed that transcripts involved in the Hif-mediated pathway were overexpressed as early as 5 dpf. O-dianisidine staining at 6 dpf showed an increase in hemoglobin within the liver and cardiac regions of the mutant AIP larvae. This study demonstrates the complex and diverse role of AIP in vertebrate embryonic development and physiology.