Expression of zebrafish anterior gradient 2 in the semicircular canals and supporting cells of otic vesicle sensory patches is regulated by Sox10.

AGR2 is a member of the protein disulfide isomerase (PDI) family, which is implicated in cancer cell growth and metastasis, asthma, and inflammatory bowel disease. Despite the contributions of this protein to several biological processes, the regulatory mechanisms controlling expression of the AGR2 gene in different organs remain unclear. Zebrafish anterior gradient 2 (agr2) is expressed in several organs, including the otic vesicles that contain mucus-secreting cells. To elucidate the regulatory mechanisms controlling agr2 expression in otic vesicles, we generated a Tg(-6.0 k agr2:EGFP) transgenic fish line that expressed EGFP in a pattern recapitulating that of agr2. Double immunofluorescence studies were used to demonstrate that Agr2 and GFP colocalize in the semicircular canals and supporting cells of all sensory patches in the otic vesicles of Tg(-6.0 k agr2:EGFP) embryos. Transient/stable transgenic analyses coupled with 5'-end deletion revealed that a 100 bp sequence within the -2.6 to -2.5 kbp region upstream of agr2 directs EGFP expression specifically in the otic vesicles. Two HMG-binding motifs were detected in this region. Mutation of these motifs prevented EGFP expression. Furthermore, EGFP expression in the otic vesicles was prevented by knockdown of the sox10 gene. This corresponded with decreased agr2 expression in the otic vesicles of sox10 morphants during different developmental stages. Electrophoretic mobility shift assays were used to show that Sox10 binds to HMG-binding motifs located within the -2.6 to -2.5 kbp region upstream of agr2. These results demonstrate that agr2 expression in the otic vesicles of zebrafish embryos is regulated by Sox10.