Identification of a Specific Granular Marker of Zebrafish Eosinophils Enables Development of New Tools for Their Study.

Eosinophils control many aspects of the vertebrate innate immune response. They contribute to homeostasis, inflammatory conditions and defense against pathogens. With the varied functions of eosinophils, they have been found to play both protective and pathogenic roles in many diseases. The zebrafish (Danio rerio) has emerged as a useful model organism for human diseases but tools to study eosinophils in this model are severely limited. Here, we characterize a new and highly specific marker gene, embp, for eosinophils in zebrafish and report a new transgenic reporter line using this gene to visualize eosinophils in vivo. In addition, we created an Embp-specific polyclonal Ab that allows the identification of eosinophils ex vivo. These new tools expand the approaches for studying eosinophils in the zebrafish model. Using these reagents, we have been able to identify Embp as a constituent of eosinophil granules in zebrafish. These advances will allow for the investigation of eosinophil biology in the zebrafish model organism, allowing researchers to identify the contribution of eosinophils to the many diseases that are modeled within zebrafish and also shed light on the evolution of eosinophils within vertebrates.