<em>In Situ</em> Hybridization Combined with Immunohistochemistry in Cryosectioned Zebrafish Embryos

As a vertebrate, the zebrafish has been widely used in biological studies. Zebrafish and humans share high genetic homology, which allows its use as a model for human diseases. Gene function study is based on the detection of gene expression patterns. Although immunohistochemistry offers a powerful way to assay protein expression, the limited number of commercially available antibodies in zebrafish restricts the application of costaining. In situ hybridization is widely used in zebrafish embryos to detect mRNA expression. This protocol describes how to obtain images by combining in situ hybridization and immunohistochemistry for zebrafish embryo sections. In situ hybridization was performed prior to cryosectioning, followed by antibody staining. Immunohistochemistry and the imaging of a single cryosection were performed after in situ hybridization. The protocol is helpful to unravel the expression pattern of two genes, first by in situ transcript detection and then by immunohistochemistry against a protein in the same section.