Using modified whole-mount hybridization to study expression in zebrafish.

In this study, we cloned the myeloperoxidase () gene of zebrafish and prepared a digoxigenin-labeled RNA probe to investigate gene expression in zebrafish during embryonic development by whole-mount hybridization (WISH). The earliest expression was detected in cells of the intermediate cell mass (ICM) at 18 h post-fertilization (hpf). It was detected 1 to 2 h later in cells in the rostral blood island (RBI) and strong signals were observed in the anterior ICM. Then, it spread over the yolk sac. By 72 hpf these -expressing cells were in the circulation and distributed throughout the embryo. We identified that the level of expression detected by WISH at an early stage was consistent with the data of cytological analyses of adult fish. The use of this method enabled us to track the gene changes that took place before morphological phenotypes were detected, as well to as investigate the hematopoietic cell fate in mutational or transgenic models . In this study, we modified several steps of WISH. The improved hybridization results demonstrated high specificity, distinct coloration and low background figures.