Combined whole-mount in situ hybridization and immunohistochemistry in avian embryos

The whole-mount in situ hybridization process has revolutionized the study of gene expression in the embryo. This procedure allows extremely sensitive detection of RNA transcripts and excellent spatial resolution. Numerous experiments benefit from the detection of more than one marker molecule in the same experimental embryo. While antisense RNA probes are extremely useful and methods for two-color in situ hybridization are available, antibodies recognizing specific protein species can help to expand the range of markers detected. Here we present a protocol that permits the simultaneous localization of RNA transcripts and immunocytochemical localization of proteins in the chick embryo.