Imaging Nuclear Clusters in Live Zebrafish Embryos.

The transcriptional machinery of a cell is often not homogenously distributed but rather forms clusters in the nucleus. These clusters are important for gene expression, but how they form and function is often not clear. The zebrafish embryo provides an excellent system to study these clusters of transcriptional machinery, because embryos are transparent and develop rapidly, making it easy to track proteins as they cluster and perform their function. Here, we provide a protocol for how to image nuclear clusters in living zebrafish embryos. The protocol includes information on the selection and encoding of proteins and fluorophores, embryo-embedding for live-cell microscopy, the use of a spinning disk microscope, staging of embryos post image acquisition, and image analysis. While the protocol is written in the context of our work with early zebrafish embryos, many of the tools will be useful in other contexts.