Two methods that permit scientists to examine critical stages in early embryogenesis are featured in this month's release of Cold Spring Harbor Protocols.
The methods, which are freely accessible online (www.cshprotocols.org), describe how to fluorescently tag cells in very young embryos. These cell-tagging techniques, combined with sophisticated imaging methods, permit scientists to visualize even subtle movements of individual cells in the embryos, as they morph, divide, and migrate.
The first protocol, available at www.cshprotocols.org/cgi/content/full/2007/24/pdb.prot4915, describes a step-by-step approach to label specific cells of live mouse embryos using fluorescent dyes called carbocyanine dyes. Carbocyanine dyes are ideal for this purpose because they can be used on living embryos. After labeling, the embryos are imaged to reveal the precisely coordinated patterns of cell movements as the embryo develops.
The protocol was contributed by Dr. Patrick Tam's group from the University of Sydney, Australia (www.medfac.usyd.edu.au/people/academics/profiles/ppltam.php). His lab uses these techniques to investigate the timing and patterning of cell movements during gastrulation, which is a critical stage in early embryonic development. Also, by performing this procedure in embryos that are both normal and genetically mutated, they can better understand the functions of specific genes involved in gastrulation.
The second featured protocol is from Dr. Rusty Lansford's lab at Caltech (quad.bic.caltech.edu/~fraserlab/people/lansford/). It describes how to insert a DNA vector into very young bird (quail and chicken) embryos using a method called electroporation. The DNA vector contains a gene of interest attached to a fluorescent marker, which allows the researchers to track the fluorescently labeled cells using imaging techniques. Lansford's group uses this method to investigate mechanisms of brain and heart development in birds.
In Lansford's protocol, the DNA is electroporated into shell-less bird eggs. There are several advantages to using shell-less eggs: each embryo can be more accurately positioned during electroporation, and the researchers can ensure that all embryos used in the experiment are at the same stage in development. The protocol is freely available here: www.cshprotocols.org/cgi/content/full/2007/24/pdb.prot4894.