The epithelial-to-mesenchymal transition is a highly dynamic cell process and 
tools such as fluorescence recovery after photobleaching (FRAP), which allow the 
study of rapid protein dynamics, enable the following of this process in vivo. 
This technique uses a short intense pulse of photons to disrupt the fluorescence 
of a tagged protein in a region of a sample. The fluorescent signal intensity 
after this bleaching is then recorded and the signal recovery used to provide an 
indicator of the dynamics of the protein of interest. This technique can be 
applied to any fluorescently tagged protein, but membrane-bound proteins present 
an interesting challenge as they are spatially confined and subject to 
specialized cellular trafficking. Several methods of analysis can be applied 
which can disentangle these various processes and enable the extraction of 
information from the recovery curves. Here we describe this technique when 
applied to the quantification of the plasma membrane-bound E-cadherin protein in 
vivo using the epidermis of the late embryo of Drosophila melanogaster 
(Drosophila) as an example of this technique.