Transposon‐mediated stable integration of genes into migrating cells during blood vessel patterning

A number of cells appear to migrate over long distances in the body during organogenesis. However, the molecular mechanisms by which such migratory behaviors are regulated remain largely unknown. It has been challenging to genetically manipulate and trace migratory cells over a long period of time. Recently, we have developed a Tol2‐transposon‐mediated gene transfer in chickens, a method that allows for stable genomic integration of electroporated genes. Co‐electroporation of a EGFP‐expressing cassette cloned into the Tol2 construct along with a transposase‐encoding plasmid results in persistent expression of EGFP until at least embryonic day 8 (E8), thus surmounting the shortcoming of conventional electroporation techniques that limit the duration of activity of exogenous genes. Using these methods, we have recently found that a subpopulation of somitic cells electroporated with Tol2‐CXCR4 is attracted to forming intercostal vessels, the thin blood vessels protruding from the dorsal aorta, and ultimately differentiates into smooth muscle cells (SMC) around these vessels at E7. The attraction of SMCs is mediated by the chemokine SDF1, which is produced at the tip of the growing vessels. Such selective migration of SMCs appears to determine the patterning of intercostal vessels since these vessels are specifically lacking in CXCR4 KO mice.