Boecke, A., Sieger, D., Neacsu, C.D., Kashkar, H., and Krönke, M. (2012) Factor Associated with Neutral Sphingomyelinase Activity Mediates Navigational Capacity of Leukocytes Responding to Wounds and Infection: Live Imaging Studies in Zebrafish Larvae. Journal of immunology (Baltimore, Md. : 1950). 189(4):1559-1566.
Factor associated with neutral sphingomyelinase activity (FAN) is an adaptor protein that specifically binds to the p55 receptor
for TNF (TNF-RI). Our previous investigations demonstrated that FAN plays a role in TNF-induced actin reorganization by connecting
the plasma membrane with actin cytoskeleton, suggesting that FAN may impact on cellular motility in response to TNF and in
the context of immune inflammatory conditions. In this study, we used the translucent zebrafish larvae for in vivo analysis
of leukocyte migration after morpholino knockdown of FAN. FAN-deficient zebrafish leukocytes were impaired in their migration
toward tail fin wounds, leading to a reduced number of cells reaching the wound. Furthermore, FAN-deficient leukocytes show
an impaired response to bacterial infections, suggesting that FAN is generally required for the directed chemotactic response
of immune cells independent of the nature of the stimulus. Cell-tracking analysis up to 3 h after injury revealed that the
reduced number of leukocytes is not due to a reduction in random motility or speed of movement. Leukocytes from FAN-deficient
embryos protrude pseudopodia in all directions instead of having one clear leading edge. Our results suggest that FAN-deficient
leukocytes exhibit an impaired navigational capacity, leading to a disrupted chemotactic response.