Car turn signal stopped working?

I have a 2001 toyota sienna. Turn signals have stopped working. Non of the light is working. I thought it could be a fuse. I checked the fuses, but I did not see a problem. I find it hard to beleive that all 4 bulbs went bad at the same time. Where else should I look?. Is it possible that one blown bulb could cause such a problem?. Thanks