Signals and slots accross threads make use of events.
To make use of events, you must run an event loop in your thread.
To run an event loop in your thread you must call the function exec() from within your thread (i.e. the run() function).

References:
http://doc.qt.nokia.com/4.7/qthread.html#exec
http://doc.qt.nokia.com/4.7/qthread.html
http://doc.qt.nokia.com/4.7/threads.html