Automatically set the ticket owner as follower

Automatically set the ticket owner as follower

Hi, we have 3 departments and when an agent moves a ticket through departments (e.g. from dept.1 to dept.2) the ticket owner sets to unassigned until another agent take cares of it. We would like to automatically set the ticket owners as followers in the ticket so that agents get notified if the ticket goes back to dept.1
Thanks in advance for your help,
Carlo