You can refer WS-Discovery functionality in below links.
http://wso2.com/blogs/architecture/2011/09/loosen-up-with-ws-discovery/
http://docs.wso2.org/wiki/display/ESB460/WS-Discovery
Further look in the below links on how to integrate WSO2 ESB and WSO2 Reg on various ways.
http://docs.wso2.org/wiki/display/ESB460/Storing+Various+WSO2+Enterprise+Service+Bus+Configurations