Your "regions" would be entities you'd place in SceneEdit. Now to implement the mouse-over effects, you'd attach a script to the entity and the script would contain something like:
on "MouseEntry"
{
this.SetSprite("path\some_active_sprite_or_image.sprite");
}
on "MouseLeave"
{
this.SetSprite("path\some_inactive_sprite_or_image.sprite");
}