First, you're probably seeing some issues because the latest version of Iron Router requires you to be on Meteor v0.8.0. If you're on a previous version of Meteor you'll need to use the older Iron Router (0.6).
To customize rendering inside of your ThreadsController you can just override the action function, or you can define a hook. Then, you can call the render method to render whichever templates you'd like. Here is an example:
ThreadsController = RouteController.extend({
action: function () {
// Example 1. render this controller's default template and all yields
this.render();
// Example 2. render myTemplate into the main yield
this.render('myTemplate');
// Example 3. render templates into yield regions
this.render('myFooter', {to: 'footer'});
}
});