Using Android.support.V4.App.FragmentActivity in places of Android.App.Activity

Hi,
I try to build a PCL application using (for Android) Android.support.V4.App.FragmentActivity in places of Android.App.Activity as start activity.
Is it possible?
If possible, what about the Forms.Init(this, bundle) ?
If not, how to mix, in application navigation, Android.App.Activity and Android.support.V4.App.FragmentActivity ?

Anyone knows?