react-native picker styling custom font

I'm using the Picker component which I have successfully customised within my styles.xml file in res/values/styles.xml:

<resources><style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar"><item name="android:spinnerItemStyle">@style/SpinnerItem</item><item name="android:spinnerDropDownItemStyle">@style/SpinnerDropDownItem</item></style><style name="SpinnerItem"><item name="android:fontFamily">Lato-Bold</item><item name="android:textSize">20dp</item></style><style name="SpinnerDropDownItem"><item name="android:fontFamily">Lato-Bold</item><item name="android:padding">10dp</item><item name="android:textSize">16dp</item><item name="android:textColor">#ffffff</item><item name="android:background">#000000</item></style></resources>

At the moment my custom fontFamily: Lato-Bold is being ignored. Does anyone know how to get a custom Spinner font to work?