<UserControl.Resources>
        <ControlTemplate x:Key="MapRegion" TargetType="ToggleButton">
      .......
        </ControlTemplate>
    </UserControl.Resources>

   <Border x:Name="ContentBorder" Style="{StaticResource ContentBorderStyle}">
            <navigation:Frame x:Name="ContentFrame" Style="{StaticResource ContentFrameStyle}" 
                              Source="/Home" Navigated="ContentFrame_Navigated" NavigationFailed="ContentFrame_NavigationFailed">
                <navigation:Frame.UriMapper>
                  <uriMapper:UriMapper>
                    <uriMapper:UriMapping Uri="" MappedUri="/Views/Home.xaml"/>
                    <uriMapper:UriMapping Uri="/{pageName}" MappedUri="/Views/{pageName}.xaml"/>
                  </uriMapper:UriMapper>
                </navigation:Frame.UriMapper>
            </navigation:Frame>
    </Border>

..
Template="{RelativeSource MapRegion}"
...