如何使用依赖属性替换UserControl构造函数中的参数？

public partial class MyUserControl : UserControl
{
    public static readonly DependencyProperty UserNameProperty =
        DependencyProperty.Register("UserName", typeof(string), typeof(MyUserControl), new PropertyMetadata(string.Empty));

    public string UserName
    {
        get { return (string)GetValue(UserNameProperty); }
        set { SetValue(UserNameProperty, value); }
    }

    public MyUserControl()
    {
        InitializeComponent();
    }
}

<UserControl x:Class="MyNamespace.MyUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:MyNamespace">
    <Grid>
        <TextBlock Text="{Binding UserName, RelativeSource={RelativeSource AncestorType={x:Type local:MyUserControl}}}" />
    </Grid>
</UserControl>

<Window x:Class="MyNamespace.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyNamespace">
    <Grid>
        <local:MyUserControl UserName="John Doe" />
    </Grid>
</Window>