<Window x:Class="ChainedBindingUserControl.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow"
    Height="350" Width="525"
    xmlns:Local="clr-namespace:ChainedBindingUserControl"
    >
    <StackPanel>
        <TextBlock Text="{Binding Data}"
                   Width="150"
                   />
        <ComboBox ItemsSource="{Binding Origin}"
                   Width="150"
                  />
        <Label Content="--------------------------------------------------"
               Width="200"
              />
        <Local:UserControl1 Liste="{Binding Origin}"
                            Noun="{Binding Data}"
                            Height="50" Width="150"
                            />
    </StackPanel>
</Window>

namespace ChainedBindingUserControl
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<String> Origin
        {
            get { return (ObservableCollection<String>)GetValue(OriginProperty); }
            set { SetValue(OriginProperty, value); }
        }
        public static readonly DependencyProperty OriginProperty =
            DependencyProperty.Register("Origin", typeof(ObservableCollection<String>), typeof(MainWindow),
                    new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.AffectsRender));

        public String Data
        {
            get { return (String)GetValue(DataProperty); }
            set { SetValue(DataProperty, value); }
        }
        public static readonly DependencyProperty DataProperty =
            DependencyProperty.Register("Data", typeof(String), typeof(UserControl1),
                    new FrameworkPropertyMetadata("Blablabla", FrameworkPropertyMetadataOptions.AffectsRender));



        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;

            ObservableCollection<String> zog = new ObservableCollection<String>();
            zog.Add("A");
            zog.Add("B");
            zog.Add("C");

            Origin = zog;
        }
    }
}

<UserControl x:Class="ChainedBindingUserControl.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d"
             Name="root"
             d:DesignHeight="300" d:DesignWidth="300">
    <StackPanel>
        <TextBlock Text="{Binding Noun}"
                   />
        <ComboBox ItemsSource="{Binding Liste}"
                  />
    </StackPanel>
</UserControl>

namespace ChainedBindingUserControl
{
    public partial class UserControl1 : UserControl
    {
        public ObservableCollection<String> Liste
        {
            get { return (ObservableCollection<String>)GetValue(ListeProperty); }
            set { SetValue(ListeProperty, value); }
        }
        public static readonly DependencyProperty ListeProperty =
            DependencyProperty.Register("Liste", typeof(ObservableCollection<String>), typeof(UserControl1),
                    new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.AffectsRender));

        public String Noun
        {
            get { return (String)GetValue(NounProperty); }
            set { SetValue(NounProperty, value); }
        }
        public static readonly DependencyProperty NounProperty =
            DependencyProperty.Register("Noun", typeof(String), typeof(UserControl1),
                    new FrameworkPropertyMetadata("", FrameworkPropertyMetadataOptions.AffectsRender));


        public UserControl1()
        {
            InitializeComponent();
            this.DataContext = this;
        }
    }
}