<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true" />
                <asp:UpdatePanel ID="upContent" runat="server" UpdateMode="Conditional" RenderMode="Inline">
                    <ContentTemplate>

                    </ContentTemplate>
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="lb1" EventName="Click" />
                    </Triggers>
                </asp:UpdatePanel>
<asp:LinkButton runat="server" ID="lb1" Text="" onclick="ButtonMenu_Click" />

    protected void ButtonMenu_Click(object sender, EventArgs e)
    {
        if (Request.Params["nameCtrl"].Length > 0)
        {
            //Chargement du contrôle
            Control c = this.LoadControl("control1.ascx");
            this.upContent.ContentTemplateContainer.Controls.Add(c);
        }
    }

    public partial class CtrlManifDetail : System.Web.UI.UserControl
    {
        LinkButton lb;

        protected override void CreateChildControls()
        {
            base.CreateChildControls();
            ScriptManager sm = ScriptManager.GetCurrent(Page);

            //Ajout de mon bouton
            lb = new LinkButton();
            lb.ID = "lbTest";
            lb.Text = "Bouton de test";
            lb.Click += new EventHandler(lbTest_save);

            this.Controls.Add(lb);
        }

        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void lbTest_save(object sender, EventArgs e)
        {
             //Mon traitement
        }