using (Ajax.BeginForm("MyAction", "MyController", null, new AjaxOptions
{
    InsertionMode = InsertionMode.Replace,
    UpdateTargetId = "content",
    LoadingElementId = "loading"
}))
{
    @Html.ValidationSummary()

    <div id="content">
        @Html.EditorFor(m => m.Panes, "EditorTemplates/PanesViewModel")
    </div>
}

<fieldset>
    <div id="wrapper">
        <table>
            @Html.EditorFor(m => m.List, "EditorTemplates/ListViewModel")
        </table>
    </div>

    <button type="submit">Submit</button>
</fieldset>

@Html.EditorFor(m => m.Items, "EditorTemplates/ItemViewModel")

<tr>
    <td>@Html.EditorFor(m => m.FieldName)</td>
</tr>

[HttpPost]
public ActionResult MyAction(PanesViewModel model)
{
    if (ModelState.IsValid)
    {
        // Do stuff
        return PartialView("EditorTemplates/PanesViewModel");
    }

    // Should retain model state and display Validation Summary.
    return PartialView("EditorTemplates/PanesViewModel", model);
}