Expression of Osr1 in the limb buds is initially restricted to the mesenchyme immediately below the endoderm .
Expression of Osr1 in the limb buds is initially shifts anteriorly and proximally by embryonic day 11.5 .
Expression of Osr1 in the limb buds is initially restricted to the mesenchyme immediately below the endoderm , but shifts anteriorly and proximally by embryonic day 11.5 .