In addition to the cardiac OFT, development of pharyngeal organs, i.e., the parathyroid glands and the thymus was also abnormal in Alk5/Wnt1-Cre mutants (see Figs. 1 and 8). Normally the thymus develops from the third pharyngeal pouch endoderm and migrates caudally to its final location in the superior mediastinum as seen in controls at E14 (Fig. 8A,B). In contrast, the thymic primordia of the Alk5 mutant littermates failed to descend caudally, and were located bilaterally in the neck region, where they were surrounded by neural crest-derived mesenchyme (Fig. 8D,E). The fate determination assay demonstrated that the thymic primordia were equally populated by NCCs both in controls and Alk5 mutants (Fig. 8B,E). Likewise the parathyroid glands failed to migrate normally in Alk5/Wnt1-Cre mutants. During normal development, the parathyroids first migrate in association with the thymic primordia, until they reach the thyroids in the neck region as seen in Fig 8C. In Alk5/Wnt1-Cre mutants, the parathyroids remained associated with the thymic primordia, and despite this abnormal rostral location, expression of parathyroid hormone was indistinguishable between Alk5 mutants and controls at E14 (Fig. 8C,F). To conclude, the observed pharyngeal organ phenotypes were also in striking contrast to those seen in Tgfbr2/Wnt1-Cre mutants [8,9].