Acknowledgements
L. McClain provided essential technical assistance and we thank P. Groen and D. Witte for initial histology and embryological analyses. D. Ash helped make targeting constructs. We thank T. Carroll for providing a Wnt9b riboprobe construct. We thank H. Liang for generation of microarray data. This work was supported by grant DK61916 from the National Institutes of Health (S.S.P.).