Eichele, G. Department of Molecular Embryology, Max Planck Institute for Experimental Endocrinology, Max Planck Society;
http://pdn.sciencedirect.com/science?_ob=MiamiImageURL&_cid=272543&_user=38661&_pii=S0012160697985894&_check=y&_origin=article&_zone=toolbar&_coverDate=1997--01&view=c&originContentFamily=serial&wchp=dGLbVBA-zSkWz&md5=1c81ec8526136c3cacdc8e0881d6c65d&pid=1-s2.0-S0012160697985894-main.pdf (Publisher version)
Helms, J. A., Kim, C. H., Hu, D., Minkoff, R., Thaller, C., & Eichele, G. (1997). Sonic hedgehog participates in craniofacial morphogenesis and is down-regulated by teratogenic doses of retinoic acid. Developmental Biology, 187(1), 25-35. doi:10.1006/dbio.1997.8589.