... that occur during evolution or as a result of disease can alter these centers and thereby generate morphological variation. * Author for correspondence (e-mail: [email protected] ) 17 10 2008 © 2009. 2009 Shh Fgf Wnt Bmp RA Facial morphogenesis Zfhx1b Chick Mouse...

..., as in vertebrates, exogenous retinoic acid (RA) posteriorizes the embryo. The mouth and gill slits never form, AmphiPax1 , which is normally downregulated where gill slits form, remains upregulated and AmphiHox1 expression shifts anteriorly in the nerve cord. To dissect the role of RA signaling in patterning...

...-tion). At present, we have not completed experiments to demonstrate whether the Hoxa-1 gene product can directly bind to regulatory regions in the Hoxb-1 gene. We were impressed with the striking similarity in the response of the Hoxb-1 / lacZ transgenic embryos that had been treated with RA...