Fig2A. [doi:10.1186/1471-213X-7-69] [PMID:17577402] Copyright: This image is from Gordon J; Xiao S; Hughes B rd; Su DM; Navarre SP; Condie BG; Manley NR, BMC Dev Biol 2007;7:69, an open-access article distributed under the terms of theCreative Commons Attribution License