tion and the transition of fins to limbs, we have identified, using a massive sequencing approach of a cDNA library, the whole set of Hox genes of the chondrichthyan, Scyliorhinus canicula. We have sequenced seven BAC clones that include all of the HoxA, HoxB and HoxD clusters. The transcriptomic data suggests that no HoxC genes have been maintained in this species. The expression of the posterior Hox genes was studied by insitu hybridization and showed that all the posterior genes of the three catshark Hox clusters are expressed differentially in the posterior part of the body and in the paired fins. Posterior HoxA and D genes were expressed during two temporal phases in both the pectoral and pelvic fin buds, while observing spatial colin- earity. Posterior HoxB transcripts were identified only in the pel- vic fin buds. Comparing this data with those for other vertebrates (tetrapods and teleosts), we have analyzed Hox code evolution in relation to the evolution of paired appendages in gnathostomes. doi:10.1016/j.mod.2009.06.656 15-P013 Inheritance and molecular genetics of floral symmetry in Dar- win’s Gloxinia peloria (Sinningia speciosa) Hao-Chun Hsu 1 , Quentin Cronk 2 , Chun-Neng Wang 1 1 National Taiwan University, Taipei, Taiwan 2 University of British Columbia, Vancouver, Canada The evolution of flower zygomorphy is an important develop- mental trait in angiosperm. The domesticated peloric cultivar of Darwin’s Gloxinia (Sinningia speciosa), which has showy actino- morphic flowers reverted from zygomorphic wild-type, provide us an exciting opportunity to explore the mechanism of floral symmetry transition. To study the inheritance of floral symmetry, we crossed the zygomorphic wild-type and the actinomorphic peloria and found the F1 hybrids flowers are always zygomorphic. The floral symmetry traits segregate in a 3:1 ratio of zygomorphy to actinomorphy among F2 offsprings. This indicates the control of floral symmetry in Darwin’s Gloxinia peloria is probably a sin- gle gene’s effect and the zygomorphic trait is dominant. As CYCLOIDEA (CYC), RADIALIS (RAD), and DIVARICATA (DIV) have been suggested to control floral symmetry, we carefully geno- typed all F2 individuals, and found that Sinningia CYC (SsCYC) allele is tightly associated with the segregation of the floral sym- metry traits. This gives a 1:2:1 ratio (72:164:84; a = 0.05, p = 0.196 ) among wild-type homozygote SsCYC alleles (C/C), heterozygote SsCYC alleles (C/c) to peloric homozygote SsCYC alleles (c/c). We also identified one major mutated site of SsCYC in peloric allele sequence (c) and that causes the coding region containing a pre- mature stop. Functional studies of SsCYC by transforming wild- type SsCYC alleles into the Peloric cultivar are on the way to fur- ther confirm SsCYC’s role in floral symmetry transition. This is the first time we could demonstrate that the domestication of Darwin’s Gloxinia peloria (c/c) is perhaps a saltational effect of CYC loss of function mutation. doi:10.1016/j.mod.2009.06.657 15-P014 Our inner fish: Do amniotes have an opercular flap? Joanna Richardson , Anthony Graham MRC Centre for Developmental Neurobiology, King’s College London, London, United Kingdom The opercular flap covers the gills of bony fish, providing pro- tection and aiding respiration by pumping water past the gills. Both the opercular flap and the gills were believed to have been lost with the evolution of the tetrapods and the colonisation of the land. However, previous data has shown that during tetrapod evolution the gills were not lost, but remain functional as the parathyroid gland, and are required for terrestrial life as they act to regulate calcium homeostasis. The current work aims to demonstrate that the opercular flap was also not lost, and that amniotes have a homologous embryonic structure. The opercular flap develops from the second pharyngeal arch and expands cau- dally over the more posterior arches. In fish, the posterior limit of the flap remains open, but in amniotes the second arch fuses with the cardiac eminence and encloses the posterior arches, a signif- icant event in tetrapod evolution allowing for the internalization of the gills. Failure of this process in humans leads to fistulae (per- sistent gill slits). Results indicate that the second arch in both zebrafish and chick express homologous genes, including Fgf8 and Shh, which is required to drive outgrowth of the flap. In the chick, a portion of the flap remains after fusion occurs, but is removed by apoptosis. Preliminary data suggests that the fusion event in amniotes may be driven by thyroid hormone, in a process similar to that of gill slit fusion in metamorphosing frogs. doi:10.1016/j.mod.2009.06.658 15-P015 Non-individualization of Dlx gene expression during teeth and dermal denticles development in the catshark Me ´ lanie Debiais-Thibaud 1 , Silvan Oulion 1 , Didier Casane 1,2 , Ve ´ ronique Borday-Birraux 1,2 1 CNRS, Gif-sur-Yvette, France 2 Universite ´ Paris7, Paris, France Serially homologous structures are thought to originate from the deployment of the same genetic cascade in different parts of the body. Teeth are repeated units that form dentitions on bones of the oral-pharyngeal cavity.These were supposed to orig- inate from the co-option of the genetic cascade responsible for dermal denticle development of elasmobranches skin. We investigated the hypothesis that there is a common devel- opmental origin for different dermal skeleton modules by exam- ining Dlx gene expression pattern during dermal denticle and tooth development in the dogfish (Scyliorhinus canicula). We com- pared these data with previous results obtained in mouse, zebra- fish and medaka, showing that teleost pharyngeal denticles and oral teeth develop after identical sequential gene initiation. Our results showed that there were no differences observed in Dlx gene expression between oral teeth and dermal denticles in the dogfish. However comparisons between homologous structures such as oral teeth in the mouse, medaka and dogfish showed S251 MECHANISMS OF DEVELOPMENT 126 (2009) S247 – S261