Meeting Abstract

99.5  Thursday, Jan. 7  Posterior HoxA and HoxD Genes in Avian Limb Development FOWLER, D.A.**; DE BAKKER, M.A.G.; RICHARDSON, M.K.; Institute of Biology Leiden (IBL), Leiden University; Institute of Biology Leiden (IBL), Leiden University; Institute of Biology Leiden (IBL), Leiden University d.a.fowler.2@umail.leidenuniv.nl

Comparative studies of regulatory networks and their constituent signaling factors provide a powerful line of study for comparative development. Non-traditional model organisms allow for testing of hypotheses generated in studies of traditional genetic model organisms. The zebra finch, Taeniopygia guttata, is an example of one such organism which we use in this study as a foil to traditional model organisms such as the chicken, Gallus gallus. The posterior Hox genes are a differentially expressed and necessary factor in the regulatory networks which coordinate the proper development of vertebrate limbs. We conducted a comprehensive survey of posterior HoxA and HoxD gene expression using in situ hybridization; these show that in some instances posterior HoxA and HoxD expression differs from current hypotheses. Although many patterns are highly conserved, these differences in expression of the posterior Hox genes occur both between the chicken and the zebra finch and between fore limb and hind limb. For example, zebra finch HoxD11 expression in the hind limb begins only after the autopodial field is established, approximately HH 25, and this expression does not extend into the zeugopodial field. This is in contrast to the chicken hind limb which begins HoxD11 expression prior to HH 17, and zebra finch fore limb which begins HoxD11 expression prior to HH20. Seen as an indicator for zeugopodial development, this result questions the nested role of the posterior HoxD genes. These spatiotemporal differences in HoxD11 limb expression indicate a change in hind limb HoxD cluster regulation independent of fore limb HoxD11 regulation. We are currently examining how these differences are related to condensation patterns and differences in skeletal morphology in the limbs of these birds.