Meeting Abstract

40.1  Jan. 6  Hedgehog signaling in differentiation, growth, and maintenance of craniofacial features during larval development in zebrafish. HERNANDEZ, L.P.; George Washington University, Washington, DC phernand@gwu.edu

Hedgehog signaling has been shown to play an important role in proper craniofacial development. While the role of this signaling pathway in early embryonic development has been well documented in zebrafish, its role in growth and maintenance during later larval development has not been investigated. We have examined the role of the Hedgehog (hh)-signaling pathway on the growth and maintenance of the viscerocranium in the zebrafish, Danio rerio. Given that hh is expressed within the pharyngeal region until relatively late in development, it is likely playing an important role in maintenance of pharyngeal structures. Cyclopamine (CyA), a pharmacological agent known to block all hh signaling, was administered to embryonic zebrafish. Different treatment times (24 hours post fertilization [hpf], 36hpf, 48 hpf, 60 hpf, 72 hpf, 96 hpf) were used to determine the role of hh signaling during different developmental time points. When embryos were treated at the earlier time points (24hpf), the treated zebrafish did not develop branchial cartilages suggesting that hh-signaling is necessary for branchial arch differentiation. Later treatment times showed reduced growth of all pharyngeal cartilages as compared with controls. Moreover, experiments with later treatment times revealed that structures that had developed normally prior to treatment with CyA were not maintained once hh signaling was blocked. These findings suggest that the hh-pathway is not only important in branchial arch differentiation, but is also important for the growth and maintenance of the pharyngeal cartilages. Surprisingly, growth of the second pharyngeal cartilage, the hyoid, did not show significantly reduced growth. These findings suggest that a different genetic pathway may control hyoid growth.