Meeting Abstract
13.2 Sunday, Jan. 4 Evolution of vertebrate chondrogenesis: Lessons from lampreys MCCAULEY, DW; University of Oklahoma, Norman dwmccauley@ou.edu
The appearance of neural crest cells in early vertebrates has been suggested to have been a key event critical to vertebrate complexity. Gene duplication has also been suggested to play a crucial role in increased vertebrate diversity and complexity. The presence of an internal supporting skeleton was important to the evolution of vertebrates and aspects of the vertebrate skeleton are derived from cranial neural crest. Chondrogenic neural crest cells emigrate from the dorsal neural tube in the hindbrain region and form the branchial skeletal elements that support the pharynx and gills in basal vertebrates. Lampreys are the basal-most extant vertebrates and are useful for understanding the origin of novel vertebrate traits in the context of gene duplication. The branchial skeleton in lampreys is comprised of fused cartilage bars that form a basket and previous studies have suggested a neural crest origin of lamprey cartilage. Here we use DiI lineage tracing to confirm the neural crest origin of chondrocytes within the branchial basket. We have found that lamprey cartilage can be stained with the commonly used cartilage stain Alcian Blue. Interestingly, we observe that lamprey cartilage can be induced to fluoresce, facilitating high-resolution whole-mount imaging of the intact branchial basket. Normal development of whole-mount branchial cartilage is compared to cartilage in lamprey embryos following morpholino knockdown of duplicated SoxE genes, shown previously to play a chondrogenic role in lamprey. Following morpholino-induced knockdown of SoxE1 and SoxE2 proteins, cartilages that would form the branchial basket do not develop. Our results demonstrate that duplicated transcription factors SoxE1 and SoxE2 regulate cartilage development at the base of the vertebrates and further suggest the chondrogenic function of Sox9 is a gnathostome synapomorphy.
