Meeting Abstract

29.3  Wednesday, Jan. 4  Expression of amphioxus and lamprey SoxE genes in zebrafish reveals ancient neural crest-specific roles in vertebrate evolution LEE, Eric Myung-Jae*; NGUYEN, Kristy; MEDERIOS, Daniel; MCCAULEY, David; University of Oklahoma, Norman; University of Colorado, Boulder

SoxE genes include a group of transcription factors (Sox8, Sox9, and Sox10) that are among key regulators of neural crest cell (NCC) development. The functional redundancy among SoxE paralogs and orthologs suggests that a function of the ancestral SoxE gene was likely in NCC regulation. Here, we investigate the inter-specific functional redundancy of SoxE genes among species that occupy critical phylogenetic positions. Using a heterospecific expression approach, we show that amphioxus and lamprey SoxE genes can induce phenotypic rescue of NCC derivatives when expressed in zebrafish mutant backgrounds. Our results suggest that the amphioxus SoxE gene can drive chondrogenesis, melanogenesis, and neurogenesis when expressed in jellyfish (Sox9a-/-) and colourless (Sox10-/-) mutants. Lamprey SoxE1 can induce cartilage condensations while SoxE2 and SoxE3, the lamprey ortholog of Sox9, have no effect on chondrogenesis. Surprisingly, expression of SoxE2 results in rescue of melanogenesis and neurogenesis in zebrafish cls mutants despite being highly divergent from gnathostome Sox10. Our data suggest that the chondrogenic, neurogenic, and melanogenic roles of gnathostome SoxE genes originated in the ancestral SoxE prior to gene duplication, and that these functions were subsequently retained by Sox8, Sox9, and Sox10 in gnathostomes. Agnathan SoxE genes appear to possess similar functions to zebrafish Sox9a and Sox10 despite a lack of phylogenetic signal through 400 million years of independent evolution. Most notably, lamprey SoxE2 appears to be functionally similar to zebrafish Sox10. Our results have implications for understanding the independent evolution of SoxE genes among jawed and jawless vertebrates, and they demonstrate that phylogenetic signal is not necessarily a reliable predictor of functional homology.