Functional analysis of chicken Sox2 enhancers highlights an array of diverse regulatory elements that are conserved in mammals

Sox2 expression marks neural and sensory primordia at various stages of development. A 50 kb genomic region of chicken Sox2 was isolated and scanned for enhancer activity utilizing embryo electroporation, resulting in identification of a battery of enhancers. Although Sox2 expression in the early embryonic CNS appears uniform, it is actually pieced together by five separate enhancers with distinct spatio-temporal specificities, including the one activated by the neural induction signals emanating from Hensen's node. Enhancers for Sox2 expression in the lens and nasal/otic placodes and in the neural crest were also determined. These functionally identified Sox2 enhancers exactly correspond to the extragenic sequence blocks conspicuously conserved between chicken and mammals, which are not discernible by sequence comparison among mammals.