Evolution of vertebrates is intimately linked to the advent of the neural crest, a migratory and multipotent cell population that gives rise to many defining vertebrate characteristics, including a well-defined head and peripheral ganglia. Jawless fish (including the lamprey Petromyzon marinus) have bona fide neural crest cells, but do not have the full complement of neural crest derivatives, lacking jaws, sympathetic and possibly enteric ganglia. Here, we will test the hypothesis that the novel deployment of transcription factors in premigratory neural crest cells may have conferred new developmental potential onto this cell population, potentiating evolution of selected neural crest derivatives. Consistent with this hypothesis, two transcription factors, Twist and Ets1, are expressed in premigratory neural crest cells of gnathostomes but not lampreys. To test regulatory connections that may have facilitated production of novel vertebrate cell types, we will utilize RNA-seq together with novel transgenesis approaches to perform the following aims:
Aim 1 : Transcriptome analysis of lamprey premigratory cranial, vagal and trunk neural crest: To investigate the differences observed between cyclostome and gnathostome neural crest, we will perform RNA-seq analysis of cranial, post-otic (i.e. vagal) and trunk dorsal neural tubes containing premigratory neural crest cells from embryonic lamprey. We will confirm expression patterns of differentially expressed genes by in situ hybridization in lamprey and chick to find differentially expressed between agnathans and gnathostomes.
Aim 2 : Phylogenomic and functional analysis/dissection of conserved regulatory elements mediating expression of neural crest genes of lamprey and other vertebrates: We will identify regulatory regions of lamprey neural crest genes, initially focusing on Ets1 and Phox2b since they are differentially expressed between lamprey and gnathostomes. These will be tested by transgenesis in both lamprey and chick embryos.
Aim 3 : Utilize conserved regulatory elements to misexpress gnathostome neural crest genes in lamprey: We will utilize cross-species and/or endogenous enhancers to ectopically express """"""""missing"""""""" transcription factors in lamprey to see if they promote formation of cell types that lamprey lack.

Public Health Relevance

In all vertebrates, the neural crest gives rise to the craniofacial skeleton, peripheral nervous system, and melanocytes. Because neural crest cells are involved in a variety of birth defects such as cleft palate and various types of cancers and syndromes, like familial dysautonomia and melanoma, our results on the normal regulatory events guiding neural crest development and evolution will provide important clues regarding the mistakes that may lead to abnormal development or loss of the differentiated state.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Genetic Variation and Evolution Study Section (GVE)
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Morris, Jill A
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California Institute of Technology
Schools of Arts and Sciences
United States
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Martik, Megan L; Bronner, Marianne E (2017) Regulatory Logic Underlying Diversification of the Neural Crest. Trends Genet 33:715-727
Green, Stephen A; Uy, Benjamin R; Bronner, Marianne E (2017) Ancient evolutionary origin of vertebrate enteric neurons from trunk-derived neural crest. Nature 544:88-91
Tai, Andrew; Cheung, Martin; Huang, Yong-Heng et al. (2016) SOXE neofunctionalization and elaboration of the neural crest during chordate evolution. Sci Rep 6:34964
Uribe, Rosa A; Gu, Tiffany; Bronner, Marianne E (2016) A novel subset of enteric neurons revealed by ptf1a:GFP in the developing zebrafish enteric nervous system. Genesis 54:123-8
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Parker, Hugo J; Bronner, Marianne E; Krumlauf, Robb (2014) A Hox regulatory network of hindbrain segmentation is conserved to the base of vertebrates. Nature 514:490-3
Green, Stephen A; Bronner, Marianne E (2014) The lamprey: a jawless vertebrate model system for examining origin of the neural crest and other vertebrate traits. Differentiation 87:44-51
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