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Session Schedule & Abstracts

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Thursday 30th June, 2016

Symposium : The vertebrate pharynx: crossroads in evolution and development 4

Room: Salon H   4:30 pm–5:00 pm

Moderator(s): A. Huysseune & A. Tucker
PHA4-1  4:30 pm  Neural crest-pharyngeal interactions that underlie the evolution of jaw size. Fish JL, University of Massachusetts Lowell; Vavrušová Z, University of California San Francisco; Chakrabarti D, University of Massachusetts Lowell; Gambino K, University of Massachusetts Lowell; Rose N, University of California San Francisco; Schneider RA*, University of California San Francisco
Abstract: The evolutionary success of vertebrates is due in large part to variation in jaw size. Developmental mechanisms that generate species-specific differences in jaw size involve neural crest mesenchyme (NCM), which is the progenitor population that migrates into the mandibular arch and forms the jaw skeleton. In particular, precisely timed interactions between NCM and pharyngeal endoderm facilitate the patterned outgrowth of the mandibular arch, and these interactions are mediated by the Sonic Hedgehog (SHH) signaling pathway. We hypothesize that the species-specific response of NCM to Shh expression in pharyngeal endoderm can alter the proliferation and differentiation of skeletal precursor cells, and ultimately lead to evolutionary variation in jaw size. We test our hypothesis by examining expression of members and targets of the SHH pathway qualitatively and quantitatively on the mRNA and protein levels in quail and duck embryos, which are two birds with distinct jaw sizes. We also analyze the cell cycle and proliferation dynamics since these are known to be closely tied to SHH signaling. Our results reveal species-specific levels of expression and differential responses to SHH signaling in quail versus duck. When we make chimeric "quck" by transplanting NCM from quail to duck, we find that donor NCM maintains its quail-like expression in duck hosts and gives rise to shorter, quail-like jaws. Overall, these experiments reveal that species-specific differences in SHH signaling are intrinsic to, and mediated by NCM, and that developmental changes to the SHH pathway in NCM may modulate jaw size during evolution. Funded in part, by NIDCR R01 DE016402 to R.A.S.

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