Undergraduate Honors Theses

Thesis Defended

Spring 2013

Document Type

Thesis

Department

Ecology and Evolutionary Biology

First Advisor

Dr. Daniel Meulemans Medeiros

Abstract

The development of the jaw was an important event in vertebrate evolution that led to their success as top predators, but little is known about the molecular mechanisms behind its development. In trying to narrow down important molecules for jaw formation we studied lamprey, a jawless vertebrate representing the most basal vertebrate. While skeletal morphology of lamprey differs greatly from jawed vertebrates, expression patterns of several genes important for skull formation indicate a similar (conserved) dorsoventral (D/V) axis in both species, despite the different physical appearances. Previous findings showed that a signaling pathway involving the ligand Jagged and receptor Notch (Jagged/Notch) is important for forming the D/V axis in fish, suggesting the possibility that these factors could be key components in the pathway that led to the development of the jaw. Furthermore, Jagged is the gene that causes Alagille syndrome, a developmental disorder in humans characterized by abnormal craniofacial structure. Using in situ hybridization, we compared the expression patterns of Jagged/Notch in lamprey and zebrafish and found that they share similar D/V expression patterns, with a few small differences. This finding indicates that this patterning is likely an ancestral trait, and that changes somewhere genetically downstream of the pathway were more important for the evolution of the jaw. Where exactly these changes occurred remains unknown, but the evidence that downstream factors of Jagged/Notch are important in axis formation puts us one step closer to understanding the developmental mechanisms behind the evolution of the jaw.

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