Publication Date

2016-05-09

Document Type

Honors Thesis

Department

Biological Sciences

Keywords

Neural crest, Zebra danio-Morphology, Pharynx-Abnormalities, Teratogenesis, Mutagenesis, Hydrocarbons, Zebrafish, Pharyngeal system, Development, Actin

Abstract

The pharyngeal arches have been a prominent topic of study for many years, as they give rise to crucial elements of the ear, jaw, and heart. Failure for the pharyngeal arches to correctly form introduces a host of developmental malformations in the adult, two of the most well examples being Treacher Collins–Franceschetti syndrome and facial clefting. As the arches give rise to many cartilaginous structures, many studies focused mainly on neural crest cells, the precursors to cartilage and ligaments. But only recently has the process of arch formation gained more attention; most notably how arch morphogenesis is the result of pouch formation. The pharyngeal pouches, though often overlooked, are required for proper arch formation and differentiation. In addition the pharyngeal endoderm, which becomes the outpocketings we know as pharyngeal pouches, is host to multiple cellular regulatory signals that are critical for arch morphogenesis, from beginning to end. This outpocketing is guided by actin webs, allowing the pharyngeal endoderm to migrate. This project started with trying to identify teratogenic defects in developing embryos induced by crude oil components, and it was found that the highest concentration water­soluble component of crude oil, naphthalene, created a reproducible phenotype in the pharyngeal system consisting of a loss of the posterior pouch, which in turn caused a lack of differentiation between the final two arches. This result was found not to be due to cellular death. Naphthalene treated embryos showed high disorganization within the pharyngeal structures, including diffuse pouches that lacked proper slit­like morphology. Treating embryos later in their development didn’t 9 affect the severity of the phenotype up until treatment at 25 HPF. Additionally, it was found that treating embryos with less naphthalene­infused embryo medium in the dish drastically reduced the severity of the phenotype. These variables were found to correlate with the small window of pre­arch development, along with naphthalenes highly volatile characteristic. Staining for F­actin filaments revealed that naphthalene causes a high disorganization of the critical actin web, which is needed for proper pouch morphogenesis. Naphthalene treatment also was found to reduce expression of dlx2a, another factor in helping to organize neural crest cells in the pharyngeal system. These results are consistent with the proposed model for pouch and arch development, showing that naphthalene intercepts this process at the level of actin­aided endoderm migration. Additional results may help narrow down what, if any, additional cellular signals expressed in the region are being affected by naphthalene, and therefore interrupting proper cell differentiation and proliferation

Language

English

Comments

68 pages : color illustrations. Honors project, Smith College, 2016. Includes bibliographical references (pages 64-68)

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