Date Thesis Awarded

5-2020

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Interdisciplinary Studies

Advisor

Margaret Saha

Committee Members

Dana Willner

Leah B. Shaw

Dennis M. Manos

Abstract

Abstract

During early development, embryos exhibit a remarkable degree of plasticity and resilience to physical, chemical, and even genetic perturbations. At some point in the developmental process, however, this plasticity diminishes, and as they grow into mature organisms, embryos can no longer recover from significant damage without scarring or defects. Understanding the molecular basis of embryonic plasticity has applications in cancer therapy and regenerative medicine. Therefore, we sought to investigate how developing Xenopus embryos respond to and compensate for perturbations to the Notch signaling pathway; the Notch signaling pathway is a conserved juxtacrine signaling network that is responsible for directing early neurogenesis during vertebrate development, and whose dysregulation has been linked to various types of neurodegenerative diseases and cancers.

Initial experiments have suggested that Xenopus embryos are able to elicit a remarkable response to both over- and underexpression of this critical pathway; unilateral injection of Notch mRNA constructs that either over- or underexpress the pathway results in initial perturbation to the system as assayed by in situ hybridization of the pan-neural marker gene tubb2b, but marker gene expression as well as normal stimuli responses are restored in embryos by early tailbud stages of development. In order to understand the molecular basis of this plasticity, we have characterized this compensatory response by performing dosage experiments and RNA-sequencing for Notch over- and under-expression at early neurula, tailbud, and tadpole stages. RNA-Seq analysis confirms the initial perturbation observed in early neurula stages, with upregulation of core Notch targets such as hes and hey genes as well as notch1 and ttyh1 observed. Further, it also suggests that while embryos appear anatomically healthy by tailbud stages, at the gene expression level, the compensatory response lasts well into tadpole stages.

Finally, having established that Xenopus laevis embryos compensate in response to perturbations in the Notch signaling pathway, we have asked whether this response is conserved across vertebrate species. We have characterized the compensatory response to Notch signaling perturbation in the closely related species Xenopus borealis. In situ hybridization assays for tubb2b as well as RNA-Seq analysis confirms that while borealis embryos are able to compensate for Notch hyperinhibition similarly to Xenopus laevis, they are unable to elicit a consistent compensatory response to Notch hyperactivation. Future directions involve understanding the differential properties of laevis and borealis that mediate this differential response to Notch hyperactivation.

Available for download on Sunday, May 08, 2022

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