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Date of Award

Spring 2025

Document Type

Masters Thesis

Department or Program Affiliation

Biology

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Cooper, W. James, 1969-

Second Advisor

Zinkgraf, Matthew

Third Advisor

Pillay, Laura

Abstract

Fish mandible length is central to determining trophic niche through its impact on feeding mechanics. Thyroid hormone (TH) plays an important role in mandible elongation as fish skulls undergo extensive changes during metamorphosis. To investigate how altered TH signaling can affect fish mandible development, I used bulk RNA-seq techniques to study developing zebrafish with different TH levels across three developmental stages: 21, 36, and 65 days post-fertilization (dpf). I measured and then excised fish mandibles and examined expression in these tissues across 18 weighted gene co-expression network analysis (WGCNA) determined modules, and the hub genes associated with them. Mandibles in specimens with both high and low TH levels are significantly longer than those in fish with normal TH at 36 and 65 dpf, but not at 21 dpf. The high and low TH specimens also had differences in modular gene expression in which high TH was most associated with immune system functions related to major histocompatibility complex and antigens, while low TH was associated with diverse functions relevant to development, cell transport, cell signaling, metabolism of amino acids, and homeostasis. Hub genes for high TH fish were not well defined but focused on the nucleotide-binding (NACHT), leucine-rich repeats (LRR) and pyrin (PYD) domain proteins. Hub genes for low TH fish include, but are not limited to: frem1a, evx1, smad6a, bmp6, slc9a5, msx1a, otx2b, scn8aa, mmp24, calb2b genes. Changes in the expression of genes important to immune system function were associated with both altered thyroid hormone levels and elongated mandibles, suggesting a potential novel mechanism for shifts in feeding mechanics. These findings are highly relevant to the diversification of fish feeding mechanics, as evolutionary changes in mandible elongation frequently accompany shifts in bite force, bite speed, the location at which fishes feed in the water column, and prey preference.

Type

Text

Keywords

zebrafish, thyroid hormone, mandible, jaw, development, feeding mechanics, RNA, differential expression

Publisher

Western Washington University

OCLC Number

1524311099

Subject – LCSH

Zebra danio--Morphogenesis; Zebra danio--Endocrinology; Mandible--Abnormalities; Hyperthyroidism; Hypothyroidism

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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