Date of Award

Spring 2022

Degree Name

Bachelor of Science

Major

Biology

First Advisor

Dr. Terri Williams

Abstract

Elongation of the anterior/posterior body axis is a critical part of embryonic development. Cell movements are known to play a significant role in embryo elongation in the red flour beetle Tribolium castaneum. In the arthropod model organism, Drosophila, Toll receptors have a demonstrated role in the elongation of the embryo by driving convergent extension, in which rows of cells intercalate with one another in one direction to extend tissue in the other. In Drosophila, Toll receptors are a link between anterior-posterior patterning genes expressed in discrete stripes and effector molecules causing cell movements. This cell movement is caused by three Toll receptors that undergo heterophilic binding to cause myosin planar polarity driving cell intercalation. A recent study demonstrated the involvement of Toll receptors 10 and 7 in T. castaneum elongation. However, the intercalary behavior of cells in T. castaneum is less orderly than in Drosophila, which may reflect a difference in underlying cellular mechanisms. Additionally, our analysis of RNAseq data revealed that Toll 6 expression increases during embryogenesis, which may indicate that it has a larger role in elongation than previously thought. To examine the purpose of these three Toll receptors in elongation, we injected beetle embryos with dsRNA to create single, double, and triple knockdowns. We then used quantitative polymerase chain reactions (qPCR) to examine the expression levels of three Toll genes and five candidate downstream effectors in the knockdowns. We found, as previously reported, that Toll 6 does not have a significant role in elongation, although it may still have a role in development. Additionally, through qPCR, we found that Toll receptors are regulating each other and regulating potential downstream effector molecules. Most interestingly, we found that injecting dsToll7 and dsToll10 simultaneously does not affect elongation when injected 11 hours after egg lay, which calls into question the timing of Toll function and the exact role Toll receptors are playing during this stage of elongation.

Comments

Senior thesis completed at Trinity College, Hartford CT for the Degree of Bachelor of Science in Biology.

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