Date of Award

Spring 2022

Degree Name

Bachelor of Science

Major

Biology

First Advisor

Terri A. Williams

Second Advisor

Robert J. Fleming

Third Advisor

Claire T. Fournier

Abstract

The embryo of the red flour beetle Tribolium castaneum develops sequentially by adding segments in an anterior-to-posterior progression using a “clock”-like mechanism similar to that of vertebrates. Previous studies indicate that the oscillations of this segmentation clock are driven by a gradient of the transcription factor caudal (cad), which activates and regulates the clock. Knocking down the cad gene using parental or early embryonic RNAi leads to animals with only head segments. We hypothesized that progressively later embryonic knockdowns would produce animals with progressively more segments if the function of cad does not change during segmentation. To examine this, we knocked down the gene using RNAi at three different timepoints prior to segmentation: 4, 8.5, and 11.5 hours after egg lay (hAEL). We found that segment addition was affected for the two earlier timepoints as expected, but late blastoderm embryos (11.5 hAEL) did not require cad to add segments despite having very few segments already patterned. Therefore, our results suggest that cad is regulating segmentation in very early development only, and we propose that a different regulatory network is controlling late segmentation. Additionally, it has been shown that the frequency of the clock changes during development, hence we hypothesized that cad might be dynamically regulated by various transcription factors during different phases. We performed bioinformatics analyses using the MCAST tool to establish predictions of transcription factor binding clusters that might be regulating cad gene expression, and used these predictions as the basis to clone putative enhancer regions for yeast one-hybrid and cross-species transgenics. We infer that a change in cad regulation causes its function to change through development as we observed in our knockdowns.

Comments

Senior thesis completed at Trinity College for the degree of Bachelor of Science in Biology.

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