Date of Graduation

Summer 8-11-2023

Document Type

Thesis

Degree Name

Master of Science in Biology

College/School

College of Arts and Sciences

Department/Program

Biology

First Advisor

James Sikes

Second Advisor

Christina Tzagarakis-Foster

Third Advisor

Mary Jane Niles

Abstract

The mechanisms that control midline specification and modification during post-embryonic development are some of the least understood in developmental biology.  Because acoel flatworms have varied modes of asexual reproduction which can involve the dramatic modification of their orthogonal axes and midline, we have chosen the acoel species Convolutriloba longifissura as a model to study the mechanisms behind midline modification.  C. longifissura asexually reproduces through a double fission process where novel midlines arise within laterally located tissues while the adult midline is destroyed prior to an initial transverse fission event, which is then followed by a second longitudinal fission.  Previous work in our lab has identified Hedgehog signaling as a candidate for midline modification after robust phenotypic abnormalities occurred in pharmacological trials inducing signal perturbation.  To determine if Hedgehog signaling plays a role in midline modification during C. longifissura fission, we characterized the expression and function of 4 genes: the hedgehog ligand; the transmembrane proteins, patched and smoothened; and the transcriptional regulator, gli.  Using qPCR, we found that Hedgehog signaling changes dynamically across the asexual reproductive cycle, with the pathway downregulated prior to transverse fission and upregulated following this fission.  RNAi mediated knockdown of Hedgehog pathway genes resulted in phenotypes where the midline modifications were disrupted during asexual reproduction.  These results suggest that Hedgehog signaling plays a functional role in the maintenance of midline identity and alteration in its regulation mediates modifications of left-right axis polarity that allows for longitudinal fission in C. longifissura.  Understanding how conserved signaling pathways can be co-opted for novel developmental processes has the potential to transform our understanding of alternative reproduction strategies in other taxa and offers insights into the molecular signals that determine body axis polarity.

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