Date of Award
Spring 5-22-2015
Degree Type
Honors Thesis
Major
Biology
Degree Name
Bachelor of Science
Department
Biology
First Advisor
James Sikes, Ph.D.
Second Advisor
Christina Tzagarakis-Foster, Ph.D.
Third Advisor
Mary Jane Niles, Ph.D.
Abstract
Acoel flatworms have varied modes of asexual reproduction that involve dramatic postembryonic modification of their anterior-posterior (AP) axis. The acoel species Convolutriloba macropyga reproduces through a reversed polarity budding process in which offspring develop from two posterior budding sites with a complete reversal of the AP axis compared to the parent. Reversed polarity budding is preceded by the development of a zone of tissue with disorganized musculature that is incapable of regeneration, suggesting a transient loss of axis polarity at each budding site. For this reason, these tissues are titled the polarity transition zone (PTZ). While this alteration of existing axial polarity seems to be required for subsequent reversal of the AP axis in the budding progeny, the mechanisms that allow for temporary axis modification and reversal are not known. Wnt, Hedgehog, and other signal transduction pathways have conserved roles in AP axis development and reestablishment during both metazoan embryogenesis and regeneration, suggesting these signals may function in mediating changes in axis polarity during budding in C. macropyga. Here, we have used a pharmacological screen to perturb conserved signaling pathways in Convolutriloba tissues and observed loss of axial polarity in tissues exposed to inhibitors of the Hedgehog pathway. Given the putative role of Hedgehog signal transduction in mediating alterations in axial polarity during budding, we have quantified changes in the expression of Hedgehog signaling components and regulators in budding tissues using qPCR. Hedgehog signaling was downregulated within the PTZ when compared to neighboring polarized tissues. RNAi mediated knockdown of Hedgehog gene products resulted in phenotypes of delayed bud detachment and failure to initiate future budding events. These data support Hedgehog as a key signaling pathway involved in the modification of AP axis polarity during asexual reproduction and may provide key insights towards better understanding the evolution of asexual reproduction strategies in other taxa.
Recommended Citation
Crowther, Laura N. and Sikes, James M. Ph.D., "Mechanisms of axial polarity modification during postembryonic development of the basal bilaterian Convolutriloba macropyga" (2015). Undergraduate Honors Theses. 3.
https://repository.usfca.edu/honors/3
