Evolution of the sponge body plan: Wnt and the development of polarity in freshwater sponges

• Author / Creator

  Windsor, Pamela J

• Body polarity is a fundamental aspect of all multicellular organisms. Metazoans – animals – are monophyletic, but is body polarity homologous among all phyla? Sponges are considered to have branched off first from other animals and therefore studies of polarity formation in the simple sponge body plan may hold key clues to fundamental metazoan characteristics like polarity. In this thesis, I studied the role of Wnt signaling in patterning the body axis of freshwater sponges.
  Lithium chloride caused the formation of extra oscula, the excurrent opening of the sponge canal system and transplant experiments showed the osculum can induce canal growth, similar to other animal tissue organizers.
  Phylogenetic analysis of sponge Wnt genes showed they are distinct from other animal Wnts and while I found no clear expression patterns by in situ hybridization, RNAi knockdown of gsk3 causes multiple oscula in the sponge. Attempts to express freshwater sponge wnts in Xenopus were unsuccessful.
  Sponges have indirect development through a non-feeding larva. Fates of larval cells in the adult sponge were followed using fluorescent probes. Ciliated cells surrounding the larva become choanocyte chambers in the juvenile, confirming the idea that inner and outer tissue layers are reversed with respect to other animals. Fluorescent labeling of the posterior pole of the larva revealed that this region becomes the osculum linking previously shown reports of wnt expression at the posterior pole with formation of the osculum and Wnt signaling. Taken together, the results here suggest that Wnt signaling in early metazoans played a role in the evolution of animal polarity.

• Subjects / Keywords

  • Polarity
  • Wnt
  • Porifera

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3S46HC94

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.