Date of Award
Scott A. Nichols
J. Todd Blankenship
Schuyler Van Engelenburg
Daniel M. Mederios
Cell type evolution, Myocyte, Myogenesis, Porifera
Whereas a great deal has been learned about the molecular underpinnings of morphological evolution in animals, much less is known about the origin of novel cell and tissue types. During the time in which the earliest animal lineages were diversifying, fundamental cell and tissue types, such as muscles, arose. Sponges are one of two animal lineages that lack muscles, yet they undergo coordinated full body contractions. Whereas the signaling processes have been studied, the physical mechanisms of contraction are completely uncharacterized. The main purpose of this work is to understand the primary contractile tissue of the sponge Ephydatia muelleri, from a structural, functional, and developmental standpoint. As there is no single unique feature that is shared by all muscle types in animals, a full picture of the contractile tissue of E. muelleri is needed to assess its homology with these tissues. Here the focus is on an endothelial-like tissue containing tissue-level organized actin bundles, which shorten during contractions. Additionally, a muscle-specific paralog of type II-Myosin heavy chain (stMyHC) is found exclusively at these structures. Contractions appear to be initiated by release of internal Ca2+stores and are regulated by phosphorylation of myosin regulatory light chain by myosin light chain kinase. From a developmental perspective, formation of contractile bundles depends on myocardin related transcription factor (MRTF), an important myogenic factor in many animals. Comparative studies on the myoepithelial muscles of the cnidarian model Nematostella vectensis, found evidence of conserved developmental regulation by MRTF. Taken together, these finding suggest the contractile tissue of E. muelleri shares elements of homology with muscles of other animals and can aid in understanding key cellular innovations involved in the evolution of this tissue type.
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Colgren, Jeffrey J., "Cellular and Developmental Insights into the Early Evolution of Muscle" (2020). Electronic Theses and Dissertations. 1733.
Received from ProQuest
Jeffrey J. Colgren
Molecular biology, Cellular biology, Evolution and development
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