Retinoic Acid Signaling in Late Vestibular Development of the Inner Ear and Techniques for Visualizing the Zebrafish Inner Ear

• Author / Creator

  Mackowetzky, Kacey

• The vertebrate inner ear is a labyrinthine sensory organ responsible for perceiving sound and body motion. A wide range of disorders of the inner ear can arise from congenital disorders, necessitating the identification of molecular components or pathways involved in its development to better understand the causative factors behind inner ear dysfunction. However, while a considerable amount work has been invested in understanding the auditory system, there is a dearth of knowledge concerning the complex developmental programme behind the apparatuses of the inner ear responsible for vestibular function. This applies particularly to our understanding of the diverse roles independent genes or pathways play at later stages of otic development, an area of research that also suffers from a lack of biological tools that can be utilized to analyze inner ear structure and function.Previous research has identified key cell signaling pathways involved with inner ear development. However, the early disruption of these pathways often produces profound phenotypes that obscure or hinder the manifestation of those that might appear later, complicating our analysis of their roles in late otic development. This applies to the Retinoic Acid (RA) signaling pathway, the disruption of which can generate robust disease phenotypes that preclude the analysis of its involvement in the later development of key vestibular structures. Therefore, using zebrafish as a model organism, we observed for changes to inner ear morphogenesis following late exposure to an RA agonist or antagonist. In doing so, we identified novel RA-responsive transcriptional targets in the inner ear and defined a role for this pathway in semi-circular canal morphogenesis and otolith maintenance. Our work has identified unique roles for this pathway at later stages of development, signifying that the disease phenotypes observed in human patients or other model organisms are not solely the result of early disruptions to RA signaling prior to or at the onset of otic development. In trying to identify biological tools that could be used in the analysis of later stages of inner ear development, we performed a screen of transgenic zebrafish lines at the National Institute of Genetics in Japan. At this institute, the Kawakami laboratory has utilized the Tol2 transposon system to generate various gene or enhancer trap lines expressing a zebrafish-optimized form of yeast Gal4 in various embryonic and larval tissues. Through our screen, we identified six lines with unique otic expression patterns that can be used to drive the expression of a visual reporter or other genetic constructs within the ear. Each line can therefore be used in future research to visualize and measure distinct vestibular features of the inner ear or manipulate target gene expression in these structures.

• Subjects / Keywords

  • vestibular system
  • developmental biology
  • otic development
  • retinoic acid signaling pathway
  • zebrafish

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-sdvc-1k54

• 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.