Regulatory factors gdf6a, tbx2b, and thr beta in generation of multiple cone photoreceptor subtypes; and intersections of genetic factors SOD1, TDP43, and gdf6a in zebrafish models of amyotrophic lateral sclerosis

• Author / Creator

  DuVal, Michele G.

• The work within this thesis may be divided into two major foci with a unifying theme of understanding neurodegeneration and expanding the foundational knowledge necessary for treatment of two major degenerative diseases: macular degeneration and amyotrophic lateral sclerosis. To these ends the zebrafish served as a genetic, whole organism model of 1) tetrachromatic cone photoreceptor development and 2) of motor neuron pathology. Summaries of these foci are provided below.
  First, the development of multiple cone photoreceptors, the specialized neurons required for bright light vision and colour discrimination, is explored. The roles of three genes in the cone subtype development network are interrogated: gdf6a, tbx2b, and thrβ. In this thesis the importance of gdf6a, a novel cone gene, toward blue- and red-sensitive cones, and its influence over tbx2b’s regulation of UV cones, is dissected using zebrafish mutants. The dynamic role of thrβ was elucidated with a combination of gene knock down and a newly-engineered dominant negative disruption model, revealing its developmental stage-dependent influence on promoting red and suppressing UV and blue cones. Thrβ and tbx2b were discovered to share an epistatic interaction in the development of UV cones, where reduction in thrβ expression can partially rescue the low abundance of UV cones in tbx2b mutants. Despite the overlapping roles of gdf6a and thrβ in red cone and opposing roles in blue cone development, their exact relationship in cone development could not be elucidated, however a novel retina lamination phenotype suggests that both factors also influence lamination. These interactions elaborate our understanding of the regulatory networks required to generate three or more types of cone photoreceptor.
  Second, the roles of three genes in the pathology of amyotrophic lateral sclerosis are explored through a series of questions, utilizing zebrafish models of motor neuron pathology. Gdf6a is investigated as a novel modifier locus for neuromuscular junction maintenance in aging. Loss of gdf6a disrupts motor neuron function and neuromuscular junction morphology, and enhances neurodegenerative phenotypes in a genetic model of amyotrophic lateral sclerosis. Subsequent work focussed on novel mutations in the amyotrophic lateral sclerosis-linked gene SOD1, including W32S, A89R, and K128N. The relevance of these novel mutations to SOD1 toxicity were tested through cell culture, axonopathy and behavioural assays, and candidate therapeutics that act via the W32 region of SOD1 were evaluated. Finally, the toxic motor neuron phenotype of SOD1 was enhanced by co-expression with another disease-associated gene, TDP43. This enhanced toxicity depended on two specific tryptophan residues in TDP43, and was reduced with a candidate therapeutic drug. These findings highlight the genetic complexities of amyotrophic lateral sclerosis, and emphasize the necessity to explore for genetic and pathological intersections within ALS and with other neurodegenerations.

• Subjects / Keywords

  • degeneration
  • vision
  • zebrafish
  • THRb
  • tbx2b
  • neuron
  • gdf6a
  • ALS
  • GDF6
  • SOD1
  • retina
  • TBX2
  • TDP43

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3DZ03H7K

• License

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