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Title: Hsp90 as a buffer of developmental eye defects in zebrafish
Author: Bancewicz, Ruth M.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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I conducted studies with zebrafish mutants and pharmacological inhibitors of Hsp90 to determine whether the penetrance or expressivity of the mutant phenotype could be altered. Zebrafish embryos were treated with low levels of the specific Hsp90 inhibitors, radicicol and geldanamycin. At the concentrations used, a heat shock response was not observed at the protein or RNA level. Homozygotes for the recessive mutations sunrise (sri) and dreumes (dre) were treated with radicicol, and the severity of the phenotype was increased in sri and marginally decreased in dreumes, with respect to control embryos from the same clutch. This effect was also observed with heat shock. Geldanamycin also increased the severity of the sunrise phenotype, but an analogue geldampicin that does not bind Hsp90 had no effect. It can be concluded from this that Hsp90 can buffer developmental defects in a vertebrate species when a pathway is destabilised by a mutation. The sri mutation was mapped in collaboration with Ralf Dahm and colleagues. Tübingen. A mis-sense mutation was identified in the homeodomain of Pax6b that causes an L to P amino acid change. This is predicted to alter the structure or stability of the Pax6b protein. Antisense oligonucleotide knock-down of Pax6b and/or Pax6a function does not phenocopy sri, showing that it is not a full loss of function mutation. Preliminary results suggest that injection of WT Pax6b mRNA rescues the sri phenotype, confirming that the mutation identified in Pax6b causes the sri phenotype. Pax6b is expressed in the pancreatic islet of WT embryos, and in sri the pancreatic islet is severely disorganised, further confirming the causative nature of the Pax6b mutation. This study demonstrates the buffering properties of Hsp90 in a vertebrate system. Pax6 mutant phenotypes in mammals in notoriously variable, and the fact that the mutation buffered here is in Pax6, in addition to the well documented structural and functional conservation of Hsp90, indicates that this mechanism may be conserved in higher vertebrates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available