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Title: A mutation in a mouse J-protein that functions in the diphthamide biosynthesis pathway
Author: Webb, Thomas Robert
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2011
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Chromosomal deletions can be used in mutagenesis strategies that screen for recessive phenotypes. Several mouse chromosomal deletions are available which remove the Pax6 gene and result in the small-eye phenotype. Deletion of the syntenic region in humans results in the phenotypically variable WAGR syndrome. The Pax6Sey~1H deletion spans 3 Mb and includes 15 genes. This deletion has been used in an ENU mutagenesis screen for phenotypes revealed when hemizygous with the deletion. One such mutation, which is lethal against the Pax6Sey~1H deletion, has been found from 233 pedigrees. Mice heterozygous for the mutation are phenotypically normal. When homozygous the mutation is generally lethal by El4, and embryos have retarded growth from as early as E9. However, some homozygous mice are born which are small and have extra digits on one or both hind limbs. Sequencing of the genes in the deletion interval identified a splice site mutation in Dnajc20 a member of the J-domain family of molecular chaperones. The mutation causes the in frame skipping of exon 4, leading to an mRNA that encodes a protein with an internal 23 amino acid deletion. The yeast orthologue of Dnajc20 has recently been identified as one of five genes required for the biosynthesis of diphthamide, a post-translational modification that is unique to translation elongation factor 2 (eEF2), the target of diphtheria toxin and Pseudomonas exotoxin A. Here it is shown that the mutation in the mouse Dnajc20 protein results in the abolition of diphthamide on eEF2 in these animals. Additionally mice mutated for Dnajc20 show remarkable similarity to the phenotype of Ovcal mutant mice. Ovcal is a tumour suppressor whose yeast orthologue was also identified as being required for diphthamide biosynthesis. The phenotypes of these two mutations suggest that the diphthamide biosynthesis pathway, which is conserved from archaebacteria to eukaryotes but absent in eubacteria, is essential for normal mammalian development and survival. Furthermore the human orthologue of Dnajc20 is suggested as the gene responsible for the manifestation of Polydactyly in some WAGR patients.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available