Oral communication, CS4 / C15

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

An induced suppressor mutation at the microphthalmia locus in the mouse reveals novel insights into bHLHZip transcription factor function

Suppressor mutations which compensate other mutations have revealed novel insights into gene function, gene interactions and genetic pathways in bacteria, in baker's yeast and in multicellular organisms such as Drosophila and C. elegans. Although few suppressor screens have been performed in the mouse, spontaneous suppressor mutations, such as dilute-suppressor (dsu), suggest that such screens can lead to important biological insights. Here we report the isolation of an intragenic mutation in Mitfmi-sp which largely corrects the phenotypic enhancement associated with the original Mitfmi-sp allele, including enhancement of the Mitfmi-vga9 loss-of-function mutation. This novel mutation (termed spotless or Mitfmi-sl) introduces a stop codon at amino acid 316 of MITF, leading to premature termination. As it was induced on the Mitfmi-sp chromosome it also lacks the alternative 6 amino acids due this mutation. We have compared the genetic, biochemical and developmental behaviour of Mitfmi-sl to that of Mitfmi-sp. Developmental studies show that the onset of pigmentation is delayed in Mitfmi-sl homozygotes whereas no differences were seen in effects on proliferation. We found no differences in DNA binding ability or protein stability. However, competition assays suggest that the suppressor mutation affects dimerization of the protein and reporter assays show promoter-specific differences. Our data indicate that the carboxyl-end of MITF is not essential for normal function in melanocytes and appears to have negative function in the wild type context. We conclude that searching for suppressor mutations in the mouse is feasible and provides a powerful tool for dissecting gene function.

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