Obtención y caracterización de mutantes funcionales del gen frataxin homologue (FH) en Drosophila.

Abstract

Friedreich ataxia is a severe autosomal recessive disease characterized by neurodegeneration, cardiomyopathy, and diabetes, resulting from reduced synthesis of the mitochondrial protein frataxin. It is the most common ataxia among the caucasian population. The research developed in in patient cells and model organisms such as yeast, worm, fruitfly and mouse have suggested several hypotheses on the frataxin function, but the full physiology of frataxin in mitochondria has not been well established yet. In our laboratory, the Drosophila frataxin gene (fh) was isolated. Very recently Drosophila has become an excellen model to study human diseases given that humans and flies have in common the most important biological processes, for example development and degeneration of nervous system, heart development, mitochondrial metabolic pathways, etc... In this work, we have carried out the study of the Drosophila frataxin function using three strategies: insertional P element mutagenesis, RNAi system and overexpression. The insertional mutagenesis was unsuccessful because fh is a small gene that lies in a crowed genomic region and is surrounded by two and even three insertional hotspots. Then we began to use a second approach based on the generation of transgenic flies overexpressing and reducing the Drosophila frataxin homolog gene by means of the UAS-GAL4 system. Full lethality, phenotypic alterations or misbehaviours (climbing deficits and shortened life span) were achieved when this gene was overexpressed or knocked down in a general or mesodermal patterns and in the PNS (the most affected tissues in the patients) due to the appearance of developmental defects in muscle, heart and nervous system. Our results showed that both an excess or a reduction of frataxin expression disturb development of muscular and nervous systems in Drosophila. As in humans, the damages are mainly focused on the Drosophila peripheral nervous elements (sensory and motor axons and neurons). Moreover, important defects have also been observed in mesodermic derivates such as somatic muscles, cardial and pericardial cells. However, the defects have only been provoked when the misexpression was carried out in the earlier stages of muscle and nervous system development. All these data together suggest that D. melanogaster could be an appropiate model organism to study Friedreich ataxia.