Molecular genetic analysis of a "sine oculis" enhancer and the "leventina" gene as a model system to study human macular degeneration in "Drosophila"

The leventina gene as a model system to study human macular degeneration in Drosophila. Age-related macular degeneration (AMD) is one of the most frequent reasons for blindness of the elderly people and accounts for approximately 50% of registered blindness in the industrial world. AMD pathogenesis is poorly understood and there is no beneficial medical or surgical treatment possible in most cases. The autosomal dominant retinal disease Malattia Leventinese (ML) has a similar phenotype to AMD and seems to be an early onset form. It has recently been shown that ML is caused by a single point mutation (Arg345Trp) that affects the extracellular matrix protein EFEMP1. Studying the molecular function of EFEMP1 could therefore be helpful to understand the pathomechanism of both, ML and AMD. In the last decade striking homologies between Drosophila and vertebrate eye development have been revealed. In addition, the fly model was useful to gain insight into the molecular mechanisms that lead to neurodegenerative diseases like Alzheimer, Parkinson and Chorea Huntington. In this thesis, Drosophila melanogaster was used as a model system in an attempt to reveal the function of EFEMP1 and its putative Drosophila homologue the leventina gene, in the molecular mechanisms of eye development and its function in the retina of adult flies. Pax-6, the master control gene of eye development, is able to induce ectopic eyes in Drosophila and ectopic eye structures in vertebrates. In the ribbonworm Lineus (Nemertini) Pax-6 is also important for regeneration and maintenance of the retina. This is in agreement with our working hypothesis that Pax-6 is involved in maintenance and regeneration of the human retina. The transmembrane receptor Notch genetically lies upstream of Pax-6. The Notch signaling cascade appears in many steps of eye development in human, mouse and Drosophila. Activation of Notch increases the expression of the transcription factor
Pax-6 in frogs.
EFEMP1 displays a high amino acid similarity to the ligands of the Notch receptor.
The point mutation in EFEMP1 that causes ML could result in a loss of its ability to
activate the Notch signaling cascade leading to a inappropriate Pax-6 transcription and
therefore cause ML. Based on this hypothesis one of our approaches was to test
whether EFEMP1 interacts with Notch. If this is the case, EFEMP1 as a soluble Notch
ligand could be a therapeutic tool to activate Notch, increase the transcription of Pax-6
and thereby slow down retinal degeneration.
With the so far used methods we were not able to get any evidence that EFEMP1 is
indeed a Notch ligand despite the convincing sequence homology to known Notch
ligands.