Understanding the Molecular Pathology of Spinal and Bulbar Muscular Atrophy by Identifying Genetic Interactors of an AR-Humanized Fly

Shaza Mokhtar^1,2, Miltiadis Paliouras ^1,2,3, Mark Trifiro^1,2,3

1. Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Quebec; 2. Department of Human Genetics, McGill University, Montreal, Quebec; 3. Department of Medicine, McGill University, Montreal, Quebec

Background: The androgen receptor (AR), a nuclear receptor belonging to the steroid/thyroid hormone receptor family, functions primarily as a DNA-binding transcription factor regulating gene expression. The AR is involved in a myriad of cellular functions that have a role in the development and growth of the male reproductive and nonreproductive systems.

Introduction: SBMA is an X-linked recessive neurodegenerative disease that is considered to be a polyglutamine (polyGln) expansion disorder. In unaffected men, 9-33 CAG repeats coding for Gln are found in exon 1, while males who inherit more than 37 CAG repeats will develop SBMA. The toxic gain of AR function that is characteristic of SBMA results in a slow progressive muscle weakness, atrophy of the tongue, fasciculations of bulbar, muscle cramping.

AR functionality extends from the transcription factor and includes the novel properties of RNA splicing, proteasomal interaction, DNA methylation and affecting RNA translation at polyribosomes. Thus, the complexity of the AR-interacting protein and RNA could involve in different pathways that function in the AR biological output. Drosophila genetic system uses for a high-throughput screen of large number of gene and genetic interactors that may decrease or increase the polyQ-AR/androgen-dependent phenotype.

Aims of the Study: We will study polyQ-AR protein and RNA initiating disease phenotype by using AR-humanized Drosophila disease model, that will lead us to express the polyQ-AR in the nervous system of the developing fly embryo. PolyQ-AR flies will be crossed with RNAi and homologous fly genes encoding AR candidate protein interactors. Then we would be able to identify the decreases or increases of polyQ-AR phenotype.

Results: A proteomics study was used to establish protein composition of wild-type-AR (WT-AR) complexes vs. polyQ-expanded-AR (polyQ-AR) complexes. Date shows that AR-interacting partners change in the AR-interacting between polyQ-AR and the WT. There are differences in the ability of polyQ-AR to interact with protein that presented by RNA binding proteins.

Conclusion: Studying the role of AR in RNA-splicing and RNA-binding is a novel discovery. Furthermore, using a Drosophila as a genetic interaction screen, will help us to understand the mechanism that is involved in SBMA disease.