SMA is a neurodegenerative disease caused by a deficiency of the Survival Motor Neuron (SMN) protein. The aim of this project is to identify factors involved in the snRNPs biogenesis pathway, able to ameliorate neurodegenerative phenotypes leading to SMA. SMN and TGS1 are strickly linked to snRNPs maturation. We recently demonstrated that TGS1, an S-adenosyl-L-methionine dependent methyltransferase responsible for snRNAs cap trimethylation, physically interacts with all subunits of Drosophila Smn complex and that both dTgs1 and Smn are required for viability of retinal progenitor cells. Downregulation of both genes leads to a reduced eye size and cell death of the retinal precursors. Importantly, overexpression of dTgs1 partially rescues the eye defects caused by Smn depletion, and vice versa, suggesting that TGS1 acts as a conserved SMN modifier and it could be potentially pointed as a possible therapeutic target for combinatorial SMA therapy. Furthermore, expression of human TGS1 transgene rescues the mutant phenotype caused by dTgs1 loss both in flies (1) and worms, underlying its evolutionarily conservation in different species. Fly eye imaginal discs could provide evidence on the mechanisms of cell death in dTgs1 and Smn depleted neuroepithelium, allowing to explore how dTgs1 and Smn cooperate to protect against neurodegeneration. Drosophila eye imaginal discs is a promising venue which will offer a convenient background to screen for novel genetic modifiers and interactors of TGS1 and SMN in order to highlight sensitive nodes in the complex circuitries that protect neuronal cells. These modifiers could help to devise new therapies for SMA.
An emerging theme of motor neuron diseases, including Spinal Muscular Atrophy (SMA), is a perturbed RNA metabolism, caused by defects in various aspects of the biogenesis and maturation of noncoding RNAs. SMA is one of the main causes of infant death. No specific therapy has been identified so far. Several clinical trials are currently aimed at increasing the amount of the SMN protein by either drug treatments or molecular therapy. The Drosophila model of SMA has been confirmed as powerful system to assess directly the consequences of mutations in individual components of the SMN pathway in various cell types and at the organismal level, and has helped uncover important aspects of SMA pathogenesis in humans.
We are currently exploring the role of Trimethylguanosine synthase 1 (TGS1), in preventing neurodegeneration in both human cells and in flies. Our recent findings support TGS1 involvement in SMA pathogenesis both in human cell and in flies (D. melanogaster). A promising venue towards understanding TGS1 and SMN function in SMA pathogenesis is provided by search for novel genetic modifiers able to protect against neurodegeneration. Using combined screens analyses on different animal models (i.e D.melanogaster, D.rerio and C.elegans), several SMN modifiers have been already identified.
Our aim is the characterization of dTgs1 novel interactors involved in snRNA maturation steps. Our recent findings reveal that NELF-B subunit ameliorates the development of the eye imaginal discs in dTgs1RNAi flies. The evidence of this approach prompts us to characterize factors implicated in snRNA maturation, unravelling sensitive nodes in the pathway in order to isolate potential candidates that have a crucial role in biogenesis pathway and that are able to compensate for the lack of TGS1. We believe that additional analyses on potential TGS1 genetic modifers will be helpful to gain insight into TGS1 and SMN interactors necessary for proper snRNAs maturation and able to ameliorate aberrant phenotypes due to their loss. Besides, we plan to unravel the causative relationships between the accumulation of aberrantly spliced transcript isoforms and neuronal death, by performing transcriptome analyses on larval retinal tissues of fly model that we recently developed. These bioinformatic analyses will help to understand how TGS1 and SMN loss affect the expression and splicing of transcripts that are relevant for the development and survival of neuronal cells and crucial aspects in snRNAs biogenesis that are necessary for neuronal stability.