Genetic, behavioural and molecular studies of Gemin3 using Drosophila melanogaster

Abstract

The DEAD-box RNA helicase Gemin3 (Gem3) is a multifunctional protein also referred to as DDX20 and DP103. It comprises of a highly conserved N-terminus harbouring the helicase core and the DEAD-domains, and a divergent C-terminus that interacts with various proteins.. Gem3 has a role in the biogenesis of spliceosomal small nuclear ribonucleoproteins (snRNPs) and is also implicated in messenger ribonucleoprotein (mRNP) transport, regulation of transcription through interactions with transcription factors, microRNA functions in gene silencing and in two signalling pathways, namely NF- КB and p53. Due to its multifaceted properties, it is not surprising that disruption of Gem3 has been associated with various diseases including spinal muscular atrophy, amyotrophic lateral sclerosis (ALS) and cancer. Aiming at identifying novel functions for Gem3, a narrow genetic screen was performed in Drosophila to identify novel genetic interactors. A functional relationship was uncovered between Gem3 and eIF4G2/NAT1, a eukaryotic initiation factor that acts as a scaffold during translation initiation and accumulates in stress granules during stress. To this end, knockdown of NAT1 in combination with loss of Gem3 function induced severe flight impairment and reduced lifespan, as well as accentuated defects during earlier stages of development. RNA-seq analysis highlighted a substantial amount of overlapping genes that were differentially expressed and/or spliced linking NAT1 and Gem3 together through various pathways, including those involved in organism development. This was further shown through the global knockdown of Gem3 or NAT1 which led to central nervous system (CNS) growth reduction, diminished mobility and altered puparial shape. Another potential genetic interaction was also uncovered between Gem3 and the transcription factor sugarbabe (sug) which is known for its functions in sugar and lipid metabolism. Detailed analysis revealed that gene expression levels of Gem3, NAT1, and sug are interdependent. Notably, this study strengthened the role of Gem3 as a multifactorial protein, a role that is congruent with the obvious developmental defects observed on loss of its function in Drosophila.