Mocs1 (Molybdenum cofactor synthesis 1) may contribute to lifespan extension in Drosophila

The experiment described in this paper resulted from a failed negative control in a study examining the effect of reducing ribosomal protein (Rp) gene expression on lifespan in Drosophila. Reduction in several different Rps has been shown to lengthen lifespan in a variety of model organisms (C. elegans, S. cerevisiae, D. melanogaster among others Steffen et al. 2008, Bell et al. 2009, Lindquist et al. 2011) presumably via impacts on Target of Rapamycin (TOR) signaling and possibly also mitochondrial function (Riera et al. 2016). As a means of knocking down Rp gene expression in vivo, we made use of the modularized miss-expression system consisting of GAL4 drivers (genetic strains of flies that express the yeast GAL4 transcription factor tissue-specifically) and responders (genetic strains of flies that possess GAL4 inducible transgenes expressing a gene of interest) (Rørth et al. 1998). When drivers and responders are crossed to each other, GAL4 induction of the gene of interest can be observed in the progeny. For the Rp experiment, we specifically employed transgenic RNAi responder lines from the Harvard Drosophila Transgenic RNAi Project (TrIP) where inducible transgenes expressing dsRNA against specific Rps were all integrated into a targeted locus on the third chromosome. This locus had been selected based on extensive expression analysis designed to minimize position effects that might shut down a transgene due to genomic location (Zirin et al. 2020). All the transgenes we used were located ~40 bp upstream of a gene called Mocs1 (CG33048), which encodes a cofactor required by enzymes that utilize Molybdenum. In our RpRNAi lifespan experiment, we used maternally inherited neuronal and fat body GAL4 inducers (drivers) to knock down Rp gene expression (paternally inherited RNAi responders) in these specific (neuronal and fat body) tissues where the intersection between nutrient sensing and metabolism correlates with lifespan modulation (Shen et al. 2009, Hoffman et al. 2013, Fabian et al. 2021). The direction of the cross appeared to matter (i.e., which parent passed the driver or responder to the experimental offspring) as results were equivocal for the reciprocal cross in a pilot. As a first negative control for the RpRNAi experiment, we used progeny from a cross between the original strain the TrIP project used to target the RNAi transgenes (this contains the att-P2 “docking site” but no inducible GAL4 transgene) and the w[1118] isogenic strain which