A Genetic Screen inDrosophilaTo Identify Novel Regulation of Cell Growth by Phosphoinositide Signaling

Abstract

Phosphoinositides are lipid signaling molecules that regulate several conserved sub-cellular processes in eukaryotes, including cell growth. Phosphoinositides are generated by the enzymatic activity of highly specific lipid kinases and phosphatases. For example, the lipid PIP3, the Class I PI3 kinase that generates it and the phosphatase PTEN that metabolizes it are all established regulators of growth control in metazoans. To identify additional functions for phosphoinositides in growth control, we performed a genetic screen to identify proteins which when depleted result in altered tissue growth. By using RNA-interference mediated depletion coupled with mosaic analysis in developing eyes, we identified and classified additional candidates in the developing Drosophila melanogaster eye that regulate growth either cell autonomously or via cell-cell interactions. We report three genes: Pi3K68D, Vps34 and fwd that are important for growth regulation and suggest that these are likely to act via cell-cell interactions in the developing eye. Our findings define new avenues for the understanding of growth regulation in metazoan tissue development by phosphoinositide metabolizing proteins.

Regulated inositol synthesis is critical for balanced metabolism and development in Drosophila melanogaster

“…Having established that inositol is causing developmental defects, some next steps would be to determine if this is due inositol's role in membrane biogenesis, signal transduction, osmoregulation, as a carbon/energy source, as an insulin mimetic, or in some other component of maintenance of homeostasis and/or metabolism. Since inositol is a precursor for the phosphatidylinositol phosphates (PIPs), it is interesting to note that dysregulation of the expression of the phosphatidylinositol synthase gene ( Pis ) causes pupal lethality ( Janardan et al, 2020 ). Inositol phosphate kinase 2 ( Ipk2 ) deletion mutants also show pupal lethality ( Seeds et al, 2015 ).…”

“…The three ways an organism can acquire inositol are: (1) transport from the extracellular environment ( Spector and Lorenzo, 1975 ), (2) recycling of inositol phosphates ( Berridge and Irvine, 1984 ; Janardan et al, 2020 ), and (3) synthesis from glucose-6-phosphate. The first and rate limiting step of inositol synthesis is catalyzed by myo -inositol-3-phosphate synthase (MIPSp, EC 5.5.1.4 alternate name myo -inositol-1-phosphate synthase) ( Loewus and Kelly, 1962 ; Eisenberg et al, 1964 ).…”

“…Pharate adults are flies that have largely undergone metamorphosis but have not emerged from the pupal case. Pupal lethality can be caused by mutations in components of the phosphoinositide pathways (PI synthase, PI4 kinase, and PI4P phosphatase) ( Del Bel and Brill, 2018 ; Janardan et al, 2020 ). The typical lifespan of a D. melanogaster adult is 20-60 days.…”

A genome engineering resource to uncover principles of cellular organization and tissue architecture by lipid signaling

“…This would allow for the generation of CRISPR edited mosaic clones useful for studying cell-cell interactions including cell competition that are integral elements of tissue development. Indeed, a recent study has presented evidence of a role of some genes involved in PI signaling as regulators of cell competition during eye development ( Janardan et al, 2020 ) and the expanded repertoire of editing reagents generated during this study will allow the mechanism by which PI signaling regulates cell competition to be analysed in greater detail.…”

Evolution and genetic basis of the plant-penetrating ovipositor, a key adaptation in herbivorous Drosophilidae

“…However, two terms surpassed a nominal cutoff of P < 0.001, and both reflect broadly conserved developmental functions in eukaryotes: phosphatidylinositol (PI) biosynthetic process and establishment of cell polarity (Table 2). Many of the candidate genes annotated with PI biosynthetic process (GO:0006661) are kinases and transferases involved in production of PI derivatives (Table S10), which act as signaling molecules that regulate cellular growth and patterning [42][43][44]. Notably, establishment of cell polarity (GO:0030010) precedes the differentiation of sensory organ precursors into distinct neural cell types through asymmetric cell division [45].…”