Scavenger Receptors Mediate the Role of SUMO and Ftz-f1 in Drosophila Steroidogenesis

Abstract

SUMOylation participates in ecdysteroid biosynthesis at the onset of metamorphosis in Drosophila melanogaster. Silencing the Drosophila SUMO homologue smt3 in the prothoracic gland leads to reduced lipid content, low ecdysone titers, and a block in the larval–pupal transition. Here we show that the SR-BI family of Scavenger Receptors mediates SUMO functions. Reduced levels of Snmp1 compromise lipid uptake in the prothoracic gland. In addition, overexpression of Snmp1 is able to recover lipid droplet levels in the smt3 knockdown prothoracic gland cells. Snmp1 expression depends on Ftz-f1 (an NR5A-type orphan nuclear receptor), the expression of which, in turn, depends on SUMO. Furthermore, we show by in vitro and in vivo experiments that Ftz-f1 is SUMOylated. RNAi–mediated knockdown of ftz-f1 phenocopies that of smt3 at the larval to pupal transition, thus Ftz-f1 is an interesting candidate to mediate some of the functions of SUMO at the onset of metamorphosis. Additionally, we demonstrate that the role of SUMOylation, Ftz-f1, and the Scavenger Receptors in lipid capture and mobilization is conserved in other steroidogenic tissues such as the follicle cells of the ovary. smt3 knockdown, as well as ftz-f1 or Scavenger knockdown, depleted the lipid content of the follicle cells, which could be rescued by Snmp1 overexpression. Therefore, our data provide new insights into the regulation of metamorphosis via lipid homeostasis, showing that Drosophila Smt3, Ftz-f1, and SR-BIs are part of a general mechanism for uptake of lipids such as cholesterol, required during development in steroidogenic tissues.

Forward and feedback regulation of cyclic steroid production in Drosophila melanogaster

“…Dashed lines correspond to time-delayed effects, whereas bold lines correspond to concurrent effects. Talamillo et al, 2013), and that DHR3 downregulation leads to late L3-arrested larvae (Caceres et al, 2011). In addition to E75, DHR3 and βFtz-f1, our study reveals that disrupting EcR in the PG also leads to developmental arrest that can be rescued by ecdysone feeding.…”

A comprehensive platform for the analysis of ubiquitin-like protein modifications using in vivo biotinylation

“…To test the functionality of the bioSmt3 transgene in vivo , we analysed its capacity to rescue the silencing of endogenous smt3 in steroidogenic tissues at larval stages. Tissue-specific knockdown of smt3 in the prothorathic gland (PG) blocks development at the end of larval stages due to a reduction in the steroid levels4950. This is achieved using a PG-specific GAL4 driver, together with UAS-Smt3 RNAi (hereinafter called smt3i ).…”

A Drosophila Genome-Wide Screen Identifies Regulators of Steroid Hormone Production and Developmental Timing

“…Gene hits associated with arrest in L1 or L2, the strongest phenotypes, include genes directly involved in the ecdysone biosynthetic pathway ( shroud , phantom , disembodied , shadow and Cyp6t3 ). The screen also identified genes associated with cholesterol trafficking ( Npc1a , GstE14/Nobo and snmp1 ), genes in major signaling pathways such as insulin/TOR ( InR, Akt1, raptor, Tif-1A ), PTTH/Torso/Ras ( torso, Ras85D ) and TGFβ ( put and tkv ), and transcription factors ( vvl , kni , mld, ouib, br, E75B, EcR and USP ) that are known to regulate ecdysone production in the PG (Caceres et al, 2011; Colombani et al, 2005; Danielsen et al, 2014; Gibbens et al, 2011; Huang et al, 2005; Komura-Kawa et al, 2015; Koyama et al, 2014; Layalle et al, 2008; Mirth et al, 2005; Moeller et al, 2013; Niwa et al, 2010; Niwa and Niwa, 2014; Ou et al, 2011; Rewitz et al, 2009; Talamillo et al, 2013; Zhou et al, 2004). This shows that our screen was successful in identifying genes with known steroidogenic roles, and an additional ~1,800 genes that have not been linked to either steroidogenesis, steroidogenic cell function or general gland viability; indeed, many of these genes have no identified function.…”