Table 3 Factors that regulate the PG in Drosophila
PG-influencing factorComments
Activin/TGF-βRegulates torso and InR expression via Baboon/Smad2; Gibbens et al. (2011).
Decapentaplegic (Dpp)/TGF-βDpp released by growing discs represses ecdysone synthesis via Thickveins (Tkv), at least in part through effects on FOXO and ban; Setiawan et al. (2018).
DILPs (via InR)Insulin signaling in the PG promotes ecdysone synthesis through effects on TOR, Warts signaling (via bantam), and cholesterol trafficking; Caldwell et al. (2005); Colombani et al. (2005); Mirth et al. (2005); Boulan et al. (2013); Moeller et al. (2017); Texada et al. (2019b). A small insulin-induced peak appears to be associated with critical weight; Shingleton et al. (2005); Koyama et al. (2014).
DILP8DILP8 secreted by damaged or unevenly growing discs acts directly on PG via Lgr3 and nitric oxide signaling to repress basal ecdysone synthesis, and thus growth of undamaged imaginal tissues; Caceres et al. (2011); Jaszczak et al. (2015); Jaszczak et al. (2016).
EcdysoneEcdysone feedback via EcR to Br-Z4 (positive feedback) and Br-Z1 (negative feedback) drives and terminates the metamorphic ecdysone pulse; Moeller et al. (2013). EcR promotes autophagic mobilization of cholesterol for ecdysone synthesis; Texada et al. (2019b). EcR promotes expression of EGF-like ligands Vein and Spitz; Cruz et al. (2020).
EGF-like signalsAutocrine signaling via ligands Spitz and Vein, induced by ecdysone feedback, drives the MAPK pathway and promotes the metamorphic ecdysone peak; Cruz et al. (2020).
Hedgehog (lipid-associated)Released from enterocytes under starvation conditions and inhibits expression of phantom and spookier; Rodenfels et al. (2014).
Juvenile hormone (JH)Inhibits basal ecdysone synthesis via Kr-h1 (Zhang et al. 2018) but does not appear to affect timing in Drosophila; Mirth et al. (2014).
PG-endogenous clockA PG-autonomous clock, interacting with central circadian rhythms and insulin signaling, is required for steroidogenesis; commentary in Danielsen and Rewitz (2016); Di Cara and King-Jones (2016).
Prothoracicotropic hormone (PTTH)Promotes PG-cell growth, endoreduplication, and Halloween-gene expression via receptor tyrosine kinase Torso; King-Jones et al. (2005, 2016); McBrayer et al. (2007); Rewitz et al. (2009b); Ghosh et al. (2010); Ou et al. (2011, 2016); Rewitz and O’Connor (2011); Ohhara et al. (2017); Shimell et al. (2018).
SerotoninSerotonergic neurons receive input from SEZ/SOG and arborize more densely on the PG under well-fed conditions. Serotonin acts via receptor 5-HT7 (Shimada-Niwa and Niwa 2014) to promote ecdysone synthesis.
TOR signalingLoss blocks pupariation; activation rescues nutritional delay; Layalle et al. (2008).
Drives endoreduplication via Snail; Ohhara et al. (2017); Zeng et al. (2020).
Regulates autophagic cholesterol trafficking; Pan et al. (2019); Texada et al. (2019b).
TyramineAutocrine tyramine signaling through Octβ3R is required for intracellular DILP and PTTH transduction and ecdysone synthesis; Ohhara et al. (2015).
  • EcR, ecdysone receptor; InR, insulin receptor; PG, prothoracic gland.