Bursicon-α subunit modulates dLGR2 activity in the adult Drosophila melanogaster midgut independently to Bursicon-β

Abstract

Bursicon is the main regulator of post molting and post eclosion processes during arthropod development. The active Bursicon hormone is a heterodimer of Burs-α and Burs-β. However, adult midguts express Burs-α to regulate the intestinal stem cell niche. Here, we examined the potential expression and function of its heterodimeric partner, Burs-β in the adult midgut. Unexpectedly, our evidence suggests that Burs-β is not significantly expressed in the adult midgut. burs-β mutants displayed the characteristic developmental defects but showed wild type-like adult midguts, thus uncoupling the developmental and adult phenotypes seen in burs-α mutants. Gain of function data and ex vivo experiments using a cAMP biosensor, demonstrated that Burs-α is sufficient to drive stem cell quiescence and to activate dLGR2 in the adult midgut.Our evidence suggests that the post developmental transactivation of dLGR2 in the adult midgut is mediated by Burs-α and that the β subunit of Bursicon is dispensable for these activities.

A Neuronal Relay Mediates a Nutrient Responsive Gut/Fat Body Axis Regulating Energy Homeostasis in Adult Drosophila

“…First, to unambiguously assess the main source of Bursα production during adulthood, we compared mRNA expression levels in mature whole adults, adult midguts, and adult animals from which the gut was removed prior to RNA extraction (“gut-less”). Confirming our previous results ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ) and subsequent independent reports ( Chen et al., 2016 , Dutta et al., 2015 ), we observed strong enrichment of bursα transcripts in adult midguts ( Figure 1 A).

Figure 1 Bursα in ee Cells Is Regulated by Nutrients (A and C) Transcript levels of bursα relative to rpl32 in indicated tissue samples from 10- to 14-day-old adult wild-type animals (A) or whole midguts from animals of the indicated genotypes (C).

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“…Ee cells are major sensors of luminal content ( Engelstoft et al., 2008 , Moran-Ramos et al., 2012 ) and coordinate gastrointestinal and systemic responses through secretory programs ( Steinert and Beglinger, 2011 ) that affect gut motility, digestion, appetite, glucose homeostasis, and energy expenditure ( Campbell and Drucker, 2013 , Field et al., 2010 , Gribble and Reimann, 2016 , Park et al., 2016 , Worthington et al., 2017 , Zietek and Daniel, 2015 ). Our previous work revealed a local role for ee-derived Bursα in the adult midgut, which was necessary and sufficient to prevent ISC proliferation ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ). Knocking down bursα from ee cells resulted in ISC hyperproliferation in the normally quiescent homeostatic adult midgut, while bursα overexpression suppressed the characteristic proliferative response of ISCs following damage and upon aging ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ).…”

“…Our previous work revealed a local role for ee-derived Bursα in the adult midgut, which was necessary and sufficient to prevent ISC proliferation ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ). Knocking down bursα from ee cells resulted in ISC hyperproliferation in the normally quiescent homeostatic adult midgut, while bursα overexpression suppressed the characteristic proliferative response of ISCs following damage and upon aging ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ). In such a context, Bursα appears to have a permissive role in the maintenance of ISC quiescence.…”

“…Given our previous reports showing a local role of Bursα in controlling ISC proliferation ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ) and nutrients being key regulators of the proliferative state of the adult Drosophila midgut ( O'Brien et al., 2011 , Obata et al., 2018 , Shim et al., 2013 ), we next explored the possibility that Bursα might be regulated by nutrients. We performed immunofluorescence staining on posterior midguts from animals fed ad libitum and following caloric deprivation.…”

“…The role of Bursicon/DLgr2 signaling has long been restricted to insect development, where the heterodimeric form of the hormone Bursicon, made by α and β subunits, is produced by a subset of neurons within the CNS during the late pupal stage and released systemically to activate its receptor DLgr2 in peripheral tissues to drive post-molting sclerotization of the cuticle and wing expansion ( Baker and Truman, 2002 , Luo et al., 2005 , Mendive et al., 2005 ). We recently demonstrated a post-developmental activity for the α subunit of Bursicon (Bursα), which is produced by a subpopulation of ee cells in the posterior midgut, where it paracrinally activates DLgr2 in the visceral muscle (VM) to maintain homeostatic intestinal stem cell (ISC) quiescence ( Scopelliti et al., 2014 , Scopelliti et al., 2016 ).…”