Drosophila germ-line modulation of insulin signaling and lifespan

Abstract

Ablation of germ-line precursor cells in Caenorhabditis elegans extends lifespan by activating DAF-16, a forkhead transcription factor (FOXO) repressed by insulin/insulin-like growth factor (IGF) signaling (IIS). Signals from the gonad might thus regulate whole-organism aging by modulating IIS. To date, the details of this systemic regulation of aging by the reproductive system are not understood, and it is unknown whether such effects are evolutionarily conserved. Here we report that eliminating germ cells (GCs) in Drosophila melanogaster increases lifespan and modulates insulin signaling. Long-lived germ-line-less flies show increased production of Drosophila insulin-like peptides (dilps) and hypoglycemia but simultaneously exhibit several characteristics of IIS impedance, as indicated by up-regulation of the Drosophila FOXO (dFOXO) target genes 4E-BP and l (2)efl and the insulin/IGF-binding protein IMP-L2. These results suggest that signals from the gonad regulate lifespan and modulate insulin sensitivity in the fly and that the gonadal regulation of aging is evolutionarily conserved.

Fig. 1.

GC loss and expansion of somatic cells in gonads from flies misexpressing bam⁺. (A–C) GC loss in adult females misexpressing bam⁺ in the germ line (y w/w¹¹¹⁸;UASp-bam⁺::gfp/+; nos-GAL4::VP16/+). GCs are stained for GC specific antigen vasa (green), somatic cells (FasIII, red), and DNA (DAPI, blue). Asterisk (*) denotes somatic cap cells. (A) GCs are rarely observed in ovarioles from 2-day-old females overexpressing bam⁺ [24/225 ovarioles (10.7%) contained GCs]. (B) GC loss is virtually complete by 7 days [3/325 ovarioles (0.9%) contained GCs]. See also Fig. S1. (C) Germarium from a 2-day-old control female. All ovarioles from control females contained GCs at 2 (n = 120) and at 7 days (n = 152). (A′–C′) shows FasIII⁺ somatic cells only. Note the expanded somatic gonad in GC-less females. (D and E) GC loss in third instar larval (L3) males overexpressing bam⁺. Control testes from L3 males (D) have a normal number of GSCs (vasa) in contact with hub cells (*) at the apical tip. (E) Males overexpressing bam⁺ show loss of GSCs by this stage. (E′) GCs present near the hub have branched fusomes (arrows) as detected by staining with antibodies to α-spectrin. Note the reduced size of the gonad. Asterisk (*) denotes the FasIII⁺ apical hub. (F and G) Expansion of somatic cells in testes from adults misexpressing bam⁺. (F) Control testes show normal distribution of FasIII⁺ hub cells (red) and TJ⁺ somatic cells (green). (G) An expansion of FasIII⁺ and TJ⁺ somatic cells is observed in testes. (Scale bars: 50 μm in A–C, F, and G; 20 μm in D and E.)

Fig. 2.

Adult GC loss extends lifespan in D. melanogaster. (A–D) Driving UASp-bam⁺ in germ line (no germ line, UASp-bam⁺/+; nos-GAL4::VP16/+) extends lifespan, both in a y w background (A, females; B, males) and a w¹¹¹⁸ background lacking one copy of bam (C, females; D, males), relative to two controls. Controls were, in the y w background, y w/y w;UASp-bam⁺::gfp/+ (control 1) and y w/w¹¹¹⁸; nos-GAL4::VP16/+ (control 2), and in the w¹¹¹⁸ background, w¹¹¹⁸/w¹¹¹⁸;UASp-bam⁺::gfp/+; bam^Δ86/+ (control 1) and w¹¹¹⁸/w¹¹¹⁸; nos-GAL4::VP16/+ (control 2). (E–H) Misexpressing UASp-bam⁺ with an alternative germ-line-specific driver, nos-GAL4-tubulin (UASp-bam⁺::gfp/NGT-GAL4), also extends lifespan, both in the y w background (E, females; F, males) and in a background lacking one copy of bam (G, females; H, males) compared with two controls (control 1: y w/y w;UASp-bam⁺::gfp/+ or w¹¹¹⁸/y w;UASp-bam⁺::gfp/+; bam^Δ86/+, respectively; control 2: y w/y¹ w*; NGT-GAL4/+). See Table S1 for statistics.

Fig. 3.

GC loss up-regulates dilp message but activates expression of dFOXO target genes. (A–D) GC-less flies (UASp-bam⁺/+; nos-GAL4::VP16/+) exhibit increased production of dilp 2, dilp 3, and dilp 5, both in the y w (A–C) and w¹¹¹⁸ backgrounds (D–F), relative to controls. (G–H) GC loss causes up-regulation of dFOXO targets 4E-BP (G) and l (2)efl (H) in both backgrounds. For details of genotypes, see Fig. 1.

Fig. 4.

GC loss up-regulates message of IMP-L2, but not of dALS. (A) GC loss does not alter message abundance of the DILP cofactor dALS. (B) In contrast, GC loss strongly up-regulates expression of the insulin/IGF- binding protein IMP-L2. See Fig. 1 for genotype information.