Unique germ-line organelle, nuage, functions to repress selfish genetic elements in Drosophila melanogaster

Abstract

), the authors note that in Fig. 4 A, the staining for Vasa in spindle-E mutant ovaries was incorrect. Consistent with Findley et al. (4), Vasa perinuclear localization is unaffected in spindle-E mutant ovaries. This does not change the major conclusion that the nuage functions to maintain genome stability by repressing the expression of the selfish genetic elements via rasiRNA-mediated gene silencing. Rather, Spindle-E may function at the same hierarchical level or downstream of Vasa to regulate the localization of Aubergine, Krimper, and Maelstrom. The corrected figure and legend appear below. Fig. 4. Nuage foci are mislocalized in the germ-line-specific RNA-silencing component mutants. Ovaries from different mutant flies were immunostained for the nuage components. Homozygous mutant alleles or allelic combinations were used for all the mutants, except for dcr-1, where clonal analysis was employed. (Scale bar: 10 m.) (A) Localization of the nuage components at the perinuclear regions of the germ-line cells reflects a hierarchical assembly. The nuage components, AUB, KRIMP, and MAEL, depend on SPN-E and VAS to localize normally to the perinuclear regions; KRIMP and MAEL depend on SPN-E, VAS, and AUB to localize to the nuage; and MAEL depends on SPN-E, VAS, AUB, and KRIMP to localize normally. (B) Nuage localization is unaffected in the conventional dicing enzyme mutants, dcr-1 and dcr-2. The nuage is an electron-dense perinuclear structure that is known to be a hallmark of animal germ-line cells. Although the conservation of the nuage throughout evolution accentuates its essentiality, its role(s) and the exact mechanism(s) by which it functions in the germ line still remain unknown. Here, we report a nuage component, Krimper (KRIMP), in Drosophila melanogaster and show that it ensures the repression of the selfish genetic elements in the female germ line. The Krimp loss-of-function allele exhibited female sterility, defects in karyosome formation and oocyte polarity, and precocious osk translation. These phenotypes are commonly observed in the other nuage component mutants, vasa (vas) and maelstrom (mael), and the RNAsilencing component mutants, spindle-E (spn-E) and aubergine (aub), suggesting a shared underlying defect that uses RNA silencing. Moreover, we demonstrated that the localization of the nuage components depends on both SPN-E and AUB and that the selfish genetic elements were derepressed to different extents in the nuage component mutants, as well as in aub and armitage (armi) mutants. In the nuage component mutants, vas, krimp, and mael, the levels of roo, I-element, and HeT-A repeat-associated small interfering RNAs were greatly reduced. Hence, our data suggest that the nuage functions as a specialized center that protects the genome in the germ-line cells via gene regulation mediated by repeat-associated small interfering RNAs.Krimper ͉ repeat-associated small interfering RNA

Drosophila Piwi functions downstream of piRNA production mediating a chromatin-based transposon silencing mechanism in female germ line

“…S2), we next looked at the impact of germ-line Piwi depletion on the localization pattern of Aub. Mutations disrupting the ping-pong amplification process can lead to mislocalization of Aub from the peri-nuclear structure nuage (13,34), the proposed site of secondary piRNA production (34). Similar to earlier observations using mutants that disrupt Piwi in both germ line and soma (14), we found no impact on Aub localization to the nuage (Fig.…”

Mutations to the piRNA Pathway ComponentAubergineEnhance Meiotic Drive of Segregation Distorter inDrosophila melanogaster

“…In the testes, these two proteins associate with other piRNA pathway components including Vasa (Vas), Armitage (Armi), and Tudor (Tud) in large electron-dense perinuclear bodies, dubbed piNG-bodies, which are thought to regulate the processing and/or targeting of piRNAs to transposable elements via sequence homology (Lim and Kai 2007;Lim et al 2009;Nishida et al 2009;Kibanov et al 2011). The localization of both Aub and AGO3 to this perinuclear region is codependent; loss of one protein through mutation results in mislocalization of the other (Cox et al 2000;Brennecke et al 2007;Nishida et al 2007;Li et al 2009;Nagao et al 2010).…”

Selfish genetic elements, genetic conflict, and evolutionary innovation

“…The scarcity of males caused by meiotic drivers and cytoplasmic sex ratio distorters has selected for changes in mating systems (78). The germ granule, a key constituent in germ cell determination, contains proteins important in TE suppression (79), and SGEs may have promoted the evolution of a sequestered germline (80). Suzuki et al (35) propose that DNA methylation suppression of TEs was a precursor for the evolution of genomic imprinting and the placenta in mammals.…”