A rapid change in P-element-induced hybrid dysgenesis status in Ukrainian populations of Drosophila melanogaster

Rahman

et al. 2019

eLife

Self Cite

Without transposon-silencing Piwi-interacting RNAs (piRNAs), transposition causes an ovarian atrophy syndrome in Drosophila called gonadal dysgenesis (GD). Harwich (Har) strains with P-elements cause severe GD in F1 daughters when Har fathers mate with mothers lacking P-element-piRNAs (i.e. ISO1 strain). To address the mystery of why Har induces severe GD, we bred hybrid Drosophila with Har genomic fragments into the ISO1 background to create HISR-D or HISR-N lines that still cause Dysgenesis or are Non-dysgenic, respectively. In these lines, we discovered a highly truncated P-element variant we named ‘Har-P’ as the most frequent de novo insertion. Although HISR-D lines still contain full-length P-elements, HISR-N lines lost functional P-transposase but retained Har-P’s that when crossed back to P-transposase restores GD induction. Finally, we uncovered P-element-piRNA-directed repression on Har-P’s transmitted paternally to suppress somatic transposition. The Drosophila short Har-P’s and full-length P-elements relationship parallels the MITEs/DNA-transposase in plants and SINEs/LINEs in mammals.

Section: Discussionmentioning

confidence: 99%

Har-P, a short P-element variant, weaponizes P-transposase to severely impair Drosophila development

Rahman

et al. 2019

eLife

Self Cite

“…When a P -element truncates to a ∼630bp Har-P variant, this non-autonomous variant dominates as the main mobilizing P -element during a dysgenic cross to induce strong GD. Therefore previous studies examining GD variability across other Drosophila strains and isolates may now be explained by whether these genomes contain both full length and very short P -elements (Bergman et al, 2017; Kozeretska et al, 2018; Ronsseray et al, 1989; Srivastav and Kelleher, 2017; Wakisaka et al, 2017; Yoshitake et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

Har-P, ashortP-element variant, weaponizesP-transposase to severely impairDrosophiladevelopment

Rahman

et al. 2019

Preprint

Self Cite

Har-P, a short P-element variant, weaponizes P-transposase to1 severely impair Drosophila development.Running title: Har-P and P-transposase drive gonadal dysgenesis. 15 16 ABSTRACT 1 Without transposon-silencing Piwi-interacting RNAs (piRNAs), transposition 2 causes an ovarian atrophy syndrome in Drosophila called gonadal dysgenesis (GD).3Harwich (Har) strains with P-elements cause severe GD in F1 daughters when Har 4 fathers mate with mothers lacking P-element-piRNAs (i.e. ISO1 strain). To address the 5 mystery of why Har induces severe GD, we bred hybrid Drosophila with Har genomic 6 fragments into the ISO1 background to create HISR-D or HISR-N lines that still cause 7 Dysgenesis or are Non-dysgenic, respectively. In these lines, we discovered a highly 8 truncated P-element variant we named "Har-P" as the most frequent de novo insertion. 9Although HISR-D lines still contain full-length P-elements, HISR-N lines lost functional 10 P-transposase but retained Har-P's that when crossed back to P-transposase restores 11 GD induction. Finally, we uncovered P-element-piRNA-directed repression on Har-P's 12 transmitted paternally to suppress somatic transposition. The Drosophila short Har-P's 13 and full-length P-elements relationship parallels the MITEs/DNA-transposase in plants 14 and SINEs/LINEs in mammals. 15 16 17 GD retention and loss in hybrid Drosophila lines with reduced P-element copy numbers.1 To genetically isolate the causative transposon strongly inducing GD and 2 facilitate discovery by whole genome sequencing (WGS), we generated hybrid lines 3 where only a minor fraction of the Har genome is within the background of the ISO1 4 reference genome sequence. We first conducted several fertility-permissive 5 backcrosses between female Har and male ISO1, selecting hybrid progeny that 6 propagated a red-eye phenotype which we attributed to the "red" eyes due to Har alleles 7 replacing the cn, bw, sp, alleles on Chromosome 2R (Chr2R) of ISO1 ( Fig. 2A-abridged 8 scheme, Fig. 2-S1-detailed scheme). We then performed an initial GD validation screen 9 with many vials of individual hybrid males crossed to ISO1 females and selecting for 10 lines that caused 100% GD from this cross. Lines were propagated with additional self-11 crosses and further in-bred with single-sibling pairs. We then subjected multiple 12 independent Har-ISO1-Selfed-Red (HISR) lines to a second GD assay. Finally, we 13 conducted qPCR to identify the lines with the greatest reduction of P-element copy 14 numbers ( Fig. 2B) and settled on 4 lines each either retaining severe paternally-induced 15 GD (HISR-D) or had lost this capacity (HISR-N) ( Fig. 2C). 16Genomic PCR genotyping of deletion loci of Har compared to ISO1 in HISR lines 17 indicated that these lines carried mostly ISO1 genomes ( Fig. 2-S2). Therefore, we 18 performed WGS of the parental Har and ISO1 strains, the 8 HISR lines, and the pi[2] 19 and Birmingham (Birm) strains, two classic strains with similar numbers of P-elements 20 but diametric capacity to induce GD (Engels et al., ...

“…Mosquito researchers can be envious of Drosophila ’s genetic tools, such as unparalleled annotation and manipulation of its genome [ 277 ], plethora of genetic markers and balancer chromosomes, and binary transgenes to trigger RNAi and CRISPR genome editing [ 278 , 279 ]. We envision that more and more investigators like in the Akbari and Lau labs [ 234 , 280 , 281 , 282 , 283 ] and other notable Drosophilists [ 284 , 285 ] will leverage their initial foundation of studies in Drosophila and extend their expertise to the mosquitoes.…”

Section: Final Thoughts: Strengthening the Fly-mosquito Partnershmentioning

confidence: 99%

Diverse Defenses: A Perspective Comparing Dipteran Piwi-piRNA Pathways

Gamez

Akbari

et al. 2020

Cells

Animals face the dual threat of virus infections hijacking cellular function and transposons proliferating in germline genomes. For insects, the deeply conserved RNA interference (RNAi) pathways and other chromatin regulators provide an important line of defense against both viruses and transposons. For example, this innate immune system displays adaptiveness to new invasions by generating cognate small RNAs for targeting gene silencing measures against the viral and genomic intruders. However, within the Dipteran clade of insects, Drosophilid fruit flies and Culicids mosquitoes have evolved several unique mechanistic aspects of their RNAi defenses to combat invading transposons and viruses, with the Piwi-piRNA arm of the RNAi pathways showing the greatest degree of novel evolution. Whereas central features of Piwi-piRNA pathways are conserved between Drosophilids and Culicids, multiple lineage-specific innovations have arisen that may reflect distinct genome composition differences and specific ecological and physiological features dividing these two branches of Dipterans. This perspective review focuses on the most recent findings illuminating the Piwi/piRNA pathway distinctions between fruit flies and mosquitoes, and raises open questions that need to be addressed in order to ameliorate human diseases caused by pathogenic viruses that mosquitoes transmit as vectors.