Wolbachia‐induced expression of kenny gene in testes affects male fertility in Drosophila melanogaster

Abstract

Wolbachia are Gram‐negative endosymbionts that are known to cause embryonic lethality when infected male insects mate with uninfected females or with females carrying a different strain of Wolbachia, a situation characterized as cytoplasmic incompatibility (CI). However, the mechanism of CI is not yet fully understood, although recent studies on Drosophila melanogaster have achieved great progress. Here, we found that Wolbachia infection caused changes in the expressions of several immunity‐related genes, including significant upregulation of kenny (key), in the testes of D. melanogaster. Overexpression of key in fly testes led to a significant decrease in egg hatch rates when these flies mate with wild‐type females. Wolbachia‐infected females could rescue this embryonic lethality. Furthermore, in key overexpressing testes terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick‐end labeling signal was significantly stronger than in the control testes, and the level of reactive oxygen species was significantly increased. Overexpression of key also resulted in alterations of some other immunity‐related gene expressions, including the downregulation of Zn72D. Knockdown of Zn72D in fly testes also led to a significant decrease in egg hatch rates. These results suggest that Wolbachia might induce the defect in male host fertility by immunity‐related pathways and thus cause an oxidative damage and cell death in male testes.

Evolution-guided mutagenesis of the cytoplasmic incompatibility proteins: Identifying CifA’s complex functional repertoire and new essential regions in CifB

“…Wolbachia-induced increases in ROS levels correlate with DNA damage in D. simulans spermatocytes [54] and an increase in lipid hydroperoxides in D. melanogaster, which are markers for ROS-induced oxidative damage [56]. Intriguingly, the immune-related gene kenny (key) is upregulated in Wolbachia-infected D. melanogaster, and experimental upregulation of key in uninfected male flies yielded increased ROS levels, DNA damage, and decreased hatching that can be rescued when mated to infected females [57]. Together, these data support a role for ROS in CI's mechanism, but more work is necessary to link CifA's catalase-rel domain to ROS variation and determine if ROS are directly responsible for CI/rescue-induction or are otherwise a symptom of other modifications in gametogenesis.…”

Symbiont-Mediated Cytoplasmic Incompatibility: What have we Learned in 50 Years?

“…First, a defensive model would predict that the pathway(s) that CI act(s) on in the host must be conserved enough for CI to be transferable between species, but also malleable enough for the pathway(s) to become resistant to CI-induction. The host genes, transcripts, and proteins described earlier in this review are excellent candidates since they can mimic CI phenotypes (Biwot et al, 2019;Huang et al, 2019;Ju et al, 2017;Yuan et al, 2015;Zheng et al, 2011). However, studies are necessary to investigate genetic variation in these host products to assess the possibility that they are under selection to suppress CI.…”

“…When differential expression is correlated with CI phenotypes, these data can yield valuable insights regarding CI's mechanism. Significant correlations between Wolbachia infection state and host expression have been measured in D. melanogaster (Biwot et al, 2019;He et al, 2019;LePage et al, 2014;Liu et al, 2014;Ote et al, 2016;Xi et al, 2008;Yuan et al, 2015;Zheng et al, 2011), D. simulans (Brennan et al, 2012;Clark et al, 2006;Xi et al, 2008), La. striatellus (Huang et al, 2019;Ju et al, 2017;Liu et al, 2019), T. urticae (Bing et al, 2019;Zhang et al, 2015), Cu.…”

“…striatellus (Ju et al, 2017), the sRNA nov-miR-12 which negatively regulates the DNA-binding protein pipsqueak (psq) in chromatin remodeling in D. melanogaster (Y. , cytosol amino-peptidase-like which are in the sperm acrosome and involved in fertilization in La. striatellus (Huang et al, 2019), two seminal fluid proteins (CG9334 and CG2668) with unknown function in D. melanogaster (Yuan et al, 2015), the histone chaperone Hira in D. melanogaster and D. simulans (Zheng et al, 2011), a Juvenile Hormone protein (JHI-26) involved in development in D. melanogaster (Liu et al, 2014), and the immunityrelated gene kenny (key) in D. melanogaster (Biwot et al, 2019). Since misexpression of these host products in aposymbiotic males mimic CI-like embryonic defects in a way that can be rescued by symbiont-bearing females, there is support that these products or their pathways are involved in CI, but how these factors relate to cause CI remains unknown, and there is no current evidence that these are binding partners with Cif proteins.…”

“…Additionally, lipid hydroperoxide markers of ROS-induced oxidative damage are higher in symbiont-bearing D. melanogaster (Driver et al, 2004), and PCNA retention is another marker for DNA damage and is observed during the first mitosis of CI-affected embryos (Landmann et al, 2009). Interestingly, overexpression of the D. melanogaster gene key increases ROS levels and DNA damage in males when mimicking rescuable CI-like hatching and embryonic defects (Biwot et al, 2019). Together, these data support a role for ROS in CI's mechanism, but direct connections remain unclear.…”