Abstract
In Drosophila melanogaster, a key germline stem cell (GSC) differentiation factor, bag of marbles (bam) shows rapid bursts of amino acid fixations between sibling species D. melanogaster and ...Drosophila simulans, but not in the outgroup species Drosophila ananassae. Here, we test the null hypothesis that bam’s differentiation function is conserved between D. melanogaster and four additional Drosophila species in the melanogaster species group spanning approximately 30 million years of divergence. Surprisingly, we demonstrate that bam is not necessary for oogenesis or spermatogenesis in Drosophila teissieri nor is bam necessary for spermatogenesis in D. ananassae. Remarkably bam function may change on a relatively short time scale. We further report tests of neutral sequence evolution at bam in additional species of Drosophila and find a positive, but not perfect, correlation between evidence for positive selection at bam and its essential role in GSC regulation and fertility for both males and females. Further characterization of bam function in more divergent lineages will be necessary to distinguish between bam’s critical gametogenesis role being newly derived in D. melanogaster, D. simulans, Drosophila yakuba, and D. ananassae females or it being basal to the genus and subsequently lost in numerous lineages.
Abstract
In Drosophila melanogaster, the maternally inherited endosymbiont Wolbachia pipientis interacts with germline stem cell genes during oogenesis. One such gene, bag of marbles (bam) is the key ...switch for differentiation and also shows signals of adaptive evolution for protein diversification. These observations have led us to hypothesize that W. pipientis could be driving the adaptive evolution of bam for control of oogenesis. To test this hypothesis, we must understand the specificity of the genetic interaction between bam and W. pipientis. Previously, we documented that the W. pipientis variant, wMel, rescued the fertility of the bamBW hypomorphic mutant as a transheterozygote over a bam null. However, bamBW was generated more than 20 years ago in an uncontrolled genetic background and maintained over a balancer chromosome. Consequently, the chromosome carrying bamBW accumulated mutations that have prevented controlled experiments to further assess the interaction. Here, we used CRISPR/Cas9 to engineer the same single amino acid bam hypomorphic mutation (bamL255F) and a new bam null disruption mutation into the w1118 isogenic background. We assess the fertility of wildtype bam, bamL255F/bamnull hypomorphic, and bamL255F/bamL255F mutant females, each infected individually with 10 W. pipientis wMel variants representing three phylogenetic clades. Overall, we find that all of the W. pipientis variants tested here rescue bam hypomorphic fertility defects with wMelCS-like variants exhibiting the strongest rescue effects. In addition, these variants did not increase wildtype bam female fertility. Therefore, both bam and W. pipientis interact in genotype-specific ways to modulate female fertility, a critical fitness phenotype.
Melanism is widely observed among animals, and is adaptive in various contexts for its thermoregulatory, camouflaging, mate-attraction or photoprotective properties. Many organisms exposed to ...ultraviolet radiation show increased fitness resulting from melanin pigmentation; this has been assumed to result in part from reduced UV-induced damage to DNA. However, to effectively test the hypothesis that melanin pigmentation reduces UV-induced DNA damage requires quantification of UV-specific DNA damage lesions following UV exposure under controlled conditions using individuals that vary in pigmentation intensity. We accomplished this using alpine genotypes of the freshwater microcrustacean
, for which we quantified cyclobutane pyrimide dimers in DNA, a damage structure that can only be generated by UV exposure. For genotypes with carapace melanin pigmentation, we found that individuals with greater melanin content sustained lower levels of UV-induced DNA damage. Individuals with more melanin were also more likely to survive exposure to ecologically relevant levels of UV-B radiation. Parallel experiments with conspecific genotypes that lack carapace melanin pigmentation provide additional support for our conclusion that melanism protects individuals from UV-induced DNA damage. Finally, within-genotype comparisons with asexually produced clonal siblings demonstrate that melanin content influences DNA damage even among genetically identical individuals raised in the same environment.
Melanism is widely observed among animals, and is adaptive in various contexts for its thermoregulatory, camouflaging, mate-attraction or photoprotective properties. Many organisms exposed to ...ultraviolet radiation show increased fitness resulting from melanin pigmentation; this has been assumed to result in part from reduced UV-induced damage to DNA. However, to effectively test the hypothesis that melanin pigmentation reduces UV-induced DNA damage requires quantification of UV-specific DNA damage lesions following UV exposure under controlled conditions using individuals that vary in pigmentation intensity. We accomplished this using alpine genotypes of the freshwater microcrustacean Daphnia melanica, for which we quantified cyclobutane pyrimide dimers in DNA, a damage structure that can only be generated by UV exposure. For genotypes with carapace melanin pigmentation, we found that individuals with greater melanin content sustained lower levels of UV-induced DNA damage. Individuals with more melanin were also more likely to survive exposure to ecologically relevant levels of UV-B radiation. Parallel experiments with conspecific genotypes that lack carapace melanin pigmentation provide additional support for our conclusion that melanism protects individuals from UV-induced DNA damage. Finally, within-genotype comparisons with asexually produced clonal siblings demonstrate that melanin content influences DNA damage even among genetically identical individuals raised in the same environment.
Abstract
In Drosophila melanogaster, the maternally inherited endosymbiont Wolbachia pipientis interacts with germline stem cell genes during oogenesis. One such gene, bag of marbles (bam) is the key ...switch for differentiation and also shows signals of adaptive evolution for protein diversification. These observations have led us to hypothesize that W. pipientis could be driving the adaptive evolution of bam for control of oogenesis. To test this hypothesis, we must understand the specificity of the genetic interaction between bam and W. pipientis. Previously, we documented that the W. pipientis variant, wMel, rescued the fertility of the bamBW hypomorphic mutant as a transheterozygote over a bam null. However, bamBW was generated more than 20 years ago in an uncontrolled genetic background and maintained over a balancer chromosome. Consequently, the chromosome carrying bamBW accumulated mutations that have prevented controlled experiments to further assess the interaction. Here, we used CRISPR/Cas9 to engineer the same single amino acid bam hypomorphic mutation (bamL255F) and a new bam null disruption mutation into the w1118 isogenic background. We assess the fertility of wildtype bam, bamL255F/bamnull hypomorphic, and bamL255F/bamL255F mutant females, each infected individually with 10 W. pipientis wMel variants representing three phylogenetic clades. Overall, we find that all of the W. pipientis variants tested here rescue bam hypomorphic fertility defects with wMelCS-like variants exhibiting the strongest rescue effects. In addition, these variants did not increase wildtype bam female fertility. Therefore, both bam and W. pipientis interact in genotype-specific ways to modulate female fertility, a critical fitness phenotype.
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