PubMed · 4882861
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D J Kushner. 1968. Halophilic bacteria.. https://doi.org/10.1016/s0065-2164(08)70189-8
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We present the first genome-wide study of recent evolution in Culex pipiens species complex focusing on the genomic extent, functional targets and likely causes of global and local adaptations. We resequenced pooled samples of six populations of C. pipiens and two populations of the outgroup Culex torrentium. We used principal component analysis to systematically study differential natural selection across populations and developed a phylogenetic scanning method to analyse admixture without haplotype data. We found evidence for the prominent role of geographical distribution in shaping population structure and specifying patterns of genomic selection. Multiple adaptive events, involving genes implicated with autogeny, diapause and insecticide resistance were limited to specific populations. We estimate that about 5-20% of the genes (including several histone genes) and almost half of the annotated pathways were undergoing selective sweeps in each population. The high occurrence of sweeps in non-genic regions and in chromatin remodelling genes indicated the adaptive importance of gene expression changes. We hypothesize that global adaptive processes in the C. pipiens complex are potentially associated with South to North range expansion, requiring adjustments in chromatin conformation. Strong local signature of adaptation and emergence of hybrid bridge vectors necessitate genomic assessment of populations before specifying control agents.
We have recently described a novel RNA, designated adapt15, which is strongly induced by a pretreatment concentration of hydrogen peroxide in hamster HA-1 fibroblasts under conditions where a protective "adaptive response" occurs. adapt15 may therefore be involved in protecting cells against the damaging effects of oxidative stress. Since two other known sequences, gadd45 and gadd153m were also found to be induced under our pretreatment conditions and are known to be growth arrest and DNA damage inducible, we decided to also assess the possible association of adapt15 with growth arrest and DNA damage. We found that, like gadd45 and gadd153, the levels of adapt15 RNA were low during proliferation, but high during density saturation- and low serum (G0)-growth arrests. Exposure of HA-1 cells to DNA-damaging agents revealed significant induction of adapt15 RNA by methylmeth- anesulfonate and cis-platinum but not X-irradiation. Near identical responses were also observed for gadd45 and gadd153 RNAs, suggesting coordinate regulation of adapt15, gadd45, and gadd153. All three RNAs were also increased relative to control following heat shock, a nongenotoxic treatment. Finally, the induction of adapt15 by hydrogen peroxide was strongly dependent upon calcium, a hallmark of gadd153 induction. The coordinate inductions of adapt15, gadd45, and gadd153 by multiple agents, and their induction by an adaptive- but not by a nonadaptive-response level of hydrogen peroxide, suggest these RNAs may act in concert to protect cells against the damaging effects of oxidative stress.
RNA secondary structure folding algorithms predict the existence of connected networks of RNA sequences with identical structure. On such networks, evolving populations split into subpopulations, which diffuse independently in sequence space. This demands a distinction between two mutation thresholds: one at which genotypic information is lost and one at which phenotypic information is lost. In between, diffusion enables the search of vast areas in genotype space while still preserving the dominant phenotype. By this dynamic the success of phenotypic adaptation becomes much less sensitive to the initial conditions in genotype space.