Localization of Candidate Regions Maintaining a Common Polymorphic Inversion (2La) in Anopheles gambiae

Chromosomal inversion polymorphisms are thought to play a role in adaptive divergence, but the genes conferring adaptive benefits remain elusive. Here we study 2La, a common polymorphic inversion in the African malaria vector Anopheles gambiae. The frequency of 2La varies clinally and seasonally in a pattern suggesting response to selection for aridity tolerance. By hybridizing genomic DNA from individual mosquitoes to oligonucleotide microarrays, we obtained a complete map of differentiation across the A. gambiae genome. Comparing mosquitoes homozygous for the 2La gene arrangement or its alternative (2L+a), divergence was highest at loci within the rearranged region. In the 22 Mb included within alternative arrangements, two ∼1.5 Mb regions near but not adjacent to the breakpoints were identified as being significantly diverged, a conclusion validated by targeted sequencing. The persistent association of both regions with the 2La arrangement is highly unlikely given known recombination rates across the inversion in 2La heterozygotes, thus implicating selection on genes underlying these regions as factors responsible for the maintenance of 2La. Polymorphism and divergence data are consistent with a model in which the inversion is maintained by migration-selection balance between multiple alleles inside these regions, but further experiments will be needed to fully distinguish between the epistasis (coadaptation) and local adaptation models for the maintenance of 2La

Transcriptomic Evidence for a Dramatic Functional Transition of the Malpighian Tubules after a Blood Meal in the Asian Tiger Mosquito <i>Aedes albopictus</i>

<div><p>Background</p><p>The consumption of a vertebrate blood meal by adult female mosquitoes is necessary for their reproduction, but it also presents significant physiological challenges to mosquito osmoregulation and metabolism. The renal (Malpighian) tubules of mosquitoes play critical roles in the initial processing of the blood meal by excreting excess water and salts that are ingested. However, it is unclear how the tubules contribute to the metabolism and excretion of wastes (e.g., heme, ammonia) produced during the digestion of blood.</p><p>Methodology/Principal Findings</p><p>Here we used RNA-Seq to examine global changes in transcript expression in the Malpighian tubules of the highly-invasive Asian tiger mosquito <i>Aedes albopictus</i> during the first 24 h after consuming a blood meal. We found progressive, global changes in the transcriptome of the Malpighian tubules isolated from mosquitoes at 3 h, 12 h, and 24 h after a blood meal. Notably, a DAVID functional cluster analysis of the differentially-expressed transcripts revealed 1) a down-regulation of transcripts associated with oxidative metabolism, active transport, and mRNA translation, and 2) an up-regulation of transcripts associated with antioxidants and detoxification, proteolytic activity, amino-acid metabolism, and cytoskeletal dynamics.</p><p>Conclusions/Significance</p><p>The results suggest that blood feeding elicits a functional transition of the epithelium from one specializing in active transepithelial fluid secretion (e.g., diuresis) to one specializing in detoxification and metabolic waste excretion. Our findings provide the first insights into the putative roles of mosquito Malpighian tubules in the chronic processing of blood meals.</p></div

Comparative Transcriptomics of Malaria Mosquito Testes: Function, Evolution, and Linkage

Testes-biased genes evolve rapidly and are important in the establishment, solidification, and maintenance of reproductive isolation between incipient species. The Anopheles gambiae complex, a group of at least eight isomorphic mosquito species endemic to Sub-Saharan Africa, is an excellent system to explore the evolution of testes-biased genes. Within this group, the testes are an important tissue in the diversification process because hybridization between species results in sterile hybrid males, but fully fertile females. We conducted RNA sequencing of A. gambiae and A. merus carcass and testes to explore tissue- and species-specific patterns of gene expression. Our data provides support for transcriptional repression of X-linked genes in the male germline, which likely drives demasculinization of the X chromosome. Testes-biased genes predominately function in cellular differentiation and show a number of interesting patterns indicative of their rapid evolution, including elevated dN/dS values, low evolutionary conservation, poor annotation in existing reference genomes, and a high likelihood of differential expression between species

Differential expression after blood feeding of transcripts associated with ammonia detoxification.

<p>Blue shading indicates significant down-regulation compared to NBF controls, whereas yellow shading indicates significant up-regulation compared to NBF controls. Lack of shading indicates no significant difference relative to NBF controls. Degree of shading is based on value of Log₂ fold change as indicated by the scale below on the right.</p

Differential expression after blood feeding of transcripts encoding subunits of the V-type H⁺-ATPase.

<p>Blue shading indicates significant down-regulation compared to NBF controls, whereas yellow shading indicates significant up-regulation compared to NBF controls. Lack of shading indicates no significant difference relative to NBF controls. Degree of shading is based on value of Log₂ fold change as indicated by the scale below on the right.</p

Principal component analysis of transcript expression in Malpighian tubules isolated from non-blood fed mosquitoes (NBF) at 3 h (gray circles), 12 h (white circles), and 24 h (black circles) and blood-fed (BF) mosquitoes at 3 h (blue circles), 12 h (red circles), and 24 h (green circles).

<p>Principal component 1 is time and principal component 2 is treatment (NBF, BF).</p

Differential expression after blood feeding of transcripts associated with heme detoxification and antioxidant mechanisms.

<p>Blue shading indicates significant down-regulation compared to NBF controls, whereas yellow shading indicates significant up-regulation compared to NBF controls. Lack of shading indicates no significant difference relative to NBF controls. Degree of shading is based on value of Log₂ fold change as indicated by the scale below on the right.</p

DAVID functional clusters that are significantly enriched among the transcripts in Malpighian tubules exhibiting a sustained, up-regulation or down-regulation after blood feeding.

<p>The transcripts that comprise each functional group are listed in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002929#pntd.0002929.s001" target="_blank">Figures S1</a>–<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002929#pntd.0002929.s015" target="_blank">S15</a>.</p

Biochemical pathways for ammonia detoxification in mosquitoes.

<p>Redrawn from Isoe and Scaraffia <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002929#pntd.0002929-Isoe1" target="_blank">[9]</a>. Yellow and blue text indicates an enzyme encoded by a transcript that is up-regulated and down-regulated, respectively, after blood feeding.</p