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PubMed1977

Effect of dietary cholesterol on the pattern of osmium deposition in the symbiote-containing cells of the pea aphid.

Pea aphids left for 48 h in unbuffered osmium tetroxide show heavy staining of many organelles in the symbiote-containing cells (mycetocytes and sheath), embryos and oenocytes very similar to that characteristic of mammalian sterol-synthesizing cells. However, the staining of the per-aphid cells is, to a large extent, dependent on the presence of cholesterol benzoate, or free cholesterol, in the aphid's diet. In aphids cultured in vitro with 3H mevalonate in the presence of added cholesterol, the incorporation of label into the cholesterol and lanosterol fractions is significantly reduced. If the dietary cholesterol effects a similar inhibition in vivo, the cholesterol-dependent osmium staining could be due to precursors(s) of cholesterol accumulating in the intracellular sites described. There is also osmium staining of large (normally electron-transparent) vacuoles in mycetocytes, gut and fat body, irrespective of dietary cholesterol.

Animals↗
PubMed2025

Analysis of Duplication and Potential Functional Divergence of Wing Gene Network Components in Pea Aphids.

A fundamental focus of evolutionary developmental biology is uncovering the genetic mechanisms responsible for the gain and loss of characters. One approach to this question is to investigate changes in the coordinated expression of a group of genes important for the development of a character of interest (a gene regulatory network). Here we consider the possibility that modifications to the wing gene regulatory network (wGRN), as defined by work primarily done in Drosophila melanogaster, were involved in the evolution of wing dimorphisms of the pea aphid (Acyrthosiphon pisum). We hypothesize that this may have occurred via changes in expression levels or by duplication followed by divergence of wGRN components. To test this, we annotated members of the wGRN in the pea aphid genome and assessed their expression levels in first and third nymphal instars of winged and wingless morphs of males and asexual females. We find that only 2 of the 32 assessed genes exhibit morph-biased expression. We also find that three wing genes (apterous (ap), warts (wts), and decapentaplegic (dpp)) have undergone gene duplication. In each case, the resulting paralogs show signs consistent with functional divergence, exhibiting either sex-, morph-, or stage-specific expression. Two gene duplicates, wts2 and dpp3, are of particular interest with respect to wing dimorphism, as they exhibit male morph-specific isoforms and wingless male-biased expression, respectively. These gene expression results provide an important first step toward identifying members of the pea aphid wGRN that may play a causative role in differentiating winged from wingless morphs. These findings supplement our understanding of trends in developmental gene network evolution, such as side-stepping pleiotropic constraint via duplication and sub-functionalization, underlying the emergence of novel phenotypes.

Animals↗
PubMed2025

Analysis of duplication and possible sub-functionalization of wing gene network components in pea aphids.

A fundamental focus of evolutionary-developmental biology is uncovering the genetic mechanisms responsible for the gain and loss of characters. One approach to this question is to investigate changes in the coordinated expression of a group of genes important for the development of a character of interest (a gene regulatory network). Here we consider the possibility that modifications to the wing gene regulatory network (wGRN), as defined by work primarily done in Drosophila melanogaster, were involved in the evolution of wing dimorphisms of the pea aphid (Acyrthosiphon pisum). We hypothesize that this may have occurred via changes in expression levels or duplication followed by sub-functionalization of wGRN components. To test this, we annotated members of the wGRN in the pea aphid genome and assessed their expression levels in first and third nymphal instars of winged and wingless morphs of males and asexual females. We find that only two of the 32 assessed genes exhibit morph-biased expression. We also find that three wing genes (apterous (ap), warts (wts), and decapentaplegic (dpp)) have undergone gene duplication. In each case, the resulting paralogs show signs of functional divergence, exhibiting either sex-, morph-, or stage-specific expression. Two gene duplicates, wts2 and dpp3, are of particular interest with respect to wing dimorphism, as they exhibit a wingless male-specific isoform and wingless male-biased expression, respectively. These results supplement our understanding of trends in developmental gene network evolution, such as side-stepping pleiotropic constraint via duplication and sub-functionalization, underlying the emergence of novel phenotypes.

dimorphism↗
PubMed1977

In vivo sterol biosynthesis by pea aphid symbiotes as determined by digitonin and electron microscopic autoradiography.

Pea aphid primary symbiotes have previously been shown to synthesize cholesterol in vitro. Two electron microscopic techniques were used here to determine whether the symbiotes also synthesize cholesterol in vivo and whether this cholesterol is made available to the aphid. We also inquired into a possible role of secondary symbiotes in chosesterol biosynthesis. Treatment of aphids with digitonin resulted in significant alteration of ultrastructural sites in primary and secondary symbiote membranes. We concluded that these sites are areas of high cholesterol concentration in the symbiotes. Electron microscopic autoradiography with 3H-mevalonate precursor indicated that both primary and secondary symbiotes synthesize cholesterol; in both cases, the majority of grains were associated with the symbiote membranes. While the frequency of grains on the symbiotes remained constant, irrespective of incubation time in labelled media, the frequency of grains over surrounding tissues increased exponentially as the time of incubation was increased from 30 min to 8 h, indicating that symbiote cholesterol is transported to other tissues. High voltage electron microscopic autoradiography permitted thick section autoradiography, reducing the time of emulsion exposure from 54 days (thin section) to 12 days (0.5 mum sections).

Animals↗
PubMed1975

Ultrastructure of pea aphid mycetocytes: evidence for symbiote secretion.

A detailed investigation into the ultrastructure of the pea aphid mycetocytes and their contained symbiotes and organelles was carried out with the transmission electron microscope. The most striking observation was the presence of small vesicles in the space between the primary symbiote cell wall and membrane envelope (outer membrane space). The vesicles appear to form by a budding process at the outer cell wall layer. Subsequently, the vesicles, we suggest, may move out into the mycetocyte cytoplasm via a similar budding of the membrane envelope; The Golgi apparatus was found to be an important structural component of the primary mycetocyte; it is continuous with the rough endoplasmic reticulum and the latter, in turn, appears to be closely connected to the primary symbiote membrane envelope. This may be of functional significance. A number of other organelles not previously described in mycetocytes were found, including transparent vacuoles, granular bodies, multi-vesicular bodies and microfilaments. The chemical composition of the various vesicles and organelles is unknown at present.

Animals↗
PubMed2026

Aphid symbiotic virus engineered for in vivo expression of insecticidal effectors.

Microbial pesticides are eco-friendly alternatives to chemical pesticides. However, few viral pesticides have been developed. Insects harbor diverse symbiotic viruses, which have the potential to be engineered for translational applications in pest control. Here, we engineered Acyrthosiphon pisum virus (APV), a symbiotic virus of the pea aphid, to deliver anti-aphid effectors using reverse genetics technology. A cytomegalovirus (CMV) promoter-driven APV infectious clone was successfully rescued in pea aphids with the assistance of nanocarrier star polymer (SPc). Based on this infectious clone, the protein coding sequence of chymotrypsin inhibitor variant 8 (Chy8) and the double-stranded RNA sequence targeting the aphid clip-domain serine protease (SPLP) were separately assembled into the APV genome to generate APV-Chy8 and APV-dsSPLP infectious clones, respectively. The recombinant APV clones reduced aphid relative survival rates by 34% and 17% by microinjection, respectively. To enhance the transcriptional efficiency, the APV-Chy8 and APV-dsSPLP clones were transcribed in vitro using the T7 promoter. The in vitro-synthesized APV-Chy8 and APV-dsSPLP clones reduced aphid relative survival rates by 48% and 45% by microinjection, respectively. These results demonstrate that engineered APV can deliver cargos and reduce aphid survival under injection-based experimental conditions, highlighting the potential of symbiotic virus-based vectors for delivering insecticidal effectors.

Animals↗
PubMed2026

Structural basis of sex pheromone detection in aphids.

Sex pheromones play a central role in regulating animal behavior and reproduction. In insects, these signals are perceived through specialized odorant receptors (ORs) that mediate species-specific communication and safeguard genetic integrity. However, the structural basis of sex pheromone detection remains largely unresolved. Here, we identified two ORs in the pea aphid Acyrthosiphon pisum, along with the conserved OR co-receptor (Orco), which together mediate recognition of the pheromone components nepetalactone and nepetalactol. Functional assays demonstrated that ApOR21-Orco and ApOR22-Orco specifically respond to nepetalactol and nepetalactone, respectively. Using cryo-electron microscopy, we resolved the structure of the ApOR22-Orco complex in three states - unbound closed, nepetalactone-bound closed, and nepetalactone-bound open - revealing a heterotetrameric ion channel formed by one ApOR22 and three ApOrco subunits. Ligand binding to ApOR22 triggers conformational rearrangements that induce asymmetric pore dilation, thereby enabling ion conduction. Together, these results provide a mechanistic framework for understanding sex pheromone perception in insects and establish a structural foundation for the rational development of environmentally sustainable pest-control strategies.

Animals↗
PubMed2025

The release of sexual conflict after sex loss is associated with evolutionary changes in gene expression.

Sexual conflict can arise because males and females, while sharing most of their genome, can have different phenotypic optima. Sexually dimorphic gene expression may help reduce conflict, but the expression of many genes may remain sub-optimal owing to unresolved tensions between the sexes. Asexual lineages lack such conflict, making them relevant models for understanding the extent to which sexual conflict influences gene expression. We investigate the evolution of sexual conflict subsequent to sex loss by contrasting the gene expression patterns of sexual and asexual lineages in the pea aphid Acyrthosiphon pisum. Although asexual lineages of this aphid produce a small number of males in autumn, their mating opportunities are limited because of geographic isolation between sexual and asexual lineages. Therefore, gene expression in parthenogenetic females of asexual lineages is no longer constrained by that of other morphs. We found that the expression of genes in males from asexual lineages tended towards the parthenogenetic female optimum, in agreement with theoretical predictions. Surprisingly, males and parthenogenetic females of asexual lineages overexpressed genes normally found in the ovaries and testes of sexual morphs. These changes in gene expression in asexual lineages may arise from the relaxation of selection or the dysregulation of gene networks otherwise used in sexual lineages.

Animals↗