Serotonin signaling regulates insulin-like peptides for growth, reproduction, and metabolism in the disease vector <i>Aedes aegypti</i>.

Abstract

Disease-transmitting female mosquitoes require a vertebrate blood meal to produce their eggs. An obligatory hematophagous lifestyle, rapid reproduction, and existence of a large number of transmittable diseases make mosquitoes the world's deadliest animals. Attaining optimal body size and nutritional status is critical for mosquitoes to become reproductively competent and effective disease vectors. We report that blood feeding boosts serotonin concentration and elevates the serotonin receptor Aa5HT2B (<i>Aedes aegypti</i> 5-hydroxytryptamine receptor, type 2B) transcript level in the fat-body, an insect analog of the vertebrate liver and adipose tissue. <i>Aa5HT2B</i> gene disruption using the CRISPR-Cas9 gene-editing approach led to a decreased body size, postponed development, shortened lifespan, retarded ovarian growth, and dramatically diminished lipid accumulation. Expression of the insulin-like peptide (ILP) genes <i>ilp2</i> and <i>ilp6</i> was down-regulated while that of <i>ilp5</i> and <i>ilp4</i> was up-regulated in response to <i>Aa5HT2B</i> disruption. CRISPR-Cas9 disruption of <i>ilp2</i> or <i>ilp6</i> resulted in adverse phenotypes similar to those of <i>Aa5HT2B</i> disruption, while <i>ilp5</i> CRISPR-Cas9 disruption had exactly the opposite effect on growth and metabolism, with significantly increased body size and elevated lipid stores. Simultaneous CRISPR-Cas9 disruption of <i>Aa5HT2B</i> and <i>ilp5</i> rescued these phenotypic manifestations. <i>Aa5HT2B</i> RNAi silencing rendered <i>ilp6</i> insensitive to serotonin treatment in the cultured fat-body, suggesting a regulatory link between Aa5HT2B and ILP6. Moreover, CRISPR-Cas9 <i>ilp6</i> disruption affects expression of <i>ilp-2</i>, -<i>5</i>, and -<i>4</i>, pointing out on a possible role of ILP6 as a mediator of the Aa5HT2B action.