Date Published: November 6, 2015
Publisher: Public Library of Science
Author(s): Keshava Mysore, Longhua Sun, Michael Tomchaney, Gwyneth Sullivan, Haley Adams, Andres S. Piscoya, David W. Severson, Zainulabeuddin Syed, Molly Duman-Scheel, Anthony A. James. http://doi.org/10.1371/journal.pntd.0004213
Abstract: The development of sex-specific traits, including the female-specific ability to bite humans and vector disease, is critical for vector mosquito reproduction and pathogen transmission. Doublesex (Dsx), a terminal transcription factor in the sex determination pathway, is known to regulate sex-specific gene expression during development of the dengue fever vector mosquito Aedes aegypti. Here, the effects of developmental siRNA-mediated dsx silencing were assessed in adult females. Targeting of dsx during A. aegypti development resulted in decreased female wing size, a correlate for body size, which is typically larger in females. siRNA-mediated targeting of dsx also resulted in decreased length of the adult female proboscis. Although dsx silencing did not impact female membrane blood feeding or mating behavior in the laboratory, decreased fecundity and fertility correlated with decreased ovary length, ovariole length, and ovariole number in dsx knockdown females. Dsx silencing also resulted in disruption of olfactory system development, as evidenced by reduced length of the female antenna and maxillary palp and the sensilla present on these structures, as well as disrupted odorant receptor expression. Female lifespan, a critical component of the ability of A. aegypti to transmit pathogens, was also significantly reduced in adult females following developmental targeting of dsx. The results of this investigation demonstrate that silencing of dsx during A. aegypti development disrupts multiple sex-specific morphological, physiological, and behavioral traits of adult females, a number of which are directly or indirectly linked to mosquito reproduction and pathogen transmission. Moreover, the olfactory phenotypes observed connect Dsx to development of the olfactory system, suggesting that A. aegypti will be an excellent system in which to further assess the developmental genetics of sex-specific chemosensation.
Partial Text: Most animal species display sexually dimorphic behaviors, the majority of which are linked to sexual reproduction . Disease vector mosquitoes are excellent subjects for studies that explore the biological basis of sexual dimorphism. Only adult female mosquitoes, which require blood meals for reproduction, bite humans and transmit pathogens. Females differ from males in morphological, physiological, and behavioral traits that are critical components of their ability to spread diseases, including feeding behaviors, longevity, and susceptibility to infections. Researchers have therefore had a long-standing interest in the potential to manipulate genetic components of the sex determination pathway and sexual differentiation for vector control. Moreover, success of the sterile insect technique (SIT) and other genetic strategies designed to eliminate large populations of mosquitoes is dependent upon efficient sex-sorting of males and females, and many have argued that such sex-sorting, as well as insect sterilization itself, is best achieved through large-scale genetic or transgenic approaches (reviewed by [2, 3]). Although the genes that regulate sex-specification and development of mosquito sexual dimorphism may represent novel targets for vector control, most of these genes have not yet been functionally characterized in vector mosquitoes.
Despite the long-standing interest in genes that regulate sex determination and sex differentiation in mosquitoes, functional genetic characterization of such loci has been a challenge. Here, siRNA-mediated gene silencing was applied for successful functional characterization of A. aegypti dsx, a terminal transcription factor in the insect sex determination pathway, during development of female mosquitoes. The adult phenotypes examined fell into four general categories that are discussed in more detail below: growth (Figs 1 and 3), reproduction (Figs 2 and 3), olfactory (Figs 4 and 5), and life span (Fig 6).
Female mosquitoes differ from males in several morphological, physiological, and behavioral traits that are critical to their ability to transmit diseases. The arthropod disease vector research community has therefore had a long-standing interest in the potential to manipulate sex determination and differentiation genes for controlling disease vectors. Our previous work  demonstrated that Dsx regulates sex-specific gene expression in the developing A. aegypti pupal nervous system. The present investigation extended these initial findings through assessment of the effects of developmental siRNA-mediated dsx silencing in adult females. Targeting of dsx resulted in decreased size of the female wing and proboscis (Fig 1). Decreased fecundity and fertility correlated with decreased ovary length, ovariole length, and ovariole number in females in which dsx was silenced during development (Figs 2 and 3). Targeting dsx also resulted in disruption of olfactory system development, as evidenced by reduced length of the female antenna and maxillary palp and their respective sensilla (Figs 1 and 4), as well as disrupted OR expression (Fig 5). Female lifespan, a critical aspect of mosquito pathogen transmission, was also significantly reduced in adult females following developmental targeting of dsx (Fig 6). These results demonstrate that developmental silencing of dsx in A. aegypti females, which disrupts development of multiple adult female traits linked directly or indirectly to reproduction and pathogen transmission, may be useful for vector control.