Semaphorin-1a Is Required for Aedes aegypti Embryonic Nerve Cord Development

Abstract

Although mosquito genome projects have uncovered orthologues of many known developmental regulatory genes, extremely little is known about mosquito development. In this study, the role of semaphorin-1a (sema1a) was investigated during vector mosquito embryonic ventral nerve cord development. Expression of sema1a and the plexin A (plexA) receptor are detected in the embryonic ventral nerve cords of Aedes aegypti (dengue vector) and Anopheles gambiae (malaria vector), suggesting that Sema1a signaling may regulate mosquito nervous system development. Analysis of sema1a function was investigated through siRNA-mediated knockdown in A. aegypti embryos. Knockdown of sema1a during A. aegypti development results in a number of nerve cord phenotypes, including thinning, breakage, and occasional fusion of the longitudinal connectives, thin or absent commissures, and general distortion of the nerve cord. Although analysis of Drosophila melanogaster sema1a loss-of-function mutants uncovered many similar phenotypes, aspects of the longitudinal phenotypes differed between D. melanogaster and A. aegypti. The results of this investigation suggest that Sema1a is required for development of the insect ventral nerve cord, but that the developmental roles of this guidance molecule have diverged in dipteran insects.

Redeployment of a conserved gene regulatory network during Aedes aegypti development

“…The expression patterns of these genes are mostly identical in the two species. However, siRNA knockdowns of A. aegypti sema-1a, fra, and comm2 revealed different severities of axonal phenotypes, with fra giving a more severe phenotype in A. aegypti than in Drosophila, sema-1a being more severe in some respects and less so in others, and comm2 being more severe in Drosophila (Clemons et al, 2011; Haugen et al, 2011; Sarro et al, 2013). These differences in midline development are subtle and reinforce the notion of essential similarity between the two species.…”

“…A small subset of axon guidance genes—sema-1a, fra, comm2, and NetA/B—have been studied in detail in A. aegypti (Clemons et al, 2011; Haugen et al, 2011; Sarro et al, 2013) as well as in Drosophila (Brankatschk and Dickson, 2006; Georgiou and Tear, 2002; Harris et al, 1996; Kolodkin et al, 1993; Kolodziej et al, 1996; Mitchell et al, 1996; Tear et al, 1996). The expression patterns of these genes are mostly identical in the two species.…”

Slit/Robo-mediated axon guidance in Tribolium and Drosophila: Divergent genetic programs build insect nervous systems

“…Illuminating the processes by which axon guidance mechanisms have changed over time may provide valuable insight into the evolution of this diverse and highly successful group of animals. While researchers have begun to investigate the function of conserved axon guidance genes in arthropods other than Drosophila (Clemons et al, 2011; Haugen et al, 2011; Linne and Stollewerk, 2011), a direct examination of the evolutionary diversification of axon guidance receptor function has not been attempted.…”

RNA Interference for Mosquito and Mosquito-Borne Disease Control

“…The embryo is an attractive life stage for delivery of RNAi triggers because cell uptake in progenitor cells conceivably facilitates widespread bio-distribution of the trigger following development. This is evident in studies which utilize siRNAs without need for transfection reagents [57,116,117]. There are some examples of RNAi-based studies of gene suppression phenotypes in embryos including regulation of embryonic nerve cord development by semaphorin A , frazzled , and commissureless2 [57,116,117].…”