Abstract
The house fly Musca domestica, a cosmopolitan dipteran insect, is a significant vector for human and animal bacterial pathogens, but little is known about its immune response to these pathogens. To address this issue, we inoculated the larvae with a mixture of Escherichia coli and Staphylococcus aureus and profiled the transcriptome 6, 24, and 48 h thereafter. Many genes known to controlling innate immunity in insects were induced following infection, including genes encoding pattern recognition proteins (PGRPs), various components of the Toll and IMD signaling pathways and of the proPO-activating and redox systems, and multiple antimicrobial peptides. Interestingly, we also uncovered a large set of novel immune response genes including two broad-spectrum antimicrobial peptides (muscin and domesticin), which might have evolved to adapt to house-fly's unique ecological environments. Finally, genes mediating oxidative phosphorylation were repressed at 48 h post-infection, suggesting disruption of energy homeostasis and mitochondrial function at the late stages of infection. Collectively, our data reveal dynamic changes in gene expression following bacterial infection in the house fly, paving the way for future in-depth analysis of M. domestica's immune system.
Highlights
Lacking acquired immune systems, insects have efficient and potent innate immune systems to discriminate and combat foreign invaders successfully [1,2]
Bacteria-challenged M. domestica transcriptome profiles were investigated and the substantial amount of transcripts was recovered, which provided a strong support for the future genomic research on M. domestica, especially on in-depth genome annotation in insects
Identified immune-candidate genes, infection markers, and putative signaling pathways were found in M. domestica and especially a considerable amount of immune-relevant genes and pathways in the house fly showed significant similarity to Drosophila, Anopheles, Apis, and Bombyx, suggesting that mechanisms underlying the innate immunity in insects might be conserved in invertebrates
Summary
Lacking acquired immune systems, insects have efficient and potent innate immune systems to discriminate and combat foreign invaders successfully [1,2]. It is generally acknowledged that the insect immune system involves cellular and humoral immune reactions against microbial infections that maintain close networks with each other and occur first in the epidermis, gut and tracheal respiratory organs and in the hemocoel [2]. One characteristic of insect immunity is rapid activation of immune genes upon microbial infection, which produces effectors such as antimicrobial peptides. Insects have evolved sensitive mechanisms for recognition of pathogens including bacteria, fungi, parasites and viruses, which subsequently trigger cellular immune [3,4] and humoral immune reactions [5,6] via signal transduction pathways. Genes encoding effectors are activated through signaling cascades and a set of these molecules are produced in specific tissues and secreted into the hemolymph [1]
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