Innate immune system function following systemic RNA-interference of the Fragile X Mental Retardation 1 gene in the cricket Acheta domesticus.

Fragile X syndrome (FXS), caused by a mutation in the Fragile X Mental Retardation 1 (FMR1) gene, is a common form of inherited mental retardation. Mutation of the gene leads to a loss of the gene product Fragile X Mental Retardation Protein (FMRP). While a loss of FMRP has been primarily associated with neural and cognitive deficits, it has also been reported to lead to immune system dysfunction in both humans and flies. We used the Acheta domesticus transcriptome to identify a highly conserved cricket ortholog of FMR1 (adfmr1). We cloned a partial cDNA of adfmr1, used systemic RNA interference (RNAi) to knockdown adfmr1 expression, and examined the impact of this knockdown (KD) on the cellular and humoral responses of the insect innate immune system. Following RNAi, both male and female crickets exhibited an increase in the number of circulating hemocytes, a decrease in total hemolymph phenoloxidase (PO) activity, and an increase in fat body lysozyme expression. Despite similar changes in these immune parameters in both sexes, male and female crickets responded differently to an immune challenge. Most KD males failed to survive an intra-abdominal injection of bacterial lipopolysaccharide, while KD females were just as likely as control females to survive this challenge. Our results support that decreased fmr1 expression can alter the cellular and humoral defenses of the insect innate immune system, and may lead to a decrease in male, but not female, immunocompetence.