Re-thinking adaptive immunity in the beetles: Evolutionary and functional trajectories of lncRNAs.

Unlike vertebrate animals, invertebrates lack lymphocytes and therefore have historically been believed not to develop immune memory. A few studies have reported evidence of immune priming in insects; however, these studies lack the molecular mechanism and proposed it might be different among taxa. Since lncRNAs are known to regulate the immune response, we identified 10,120 lncRNAs in Tribolium castaneum genome-wide followed by transcriptome analysis of primed and unprimed larvae of different infectious status. A shift in lncRNA expression between Btt primed larvae and other treatment groups provides evidence of immune memory response. A few "priming" lncRNAs (n = 9) were uniquely regulated in Btt primed larvae. Evidence suggests these lncRNAs are likely controlling immune priming in Tribolium by regulating expression of genes involved in proteasomal machinery, Notch system, zinc metabolism, and methyltransferase activity, which are necessary to modulate phagocytosis. Our results support a conserved immune priming mechanism in a macrophage-dependent manner.