Current Status of Immune Deficiency Pathway in Tenebrio molitor Innate Immunity

Abstract

Yellow mealworm (Tenebrio molitor) is a highly beneficial beetle that serves as an excellent source of edible protein as well as a practical study model. Therefore, studying its immune system is important. Like in other insects, the innate immune response effected through antimicrobial peptides production provides the most critical defense armory in T. molitor. Immune deficiency (Imd) signaling is one of the major pathways involved in the humoral innate immune response in this beetle. However, the nature of the molecules involved in the signaling cascade of the Imd pathway, from recognition to the production of final effectors, and their mechanism of action are yet to be elucidated in T. molitor model. In this review, we present a general overview of the current literature available on the Imd signaling pathway and its identified interaction partners in T. molitor.

Keywords: Imd pathway; Tenebrio molitor; antimicrobial peptides; cross-regulation; innate immunity.

Figure 1

Schematic illustration of the proposed Imd pathway in Tenebrio molitor and its possible cross-talks. Pattern recognition receptors (PRRs; PGRP-LC and PGRP-LE) are triggered by DAP-type PGN of the bacterial cell wall. Recognition of Gram-negative bacteria further triggers the recruitment of intracellular proteins TmIMD, TmFADD, and TmDREDD. TmTAK1/TmTAB2, activated by TmIMD, further activates TmIKK complex. TmRelish is subsequently phosphorylated by the TmIKK complex and then cleaved by TmDredd. Eventually, it leads to the translocation of TmRelish into the nucleus, where it binds to the relevant transcription response elements and triggers AMP production. Solid black arrows indicate the identified interactions between Imd signaling compartments. Blue dashed arrows indicate putative cross-talks between Imd and other signaling pathways via TmIKKs complex, TmRelish, and ligand Spaetzle in T. molitor. Red dashed arrows indicate the putative cross-talks identified in other insects. Abbreviations: PGRP; Peptidoglycan recognition protein, IMD; Immune deficiency, FADD; Fas-associated protein with death domain, DREDD; death-related ced-3/Nedd2-like protein, TAK1; Transforming growth factor-activated kinase1, TAB2; TAK binding protein 2, IKK; Inhibitor of nuclear factor-κB (IκB) kinase, AMP; Antimicrobial peptide, JNK; c-Jun N-terminal kinase.