Serine Protease Networks Mediate Immune Responses in Extra-Embryonic Tissues of Eggs in the Tobacco Hornworm, < b > < i > Manduca sexta < /i > < /b >

The melanization and Toll pathways, regulated by a network of serine proteases and noncatalytic serine protease homologs (SPHs), have been investigated mostly in adult and larval insects. However, how these innate immune reactions are regulated in insect eggs remains unclear. Here we present evidence from transcriptome and proteome analyses that extra-embryonic tissues (yolk and serosa) of early-stageManduca sexta eggs are immune competent, with expression of immune effector genes including prophenoloxidase and antimicrobial peptides. We identified gene products of the melanization and Toll pathways inM. sexta eggs. Through in vitro reconstitution experiments, we demonstrated that constitutive and infection-induced serine protease cascade modules that stimulate immune responses exist in the extra-embryonic tissues ofM. sexta eggs. The constitutive module (HP14b-SP144-GP6) may promote rapid early immune signaling by forming a cascade activating the cytokine Sp ätzle and regulating melanization by activating prophenoloxidase (proPO). The inducible module (HP14a-HP21-HP5) may trigger enhanced activation of Spätzle and proPO at a later phase of infection. Crosstalk between the two modules may occur in transition from the constitutive to the induced respons e in eggs inoculated with bacteria. Examination of data from two other well-studied insect species,Tribolium castaneum andDrosophila melanogaster, supports a role for a serosa-dependent constitutive protease cascade in protec...
Source: Journal of Innate Immunity - Category: Allergy & Immunology Source Type: research