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

Abstract

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-stage &lt;i&gt;Manduca sexta&lt;/i&gt; 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 in &lt;i&gt;M. sexta&lt;/i&gt; 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 of &lt;i&gt;M. sexta&lt;/i&gt; eggs. The constitutive module (HP14b-SP144-GP6) may promote rapid early immune signaling by forming a cascade activating the cytokine Spätzle 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 response in eggs inoculated with bacteria. Examination of data from two other well-studied insect species, &lt;i&gt;Tribolium castaneum&lt;/i&gt; and &lt;i&gt;Drosophila melanogaster&lt;/i&gt;, supports a role for a serosa-dependent constitutive protease cascade in protecting early embryos against invading pathogens.

Identification of immune‐related genes from the transcriptome of the venom gland in Cotesia plutellae

“…8B). SPs are found in eggs, larvae, and adults of Manduca sexta , and involved in the activation of the cytokine Spätzle and the regulation of melanization (Shan et al 2022). In addition, SPs act in encapsulation of cells and digestion of host tissues by parasitoids (Danneels et al 2010; Scherfer et al 2008).…”

An evolutionarily conserved serine protease network mediates melanization and Toll activation in Drosophila

“…The functional interrelatedness of the melanization and Toll cascade pathways may be rooted in their common evolutionary origin and might reflect a common readiness or priming to face newly perceived threats. In Manduca , the ortholog of Grass, Ms-HP5, has also been shown to activate proSpz directly ( 40 ). The ability of Grass and Ms-HP5 to process proSpz is supported by the structure-based classification of clip-domain serine proteases, which places them in the terminal protease group along with Dm-Easter, Dm-SPE, Ms-HP8, and Tm-SPE ( 60 , 61 ).…”

“…The activation of Toll signaling is mediated by the sequential activation of HP14 (32)(33)(34), HP21 (37), HP5 (11), HP6 (38), HP8 (39), and Spz1. HP5 is also capable of propagating immune signaling through direct activation of Spz1 in extra-embryonic tissues (40). This Toll cascade branches at the position of HP21 and HP6 to activate PAP2/PAP3 (37,41) and PAP1 (38), respectively, which, in turn, activate a PPO heterodimer (42)(43)(44).…”

Comparative Transcriptomic Analysis of Insecticide-Resistant Aedes aegypti from Puerto Rico Reveals Insecticide-Specific Patterns of Gene Expression

“…Serine protease has been reported to be highly upregulated in An. gambiae resistant to DDT [ 46 ] as well as in Culex pipiens pallens resistant to deltamethrin [ 47 ], where it was suggested to play a crucial role in the innate immunity in this species and other insects [ 48 , 49 , 50 ]. This finding suggests that the increase in protease activity may be important in modulating Ae.…”