A Novel Peptide Mediates Aggregation and Migration of Hemocytes from an Insect

Abstract

Insect blood cells (hemocytes) comprise an essential arm of the immune system [1-7]. Several factors mediating recognition and phagocytosis of foreign intruders by hemocytes have been identified, but the mechanisms regulating hemocyte movement remain fragmentary. Embryonic hemocytes from Drosophila migrate along stereotypical routes in response to chemotactic signals from PVF ligands, members of the platelet-derived growth factor family [8-12]. Embryonic and larval hemocytes also accumulate at external wounds [11-13], but PVFs are not required for this response, suggesting involvement by other, unknown factors. Here we report the identification of hemocyte chemotactic peptide (HCP) from the moth Pseudaletia separata and present evidence that it stimulates aggregation and directed movement of phagocytic hemocytes. Spatiotemporal studies revealed that HCP is expressed in both epidermal cells and hemocytes, whereas structure-function studies identified post-translational modifications important for activity. HCP also shares similarities with another group of cytokines from moths called ENF peptides [14-17]. Taken together, our results identify HCP as a chemotactic cytokine that enhances clotting at wound sites in larvae.

Adaptor protein is essential for insect cytokine signaling in hemocytes

“…Changes in the adhesive state of mammalian immunocytes are regulated by signaling molecules (cytokines), cell adhesion molecules, and their cognate receptors; for example, chemokine-triggered activation of leukocytes induces up-regulation of the expression levels and activation states of the integrins that enable leukocytes to adhere to the endothelial cells of the blood vessel walls before migrating into the tissues (10). We recently identified a chemokine-like peptide (hemocyte chemotactic peptide) in insects (11). This peptide and another cytokine family known as the ENF peptide family, a name based on the consensus sequence of their N termini (Glu-Asn-Phe-), are known to increase hemocyte adhesion (12)(13)(14)(15)(16).…”

Coagulation in Invertebrates

“…Although it has not been demonstrated, one may speculate that these hemocytes could contribute to the clotting process. In Drosophila , it is not known what factor(s) attract the hemocytes, but a chemotactic peptide was recently identified in the moth Pseudaletia separata that possibly acts as a cytokine influencing clotting at wound sites [30] . In another insect, i.e.…”

Characteristics common to a cytokine family spanning five orders of insects

“…Hemocytes were monitored by phase-contrast microscopy using an Olympus inverted microscope IX70. Twenty minutes after adding a test sample, the number of individual (non-aggregated free) hemocytes that remained in the field of view was determined with an aggregation index equaling (1500 cells e the number of free cells)/1500 cells  100 (%) as described previously (Nakatogawa et al, 2009). Bioassays with each sample were always paired with assays of bovine serum albumin (BSA) to control any variation in aggregation response that might exist between hemocyte samples (Aizawa et al, 2001).…”

“…While a large number of cytokines in mammals have been extensively studied, our knowledge of insect cytokines is quite limited. Although it is not easy to define 'cytokine' clearly, several cytokines or cytokinelike factors have been reported in insects: spaetzle (Weber et al, 2003), Unpaired-3 (Agaisse et al, 2003), eda-like cell death trigger (eiger) (Mabery and Schneider, 2010), sex peptides (Peng et al, 2005), hemocyte chemotactic peptide (HCP) (Nakatogawa et al, 2009), and stress-responsive peptide (SRP) (Yamaguchi et al, 2012). The first family of insect cytokines was originally referred to as the ENF peptides, based on their common N-terminal sequence, Glu-Asn-Phe- (Strand et al, 2000).…”