Extracellular matrix proteins Pericardin and Lonely heart mediate periostial hemocyte aggregation in the mosquito Anopheles gambiae.

An infection induces the migration of immune cells called hemocytes to the insect heart, where they aggregate around heart valves called ostia and phagocytose pathogens in areas of high hemolymph flow. Here, we investigated whether the cardiac extracellular matrix proteins, Pericardin (Prc) and Lonely heart (Loh), regulate the infection-induced aggregation of periostial hemocytes in the mosquito, An. gambiae. We discovered that RNAi-based post-transcriptional silencing of Prc or Loh did not affect the resident population of periostial hemocytes in uninfected mosquitoes, but that knocking down these genes decreases the infection-induced migration of hemocytes to the heart. Knocking down Prc or Loh did not affect the proportional distribution of periostial hemocytes along the periostial regions. Moreover, knocking down Prc or Loh did not affect the number of sessile hemocytes outside the periostial regions, suggesting that the role of these proteins is cardiac-specific. Finally, knocking down Prc or Loh did not affect the amount of melanin at the periostial regions, or the intensity of an infection at 24 h after challenge. Overall, we demonstrate that Prc and Loh are positive regulators of the infection-induced migration of hemocytes to the heart of mosquitoes.