Genetic Analysis of Contributions of Dorsal Group and JAK-Stat92E Pathway Genes to Larval Hemocyte Concentration and the Egg Encapsulation Response in Drosophila

Abstract

Drosophila larvae defend themselves against parasitoid wasps by completely surrounding the egg with layers of specialized hemocytes called lamellocytes. Similar capsules of lamellocytes, called melanotic capsules, are also formed around "self" tissues in larvae carrying gain-of-function mutations in Toll and hopscotch. Constitutive differentiation of lamellocytes in larvae carrying these mutations is accompanied by high concentrations of plasmatocytes, the major hemocyte class in uninfected control larvae. The relative contributions of hemocyte concentration vs. lamellocyte differentiation to wasp egg encapsulation are not known. To address this question, we used Leptopilina boulardi to infect more than a dozen strains of host larvae harboring a wide range of hemocyte densities. We report a significant correlation between hemocyte concentration and encapsulation capacity among wild-type larvae and larvae heterozygous for mutations in the Hopscotch-Stat92E and Toll-Dorsal pathways. Larvae carrying loss-of-function mutations in Hopscotch, Stat92E, or dorsal group genes exhibit significant reduction in encapsulation capacity. Larvae carrying loss-of-function mutations in dorsal group genes (including Toll and tube) have reduced hemocyte concentrations, whereas larvae deficient in Hopscotch-Stat92E signaling do not. Surprisingly, unlike hopscotch mutants, Toll and tube mutants are not compromised in their ability to generate lamellocytes. Our results suggest that circulating hemocyte concentration and lamellocyte differentiation constitute two distinct physiological requirements of wasp egg encapsulation and Toll and Hopscotch proteins serve distinct roles in this process.

Drosophila Hemopoiesis and Cellular Immunity

“…They found that both the JAK/STAT and Toll pathways responded to parasitization. This corresponds with work showing that both the Drosophila JAK homolog Hop and the Toll pathway are required for a proper encapsulation response (27). It could be that these pathways are required for prohemocytes to react to some signal from activated circulating hemocytes.…”

“…1B). Yet, in hop loss-of-function larvae, the numbers of circulating hemocytes are comparable to wildtype larvae (26,27). Interestingly, Hop is required for the larvae FIGURE 1.…”

“…to mount an effective immune response to parasitization by parasitoid wasps (27). This may be due to an inability of a hemopoietic organ, known as the lymph gland, to be activated.…”

Structural and functional characterization of pseudopodocyte, a shaggy immune cell produced by two Drosophila species of the obscura group

“…They are considered essential for encapsulation and were long described as a plasmatocyte-derived form Rizki, 1980, 1984). Many studies established that plasmatocytes and lamellocytes follow specific differentiation pathways (Lanot et al, 2001;Sorrentino et al, 2002Sorrentino et al, , 2004Meister, 2004;Crozatier et al, 2004;Krzemień et al, 2007). However, recent works on Drosophila hemocytes lineage showed that plasmatocytes could indeed differentiate into lamellocytes (Honti et al, 2010;Avet-Rochex et al, 2010;Stofanko et al, 2010).…”

A directed screen for genes involved in Drosophila blood cell activation

“…Many mutants show increased lamellocyte numbers and form melanotic masses, ''pseudotumors,'' in what is probably an overreaction of the cellular immune response (18,19). Notably, mutations that activate the Toll and Jak͞Stat pathways show this phenotype, suggesting an important role for these pathways in the cellular response (20)(21)(22)(23). Furthermore, Notch function is required for a normal cellular response (16).…”