The work performed by these two teams shows that the topological compartmentalization of the larval hematopoietic organ in distinct lobes is paralleled by molecular, ontogenic and functional differences among the blood cell progenitors present in the different lobes. Notably, in response to infection by parasitoid wasps, progenitors in the anterior lobes differentiate into specialized blood cells involved in wasp egg neutralisation, whereas progenitors from the posterior lobes remain undifferentiated. This specificity of response is at least partly mediated by differential regulation of the the JAK/STAT signaling pathway between cells of anterior and posterior lobes. Interestingly, the lack of differentiation of the blood cell progenitors located in the posterior lobes is important for Drosophila survival to this immune challenge, suggesting that hematopoietic progenitor diversity is crucial to mount an efficient innate immune response.
Confocal image of the Drosophila larval hematopoietic organ. The different lobes are delimited by white dashed lines. Blood cell progenitors express the red/green markers differently according to their antero-posterior position. Nuclei are stained in blue.