Abstract
Most hematological malignancies are associated with reduced expression of one or more components of the Endosomal Sorting Complex Required for Transport (ESCRT). However, the roles of ESCRT in stem cell and progenitor maintenance are not resolved. The difficulty in parsing signaling pathway roles in relation to their canonical cargo sorting function poses a challenge. The Drosophila hematopoietic organ, the larval lymph gland, provides a path to dissect the roles of cellular trafficking pathways such as ESCRT in blood development and maintenance. Drosophila has 13 core ESCRT components. Knockdown of individual ESCRTs showed that only Vps28 and Vp36 were required in all lymph gland progenitors. Using the well-conserved ESCRT-II complex (Vps22, Vps25 and Vps36) as an example of the range of phenotypes seen upon ESCRT depletion, we show that ESCRTs have cell autonomous as well as non-autonomous roles in progenitor maintenance and differentiation. ESCRT depletion also sensitized posterior lymph gland progenitors to respond to immunogenic cues such as wasp infestation. We also identify key heterotypic roles for ESCRT in position-dependent control of Notch activation to suppress crystal cell differentiation. Our study shows that the cargo sorting machinery can determine progenitor identity and capacity to adapt to the dynamic environments that blood cells are exposed to. These mechanisms for control of cell fate may tailor developmental diversity in multiple contexts.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
In this updated version of the manuscript, we have furthered our knowledge regarding the requirement of ESCRT components for progenitor maintenance and immune response. For ESCRT-II core components, we previously showed that only one of the three components, Vps36, is essential for lamellocyte differentiation. To understand whether there was a functional compensation operating between the other two components (Vps25 and Vps22), we performed a double knockdown (KD) experiment and observed that they are completely dispensable for lamellocyte differentiation. This strengthens our claim that ESCRT has non-compensatory roles in controlling progenitor fate choice. Further, we introduced pathogenic stress in the larvae using wasp infestation to observe the effect of ESCRT KD on immune response. We see that posterior progenitors are sensitized to immunological cues upon KD of ESCRT in the blood progenitor. We have added quantification for this in the revised version. Additionally, we have quantified the development of ESCRT KD flies and their survival upon immune challenge. The manuscript has been rewritten quite extensively from the last submitted version, and a major part of the descriptive data and results have been moved to supplementary results. The title has been modified to reflect the role of ESCRT in hematopoiesis with greater clarity. New data has been added to the figures. The figure order and some of the panels have been rearranged.