Dissecting Slit Signaling: Regulating Stem Cells, Proteolytic Cleavage and its Emerging Roles in Metabolism
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Authors
Anand, Ria
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Cell and Molecular Biology
Alternative Title
Abstract
Stem cells, immune cells, and metabolic tissues rely on tightly coordinated signaling pathways to maintain homeostasis and respond to stress and environmental changes. The Slit family of secreted proteins — originally identified as axon guidance cues — has emerged as a multifaceted signaling system beyond the nervous system. Full-length Slit (Slit-FL) is a large, secreted axon guidance molecule that functions as a chemorepellent by signaling through Robo receptors on migrating neurons. This thesis explores how Slit proteins, their proteolytic fragments, and corresponding receptors regulate stem cell behavior, intercellular communication, and lipid metabolism in Drosophila, with mechanistic insights into the regulation of immune-metabolic communication.Chapter 1 reviews the conserved roles of Slit/Robo signaling in diverse stem cell populations. From regulating hematopoietic stem cells in both Drosophila and mammals, to maintaining niche adhesion in the testis and controlling asymmetric cell division in mammary and intestinal stem cells, Slit/Robo signaling governs critical fate decisions across multiple cell types. This chapter highlights how Slit signaling influences self-renewal and differentiation. It also underlines broader implications in development, disease biology, and potential therapeutic applications.
In Chapter 2, building on our previous identification of the Tolloid family metalloprotease, Tok, as the Drosophila protease for Slit cleavage, we sought to identify the vertebrate counterpart involved in SLIT2 processing. Towards this, demonstrate that proteolytic cleavage of SLIT2 generates functionally distinct fragments. Using Drosophila and mammalian systems, we show that Tolloid-like 1 (TLL1) is the vertebrate protease responsible for cleaving SLIT2, and that this cleavage is regulated by proprotein convertase 2 (PC2) via activation of TLL1. These findings clarify the mechanisms by which Slit proteolysis diversifies signaling, suggesting receptor-specific and context-dependent functions.
Chapter 3 investigates the non-neural functions of Slit fragments in metabolic regulation. Slit-C, produced through Tok-mediated cleavage, promotes hemocyte dispersal in a Pvr (PDGFR/VEGFR)-dependent manner, while Slit-FL retains hemocytes in hematopoietic niches. Starvation induces Tok expression in the fat body, enhancing Slit cleavage and modifying systemic immune and metabolic responses. Slit-C also physically interacts with Pvr in Drosophila and with PDGFR-α in vertebrates, suggesting conserved roles in lipid metabolism and immune regulation.
Chapter 4 discusses the findings from Chapter 3 in greater depth, addressing experimental caveats, challenges in interpreting ligand-receptor interactions with matricellular proteins and directions for future research to expand on Slit’s function in metabolic tissues. The chapter also connects this work to emerging clinical studies that highlight SLIT’s therapeutic potential in treating metabolic and immune disorders.
Together, this thesis uncovers novel roles for Slit signaling beyond axon guidance, highlighting its emerging function as a regulator of immune-metabolic crosstalk and laying the groundwork for future investigation into its physiological and therapeutic relevance.