SummaryMost cancer cells release heterogeneous populations of extracellular vesicles (EVs) containing proteins, lipids, and nucleic acids. In vitro experiments showed that EV uptake can lead to transfer of functional mRNA and altered cellular behavior. However, similar in vivo experiments remain challenging because cells that take up EVs cannot be discriminated from non-EV-receiving cells. Here, we used the Cre-LoxP system to directly identify tumor cells that take up EVs in vivo. We show that EVs released by malignant tumor cells are taken up by less malignant tumor cells located within the same and within distant tumors and that these EVs carry mRNAs involved in migration and metastasis. By intravital imaging, we show that the less malignant tumor cells that take up EVs display enhanced migratory behavior and metastatic capacity. We postulate that tumor cells locally and systemically share molecules carried by EVs in vivo and that this affects cellular behavior.

SummaryThe rapid turnover of the mammalian intestinal epithelium is supported by stem cells located around the base of the crypt1. Alongside Lgr5, intestinal stem cells have been associated with various markers, which are expressed heterogeneously within the crypt base region1-6. Previous quantitative clonal fate analyses have proposed that homeostasis occurs as the consequence of neutral competition between dividing stem cells7-9. However, the short-term behaviour of individual Lgr5+ cells positioned at different locations within the crypt base compartment has not been resolved. Here, we established the short-term dynamics of intestinal stem cells using a novel approach of continuous intravital imaging of Lgr5-Confetti mice. We find that Lgr5+ cells in the upper part of the niche (termed ‘border cells’) can be passively displaced into the transit-amplifying (TA) domain, following division of proximate cells, implying that determination of stem cell fate can be uncoupled from division. Through the quantitative analysis of individual clonal lineages, we show that stem cells at the crypt base, termed ‘central cells’, experience a survival advantage over border stem cells. However, through the transfer of stem cells between the border and central regions, all Lgr5+ cells are endowed with long-term self-renewal potential. These findings establish a novel paradigm for stem cell maintenance in which a dynamically heterogeneous cell population is able to function long-term as a single stem cell pool.

(1,2). Although the stem cell niche varies in nature and location between different organs, in general terms it provides a unique signaling environment to maintain tissue homeostasis, inhibit stem cell loss, and control cell differentiation (1, 3, 4). The mammalian small intestine (SI) and colon represent unique models to study tissue stem cells and their niches because of their stereotypic and compact architecture combined with their exceedingly fast self-renewing kinetics (5, 6). In both SI and colon crypts, cycling stem cells are marked by leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5) (7). Murine SI stem cells divide approximately every 24 h to fill a proliferative transit-amplifying compartment that occupies the remainder of the crypts. Cells exiting crypts arrest their cell cycle, differentiate, and move up the flanks of the villi. One of the differentiated cell types derived from the SI stem cell, the Paneth cell, is located at crypt bottoms and is in direct contact with Lgr5 stem cells. It produces factors that promote stem cell maintenance, including epidermal growth factor (EGF) and the related TGF-α, the Notch ligands Dll-1 and Dll-4, and Wnt3 (8-10). Whereas Paneth cells are dispensable for in vivo crypt function (as niche factors are also secreted from nonepithelial cells), Paneth cells are indispensable for the growth of epithelial miniguts in culture (9,11,12