Endocytosis and stress: From mechanisms to cellular physiology.

This issue presents a series of articles and reviews on the theme “Endocytosis and stress.” The purpose of this issue was to cover various aspects of the functions of endocytosis, but also in a variety of model organisms to highlight how this conserved process has been exploited throughout evolution. A series of reviews highlight connections between endocytosis and the properties of the extracellular environment, including signaling molecules, nutrient availability, or biophysical constraints, as well as the importance of endocytosis in cellular function, adaptation, and pathologies. The plethora of cellular functions regulated by endocytosis is well discussed by Giangreco et al. (2021) who provide a series of examples illustrating the various functions of endocytic proteins in cellular physiology, and the pathologies derived from their malfunction. This includes the role of adaptor proteins in clathrinmediated endocytosis (CME) and non-clathrin-mediated endocytosis (NCE), how this regulates signaling pathways, and the links with tumorigenesis.Two reviews then detail the connections between endocytosis and the regulation of signaling pathways. Wu et al. (2021) focus on the mechanisms by which Wnt signaling, a key pathway in development and morphogenesis in animals, is regulated by endocytosis and endosomal trafficking. They notably highlight work in Caenorhabditis elegans on the involvement in Wnt signaling and stress response. Seib and Klein (2021) then discuss the role of endocytosis in the activation of Notch signaling. They mention the importance of endocytosis in generating pulling forces leading to Notch cleavage, a crucial step in Notch pathway activation, but also additional functions in the recycling of Notch ligands. The interplay between membrane tension and CME is carefully reviewed by Djakbarova et al. (2021). The importance of membrane tension in physiological processes such as cell division, migration, or spreading is also underscored. In their monograph, the authors detail how membrane tension is established, regulated, and how this regulates CME. Two additional reviews focus on the regulation of nutrient transporters by endocytosis. Ivanov and Vert (2021) describe the exquisite molecular mechanisms by which