R-SMAD stability is essential for TGF-β signaling. In this study, Zhou and Dabiri et al. describe a new role of the tumor suppressor pVHL as an E3 ligase for R-SMAD ubiquitination, implicating the potential interaction between oxygen sensing and TGF-β signaling in human cells and Drosophila tissue development.

Uchino et al. have developed a genetically encoded probe to specifically detect the Ser2-phosphorylated, elongating form of RNA polymerase II in living cells. Ser2-phosphorylated RNA polymerase foci exhibit more dynamic motion than chromatin replication domains and p300-enriched foci.

ORP10 localizes in a PI4P-dependent manner at ER–endosome membrane contact sites tethered by ORP9 and VAP, where it mediates countertransport of PI4P and PS. This in turn supplies endosomes with PS, thereby promoting EHD1 recruitment and endosome fission.

Van der Beek et al. introduce a quantitative CLEM method using fluorescence to label electron microscopy images by overlay. By comparing the ultrastructural distributions of the endosomal regulators Rab5, Rab7, EEA1, APPL1, and PI(3)P, they reveal distinct endosomal subpopulations and an unexpected localization of EEA1 to late endosomes.

Aguilera et al. show that ferroptosis, an oxidative and iron-dependent form of regulated cell death, plays an important role in the cyanobacterium Synechocystis sp. PCC 6803 in response to heat stress.

Human atlastin GTPases are assumed to catalyze ER membrane fusion, but their fusion activity has not previously been reconstituted. Crosby et al. show that purified atlastin1 and atlastin2 are capable of fusion catalysis and that each is negatively regulated by a variable C-terminal extension.

Yu-Kemp et al. explore mechanisms that epithelial cells use to assemble supramolecular actomyosin structures at E-Cadherin–based cell–cell junctions. They find that individual actin assembly pathways are not essential. Instead, microscopy and pharmacologic inhibition suggest that micron-scale supramolecular myosin arrays help bundle actin at mature junctions.