ONLINE COVER Lava spews from the southeast crater of the Etna Volcano in Catania, Italy on Dec. 22, 2018. Through geochemical data analysis, Paonita et al. found that a longstanding build-up of magma and gas caused the volcano to be extremely overpressurized in the weeks before the eruption. Accurate assessment of the gas balance in active volcanoes will allow for instrumental hazard evaluation during future volcanic events. [CREDIT: Fabrizio Villa/Getty Images]

ONLINE COVER Critical Crossroads. This month's cover features an immunofluorescence image of a murine tumor-draining lymph node containing metastatic melanoma cells (GFP-expressing YUMM1.7 cells; cyan). Tumor cells reach the tumor-draining lymph node via afferent lymphatic vessels that intersect with the subcapsular and interfollicular sinuses (sinus-lining lymphatic endothelial cells stained with anti-LYVE-1; orange). The sinuses run around and between B cell follicles (B cells stained with anti-B220; purple). A Review by du Bois, Heim, and Lund summarizes our current understanding of the structural biology of tumor-draining lymph nodes, how they are primed to receive metastasizing tumor cells, and their unique impact on prognosis and immunotherapy.

ONLINE COVER Special Issue on Human-Robot Interaction. Prosthetic systems that provide a strong sense of agency and ownership between the user and the prosthesis will improve performance and reduce the rate of device abandonment. Marasco et al. have developed a neural-machine interface for a bionic prosthetic arm that leverages the sense of touch to enhance physical ownership and provides grip kinesthesia to enhance agency. This month's cover is a photograph of the inside socket of a bionic prosthetic arm (see also Focus by Ortiz-Catalan). [CREDIT: Courtney Shell, Dylan Beckler, Zachary Thumser, and Paul Marasco/Laboratory for Bionic Integration, Cleveland Clinic]

Image: Microscopy Core Facility, VIB Gent/Science Source

ONLINE COVER Minimizing Metastases. This scanning electron micrograph shows metastatic mouse tumor cells (in green) invading the lung parenchyma and stroma, in close contact with nearby capillaries (red). Singhal et al. studied the vascular niche after surgical resection of spontaneously metastasizing primary tumors in mice. Using transcriptomics and proteomics, they identified leucine-rich alpha-2 glycoprotein 1 (LRG1), produced by endothelial cells in response to tumor-induced inflammation, as a prometastatic molecule. Treatment with LRG1-neutralizing antibodies led to decreased metastatic burden and prolonged survival in these mice, suggesting that LRG1 may be a potential target to restrict metastatic tumor growth.[CREDIT: Eye of Science]