SummaryTo understand organ function, it is important to have an inventory of its cell types and of their corresponding marker genes. This is a particularly challenging task for human tissues like the pancreas, because reliable markers are limited. Hence, transcriptome-wide studies are typically done on pooled islets of Langerhans, obscuring contributions from rare cell types and of potential subpopulations. To overcome this challenge, we developed an automated platform that uses FACS, robotics, and the CEL-Seq2 protocol to obtain the transcriptomes of thousands of single pancreatic cells from deceased organ donors, allowing in silico purification of all main pancreatic cell types. We identify cell type-specific transcription factors and a subpopulation of REG3A-positive acinar cells. We also show that CD24 and TM4SF4 expression can be used to sort live alpha and beta cells with high purity. This resource will be useful for developing a deeper understanding of pancreatic biology and pathophysiology of diabetes mellitus.

Cell dynamics in subcutaneous and breast tumors can be studied through conventional imaging windows with intravital microscopy. By contrast, visualization of the formation of metastasis has been hampered by the lack of long-term imaging windows for metastasis-prone organs, such as the liver. We developed an abdominal imaging window (AIW) to visualize distinct biological processes in the spleen, kidney, small intestine, pancreas, and liver. The AIW can be used to visualize processes for up to 1 month, as we demonstrate with islet cell transplantation. Furthermore, we have used the AIW to image the single steps of metastasis formation in the liver over the course of 14 days. We observed that single extravasated tumor cells proliferated to form "pre-micrometastases," in which cells lacked contact with neighboring tumor cells and were active and motile within the confined region of the growing clone. The clones then condensed into micrometastases where cell migration was strongly diminished but proliferation continued. Moreover, the metastatic load was reduced by suppressing tumor cell migration in the pre-micrometastases. We suggest that tumor cell migration within pre-micrometastases is a contributing step that can be targeted therapeutically during liver metastasis formation.

Cell identity switches, where terminally-differentiated cells convert into different cell-types when stressed, represent a widespread regenerative strategy in animals, yet they are poorly documented in mammals. In mice, some glucagon-producing pancreatic α-cells and somatostatin-producing δ-cells become insulin expressers upon ablation of insulin-secreting β-cells, promoting diabetes recovery. Whether human islets also display this plasticity, especially in diabetic conditions, remains unknown. Here we show that islet non-β-cells, namely α-cells and PPY-producing γ–cells, obtained from deceased non-diabetic or diabetic human donors, can be lineage-traced and reprogrammed by the transcription factors Pdx1 and MafA to produce and secrete insulin in response to glucose. When transplanted into diabetic mice, converted human α-cells reverse diabetes and remain producing insulin even after 6 months. Surprisingly, insulin-producing α-cells maintain α-cell markers, as seen by deep transcriptomic and proteomic characterization. These observations provide conceptual evidence and a molecular framework for a mechanistic understanding of in situ cell plasticity as a treatment for diabetes and other degenerative diseases.