Research Resource: Genetic Labeling of Human Islet Alpha Cells

The 2 most abundant human pancreatic islet cell types are insulin-producing beta-cells and glucagonproducing alpha-cells. Defined cis-regulatory elements from rodent Insulin genes have permitted genetic labeling of human islet beta-cells, enabling lineage tracing and generation of human beta-cell lines, but analogous elements for genetically labeling human alpha-cells with high specificity do not yet exist. To identify genetic elements that specifically direct reporter expression to human alpha-cells, we investigated noncoding sequences adjacent to the human GLUCAGON and ARX genes, which are expressed in islet alpha-cells. Elements with high evolutionary conservation were cloned into lentiviral vectors to direct fluorescent reporter expression in primary human islets. Based on the specificity of reporter expression for alpha- and beta-cells, we found that rat glucagon promoter was not specific for human alpha-cells but that addition of human GLUCAGON untranslated region sequences substantially enhanced specificity of labeling in both cultured and transplanted islets to a degree not previously reported, to our knowledge. Specific transgene expression from these cis-regulatory sequences in human alpha-cells should enable targeted genetic modification and lineage tracing.