Characterizing dynamics and lineage of bihormonal cell in mammalian pancreatic islets [Smart-seq3xpress]

The precise roles and prevalence of bihormonal cells within pancreatic islets are not fully understood. Here, we utilized genetically engineered mouse strains with specific fluorescent markers for pancreatic endocrine cells and advanced imaging flow cytometry to investigate the presence of bihormonal cells in adult mouse islets. Our results revealed a marginal presence of such cells, contradicting the hypothesis that transdifferentiation contributes significantly to β-cell restoration in diabetic mice or during pregnancy-induced β-cell proliferation. Employing single-cell RNA sequencing (scRNA-seq), we observed that Gcg+Ppy+ bihormonal cells closely resemble either α- or PP-cells, lacking distinct gene expression profiles. This finding suggests bihormonal cells may not represent a unique lineage but could be transitional states in cellular differentiation. Furthermore, a dual-genetic tracing approach revealed that embryonic Ins+Gcg+ cells differentiate into α-cells postnatally. By integrating gene co-expression network analysis with 10x Genomics scRNA-seq data, we established a hierarchical classification of endocrine cells in mouse and human islets, identifying distinct populations with minimal overlap in conserved genes between species. This study not only refines our understanding of bihormonal cells in islet function and development but also highlights the complexities in translating murine model findings to human applications, emphasizing the need for species-specific considerations in diabetes research and therapy development.