A Peninsular Structure Coordinates Asynchronous Differentiation with Morphogenesis to Generate Pancreatic Islets

Abstract

SUMMARY The pancreatic islets of Langerhans regulate glucose homeostasis. The loss of insulin-producing β cells within islets results in diabetes, and islet transplantation from cadaveric donors can cure the disease. In vitro production of whole islets, not just β cells, will benefit from a better understanding of endocrine differentiation and islet morphogenesis. We used single-cell mRNA sequencing to obtain a detailed description of pancreatic islet development. Contrary to the prevailing dogma, we find islet morphology and endocrine differentiation to be directly related. As endocrine progenitors differentiate, they migrate in cohesion and form bud-like islet precursors, or “peninsulas” (literally “almost islands”). α cells, the first to develop, constitute the peninsular outer layer, and β cells form later, beneath them. This spatiotemporal collinearity leads to the typical core-mantle architecture of the mature, spherical islet. Finally, we induce peninsula-like structures in differentiating human embryonic stem cells, laying the ground for the generation of entire islets in vitro.

Comprehensive single cell mRNA profiling reveals a detailed roadmap for pancreatic endocrinogenesis

“…1B). This data is in line with the idea that at the Ngn3-expressing state, EP progenitors get specified in the pancreatic epithelium and endocrine precursor delaminate into the surrounding mesenchyme to form protoislet clusters (Gouzi et al, 2011;Sharon et al, 2019). During development, Ngn3 is expressed at low levels in progenitors, reach peak levels in precursors and the levels are reduced upon differentiation of the precursors into the endocrine hormone + lineage (Bechard et al, 2016).…”

“…Yet, during progressive lineage restriction from specified EP progenitors to determined EP precursors the molecular signature changes over time and the mechanisms underpinning lineage allocation towards a specific endocrine subtype fate have remained largely elusive. Although several recent studies (Byrnes et al, 2018;Krentz et al, 2018;Ramond et al, 2018;Scavuzzo et al, 2018;Sharon et al, 2019;Stanescu et al, 2016;Yu et al, 2018Yu et al, , 2019 have shed light on the transcriptional profiles of EPs, the importance of these cells for endocrine cell formation still necessitates a comprehensive temporally resolved and fine-grained mapping of gene expression on the single cell level. The low percentage of EPs within the embryonic pancreas together with the limitation of transgenic reporter lines to reflect accurately the transient expression of the Ngn3 protein have been major obstacles to establishing a detailed roadmap of endocrinogenesis.…”

Morphogenesis of the islets of Langerhans is guided by extra-endocrine Slit2/3 signals

“…However, we further provide evidence to suggest mesenchymal Slits repel -cells during islet morphogenesis. These results are in support of the recent observation that endocrine progenitors remain physically connected throughout islet morphogenesis (Sharon et al, 2019), and suggest that after -cell delamination, repulsion of the -cells by mesenchymal Slits pushes them into the center of the islet, thus maintaining the core-mantle architecture. Taken together, we propose that both attractive and repulsive signals operate together in forming the canonical murine islet architecture.…”

Beta-Cell Dedifferentiation in Type 2 Diabetes: Concise Review

“…Similarly, expression of the mesenchymal marker vimentin in T2D pancreas insulin‐positive cells may reflect cell dedifferentiation, resembling epithelial‐mesenchymal transition (EMT) observed in β cells cultured from normal human islets, which manifest proliferation associated with dedifferentiation . Given that brief and reversible EMT occurs in islet progenitor cells in the pancreatic ductal epithelium, as part of normal islet development , vimentin expression in T2D β cells may reflect dedifferentiation to a progenitor‐like state. On the other hand, it is difficult to exclude activation of insulin expression in mesenchymal cells recruited to the islets as part of a regenerative process.…”