single-cell-transcriptomic-analyses-mouse-pancreatic-endocrine

Single-cell Transcriptomic Analyses of Mouse Pancreatic Endocrine Cells

Pancreatic endocrine cells, which are clustered in islets, regulate blood glucose stability and energy metabolism. The distinct cell types in islets, ...

Peking University

Pancreatic β and α cells play essential roles in maintaining glucose homeostasis. However, the mechanisms by which these distinct cell populations are generated, expand, and mature during pancreas development remain unclear. In this study, we addressed this critical question by performing a single-cell transcriptomic analysis of mouse β and α cells sorted from fetal to adult stages. We discovered that β and α cells use different regulatory strategies for their maturation and that cell proliferation peaks at different developmental times. However, the quiescent and proliferative cells in both the β lineage and α lineage are synchronous in their maturation states. The heterogeneity of juvenile β cells reflects distinct cell-cycling phases, origins, and maturation states, whereas adult β cells are relatively homogeneous at the transcriptomic level. These analyses provide not only a high-resolution roadmap for islet lineage development but also insights into the mechanisms of cellular heterogeneity, cell number expansion, and maturation of both β and α cells.

Deciphering Pancreatic Islet β Cell and α Cell Maturation Pathways and Characteristic Features at the Single-Cell Level.

How bipotential hepatoblasts differentiate into hepatocytes and cholangiocytes remains unclear. Here, using single-cell transcriptomic analysis of hepatoblasts, hepatocytes, and cholangiocytes sorted from embryonic day 10.5 (E10.5) to E17.5 mouse embryos, we found that hepatoblast-to-hepatocyte differentiation occurred gradually and followed a linear default pathway. As more cells became fully differentiated hepatocytes, the number of proliferating cells decreased. Surprisingly, proliferating and quiescent hepatoblasts exhibited homogeneous differentiation states at a given developmental stage. This unique feature enabled us to combine single-cell and bulk-cell analyses to define the precise timing of the hepatoblast-to-hepatocyte transition, which occurs between E13.5 and E15.5. In contrast to hepatocyte development at almost all levels, hepatoblast-to-cholangiocyte differentiation underwent a sharp detour from the default pathway. New cholangiocyte generation occurred continuously between E11.5 and E14.5, but their maturation states at a given developmental stage were heterogeneous. Even more surprising, the number of proliferating cells increased as more progenitor cells differentiated into mature cholangiocytes. Based on an observation from the single-cell analysis, we also discovered that the protein kinase C/mitogen-activated protein kinase signaling pathway promoted cholangiocyte maturation.

A single-cell transcriptomic analysis reveals precise pathways and regulatory mechanisms underlying hepatoblast differentiation.

Pancreatic endocrine lineages are derived from pancreatic progenitors that undergo a cell fate transition requiring a switch from low to high Ngn3 expression. However, the underlying chromatin regulatory mechanisms are unclear. Here, we performed epigenomic analysis of gene regulatory loci featuring histone marks in cells with low or high level of Ngn3 expression. In combination with transcriptomic analysis, we discovered that in Ngn3-high cells, the removal of H3K27me3 was associated with the activation of key transcription factors and the establishment of primed and active enhancers. Deletion of , a histone demethylase for H3K27me3, at the pancreatic progenitor stage impaired the efficiency of endocrine cell fate transition and thereafter islet formation. Curiously, single-cell RNA-seq revealed that the transcriptome and developmental pathway of Ngn3-high cells were not affected by the deletion of  Our study indicates sequential chromatin events and identifies a crucial role for Jmjd3 in regulating the efficiency of the transition from Ngn3-low to Ngn3-high cells.

Dynamics of chromatin marks and the role of JMJD3 during pancreatic endocrine cell fate commitment.

The pancreas of vertebrates is separately derived from both the dorsal and ventral endodermal domains. However, the difference between these two programs has been unclear. Here, using a pancreatic determination gene, , driven GFP transgenic mouse strain, we identified Pdx1-GFP highly expressing cells (Pdx1) and Pdx1-GFP lowly expressing cells (Pdx1) in both embryonic dorsal Pdx1-expressing region (DPR) and ventral Pdx1-expressing region (VPR). We analyzed the transcriptomes of single Pdx1 and Pdx1 cells from the DPR and VPR. In the VPR, Pdx1 cells have an intermediate progenitor identity and can generate hepatoblasts, extrahepatobiliary cells, and Pdx1 pancreatic progenitor cells. In the DPR, Pdx1 cells are directly specified as pancreatic progenitors, whereas Pdx1 cells are precocious endocrine cells. Therefore, our study defines distinct road maps for dorsal and ventral pancreatic progenitor specification. The findings provide guidance for optimization of current β-cell induction protocols by following the  dorsal pancreatic specification program.

Article	Year
Deciphering Pancreatic Islet β Cell and α Cell Maturation Pathways and Characteristic Features at the Single-Cell Level. Cell metabolism\| PubMed ID: 28467935	2017
A single-cell transcriptomic analysis reveals precise pathways and regulatory mechanisms underlying hepatoblast differentiation. Hepatology (Baltimore, Md.)\| PubMed ID: 28681484	2017
Dynamics of chromatin marks and the role of JMJD3 during pancreatic endocrine cell fate commitment. Development (Cambridge, England)\| PubMed ID: 29559448	2018
Single-cell transcriptomic analyses reveal distinct dorsal/ventral pancreatic programs. EMBO reports\| PubMed ID: 30065074	2018

Wei-Lin Qiu

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