Endocrine Abstracts

Mammalian tissues are composed of heterogeneous populations of cells, interacting in highly structured microenvironments to achieve physiologic goals. Understanding the design principles of endocrine tissues organization requires approaches to analyze spatially-resolved sub-populations of cells within the tissue. The mammalian liver consists of hexagonal-shaped lobules, radially polarized by blood flow and morphogens. Key liver are differentially expressed along the lobule axis, a phenomenon termed zonation. These diverse functions are carried out by hepatocytes that closely interact with supporting cells termed non-parenchymal cells (NPCs). Spatially resolved single-cell RNA sequencing (scRNAseq) is a powerful approach to infer connections between tissue coordinates and molecular identities. We have recently combined two powerful technologies - Single cell RNAsDefault (scRNAseq) and single molecule Fluorescence In-Situ Hybridization (smFISH) to reconstruct the spatial gene expression gradients of both hepatocyte and liver endothelial genes. Using this approach, we obtain the zonation profiles of all liver genes with high spatial resolution. Our work revealed an unexpected breadth of liver spatial heterogeneity, with ~50% of liver genes expressed in spatially non-uniform patterns. The spatial division of labor we uncovered is in line with previous theory suggesting that liver zonation confers optimality for liver function. Pancreatic beta cells are heterogeneous at multiple levels. However, interrogating transcriptional heterogeneity in the intact tissue has been challenging. We used an optimized smFISH protocol to identify a sub-population of ‘extreme’ beta-cells with elevated mRNA levels of insulin. Extreme beta cells contain higher ribosomal and proinsulin content, but lower levels of insulin protein in a fasted state, suggesting that they may be tuned for basal insulin secretion. In addition, the proportion of extreme cells increases in db/db diabetic mice, potentially facilitating the required increase in basal insulin. Our results thus highlight a sub-population of beta-cells that may carry distinct functional roles along physiological and pathological time scales. Understanding the relation between structure of tissues and their single-cell gene expression patterns in healthy states can help up reveal how these interactions are perturbed in disease.