Cell population characterisation and discovery using single cell technologies in endocrine systems.

In the last 15 years, single-cell technologies have become robust and indispensable tools to investigate cell heterogeneity. Beyond transcriptomic, genomic and epigenome analyses, technologies are constantly evolving, in particular toward multi-omics, where analyses of different source materials from a single cell are combined, and spatial transcriptomics where resolution of cellular heterogeneity can be detected in situ. While some of these techniques are still being optimised, single-cell RNAseq has commonly been used because the examination of transcriptomes allows characterization of cell identity, and therefore unravel previously uncharacterised diversity within cell populations. Most endocrine organs have now been investigated using this technique, and this has given new insights into organ embryonic development, characterization of rare cell types, and disease mechanisms. Here we highlight recent studies, particularly on the hypothalamus and pituitary, and examine recent findings on the pancreas and reproductive organs where many single-cell experiments have been performed.