Not applicable.

Data availability RNA sequencing data that support the findings of this study have been deposited in the ArrayExpress database at EMBL-EBI (www.ebi.ac.uk/arrayexpress) under accession number E-MTAB-7660. All other data supporting the findings of this study are available from the corresponding author on reasonable request. Code for the biophysical modelling is provided as a Supplementary file.

Human organogenesis remains relatively unexplored for ethical and practical reasons. Here, we report the establishment of a single-cell transcriptome atlas of the human fetal pancreas between 7 and 10 post-conceptional weeks of development. To interrogate cell–cell interactions, we describe InterCom, an R-Package we developed for identifying receptor–ligand pairs and their downstream effects. We further report the establishment of a human pancreas culture system starting from fetal tissue or human pluripotent stem cells, enabling the long-term maintenance of pancreas progenitors in a minimal, defined medium in three-dimensions. Benchmarking the cells produced in 2-dimensions and those expanded in 3-dimensions to fetal tissue identifies that progenitors expanded in 3-dimensions are transcriptionally closer to the fetal pancreas. We further demonstrate the potential of this system as a screening platform and identify the importance of the EGF and FGF pathways controlling human pancreas progenitor expansion.

Context The endocrine function of human fetal adrenals (HFAs) is activated already during first trimester, but adrenal steroidogenesis during fetal life is not well characterized. Objective This study aimed to investigate HFA steroidogenesis by analyzing adrenal glands from first and second trimesters. Design and Setting Male and female HFA from gestational weeks (GWs) 8 to 19 were examined, including a total of 101 samples from 83 fetuses. Main Outcome Measure(s) Expression level of steroidogenic genes and protein expression/localization were determined by quantitative PCR and immunohistochemistry, respectively, and intra-adrenal steroid levels were quantified by LC-MS/MS. Results Transcriptional levels of StAR, CYP11A1, CYP17A1, CYP21A2, CYP11B1/2, and SULT2A1 were significantly higher in second trimester compared to first trimester (P < 0.05), whereas expression levels of 3β-HSD2 and ARK1C3 were unaltered between GWs 8 and 19. All investigated steroidogenic proteins were expressed in a distinct pattern throughout the investigated period, with most enzymes expressed primarily in the fetal zone, except 3β-HSD1/2, which was expressed mainly in the definitive zone. Abundant steroidogenic enzyme expression was reflected in overall high intra-adrenal tissue concentrations of mineralocorticoids, glucocorticoids, and androgens; cortisol was the most abundant (1071 to 2723 ng/g tissue), and testosterone levels were the lowest (2 to 14 ng/g tissue). Conclusions The expression profiles of HFA steroidogenic enzymes are distinct from first to second trimester, with no major differences between male and female samples. Intra-adrenal steroid hormone concentrations confirm that cortisol is produced throughout first and second trimesters, suggesting continued regulation of the hypothalamus-pituitary-adrenal axis during this entire period.