Understanding how fate choices are made by multipotent progenitors during pancreas development is valuable information in the quest for regenerative medicine and cell therapy to treat diabetes mellitus. Pancreatic differentiation is well defined and understood in rodents however, human data are comparably scarce. Specifically, when human pancreatic progenitors are multipotent is unknown as are the epigenetic changes that these cells undergo during their differentiation to beta-cells. We have addressed this in human embryos by studying expression of critical transcription factors and applied chromatin immunoprecipitation/next generation sequencing (ChIP-seq) to examine genome-wide chromatin modifications linked to expression (using anti-H3K4me3 and anti-H3K4me1).
Pancreas was first observed at Carnegie Stage (CS12; 26 days post-conception (dpc)) at which stage the pancreatic epithelial cells expressed nuclear PDX1 and GATA4 in the presumptive dorsal and ventral buds. SOX9 expression appeared in pancreatic progenitor cells slightly later in development. GATA4 detection declined in intensity later in the embryonic period and by 8 weeks of development it had become restricted to the peripheral tip cells of pancreatic epithelial nests demarcating the earliest report of exocrine cells.
Based on these data, pancreas at ~5054 dpc was isolated and processed for ChIP-seq. Analyses for potential growth factor signals that might regulate early human development identified multiple loci of interest. For instance, compared to our data from adult islets (Gaulton et al. Nature Genetics 42 255259, 2010) INSULIN was largely silenced in progenitor cells whereas the adjacent IGF2 locus was active in progenitors but silenced in adult islets.
Taken together, these data define for the first time when multipotent human pancreatic epithelial cells are present facilitating opportunities to determine what regulates their differentiation into different pancreatic cell lineages. Discovering these data will underpin either beta-cell regenerative approaches or the assessment of insulin-secreting cells generated from human ES cells.