Person:

Shivdasani, Ramesh

Lgr5+ intestinal stem cells (ISC) drive epithelial self-renewal, and their immediate progeny – intestinal bipotential progenitors – produce absorptive and secretory lineages via lateral inhibition. To define features of early transit from the ISC compartment, we used a microfluidics approach to measure selected stem- and lineage-specific transcripts in single Lgr5+ cells. We identified two distinct cell populations, one that expresses known ISC markers and a second, abundant population that simultaneously expresses markers of stem and mature absorptive and secretory cells. Single-molecule mRNA in situ hybridization and immunofluorescence verified expression of lineage-restricted genes in a subset of Lgr5+ cells in vivo. Transcriptional network analysis revealed that one group of Lgr5+ cells arises from the other and displays characteristics expected of bipotential progenitors, including activation of Notch ligand and cell-cycle inhibitor genes. These findings define the earliest steps in ISC differentiation and reveal multilineage gene priming as a fundamental property of the process.

Most pancreatic neuroendocrine tumors (PNETs) do not produce excess hormones and are therefore considered ‘non-functional’. As clinical behaviors vary widely and distant metastases are eventually lethal, biological classifications might guide treatment. Using enhancer maps to infer gene regulatory programs, we find that non-functional PNETs fall into two major sub-types whose epigenomes and transcriptomes partially resemble islet alpha and beta cells. Transcription factors ARX and PDX1 specify these normal cells, respectively, and 84% of 142 non-functional PNETs expressed one or the other factor, occasionally both. Among 103 cases, distant relapses occurred almost exclusively in patients with ARX+PDX1- tumors and, within this sub-type, in cases with alternative lengthening of telomeres (ALT). These markedly different outcomes belied similar clinical presentations and histology and, in one cohort, occurred irrespective of MEN1 mutation. This robust molecular stratification provides insight into cell lineage correlates of non-functional PNETs, accurately predicts disease course, and can inform post-operative clinical decisions.