FUCCI tracking shows that Neurog3 levels vary with cell-cycle phase in endocrine-biased pancreatic progenitors

Neurog3 HI endocrine-committing cells are generated from a population of Sox9 + mitotic progenitors with only a low level of Neurog3 transcriptional activity ( Neurog3 TA.LO ). Low-level Neurog3 protein, in Neurog3 TA.LO cells, is required to maintain their mitotic endocrine-lineage-primed status. Herein, we describe a Neurog3 -driven FUCCI cell-cycle reporter ( Neurog3 P2A.FUCCI ) derived from a Neurog3 BAC transgenic reporter that functions as a loxed cassette acceptor (LCA). In cycling Sox9 + Neurog3 TA.LO progenitors, the majority of cells in S-G 2 -M phases have undetectable levels of Neurog3 with increased expression of endocrine progenitor markers, while those in G 1 have low Neurog3 levels with increased expression of endocrine differentiation markers. These findings support a model in which variations in Neurog3 protein levels are coordinated with cell-cycle phase progression in Neurog3 TA.LO progenitors with entrance into G 1 triggering a concerted effort, beyond increasing Neurog3 levels, to maintain an endocrine-lineage-primed state by initiating expression of the downstream endocrine differentiation program prior to endocrine-commitment.