FUCCI tracking shows cell‐cycle‐dependent Neurog3 variation in pancreatic progenitors

Abstract

During pancreas organogenesis, Neurog3HI endocrine-committing cells are generated from a population of Sox9+ mitotic progenitors with only a low level of Neurog3 transcriptional activity (Neurog3TA.LO). Low-level Neurog3 protein, in Neurog3TA.LO cells, is required to maintain their mitotic endocrine-lineage-primed status. Herein, we describe a Neurog3-driven FUCCI cell-cycle reporter (Neurog3P2A.FUCCI) derived from a Neurog3 BAC transgenic reporter that functions as a loxed cassette acceptor (LCA). In cycling Sox9+ Neurog3TA.LO progenitors, the majority of cells in S-G2-M phases have undetectable levels of Neurog3 with increased expression of endocrine progenitor markers, while those in G1 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 Neurog3TA.LO progenitors with entrance into G1 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.

Cell cycle-dependent phosphorylation and regulation of cellular differentiation

“…While neural and muscle tissue have long been studied for the association between cell cycle and differentiation, investigations in the pancreas have been more recent and generally focus on specification of the endocrine lineage (50)(51)(52)(53). Endocrine differentiation is driven by the activity of the bHLH transcription factor Neurogenin3 (Ngn3), and similar to the apparently contrasting roles of Ascl1 in driving both proliferation and differentiation target genes (30), Ngn3 also exhibits this paradox.…”

“…Interestingly, the transition between low-to-high Ngn3 states has been linked to variations in cell cycle length and to the activity of Cyclin/Cdks (50)(51)(52)(53). In particular, lengthening of the G1 phase of the cell cycle is essential for proper induction of Ngn3 and initiation of endocrine cell differentiation (51).…”