Continuous regeneration of digestive enzyme (zymogen)-secreting chief cells is a normal aspect of stomach function that is disrupted in precancerous lesions (e.g. metaplasias, chronic atrophy). The cellular and genetic pathways that underlie zymogenic cell (ZC) differentiation are poorly understood. Here,we describe a gene expression analysis of laser capture microdissection purified gastric cell populations that identified the bHLH transcription factor Mist1 as a potential ZC regulatory factor. Our molecular and ultrastructural analysis of proliferation, migration and differentiation of the gastric unit in Mist1-/- and control mice supports a model whereby wild-type ZC progenitors arise as neck cells in the proliferative (isthmal) zone of the gastric unit and become transitional cells(TCs) with molecular and ultrastructural characteristics of both enzyme-secreting ZCs and mucus-secreting neck cells as they migrate to the neck-base zone interface. Thereafter, they rapidly differentiate into mature ZCs as they enter the base. By contrast, Mist1-/- neck cells differentiate normally, but ZCs in the mature, basal portion of the gastric unit uniformly exhibit multiple apical cytoplasmic structural abnormalities. This defect in terminal ZC differentiation is also associated with markedly increased abundance of TCs, especially in late-stage TCs that predominantly have features of immature ZCs. Thus, we present an in vivo system for analysis of ZC differentiation, present molecular evidence that ZCs differentiate from neck cell progenitors and identify Mist1 as the first gene with a role in this clinically important process.

Innate immune signaling has recently been shown to play an important role in nuclear reprogramming, by altering the epigenetic landscape and thereby facilitating transcription. However, the mechanisms that link innate immune activation and metabolic regulation in pluripotent stem cells remain poorly defined, particularly with regard to key molecular components. In this study, we show that hypoxiainducible factor 1a (HIF1a), a central regulator of adaptation to limiting oxygen tension, is an unexpected but crucial regulator of innate immune-mediated nuclear reprogramming. HIF1a is dramatically upregulated as a consequence of Toll-like receptor 3 (TLR3) signaling and is necessary for efficient induction of pluripotency and transdifferentiation. Bioenergetics studies reveal that HIF1a regulates the reconfiguration of innate immune-mediated reprogramming through its well-established role in throwing a glycolytic switch. We believe that results from these studies can help us better understand the influence of immune signaling in tissue regeneration and lead to new therapeutic strategies.