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Transit amplifying cells

competition diagramIn many epithelial tissues, newly produced daughter cells differentiate slowly, over the course of several divisions [1]. This “transit amplifying” stage is poorly understood.  Although transit amplifying cells have exited the niche and thus are no longer receiving niche signals, at least some retain the capacity to re-enter the niche and acquire the stem cell fate. 

However, many cells in the transit amplifying population are receiving new signals that direct them down a path toward differentiation. This suggests that there is heterogeneity in the transit amplifying population, but little is known about whether or how transit amplifying cells differ from one another. We discovered a mechanism that allows newly produced transit amplifying cells in the follicle stem cell lineage to retain a molecular memory of the niche signal that persists for a short period of time [2]. Our data suggest that this memory delays differentiation, allowing the cells to participate in stem cell replacement or to increase in number before committing to a cell fate choice. We are using quantitative fluorescence microscopy, clonal analysis, and high-throughput molecular and genetic methods to understand how cell fate is controlled during this labile period of differentiation.