Identification of dynamic undifferentiated cell states within the male germline.

La, Hue M; Mäkelä, Juho-Antti; Chan, Ai-Leen; Rossello, Fernando J; Nefzger, Christian M; Legrand, Julien M D; De Seram, Mia; Polo, Jose M et al. · Nat Commun · 2018

basic_science · Level V

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Abstract

The role of stem cells in tissue maintenance is appreciated and hierarchical models of stem cell self-renewal and differentiation often proposed. Stem cell activity in the male germline is restricted to undifferentiated A-type spermatogonia (A<sub>undiff</sub>); however, only a fraction of this population act as stem cells in undisturbed testis and A<sub>undiff</sub> hierarchy remains contentious. Through newly developed compound reporter mice, here we define molecular signatures of self-renewing and differentiation-primed adult A<sub>undiff</sub> fractions and dissect A<sub>undiff</sub> heterogeneity by single-cell analysis. We uncover an unappreciated population within the self-renewing A<sub>undiff</sub> fraction marked by expression of embryonic patterning genes and homeodomain transcription factor PDX1. Importantly, we find that PDX1 marks a population with potent stem cell capacity unique to mature, homeostatic testis and demonstrate dynamic interconversion between PDX1+ and PDX1- A<sub>undiff</sub> states upon transplant and culture. We conclude that A<sub>undiff</sub> exist in a series of dynamic cell states with distinct function and provide evidence that stability of such states is dictated by niche-derived cues.

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