A multistate stem cell dynamics maintains homeostasis in mouse spermatogenesis.

Toshinori Nakagawa,Gen Kondoh,Miyako Fujita,Seiya Mizuno,Yoshiki Omatsu,Shosei Yoshida,Hitomi Watanabe,Takashi Nagasawa,David J Jörg,Satoru Takahashi,Seungmin Han,Tatsuro Ikeda,Keiko Nishimura,Benjamin D Simons

doi:10.1016/j.celrep.2021.109875

Abstract

In mouse testis, a heterogeneous population of undifferentiated spermatogonia (Aundiff) harbors spermatogenic stem cell (SSC) potential. Although GFRα1+ Aundiff maintains the self-renewing pool in homeostasis, the functional basis of heterogeneity and the implications for their dynamics remain unresolved. Here, through quantitative lineage tracing of SSC subpopulations, we show that an ensemble of heterogeneous states of SSCs supports homeostatic, persistent spermatogenesis. Such heterogeneity is maintained robustly through stochastic interconversion of SSCs between a renewal-biased Plvap+/GFRα1+ state and a differentiation-primed Sox3+/GFRα1+ state. In this framework, stem cell commitment occurs not directly but gradually through entry into licensed but uncommitted states. Further, Plvap+/GFRα1+ cells divide slowly, in synchrony with the seminiferous epithelial cycle, while Sox3+/GFRα1+ cells divide much faster. Such differential cell-cycle dynamics reduces mitotic load, and thereby the potential to acquire harmful de novo mutations of the self-renewing pool, while keeping the SSC density high over the testicular open niche.

Highlights

Tissue homeostasis is maintained through the continual replenishment of differentiated cells by residential stem cells
Plvap and Sox3 expression represents subfractions of GFRa1+ a heterogeneous population of undifferentiated spermatogonia (Aundiff) By comparing gene expression between fractions of Aundiff showing different levels of GFRa1 expression including GFRa1high, GFRa1low, and GFRa1– fractions, we found that cells showing the highest levels of GFRa1 were highly enriched in the expression of Plvap (Figures 1B, S1A, and S1B)
Developing a fluorescence-activated cell-sorting (FACS) strategy that expands the Aundiff (E-Cad+/KIT–) population based on the levels of surface GFRa1 and PLVAP, we found that GFRa1+ Aundiff comprises a continuum in which PLVAP expression is restricted to GFRa1high cells (Figures 1B, S1C, and S1D)

Summary

Introduction

Tissue homeostasis is maintained through the continual replenishment of differentiated cells by residential stem cells. Tissue stem cells are thought to comprise a restricted compartment of undifferentiated cells that perfectly self-renew while giving rise to committed cells, which terminally differentiate either directly or through a limited series of divisions (Watt and Hogan, 2000). Recent studies have challenged these prevailing views: in many tissues, it has been shown that cells normally committed to differentiation can reacquire self-renewal potential in response to. Self-renewal potential extends over multiple cell states, questioning whether such cellstate interchange may contribute during long-term tissue homeostasis. The slow-cycling property of tissue stem cell function has been called into question: for example, while hematopoietic stem cells are shown to be slow cycling (Busch et al, 2015; Cheshier et al, 1999), in the small intestinal epithelium, evidence suggests that label-retaining cells positioned in the vicinity of row +4 in the crypt are destined for differentiation (Buczacki et al, 2013), while the major Lgr5+ stem cell compartment divides rapidly (Barker et al, 2007; Buczacki et al, 2013; Snippert et al, 2010)

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Conclusion