Identification of dynamic undifferentiated cell states within the male germline

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 (Aundiff); however, only a fraction of this population act as stem cells in undisturbed testis and Aundiff hierarchy remains contentious. Through newly developed compound reporter mice, here we define molecular signatures of self-renewing and differentiation-primed adult Aundiff fractions and dissect Aundiff heterogeneity by single-cell analysis. We uncover an unappreciated population within the self-renewing Aundiff 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− Aundiff states upon transplant and culture. We conclude that Aundiff 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.

DAZL mediates a broad translational program regulating expansion and differentiation of spermatogonial progenitors

“…To confirm these results, we isolated late progenitor and early differentiating spermatogonia expressing the Pou5f1:EGFP reporter at 6-8 months via FACS (Figure 1 -figure 7 supplement 3A-B) (Garcia and Hofmann, 2012;La et al, 2018b) In sum, the loss of Dazl results in dramatically fewer differentiating spermatogonia for two reasons: progenitor spermatogonia fail to fully expand their population, and they do not 10 differentiate efficiently.…”

Open niche regulation of mouse spermatogenic stem cells

“…Other differentiation-primed subpopulations of undifferentiated spermatogonia (i.e., Miwi2 + , Oct4 + , and Pdx1 − ) have been shown, similarly, to contribute to the self-renewing pool and support longterm repopulation in such regenerative contexts (Carrieri et al, 2017;La et al, 2018). Such flexible fate changes of differentiationprimed cells were first discovered in Drosophila female and male germlines (Brawley & Matunis, 2004;Kai & Spradling, 2004).…”

“…However, in regenerative contexts (e.g., after tissue insult by a cytotoxic reagent, busulfan, or after transplantation into the seminiferous tubules of host mice), Ngn3 + cells convert reversely to the GFRα1 + state and contribute to the self‐renewing pool (Nakagawa et al., , ). Other differentiation‐primed subpopulations of undifferentiated spermatogonia (i.e., Miwi2 + , Oct4 + , and Pdx1 − ) have been shown, similarly, to contribute to the self‐renewing pool and support long‐term repopulation in such regenerative contexts (Carrieri et al., ; La et al., ). Such flexible fate changes of differentiation‐primed cells were first discovered in Drosophila female and male germlines (Brawley & Matunis, ; Kai & Spradling, ).…”

“…Although comprising a tiny portion of spermatogonia, GFRα1 + cells are still heterogeneous both in topology (including A s , A pr , and A al cells (Hofmann et al., ; Nakagawa et al., ; Grasso et al., )) and gene expression (including subpopulations expressing Erbb3 , Id4 , Shisa6 , T ( Brachyury ), Pdx1 , and so on (Abid et al., ; Chan et al., ; La et al., ; Oatley, Racicot, & Oatley, ; Tokue et al., ). Emerging single‐cell analysis has been enriching information regarding the heterogeneous nature of this and other spermatogonial populations (Chen et al., ; Green et al., ; Hammoud et al., ; Hermann et al., ; La et al., ). Single‐cell transcriptomics has also enabled substantial assessments for the composition of human spermatogonia (Guo et al., ; Wang et al., ).…”

“…In addition to Sertoli cells and myoid cells, macrophages that located in the peritubular and interstitial regions are also involved in the regulation of SSCs (Defalco et al, 2015) (Figure 2c). Finally, the roles of interstitial cells (other than macrophages) and arterioles/venules should be important for SSC regulation, too, given the spatial correlation between these vasculatures and SSCs La et al, 2018;Yoshida, Sukeno et al, 2007).…”