ID4 levels dictate the stem cell state in mouse spermatogonia [RESEARCH ARTICLE]

Aileen R. Helsel, Qi-En Yang, Melissa J. Oatley, Tessa Lord, Fred Sablitzky, and Jon M. Oatley

Spermatogenesis is a classic model of cycling cell lineages that depend on a balance between stem cell self-renewal for continuity and formation of progenitors as the initial step in production of differentiated cells. However, the mechanisms guiding the continuum of spermatogonial stem cell (SSC) to progenitor spermatogonial transition and precise identifiers of subtypes in the process are undefined. Here we used an Id4-eGfp reporter mouse to discover that EGFP intensity is predictive of the subsets with the ID4-EGFP^Bright population being mostly, if not purely, SSCs while the ID4-EGFP^Dim population is in transition to the progenitor state. These subsets are also distinguishable by transcriptome signatures. Moreover, using a conditional overexpression mouse model, we found that transition from the stem cell to immediate progenitor state requires down-regulation of Id4 coincident with a major change in the transcriptome. Collectively, our results demonstrate that the level of ID4 is predictive of stem cell or progenitor capacity in spermatogonia and dictates the interface of transition between the different functional states.

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