A-Single Spermatogonia Heterogeneity and Cell Cycles Synchronize with Rat Seminiferous Epithelium Stages VIII–IX1

Abstract

In mammalian testes, "A-single" spermatogonia function as stem cells that sustain sperm production for fertilizing eggs. Yet, it is not understood how cellular niches regulate the developmental fate of A-single spermatogonia. Here, immunolabeling studies in rat testes define a novel population of ERBB3(+) germ cells as approximately 5% of total SNAP91(+) A-single spermatogonia along a spermatogenic wave. As a function of time, ERBB3(+) A-single spermatogonia are detected during a 1- to 2-day period each 12.9-day sperm cycle, representing 35%-40% of SNAP91(+) A-single spermatogonia in stages VIII-IX of the seminiferous epithelium. Local concentrations of ERBB3(+) A-single spermatogonia are maintained under the mean density measured for neighboring SNAP91(+) A-single spermatogonia, potentially indicative of niche saturation. ERBB3(+) spermatogonia also synchronize their cell cycles with epithelium stages VIII-IX, where they form physical associations with preleptotene spermatocytes transiting the blood-testis barrier and Sertoli cells undergoing sperm release. Thus, A-single spermatogonia heterogeneity within this short-lived and reoccurring microenvironment invokes novel theories on how cellular niches integrate with testicular physiology to orchestrate sperm development in mammals.

Single-cell RNA-Seq Resolves Cellular Heterogeneity and Transcriptional Dynamics in Spermatogonial Stem Cells Establishment

“…In contrast, Cluster III cells, which display higher expression of differentiation regulator Sohlh1, are the immediate progenitors ( Figure 2C). The expression level of bona fide adult stem cell markers in Cluster II and III also reflected their cellular identities (Abid et al, 2014;Aloisio et al, 2014;Oatley et al, 2011). The majority of cells with high Id4 expression fell into Cluster II (15 out of 23 cells, log2(TPM)>10)), consistent with the recent observation that cells with high level of Id4 represent true SSCs ( (Helsel et al, 2017)).…”

PAX7 expression defines germline stem cells in the adult testis

“…This finding also suggests the existence of further A single subtypes, which may be characterized by the expression of other distinct markers, such as ID4 or ERBB3 (9,49,50). PAX7 defined an unexpectedly small subset of A single spermatogonia.…”

“…The number of such transit-amplifying steps between PAX7 + A single and A pair spermatogonia is unknown. It will be interesting to determine whether ID4 and ERBB3, expressed in A single spermatogonia, are expressed in overlapping or nonoverlapping subsets of spermatogonia relative to PAX7 (9,49,50). Other models are possible, such as ones combining different aspects of these models (i.e., fragmentation with the presence of PAX7 + spermatogonia, if fragmentation is confirmed as a functionally significant biological process).…”

Open niche regulation of mouse spermatogenic stem cells

“…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., ).…”