Endogenously produced FGF2 is essential for the survival and proliferation of cultured mouse spermatogonial stem cells

AIP1-mediated actin disassembly is required for postnatal germ cell migration and spermatogonial stem cell niche establishment

In mammals, spermatogonial stem cells (SSCs) arise from early germ cells called gonocytes, which are derived from primordial germ cells during embryogenesis and remain quiescent until birth. After birth, these germ cells migrate from the center of testicular cord, through Sertoli cells, and toward the basement membrane to form the SSC pool and establish the SSC niche architecture. However, molecular mechanisms underlying germ cell migration and niche establishment are largely unknown. Here, we show that the actin disassembly factor actin interacting protein 1 (AIP1) is required in both germ cells and Sertoli cells to regulate this process. Germ cell-specific or Sertoli cell-specific deletion of Aip1 gene each led to significant defects in germ cell migration after postnatal day 4 or 5, accompanied by elevated levels of actin filaments (F-actin) in the affected cells. Furthermore, our data demonstrated that interaction between germ cells and Sertoli cells, likely through E-cadherin-mediated cell adhesion, is critical for germ cells' migration toward the basement membrane. At last, Aip1 deletion in Sertoli cells decreased SSC self-renewal, increased spermatogonial differentiation, but did not affect the expression and secretion levels of growth factors, suggesting that the disruption of SSC function results from architectural changes in the postnatal niche.

Estrogen mediated epithelial proliferation in the uterus is directed by stromal Fgf10 and Bmp8a

To define endometrial stromal-derived paracrine mediators that participate in estradiol-17β (E2)-induced epithelial proliferation, microarray analysis of gene expression was carried out in mouse uterine epithelial-stromal co-culture systems under the condition of E2 or vehicle (control). Our results demonstrated gene alteration by E2: in epithelial cells, we found up-regulation of 119 genes and down-regulation of 28 genes, while in stroma cells we found up-regulation of 144 genes and down-regulation of 184 genes. A functional enrichment analysis of the upregulated epithelial genes implicated them for proliferation, while upregulated stromal genes were associated with extracellular functions. Quantitative RT-PCR and in situ hybridization results confirmed differential gene expression in both cell cultures and ovariectomized uteri after the above treatments. Based on our identification of stromal secretory factors, we found evidence that suppression by siRNA specifically for Bmp8a and/or Fgf10 in the stromal layer caused significant inhibition of proliferation by E2 in the co-culture system, suggesting Bmp8a and Fgf10 act as paracrine mediators during E2-dependent control of uterine proliferation. The localization of receptors and receptor activation signaling in epithelial cells in both the co-culture system and uteri was consistent with their involvement in ligand-receptor signaling. Interestingly, loss of Bmp8a or Fgf10 also caused abrogation of E2-regulated epithelial receptor signaling in co-culture systems, suggesting that stroma-derived Fgf10 and Bmp8a are responsible for epithelial communication. Overall, stromal Fgf10 and Bmp8a serve as potential paracrine factors for E2-dependent regulation of epithelial proliferation in the uterus.

IGF-1R signaling is essential for the proliferation of cultured mouse spermatogonial stem cells by promoting the G2/M progression of the cell cycle

Culture of mouse spermatogonial stem cells (mSSCs) contributes to understanding the mechanisms of mammalian spermatogenesis. Several key growth factors such as GDNF and FGF2 have been known to be essential for the proliferation of cultured mSSCs. However, additional factors regulating SSC proliferation remain to be identified. In this study, we report that IGF-1R signaling is required for the proliferation of cultured mSSCs by promoting the G2/M progression of the cell cycle. IGF-1 and its receptor IGF-1R are expressed in cultured mSSCs as well as in isolated Sertoli cells and interstitial cells. Blockage of IGF-1R signaling either by knockdown of IGF-1R or by the IGF-1R-specific inhibitor picropodophyllin (PPP) significantly reduced the proliferation of mSSCs, increased their apoptosis, and impaired their stem cell activity in an insulin-independent manner. PPP treatment of mSSCs blocked the G2/M progression. In contrast, both GDNF withdrawal and FGF2 signaling blockade decreased the entry of mSSCs into their S phases. Consistently, IGF-1 promoted the G2/M progression of thymidine-treated mSSCs, which were arrested at G1/S boundary synchronously; while GDNF and/or FGF2 stimulated their entry into the S phase. Moreover, IGF-1 activated the phosphorylation of AKT but not that of ERK1/2 in mSSCs. These results indicate that IGF-1R signaling stimulates the proliferation of mSSCs using a distinct mechanism from those by GDNF and FGF2, and will contribute to the establishment of a chemically defined culture system.

Regulation of spermatogonial stem cell self-renewal and spermatocyte meiosis by Sertoli cell signaling

Spermatogenesis is a continuous and productive process supported by the self-renewal and differentiation of spermatogonial stem cells (SSCs), which arise from undifferentiated precursors known as gonocytes and are strictly controlled in a special 'niche' microenvironment in the seminiferous tubules. Sertoli cells, the only somatic cell type in the tubules, directly interact with SSCs to control their proliferation and differentiation through the secretion of specific factors. Spermatocyte meiosis is another key step of spermatogenesis, which is regulated by Sertoli cells on the luminal side of the blood-testis barrier through paracrine signaling. In this review, we mainly focus on the role of Sertoli cells in the regulation of SSC self-renewal and spermatocyte meiosis, with particular emphasis on paracrine and endocrine-mediated signaling pathways. Sertoli cell growth factors, such as glial cell line-derived neurotrophic factor (GDNF) and fibroblast growth factor 2 (FGF2), as well as Sertoli cell transcription factors, such as ETS variant 5 (ERM; also known as ETV5), nociceptin, neuregulin 1 (NRG1), and androgen receptor (AR), have been identified as the most important upstream factors that regulate SSC self-renewal and spermatocyte meiosis. Other transcription factors and signaling pathways (GDNF-RET-GFRA1 signaling, FGF2-MAP2K1 signaling, CXCL12-CXCR4 signaling, CCL9-CCR1 signaling, FSH-nociceptin/OPRL1, retinoic acid/FSH-NRG/ERBB4, and AR/RB-ARID4A/ARID4B) are also addressed.

Generation of male germ cells from mouse induced pluripotent stem cells in vitro

Germ cells are the only cell type that passes genetic information to the next generation. In most metazoan species, primordial germ cells (PGCs) were induced from epiblasts by signals from the neighboring tissues. In vitro derivation of germ cells from the pluripotent stem cells (PSCs) such as embryonic stem cells (ESCs) and induced PSCs (iPSCs) are of great values for the treatment of infertility, for animal breeding, and for studying the mechanism of germ cell development. Although the derivations of male germ cells from PSCs have been previously reported, most of the studies failed to conduct the induction in a well-controlled and highly efficient manner. Here, we report the derivation of induced PGC-like cells (iPGCLCs) from mouse iPSCs via induced epiblast-like cells (iEpiLCs) as being monitored by the expression of enhanced green fluorescent protein gene under the control of the promoter of stimulated by retinoic acid 8 (Stra8-EGFP). The identity of iPGCLCs was characterized by examining the expression of multiple marker genes as well as by the recovery of spermatogenesis after they were transplanted to the testis of infertile W/W(v) mice. Furthermore, iPGCLCs were either induced to germline stem cell-like cells (iGSCLCs) or reverted back to embryonic germ cell-like cells (iEGCLCs). In conclusion, we have established an efficient procedure for inducing iPSCs into iPGCLCs that can be further expanded and induced to more developed germ cells. This work indicates that the technology of in vitro germ cell induction is becoming more sophisticated and can be further improved.