Modeling mammalian spermatogonial differentiation and meiotic initiation in vitro

Retinoic acid is dispensable for meiotic initiation but required for spermiogenesis in the mammalian testis

Retinoic acid (RA) is the proposed mammalian 'meiosis inducing substance'. However, evidence for this role comes from studies in the fetal ovary, where germ cell differentiation and meiotic initiation are temporally inseparable. In the postnatal testis, these events are separated by more than 1 week. Exploiting this difference, we discovered that, although RA is required for spermatogonial differentiation, it is dispensable for the subsequent initiation, progression and completion of meiosis. Indeed, in the absence of RA, the meiotic transcriptome program in both differentiating spermatogonia and spermatocytes entering meiosis was largely unaffected. Instead, transcripts encoding factors required during spermiogenesis were aberrant during preleptonema, and the subsequent spermatid morphogenesis program was disrupted such that no sperm were produced. Taken together, these data reveal a RA-independent model for male meiotic initiation.

Differential responsiveness of spermatogonia to retinoic acid dictates precocious differentiation but not meiotic entry during steady-state spermatogenesis†

The foundation of mammalian spermatogenesis is provided by undifferentiated spermatogonia, which comprise of spermatogonial stem cells (SSCs) and transit-amplifying progenitors that differentiate in response to retinoic acid (RA) and are committed to enter meiosis. Our laboratory recently reported that the foundational populations of SSCs, undifferentiated progenitors, and differentiating spermatogonia are formed in the neonatal testis in part based on their differential responsiveness to RA. Here, we expand on those findings to define the extent to which RA responsiveness during steady-state spermatogenesis in the adult testis regulates the spermatogonial fate. Our results reveal that both progenitor and differentiating spermatogonia throughout the testis are capable of responding to exogenous RA, but their resulting fates were quite distinct-undifferentiated progenitors precociously differentiated and proceeded into meiosis on a normal timeline, while differentiating spermatogonia were unable to hasten their entry into meiosis. This reveals that the spermatogonia responding to RA must still complete the 8.6 day differentiation program prior to their entry into meiosis. Addition of exogenous RA enriched testes with preleptotene and pachytene spermatocytes one and two seminiferous cycles later, respectively, supporting recent clinical studies reporting increased sperm production and enhanced fertility in subfertile men on long-term RA analog treatment. Collectively, our results reveal that a well-buffered system exists within mammalian testes to regulate spermatogonial RA exposure, that exposed undifferentiated progenitors can precociously differentiate, but must complete a normal-length differentiation program prior to entering meiosis, and that daily RA treatments increased the numbers of advanced germ cells by directing undifferentiated progenitors to continuously differentiate.

OCT4 protein and gene expression analysis in the differentiation of spermatogonia stem cells into neurons by immunohistochemistry, immunocytochemistry, and bioinformatics analysis

BACKGROUND

Spermatogonia Stem Cells (SSCs) are potential candidates for reprogramming and regeneration. Recent studies have revealed that differentiated cells can be reverted to pluripotent by overexpressing a set of pluripotent transcription factors. OCT4 (encoded by pou5f1), a POU transcription factor family member, is essential to the potential that controls pluripotency, and it is widely expressed in pluripotent stem cells, although it decreased or suppressed after differentiation.

METHODS

In this investigated research, we examined the OCT4 expression during the differentiation of SSCs into neurons (involving four stages in the following order: SSCs in vivo and in-vitro, embryonic Stem Cell-like (ES-like), Embryonic Bodies (EBs), and finally Neurons) by Immunocytochemistry (ICC), Immunohistochemistry (IMH), and Fluidigm Real-Time polymerase chain reaction. In addition, we use some databases like STRING to predict protein-protein interaction and enrichment analysis.

RESULTS

We evaluated the expression of OCT4 in this process, and we observed that it is expressed in SSCs, ES-like, and EBs during the differentiation of spermatogonia stem cells into adult neurons. We show that by adding RA to EBs, the expression of OCT4 is reduced and is not expressed in the neuron cells. We observed that the expression of OCT4 is linked and interacts with the differentiation of spermatogonia stem cells into neuron cells, and it has been shown to be biologically functional, like stem cell maintenance and somatic cell reprogramming.

CONCLUSION

Our findings can help us better understand the process of differentiation of spermatogonia stem cells into neurons, and it can be effective in finding new and more efficient treatments for neurogenesis and repair of neurons. We examined the OCT4 expression during the differentiation of SSCs into neurons (involving four stages in the following order: SSCs in vivo and in-vitro, embryonic Stem Cell-like (ES-like), Embryonic Bodies (EBs), and finally Neurons) by Immunocytochemistry (ICC), Immunohistochemistry (IMH), and Fluidigm Real-Time polymerase chain reaction. In addition, we use some databases like STRING to predict protein-protein interaction and enrichment analysis. We evaluated the expression of OCT4 in this process, and we observed that it is expressed in SSCs, ES-like, and EBs during the differentiation of spermatogonia stem cells into adult neurons. We show that by adding RA to EBs, the expression of OCT4 is reduced and is not expressed in the neuron cells. We observed that the expression of OCT4 is linked and interacts with the differentiation of spermatogonia stem cells into neuron cells, and it has been shown to be biologically functional, like stem cell maintenance and somatic cell reprogramming.