High Resolution Transcriptome Analysis of the Primate Testis

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ABSTRACT Infertility is a prevalent condition that affects 15% of couples globally, with male factor infertility contributing to 50% of cases. Assisted reproductive technologies (ARTs), fertility treatments and changes in lifestyle are helping infertile men achieve their reproductive goals. However, these therapies are dependent on the infertile male producing at least a few mature sperm which is impossible in many cases such as infertility secondary to cancer treatment or genetic abnormalities. Testicular biopsies containing spermatogonial stem cells (SSCs), can be obtained from these men and cryopreserved for experimental stem cell-based therapies for infertility. SSCs balance self-renewal and differentiation to ensure continuous sperm production throughout an adult males reproductive life. But the molecular mechanisms governing this balance are still not well defined particularly, in higher primates. Identifying the protein markers of human and monkey SSCs as well as the signaling pathways regulating their self-renewal and proliferation, will facilitate the development of efficient, effective and safe SSC-based therapies for the treatment of male infertility. We performed high throughput, unbiased, single-cell RNA-sequencing of healthy adult primate (human and rhesus macaque) testicular tissue, generating ~33,800 single cell transcriptomes. Clustering coupled with the analysis of the expression patterns of validated marker genes, have identified most of the known cell types of the primate testis. Based on preliminary data, I hypothesize that primate single cell transcriptomic data will reveal spermatogonial markers/niche signaling pathways that can be exploited to isolate and enrich primate SSCs (pSSCs) and expand them in culture. We have identified novel genes CDK17, GPX1, MORC1, GPC4 and GPC3, DNAJB6, MAGEB2, FMR1, TCF3 as potential markers stem/progenitor spermatogonia that are conserved in human and monkey. These genes are implicated in signaling pathways (i.e. WNT, BMP, FGF) that have been associated with regulating rodent SSC self-renewal and proliferation. I will validate the expression of our candidate markers by immunohistochemistry and colorimetric staining, to correlate the expression of these genes with classic descriptions of nuclear staining intensity of Adark and Apale spermatogonia. Cell surface markers like GPC4, GPC3 and TSPAN33 may be used to enrich SSCs. We will investigate this possibility through immunohistochemistry, flow cytometry analysis and SSC transplantation to quantify transplantable stem cell activity in marker positive cell populations. I will also use the primate scRNAseq data to determine niche growth factor signals influencing pSSC self-renewal and proliferation. This will provide candidate growth factors to test in primate SSC culture to establish conditions that promote their long-term propagation in vitro. Our single cell data may contribute an improved understanding of primate SSCs biology and may enable stem cell applications in the male infertility clinic. Completion of this project will greatly expand my scientific and technical knowledge, giving me the strong foundation I need to have a successful research career.