A Novel Organoid Model of In Vitro Spermatogenesis Using Human Induced Pluripotent Stem Cells

Infertility is thought to be caused by genetic mutations and dysfunction in the cellular niche where spermatogenesis takes place. An understanding of the specialized cellular processes which drive spermatogenesis is needed to develop treatments; however, the development of in vitro systems to study these cells has been hindered by our reliance on rarely available human testicular tissues for research. Human induced pluripotent stem cells (hiPSCs) can be used to derive human testicular-like cells, and thus provide an avenue for the development of in vitro testicular model systems. Therefore, this study set out to engineer a human testicular tissue model using hiPSCs for the first time. We demonstrate the ability of hiPSC-derived testicular cells to self-organize and mature into testicular-like tissues using organoid culture. Moreover, we show that hiPSC-derived testicular organoids promote testicular somatic cell maturation and spermatogenesis up to the post-meiotic spermatid stage. These hiPSC-derived testicular organoids have the potential to replace rarely available primary testicular tissues to further infertility research in an in vitro setting. ### Competing Interest Statement The authors have declared no competing interest. * Differentiating : A term for the process of stem cell development into specialized cell types. endothelial cells : Endothelial cells form the barrier between vessels and tissue and control the flow of substances and fluid into and out of a tissue. Gonadotoxic : Gonadotoxicity is the temporary or permanent damage to ovaries or testes after exposure to certain substances or drugs haploid : Haploid is the quality of a cell having a single set of chromosomes. human induced pluripotent stem cells : iPSC are derived from skin or blood cells that have been reprogrammed back into an embryonic-like pluripotent state that enables the development of an unlimited source of any type of human cell needed for therapeutic purposes. in vitro : Outside of the body, typically referring to a laboratory setting in vitro fertilization (IVF) : In vitro fertilization (IVF) is a method of assisted reproduction that involves the removal of eggs from the body, and the combining of eggs and sperm in the embryology laboratory to form embryos. The resulting embryos can then be placed into the uterus in the hopes of achieving a pregnancy. in vivo : Within the body Leydig cells : Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH) Matrigel : Matrigel is the trade name for a gelatinous protein mixture secreted by Engelbreth-Holm-Swarm (EHS) mouse sarcoma cells produced by Corning Life Sciences. meiosis : Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. organoid : An organoid is a miniaturized and simplified version of an organ produced in vitro in three dimensions that shows realistic micro-anatomy. They are derived from one or a few cells from a tissue, embryonic stem cells or induced pluripotent stem cells, which can self-organize in three-dimensional culture owing to their self-renewal and differentiation capacities. paracrine signaling : Paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. peritubular myoid cells : A peritubular myoid cell is one of the smooth muscle cells which surround the seminiferous tubules in the testis. personalized medicine : Personalized medicine, also referred to as precision medicine, is a medical model that separates people into different groups— with medical decisions, practices, interventions and/or products being tailored to the individual patient based on their predicted response or risk of disease quiescent : A term for “reserve” pools of stem cells that in a state of inactivity or dormancy. Sertoli cells : A Sertoli cell (a kind of sustentacular cell) is a “nurse” cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis, the production of sperm. It is activated by follicle-stimulating hormone (FSH) secreted by the adenohypophysis, and has FSH receptor on its membranes spermatid : The spermatid is the haploid male gametid that results from division of secondary spermatocytes. spermatogenesis : Spermatogenesis is the process by which haploid spermatozoa develop from spermatogonial stem cells in the seminiferous tubules of the testis spermatogonial stem cells : A spermatogonial stem cell, also known as a type A spermatogonium, is a spermatogonium that does not differentiate into a sperm cell. Instead, they continue dividing into other spermatogonia or remain dormant to maintain a reserve of spermatogonia. tissue banking : The process of cryopreserving tissues for long-term storage and viability.