In vitro spermatogenesis: A century‐long research journey, still half way around

Abstract

BackgroundSpermatogenesis is one of the most complicated cellular differentiation processes in a body. Researchers struggled to find and develop a micro‐environmental condition that can support the process in vitro. Such endeavors can be traced back to a century ago and are yet continuing.MethodsReports on in vitro spermatogenesis and related works were selected and classified into four categories based on the method used; organ culture, tubule culture, cell culture, and 3‐dimensional cell culture methods. Each report was critically reviewed from the present point of view by authors who have been working on in vitro spermatogenesis with organ culture method over a decade.ResultsThe organ culture method has the longest history and is the most successful method, which produced fertile mouse sperm from spermatogonial stem cells. Formulation of the medium was a key factor, most importantly serum‐derived substances. However, factors in the serum that induce and support spermatogenesis in the cultured tissue remain to be identified. In addition, the success of mouse spermatogenesis is yet to be applied to other animals. On looking into the history of cell culture method, it became clear that Sertoli cells as feeder cells play an important role. Even with Sertoli cells, however, spermatogenic development has been limited to small parts of spermatogenesis, a segmented period of meiotic prophase for instance. Recent developments of organoid or 3‐dimensional culture techniques are promising but they still need further refinements.ConclusionThe study of in vitro spermatogenesis progressed significantly over the last century. We need more work, however, to establish a culture system that can induce and maintain complete spermatogenesis of many if not all mammalian species.

In vitro spermatogenesis in two‐dimensionally spread mouse testis tissues

“…Using a classical organ culture method, according to gas‐liquid interphase principle, we succeeded in reproduce mouse spermatogenesis in vitro in 2011 . The method is quite simple in that immature testis tissue pieces were placed on the agarose gel block which was half‐soaked in the culture media.…”

Approaches and Technologies in Male Fertility Preservation

“…The cryopreserved testicular cells or tissue could be used for prepubertal human male fertility preservation with different approaches that are already used in rodents [27][28][29][30]. The main limitation of using autologous testicular tissue or cells in human therapy from cancer patients is the possibility of the presence of residual cancer cells, which may restore and evoke the disease.…”

“…The main limitation of this technology in humans is the possible contamination of testicular cells with cancer cells that may reintroduce malignancy to the patient after recovery. Today, there is no accurate and safe method that isolates pure SSCs from the testis of patients [50,62,63], in addition to the very small amount of testicular biopsy that could be used, it also contains very small numbers of these cells [4,14,24,27,29,58,64,65].…”

“…This microenvironment that provides optimal cell-cell interactions and the spatial environment for complete spermatogenesis is produced by the seminiferous tubules and interstitial compartment. This technology was proven successful in both autografting/xenografting and in vitro as organ culture [27][28][29][30]. Testicular tissue xenograft was successfully performed in immunodeficient mice while using testicular tissue from different species, which was grafted under the skin, producing complete spermatogenesis.…”

“…As mentioned above, the main benefit of using testicular fragments to develop spermatogenesis in vitro is the presence of testicular somatic cells and the three-dimension (3D) microenvironment that is suitable for the optimal development of SSCs to complete spermatogenesis [25][26][27][28][29]77]. Spermatogenesis development using organ culture to proceed to the meiotic stages was performed in the past without success [77][78][79][80].…”