In vitro differentiation of rat spermatogonia into round spermatids in tissue culture.

STUDY QUESTION: Do the organ culture conditions, previously defined for in vitro murine male germ cell differentiation, also result in differentiation of rat spermatogonia into post-meiotic germ cells exhibiting specific markers for haploid germ cells?

SUMMARY ANSWER: We demonstrated the differentiation of rat spermatogonia into post-meiotic cells in vitro, with emphasis on exhibiting, protein markers described for round spermatids.

WHAT IS KNOWN ALREADY: Full spermatogenesis in vitro from immature germ cells using an organ culture technique in mice was first reported 5 years ago. However, no studies reporting the differentiation of rat spermatogonia into post-meiotic germ cells exhibiting the characteristic protein expression profile or into functional sperm have been reported.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS: Organ culture of testicular fragments of 5 days postpartum (dpp) neonatal rats was performed for up to 52 days. Evaluation of microscopic morphology, testosterone levels, mRNA and protein expression as measured by RT-qPCR and immunostaining were conducted to monitor germ cell differentiation in vitro. Potential effects of melatonin, Glutamax® medium, retinoic acid and the presence of epidydimal fat tissue on the spermatogenic process were evaluated. A minimum of three biological replicates were performed for all experiments presented in this study. One-way ANOVA, ANOVA on ranks and student's t-test were applied to perform the statistical analysis.

MAIN RESULTS AND THE ROLE OF CHANCE: Male germ cells, present in testicular tissue pieces grown from 5 dpp rats, exhibited positive protein expression for Acrosin and Crem (cAMP (cyclic adenosine mono phosphate) response element modulator) after 52 days of culture in vitro. Intra-testicular testosterone production could be observed after 3 days of culture, while when epididymal fat tissue was added, spontaneous contractility of cultured seminiferous tubules could be observed after 21 days. However, no supportive effect of the supplementation with any factor or the co-culturing with epididymal fat tissue on germ cell differentiation in vitro or testosterone production was observed.

LIMITATIONS, REASONS FOR CAUTION: The human testis is very different in physiology from the rat testis, further investigations are still needed to optimize the organ culture system for future use in humans.

WIDER IMPLICATIONS OF THE FINDINGS: The successful differentiation of undifferentiated spermatogonia using the testis explant culture system might be employed in future to produce sperm from human spermatogonia as a clinical tool for fertility preservation in boys and men suffering infertility.

LARGE SCALE DATA: None.

STUDY FUNDING AND COMPETING INTERESTS: This work was supported financially by the Frimurare Barnhuset in Stockholm, the Paediatric Research Foundation, Jeanssons Foundation, Sällskåpet Barnåvard in Stockholm, Swedish Research Council/Academy of Finland, Emil and Wera Cornells Foundation, Samariten Foundation, the Swedish Childhood Cancer Foundation as well as through the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet. All authors declare no conflicts of interests.