A novel culture system for mouse spermatid maturation which produces elongating spermatids capable of inducing calcium oscillation during fertilization and embryonic development

Purpose: To establish an in vitro culture system for mouse round spermatids that models spermiogenesis and enables the assessment of oocyte activation ability. Methods: Round spermatids and Sertoli cells were isolated from testicular tissues of B6D2F1 male mice and co-cultured in the presence of testosterone and recombinant FSH. Cultured spermatids were examined for morphology and condensation of nuclei, fertilization and development rate, and Ca²⁺ oscillation pattern after ICSI. Results: The cultured spermatids elongated and resembled normal elongating spermatids in terms of both morphology and nuclear condensation. No significant differences in fertilization and development rates were observed between fresh and cultured elongating spermatids. Moreover, cultured spermatids showed similar Ca²⁺ oscillation patterns to fresh elongating spermatids during an initial stage in oocyte activation. Conclusions: These data suggest that a co-culture system of spermatids and Sertoli cells, supplemented with testosterone and recombinant FSH, supports normal differentiation of round spermatids into elongating spermatids, as assessed by their morphology, nuclear condensation, and oocyte activation ability.