Mouse round spermatids developed in vitro from preexisting spermatocytes can produce normal offspring by nuclear injection into in vivo-developed mature oocytes.
Marh J, Tres LL, Yamazaki Y, Yanagimachi R, Kierszenbaum AL. Mouse round spermatids developed in vitro from preexisting spermatocytes can produce normal offspring by nuclear injection into in vivo-developed mature oocytes. Biol Reprod. 2003 Jul; 69(1):169-76.