A haploid and a diploid cell coexist in an in vitro immortalized spermatogenic cell line

We have recently established a conditionally immortalized germ cell line [GC-2spd(ts)] that, at the permissive temperatures of 37 degrees C and 32 degrees C, is able to undergo meiosis in vitro and form round spermatids [Hofmann et al., (1994): Proc Natl Acad Sci USA 91:5533-5537]. In this report, we provide data that indicate that the GC-2spd(ts) cell line consists of two cell populations undergoing a haploid (n/2n) cell cycle and a diploid (2n/4n) cell cycle, respectively. The cells containing 2n DNA, when sorted by fluorescence-activated cell sorting, are able to reconstitute the full population of n/2n/4n DNA cells, indicating that they are able to commit to the reductive meiotic division and form haploid spermatids or to continue self-replication through a diploid cell cycle. This GC-2spd(ts) cell line provides a valuable tool to study the molecular mechanisms involved in the cellular decision between self-renewal by mitosis and commitment to meiosis.