Primary culture of medaka (<Emphasis Type="Italic">Oryzias latipes</Emphasis>) testis: a test system for the analysis of cell proliferation and differentiation

An in vitro test system using primary testis cells of the medaka (Oryzias latipes) was established that provides quantitative data on cell proliferation and spermatocyte differentiation. The primary cultures were characterised over a period of 2 days with respect to cell viability and the distribution of adherent and suspended cells. These two cell populations were maintained at a dynamic equilibrium in vitro for several days. The proliferating cells were predominantly present amongst the clusters of suspended cells as determined by BrdU labelling (cytological identification and quantification by ELISA). Based on cytological criteria the proliferating cells were mostly spermatogonia and preleptotene spermatocytes. Differentiation of spermatocytes to spermatids or spermatozoa was also observed mainly amongst suspended cells. Quantification of cell proliferation and cell differentiation by flow cytometry was achieved by labelling the primary cells with carboxyfluorescein diacetate N-succinimidyl ester, which allowed the identification and quantification of meiotically or mitotically dividing primary cells. Addition of the flavonoid genistein (10 µg/ml) to the primary cultures inhibited both cell proliferation and cell differentiation significantly. The test system is suitable for the study of the effect of substances which interfere with spermatogenesis in the vertebrate medaka model.