In vivo fluorescent imaging technique is a strong tool to visualize the various cellularevents such as the proliferation, differentiation, migration, and a lineage tracing inliving cells requiring no further experimental procedure such as immunostaining. Someunique and dynamic histone exchanges occur. Since the timing and types of histoneexchanges defines the particular stages of spermatogenesis, visualizing certain types ofhistones in testes is useful not only for researching specific histone dynamics, but alsofor monitoring the stages of spermatogenesis in vivo. In this study, we report theestablishment of two transgenic (Tg) mouse lines expressing histone H4-Venus (H4V)and histone H3.3-mCherry (H33C) fusion proteins in testicular germ cells, anddemonstrated their utility for monitoring germ cell development in vivo. Because of thechoice of promoter as well as the nature of these histones, H4V and H33C wereexclusively expressed in the germ cells of the distinct stages, which allowed thedetermination of spermatogenic stages in real time. In addition, disappearance of H4Vand H33C at particular stages of differentiation/fertilization also represented dynamichistone removal. Collectively, these Tg mice are a valuable resource not only formonitoring differentiation stages, but also for studying the chromatin dynamics ofpost-natal testicular germ cell development in vivo.