RNA synthesis in different stages of rat seminiferous epithelial cycle

In vitro RNA synthesis has been analyzed using autoradiographic and electrophoretic methods in isolated 1-2 mm segments of rat seminiferous tubules. The cellular composition of each segment was accurately identified using microscopic analysis of the transillumination pattern of the freshly isolated, unstained, seminiferous tubules combined with phase-contrast microscopy of the living spermatogenic cells. The RNA synthesized in the seminiferous tubules was found to be mostly heterogenous nuclear RNA (HnRNA), which appeared to have a long lifetime. It was most actively formed in the stages which contain mid-pachytene spermatocytes. Formation of rRNA was slow in all stages and it was first observed when a 2-h pulse with [3H]uridine was followed by a 6-h chase. A very low RNA synthetic rate was observed in the stage containing the meiotic reduction divisions. The function of the meiotic RNA in regulation of spermiogenesis is discussed.