Mammalian spermatogenesis is a highly coordinated process in which spermatogonia differentiate and spermatocytes initiate meiosis concurrently and cyclically (every 8.6 days in mice), resulting in the spatiotemporal associations of germ cells in seminiferous epithelium known as “stages of the epithelial cycle”. More precisely, A-aligned spermatogonia differentiate to become A1 spermatogonia, and A1 spermatogonia then undergo six successive mitotic divisions to become preleptotene spermatocytes, which initiate meiosis. Both spermatogonial differentiation and meiotic initiation have been found to require retinoic acid. Our laboratory has found that Stra8, a retinoic acid-responsive gene expressed specifically in germ cells, is involved in spermatogonial differentiation and meiotic initiation. In the present study, we have asked whether the periodicity of the two developmental steps, spermatogonial differentiation and meiotic initiation, is intrinsically programmed in germ cells, or determined by extrinsic retinoic acid levels. We show that STRA8 is cyclically expressed in spermatogonia and spermatocytes of adult mouse testes. Injecting retinoic acid into adult mice induces STRA8 expression in A-aligned (undifferentiated) spermatogonia, in stages where they normally do not express STRA8 and are in a quiescent state. Interestingly, the A-aligned spermatogonia precociously expressing STRA8 after retinoic acid injection differentiate prematurely into A1 spermatogonia and develop into spermatocytes, independently of the stages of the epithelial cycle. Furthermore, we show that preleptotene spermatocytes enter meiotic prophase earlier than normal after injection of retinoic acid. We conclude that quiescent A-aligned spermatogonia are already competent to differentiate in response to retinoic acid. Likewise early preleptotene spermatocytes are competent to start meiotic prophase but wait for a retinoic acid signal to do so. This suggests that retinoic acid levels in the seminiferous epithelium determine the timing of the events, resulting in coordination of the “epithelial cycle”.