REGULATION AND KINETICS OF SPERMATOGONIAL PROLIFERATION IN ARENICOLA MARINA (ANNELIDA, POLYCHAETA) II. KINETICS

Abstract

The rate of accumulation of mitoses in the testis of Arenicola marina has been estimated by the colchicine method. The rate is low in February but increases during spring to a maximum in June. The rate remains high during July and August but decreases in September. A second temporary and minor rise was observed in October or November prior to spawning.The rate of accumulation of mitoses (with respect to the duration of metaphase arrest) is logarithmic from February to June, but is arithmetic during the latter part of the reproductive cycle (July‐October). The transition from one phase to the next coincides with the initiation of spermatocyte release from the testis into the coelom.The rate of accumulation of mitoses has also been recorded in testes cultured in vitro. The rate in vitro does not differ from that in vivo in May when the rate is high, but in September when the rate in vivo is depressed, culture in vitro significantly increases the mitotic rate.The cell cycle time of the proliferating spermatogonia has been estimated by a modified per cent labelled mitosis technique. The cell cycle time is unusually long (in excess of 20 days) and the G2 period is at least 5 days. It is suggested that the testis of A. marina is an exponentially growing cell population from February until early June when coelomic spermatocytes first appear. The rate of cell release then temporarily exceeds the rate of renewal: eventually they become equal and the testis remains in steady state until September when the mitotic rate is depressed due to the presence of maturing spermatocytes. The depression of the mitotic rate in September is achieved by the arrest of spermatogonia in G2. Explanting the gonads in organ culture removes the inhibition and causes an increased flow of cells from G2 into mitosis.