Control of cell proliferation in the corpora allata during the reproductive cycle of the cockroach Diploptera punctata

Abstract

Unlike in Blettella germanica and Supella longipalpa, the corpora allata (CA) of Diploptera punctata exhibited cyclic changes in cell number during the reproductive cycle. In mated females, a wave of DNA synthesis followed by mitosis resulted in a significant increase in CA cell number from about 9,000 cells on day 0 to 12,000 cells at ovulation on day 8. Subsequently, the number of cells per CA underwent a gradual decline to about 10,000 cells by day 64. During this long period of gestation, mitotic activity was undetectable (by colchicine arrest) and pycnotic nuclei were frequently observed by transmission electron microscopy. Just before parturition on day 72 another mitotic wave was detected and CA cell number increased again. The early wave of CA cell proliferation could be postponed by delaying mating or abolished by maintaining females as virgins. Neural disconnection of the CA from the brain mimicked the effect of mating, suggesting that enhanced cell proliferation is permitted by the removal of inhibitory signals from cerebral neurosecretory cells. The proliferative activities after mating were neither abolished by ovariectomy, which suppressed the normal increase in JH synthesis, nor elevated by unilateral allalectomy, which doubled the rates of JH synthesis in the remaining CA. These data corroborate previous results (Szibbo and Tobe, 1981a; Tobe et al., 1984; Johnson et al., 1993) and suggest that waves of cell proliferation and JH synthesis, though simultaneous, are regulated independently by inhibitory signals from cerebral neurosecretory cells. © 1996 Wiley-Liss, Inc.