The epidermal cell cycle during the metamorphosis of Tenebrio molitor L. (Insecta Coleoptera)

Abstract

The main features of epidermal cell cycle during the metamorphosis of Tenebrio molitor have been investigated by cell density study, [ 3H]thymidine incorporation, and cytophotometry. G 1, S, and M phases are restricted to short periods during each larval stage. The pupal mitotic wave is relatively longer than the larval ones. Outside of each mitotic period, 95 to 100% of the epidermal cells are blocked in G 2 (4C DNA content). The cell density study shows that during the penultimate larval instar, numerous cells bypass the mitotic period without dividing while during the mitotic period of the last larval instar and of the pupal stage, each cell divides once and twice for some cells. After the pupal mitotic period, numerous adult cells are definitely blocked in G 2 but 20 to 30% of cells present in old adults are in G 1. Adult epidermal oenocytes differentiate during the last larval mitotic period, becoming 8 to 32C. From these results, it can be concluded that the G 2 block and the release of G 2-blocked cells into M are two critical events of each molting cycle. A possible hormonal control of these events is discussed.