CYTO-DIFFERENTIATION OF THE NEUROBLASTS FROM THE NEURAL ECTODERMAL CELLS IN GRASSHOPPER, CHORTOPHAGA-VIRIDIFASCIATA (DE-GEER) (ORTHOPTERA, ACRIDIDAE) EMBRYOS

The first sign of neurogenesis in the embryo of grasshopper, Chortopha ga viridifasciata (Orthoptera: Acrididae), is signaled by a partition of the ectodermal cells into non-neural ectodermal cells and neural ec todermal cells. The neuroblasts are differentiated from neural ectoder mal cells. In the present study, we examined the pattern of mitotic ac tivity in the developing embryo by tracing the incorporation of BrdU i n S phase nuclei. The results indicate that the ectodermal cells in 6- day old embryos do not show any signs of differentiation. In 7-day old embryos, in which ectodermal cells become partitioned into 2 types, a lmost no neural ectodermal cells are incorporated with BrdU, whereas a constant incorporation is revealed in non-neural ectodermal cells. Am ong the mitotically quiescent neural ectodermal cells, which are arres ted at the G1 stage of the cell cycle, in 8-day old embryos, the neuro blasts are the first to resume their mitotic activity, while the other cells are then released from the mitotic quiescence. It seems that th e mitotic quiescence may be an essential process to acquire a neural f ate. Copyright (C) 1996 Elsevier Science Ltd.