Development of segment specificity in identified lineages of the grasshopper CNS

摘要: The purpose of this study was to determine the factors underlying differences in population size and composition between segmentally homologous neuronal lineages. segmental median neuroblasts (MNBs) grasshoppers are identified stem cells that each produce a midline group neurons. We traced embryonic development two disparate segments, counting MNB progeny profiles dying fixed stained preparations staged embryos. In metathoracic segment (T3), about 95 survive development, whereas next posterior segment, first abdominal (A1), only 60 survive. T3, arises at 29% embryogenesis dies 78%, A1 30% 73%. number initially increases steady rate, 10 being added per 5% embryogenesis. Between 70% 78% growth tapers off; although T3 continues divide, die same time, specifically removing last-born progeny. By contrast, increase phases, one from 45% other 60% 73%, again rate 5%. is stable. but earlier-born episodes cell death coincide with molts, thus may be hormonally triggered. Cell greater than accounting for most difference size. longevity makes lesser contribution. present data, together corollary anatomical data (Thompson Siegler, 1991), support hypothesis fated become certain types selectively removed lineages: intersegmental interneurons efferent neurons local A1.