A review of early development of the nervous system in some arthropods: Comparison between insects, crustaceans and myriapods

The study of the early development of the central nervous system of differe nt arthropods reveals a remarkable conservation of structure. In several in sects and malacostracan crustaceans, development begins with the segregatio n of a similar stereotyped array of neuroblasts from each segment. These ar e stem cells that divide unequally to generate a specific number of neurons . The use of molecular markers has provided evidence for homology of specif ic neuroblasts in different species. In contrast, stem cells have not been seen in myriapods. In insects the axonal pathways of the central nervous sy stem are established by a set of central neurons that arises in a repeated pattern in each segment. A similar strategy is employed by crustaceans and some of the early forming neurons are conserved between insects and crustac eans. This suggests a common basis for early nervous system development in these arthropods. Myriapods are rather different; their pioneering neurons arise in the brain. Mechanisms for evolutionary changes in these early even ts are discussed, in the light of the genetic analyses carried out in an in sect, Drosophila melanogaster.