Analysis of segmentation gene function and expression during arthropod CNS development.

摘要

In addition to their role in the specification of the epidermal pattern in each segment, several segment polarity genes, including gooseberry (gsb), specify cell fate in the Drosophila CNS. In the first part of this investigation, the role of gsb in Drosophila CNS development was examined. In the past, analyses of the gsb mutant CNS phenotype were complicated by the fact that the previously available gsb mutants, large deficiencies, have severe segmentation defects and also lack a number of additional genes. In this study, two novel gsb alleles, which have CNS defects, but have weak or no epidermal defects, were characterized. Characterization of these mutants led to a more accurate description of the gsb neural phenotype. Two defects, duplication of the RP2 neurons, and loss of the posterior commissure, were analyzed in more detail. Both defects appear to result from the mis-patterning of neuroblasts (NBs).; In the second part of this investigation, knowledge of Drosophila development was extended in order to compare neural development among distantly related arthropods. Morphological studies suggest that insects and crustaceans of the Class Malacostraca share a set of homologous neurons. However, expression of molecular markers in these neurons has not been investigated, and the homology of insect and malacostracan NBs, the neural stem cells that produce these neurons, has been questioned. In an attempt to resolve these issues, expression of Even-skipped (Eve) and Engrailed (En), two insect embryonic CNS markers, was examined across a number of arthropod species. This molecular analysis allowed for verification of the homology of previously identified malacostracan neurons and identification of additional potentially homologous neurons. Engrailed NB expression was also found to be conserved, indicating that insect and crustacean NBs are homologous.; In an attempt to examine expression of a second insect NB marker in crustaceans, a wingless (wg) orthologue was cloned from the malacostracan crustacean Mysidium columbiae (mysid). Although analysis of the expression of this gene did not lead to a better understanding of mysid neurogenesis, it provides the first molecular evidence suggesting that the processes of mesodermal and retinal patterning are conserved among distantly related arthropods.