A study of clonal migration in the developing central nervous system

This study addressed several questions relating to the ontogeny of the central nervous system. By using a cell lineage marker, surgical and histochemical techniques coupled with three-dimensional reconstruction, the phenotype and spatial distribution of individual clones of cells in the rat somatosensory cortex were examined. This area contains a unique arrangement of cells, termed barrel/columns, which are thought to be morphological examples of the modular processing units in the neocortex. A retroviral vector was used as the lineage marker and was introduced into the lateral ventricle of embryos In utero. After birth the cerebral cortices of infected animals were processed histochemically in order to visualize barrel/columns and retrovirally labelled cells. Using computer aided three-dimensional reconstruction, clonal relationships were inferred by propinquity. The criteria used to define clones were probably correct as clones were found to be oriented non-randomly. Furthermore both the proportion of clonal types and their size were similar to those reported in previous experiments. A total of 112 clones of neurones were found in the reconstructions although only 28 of them were within barrel/columns. Twelve of these 28 clones were multicellular, yet in only one of these 12 cases were all the cells of a clone in the same barrel/column. The remaining clones spread across barrel/column boundaries. Although my findings were unexpected they were accounted for by several known features of cortical development. In addition an attempt was made to produce an amphotropic retroviral vector capable of infecting cells in the early avain neural tube. Unfortunately all attempts at infection in ovo, with this or other retroviral vectors, were unsuccessful