Clonal analysis of Drosophila embryonic neuroblasts: neural cell types, axon projections and muscle targets

Abstract

An experimental analysis of neurogenesis requires a detailed understanding of wild-type neural development. Recent DiI cell lineage studies have begun to elucidate the family of neurons and glia produced by each Drosophila embryonic neural precursor (neuroblast). Here we use DiI labeling to extend and clarify previous studies, but our analysis differs from previous studies in four major features: we analyze and compare lineages of every known embryonic neuroblast; we use an in vivo landmark (engrailed-GFP) to increase the accuracy of neuroblast identification; we use confocal fluorescence and Nomarski microscopy to collect three-dimensional data in living embryos simultaneously for each DiI-labeled clone, the engrailed-GFP landmark, and the entire CNS and muscle target field (Nomarski images); and finally, we analyze clones very late in embryonic development, which reveals novel cell types and axon/dendrite complexity. We identify the parental neuroblasts for all the cell types of the embryonic CNS: motoneurons, intersegmental interneurons, local interneurons, glia and neurosecretory cells (whose origins had never been determined). We identify muscle contacts for every thoracic and abdominal motoneuron at stage 17. We define the parental neuroblasts for neurons or glia expressing well-known molecular markers or neurotransmitters. We correlate Drosophila cell lineage data with information derived from other insects. In addition, we make the following novel conclusions: (1) neuroblasts at similar dorsoventral positions, but not anteroposterior positions, often generate similar cell lineages, and (2) neuroblasts at similar dorsoventral positions often produce the same motoneuron subtype: ventral neuroblasts typically generate motoneurons with dorsal muscle targets, while dorsal neuroblasts produce motoneurons with ventral muscle targets. Lineage data and movies can be found at http://www.biologists. com/Development/movies/dev8623.html http://www.neuro.uoregon. edu/doelab/lineages/