The Journal of Neuroscience, February 1, 1998, 18(3):999-1008
Single Neuron Mosaics of the Drosophila gigas Mutant
Project beyond Normal Targets and Modify Behavior
Inmaculada
Canal2,
Angel
Acebes1, and
Alberto
Ferrús1
1 Instituto Cajal, Consejo Superior de Investigaciones
Científicas, Madrid 28002, Spain, and
2 Departamento de Biología, Universidad
Autónoma de Madrid, Madrid 28049, Spain
gigas is a lethal mutant that differentiates
enlarged cells, including the nucleus. This trait manifests only after
the completion of the mitotic program. We have taken advantage of this
phenotype to test in vivo the capacity of normal target
cells to arrest the growth of mutant sensory axons. Single neuron
connectivity changes have been analyzed in mosaics after horseradish
peroxidase retrograde tracings. A mutant mechanoreceptor neuron,
growing over a genetically normal substrate, contacts its normal
target, and in addition projects to novel areas of the CNS. The mutant axon does terminate its growth eventually, and the new additional targets that are reached correspond to mechanoreceptor domains in other
ganglia, indicating that this territorial constraint is operational in
the mutant. gigas neurons maintain their stereotyped profile and represent an expanded version of the normal branching pattern. The ultrastructure of the invading projections does not reveal
gliotic or necrotic reactions from the new cell contacts. The
functional consequences of the connectivity changes produced by the
mutant mechanoreceptors have been studied in grooming behavior. Mosaic
flies carrying a single gigas mechanoreceptor show
modified, albeit context-coherent, grooming responses after stimulation of the mutant bristle, whereas the response from neighboring normal sensory neurons remains unchanged. All of these experiments indicate that target recognition and growth arrest are two dissectible processes
of neural development, and they highlight the autonomous features of
the growth cone during pathfinding.
Key words:
mechanoreceptor; target recognition; growth cone; neural
branching; pathfinding; grooming reflex
Copyright © 1998 Society for Neuroscience 0270-6474/98/183999-10$05.00/0
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