The Journal of Neuroscience, February 1, 2002, 22(3):832-841
Persistent engrailed Expression Is Required to
Determine Sensory Axon Trajectory, Branching, and Target Choice
Bruno
Marie1,
Lillian
Cruz-Orengo2, and
Jonathan M.
Blagburn1, 2
1 Institute of Neurobiology and
2 Department of Physiology, Medical Sciences Campus,
University of Puerto Rico, San Juan, Puerto Rico 00901
The transcription factor Engrailed (En) directs, in the cockroach
cercal system, the shape of the axonal arborization and the choice of
postsynaptic partners of an identified sensory neuron (6m). Knock-out
of En using double-stranded RNA interference transforms 6m so that it
resembles a neighboring neuron that normally does not express the
en gene, has a different arbor anatomy, and makes different connections. We characterized the development of 6m and
perturbed en expression at different stages. Our results
show that En is not required before birth for 6m to become a neuron, but that it is required in the postmitotic neuron to control axonal arborization and synaptic specificity. Knock-out of En after 6m has
entered the CNS does not change the axonal trajectory and has minor
effects on axonal branches but causes the formation of synaptic
connections typical of an En-negative cell. This suggests that En
controls target recognition molecules independently from those guiding
the axon. In contrast, double-stranded RNA injection 1 d later
does not have any effects on the phenotype of 6m, suggesting that the
period of synapse formation is over by the time En levels have fallen
or, if synapse turnover occurs, that En is not required to maintain the
specificity of synaptic connections. We conclude that persistent
en expression is required to determine successive stages
in the differentiation of the neuron, suggesting that it is not far
upstream from those genes encoding axon guidance and synaptic
recognition molecules.
Key words:
Engrailed; RNA interference; mechanosensory; homeodomain; synaptic specificity; axon guidance
Copyright © 2002 Society for Neuroscience 0270-6474/02/223832-10$05.00/0