Even-skipped (Eve) is a transcriptional repressor found within the nuclei of a subset of neurons in the embryonic central nervous system of insects. It is necessary for neuronal pathfinding and promotes adhesion of developing motor axons to the intersegmental nerve. Here we show by immunohistochemical staining that Eve is also expressed in the nuclei of a small set of neurons in the thoracic nervous system of larval and adult locusts, suggesting a postembryonic role in transcriptional control. Thirty-two to 39 Eve-positive neurons in four distinct subsets were found in the mesothoracic ganglion of fourth instar larvae and in adults: an anterior, bilaterally paired group of 2-4 neurons; a posterior, bilaterally paired group of 12-15 neurons; 1-2 neurons in a midline position, at the centre of the ganglion; and 1-2 neurons near the midline in a posterior position. These subsets did not change in position or number of neurons within them from fourth instars through to adults, 2 and 35 days post-final moult. The metathoracic ganglion had approximately 48 Eve-positive neurons in four subsets: an anterior, bilaterally paired group of 3-4 neurons; a posterior, bilaterally paired group of 8-10 neurons; a diffuse group of 19 neurons at the midline and a group of 4 neurons in a midline, posterior position. These results suggest that Eve demonstrates both phasic and persistent expression throughout the insect's lifetime and that changes in expression are segment-specific. We suggest Eve helps maintain neural phenotype in the adult CNS, possibly by regulating the expression of cell adhesion molecules.
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