Because the achaete-scute (ac/sc) genes seem to initiate nervous system development in all arthropods, knowing how their number and function varies between Arthropoda species should provide insights into the evolution of nervous system development in insects. On , Wheeler et al. describe the ac/sc genes of the red flour beetle (Tribolium castaneum), which diverged from Drosophila ∼300 million years ago. Both species encode a single neural precursor gene -asense - which is expressed in all neural precursors. However,whereas Drosophila encodes three proneural genes (achaete,scute and lethal of scute), which promote neural precursor formation, Tribolium encodes a single proneural gene -achaete-scute homologue (Tc-ASH). Tc-ASH alone can promote neural precursor formation from ectodermal cells, but unlike achaete and scute, it plays no apparent role in the fate specification of individual neural precursors, hinting at a recent evolutionary specialisation in the Drosophila lineage.
