Shaking hands is a putative terminal selector and controls axon outgrowth of central complex neurons in the insect modelTribolium

Abstract

Individual cell types are specified by transcriptional programs which act during development. Gene regulatory mechanisms which specify subtype identity of central complex (CX) neurons are the subject of intense investigation. The CX is a compartment within the brain common to all insect species. The CX functions as a “command center” by initiating motor actions in response to incoming information. The CX is made up of several thousand neurons with more than 60 morphologically distinct identities. Accordingly, transcriptional programs must effect the specification of at least as many neuronal subtypes. Here we demonstrate a role for the transcription factor Shaking hands (Skh) in the specification of embryonic CX neurons in Tribolium. The developmental dynamics of Tc-skh expression are characteristic for terminal selectors of neuronal subtype identity. In the embryonic brain Tc-skh expression is restricted to a subset of neurons, many of which survive to adulthood and contribute to the mature CX. Tc-skh expression is maintained throughout the lifetime of the respective CX neurons. Tc-skh knock-down results in severe axon outgrowth defects thus preventing the formation of an embryonic CX primordium. The as yet unstudied Drosophila skh shows a similar embryonic expression pattern suggesting that subtype specification of CX neurons may be conserved.