Circadian activator proteins appear days before starting the body clock in fruit fly timing neurons

CLK-GFP is expressed in four of five clusters of late pacemaker neurons during the third instar larval stage.

• Circadian pacemaker neurons in Drosophila are categorized into early or late groups based on when they start expressing certain genes.
• Late pacemaker neurons begin to develop before the third instar larval stage, as indicated by the early expression of CLK-GFP.
• CLK-GFP is found only in postmitotic neurons during the third instar larval stage.
• CYC is also expressed exclusively in pacemaker neurons from third instar larval brains, similar to CLK.
• CLK-CYC expression does not trigger the activation of circadian genes in late pacemaker neurons at the third instar stage.

Simplified