Scientists at the MRC London Institute of Medical Sciences have identified a DNA element acting as a 'dimmer switch' that precisely controls the temporal expression of the critical developmental gene Cdx2 during early embryogenesis. Unlike traditional enhancers or silencers, this cis-regulatory element modulates gene activity in a cell type- and time-specific manner, influencing spinal cord progenitor formation. The discovery advances understanding of embryonic gene regulation with implications for therapeutic gene modulation.