A 2160bp fragment of the hh promoter region (designated 'A', from position -2265 to -105bp) is cloned upstream of a 1051bp hh promoter fragment (designated 'C',from position -4265 to -3214bp upstream of the hh-RB transcript start site) fused with another fragment of 656bp (designated 'B', from position -2996 to -2340bp upstream of the hh-RB transcript start site). This promoter fusion drives the expression of lacZ under the additional control of a minimal hsp43 promoter.