Construct: A dicistronic transgene consisting of the first cistron: hb promoter sequence, cad 5' UTR and ftz coding sequence. A 250 nucleotide fragment derived from exon 4 of the Antp leader sequence which contains the internal ribosome entry site (IRES) inserted between the coding regions. The second cistron is the cad coding region fused to Ecol\lacZ with the cad 3' UTR.