The transgenic construct contains a 637-bp Grm6 (mGluR6) promoter fragment upstream of a codon-improved cre (iCre) and a polyadenylation sequence. A 9.5 kb fragment of the Grm6 5' upstream region was inserted to reconstitute the full-length Grm6 promoter. The construct was injected into fertilized oocytes and two founder lines were obtained. Only one line was found to express cre in the retina.