We used the bioinformatics method Digital Differential Display (NCBI, UniGene) to screen novel mouse genes expressed preferentially in the retina. Some of the clusters in the UniGene database were mainly from mouse retinal cDNAs. One clone in these clusters (#Mm. 246385) has a weak homology with the polyhomeotic family genes. A 735-bp cDNA fragment of this clone, encoding amino acids 140–384 was amplified by RT-PCR from mouse P0 retinal cDNA. This fragment was used as the probe for library screening, in situ hybridization and Northern hybridization. A mouse P0-P3 retinal cDNA library was screened using this mouse cDNA fragment. Positive bacteriophage clones were isolated and the full-length mr-s fragment was inserted into pBluescriptII (Stratagene). DNA sequencing was performed on both strands by the cycle sequencing method. The nucleotide sequence for mr-s gene has been deposited in the GenBank database under GenBank Accession Number #AY458844.