A targeting construct containing cre recombinase, an IRES, and cDNA encoding EGFP replaced the Syt10 exon 1 sequence following the initiating ATG codon in ES cells. An Frt-flanked neomycin selection cassette after the EGFP sequence was also included. This was subsequently deleted from F1 animals by crossing to Gt(ROSA)26Sortm1(FLP1)Dym mice on a C57BL/6 background. No transcripts of Syt10 are detected in the suprachiasmatic nuclei or other sites of endogenous expression in the brain. Breeding experiments show that cre is active in the male germline.