The regulatory region of the murine thy1.2 gene from the promoter to the intron following exon 4, excluding exon 3 and its flanking introns drives an enhanced green fluorescent protein (EGFP) sequence. This transgene was injected into fertilized oocytes. Transgenic founders (line O) were bred with C57BL/6J to generate the Thy1-GFP line O colony.