Strain specific analysis of CTSG mRNA expression in wild-type C57BL/6 mice and B-hCTSG mice by RT-PCR. BM RNA was isolated from wild-type C57BL/6 mice (+/+) and homozygous B-hCTSG mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human CTSG primers. Mouse CTSG mRNA was detectable only in wild-type C57BL/6 mice. Human CTSG mRNA was detectable only in homozygous B-hCTSG mice but not in wild-type mice.