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