Strain specific analysis of MC4R mRNA expression in wild-type C57BL/6N mice and B-hMC4R mice by RT-PCR. Brain RNA were isolated from wild-type C57BL/6N mice (+/+) and homozygous B-hMC4R mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human MC4R primers. Mouse Mc4r mRNA was detectable only in wild-type C57BL/6N mice. Human MC4R mRNA was detectable only in homozygous B-hMC4R mice but not in wild-type mice.