Constitutive expression of RET transcripts (semiquantitative RT-PCR) and GDNFR-α (RT-PCR) in human leukemia/lymphoma cell lines. One microgram of total RNA was reverse-transcribed in a 20-μL reaction mix containing hexadeoxyribonucleotides random primers. Conditions for RT-PCR, blotting, hybridization, semiquantitative analysis, and controls were as described in Fig 2.