Tissue expression of human GPVI using RT-PCR or Northern blot analysis.

(A) Northern blot analysis of human tissues. A 2-kb transcript is observed only in bone marrow and fetal liver. A signal is also observed with peripheral blood leukocytes (PBLs). However, when the same blot was hybridized with a GPIIb probe, a platelet protein absent in PBLs, transcripts were also detected, which suggests that the signal was due to platelet RNA contamination. There was no signal observed in a different PBL sample or in samples of brain, heart, skeletal muscle, colon, thymus, spleen, kidney, liver, small intestine, placenta, lung, or lymph node (data not shown). Sp indicates spleen; LN, lymph node; Thy, thymus; PBL, peripheral blood leukocytes; BM, bone marrow; and FL, fetal liver. (B) RT-PCR analysis from human samples. We coamplified β₂ microglobulin (β₂) and GPVI transcripts. The high molecular weight fragment (830 base pair [bp]) was generated from the GPVI primers, and the low molecular weight fragment (603 bp) was generated from the β₂ microglobulin primers. The β₂ microglobulin PCR product, used as a loading control, is present in all the samples in similar quantity. In contrast, GPVI is amplified only in megakaryocyte-enriched samples (adult and newborn); in cell lines displaying strong MKC features (HEL, MEG01, DAMI, MO7E, and mpl-UT7); and to a lesser extent, in fetal liver cells. A very low signal was also detected in the K562 and KG1 cell lines, 2 cell lines that also express platelet GPIIb at low levels, but there was no expression detected in the other samples.