Expression patterns of Trk receptors on human SMCs from patients with mastocytosis and healthy control participants. (A) FL TrkA and alternatively spliced trkA mRNA isoforms in human SMCs. (B) Expression of TrkB transcripts in human SMCs. Amplified exons of the TrkB receptor are depicted on the right side, and names of alternative TrkB isoforms are shown on the left. (C) Expression of tyrosine kinase domain (TK1: exons 13-14; TK2: exons 15-17) and truncated isoforms of TrkC in human SMCs. Representative PCR results of cDNAs from SMCs of patients with mastocytosis (MAST, n = 13: n = 5 for CM; n = 7 for ISM; and n = 1 for SM-AHNMD) and healthy individuals (CTR; n = 14) are shown. (D) Schematic drawing of TrkB-FL and TrkB-T1 mRNA and protein isoforms expressed on human SMCs. Exons are shown as boxes, and introns are shown as lines. C, cysteine-rich region; Leu rich, leucine-rich region; IG like, immunoglobulin-like domain; SHC, Shc-binding domain; and PLC-γ, PLC-γ–binding domain.