JAK2V617 mutation in FACS-sorted splenic ECs from patient number 6. Splenic ECs show only mutated alleles, confirming the homozygosity found in the circulating polymorphonuclear cells of this patient. The HEL cell line was used as a positive control for the JAK2V617F mutation; the K562 cell line was used as a positive control for the wild-type JAK2 gene. Amplified fragments, obtained as described in “Methods” and in Baxter et al²⁵  are shown before (−) and after (+) digestion with BsaXI. The expected sizes for amplified fragments after digestion with BsaIX are 241, 189, and 30 bp for the wild-type allele; the V617F allele remained undigested (460 bp). The 30-bp fragment derived from the digestion of the wild-type alleles ran outside the gel.