THPO and Thrombocytosis: In contrast to restoration of one MPL allele in the JAK2V617F/MPLdel/+ mouse (Fig 1B), restoration of one THPO allele in the JAK2V617F mouse (JAK2V617F /THPOdel/+) delayed the erythrocytosis until 15 weeks, completely restored the neutrophil leukocytosis and thrombocytosis (Fig 1C), spleen weight (Fig 4) and marrow and spleen histology (Fig 5).