In part, the present disclosure relates methods for treating, preventing, or reducing the severity of a myeloproliferative disorder (e.g., polycythemia vera, essential thrombocythemia, and myelofibrosis) or one or more complications of a myeloproliferative disorder. The present disclosure further relates methods for treating, preventing, or reducing the severity of a Janus kinase-associated disorder or one or more complications of a Janus kinase-associated disorder. In certain aspects the disclosure provides TβRII antagonists for treating, preventing, or reducing the severity of a myeloproliferative disorder (e.g., polycythemia vera, essential thrombocythemia, and myelofibrosis) or a Janus kinase-associated disorder or one or more complications of a myeloproliferative disorder or a Janus kinase-associated disorder.