The present invention relates to methods and compositions for the diagnosis and treatment of hematological disorders, including, but not limited to, apalstic anemia, hemophilia, sickle cell anemia, thalassisemia, blood loss and other blood disorders, e.g., blood diorders related to bone marrow irradiation or chemotherapy treatment or renal failure. The invention further provides methods for identifying a compound capable of treating a hematological disorder. The invention also provides methods for identifying a compound capable of modulating a hematopoietic cell activity. Yet further, the invention provides a method for modulating a hematopoietic cell activity. In addition, the invention provides a method for treating a subject having a hematological disorder characterized by aberrant 2777 polypeptide activity or aberrant 2777 nucleic acid expression. In another aspect, the invention provides methods for increasing hematopoietic cell proliferation in a subject and methods for modulating hematopoietic cell apoptosis in a subject.