MPL and myeloproliferative neoplasm: We acknowledge that our studies have focussed on murine Mpl, and that differences with human Mpl may exist in the context of MPN, for example species differences in the degree of Mpl activation by mutant CALR [50] and that distinct conformations of human Mpl, but not the murine receptor, have been shown to mediate activation of wild-type JAK2 and JAK2-V617F [51].