Scl mRNA domains of expression mark distinct branches of the hematopoietic tree. Schematic representation of the successive stages leading to hematopoietic differentiation from LT-HSCs to mature blood lineages.⁵⁴  The branches exhibiting expression of Scl mRNA are shaded in gray, with darker gray representing higher expression levels. During T-cell differentiation, SCL is downregulated at the DN3 stage. The stage of T-cell development first sensitive to SCL:LMO1/2 ectopic expression (red zigzag) and the subsequent block in differentiation (red bar) in T-ALL mouse models are shown. In human patients, maturation arrest occurs at the late cortical DP CD3^high stage (not shown).⁵⁵  CLP, common lymphoid progenitor; CMP, common myeloid progenitor; DN1-4, CD4⁻CD8⁻ double-negative populations, stages 1 to 4; DP, CD4⁺CD8⁺ double-positive population; ETP, early thymic progenitor; GMP, granulocyte/macrophage progenitor; LMPP, lymphoid/myeloid-primed progenitor; LT-HSC, long-term HSC; MEP, megakaryocytic/erythroid progenitor; MPP, multipotent progenitor; ST-HSC, short-term HSC.