Figure 1. Phenotypic classification of a novel c-Myc-positive stage of large pre-B cells.

(A) Flow cytometry analysis of c-Myc, CD25 expression, and cell size in bone marrow cells from c-Myc^eGFP/eGFP and RAG mice gated as B220⁺/CD43⁺ cells of Fr. A (CD24⁻/BP.1⁻), B (CD24⁺/BP.1⁻), C (CD24^med/BP.1⁺/CD25⁻) and C’ (CD24⁺/BP.1⁺/CD25⁻); note the absence of C’-1 (c-Myc⁺/CD25⁻) and C’-2 (c-Myc⁻/CD25⁺) cells in RAG mice. Data is representative of over 20 independent experiments (n>30). (B) Intracellular µHC staining. Fr. C’-1, and C’-2 bone marrow cells were sorted by FACS from c-Myc^eGFP/eGFP mice, labeled with anti-µHC or isotype control, and analyzed by flow cytometry, as indicated. Sorted B220⁺/IgD⁻ immature B cells from spleen of WT mice and B220⁺/CD43⁺ cells from bone marrow of Rag-1-deficient mice were used as a positive and a negative control, respectively. Data shown is representative of two independent experiments (n=4).