Low levels of TFAP4 endow interclonal competition of pretransformed B-cell precursors with aberrant c-MYC expression. (A) Expression of Tfap4 mRNA in pretransformed B220⁺IgM⁻ BM (Pre-tumor) or B220⁺ IgM⁻ tumor (Tumor) cells harvested from Eμ-Myc mice with the indicated Tfap4 genotypes. Tfap4 mRNA expression, measured by quantitative reverse transcription polymerase chain reaction (PCR), was normalized to Hprt1 expression. (B) Genomic PCR detecting the region of the Tfap4 allele encompassing exons 2-4 in tumor DNA (T) and tail DNA (GL, germline) of each corresponding mouse. A genomic region containing Runx1 located on the same chromosome was used as an internal control. Three of 5 lymphomas with low Tfap4 mRNA expression were analyzed by genomic PCR; the red dashed box indicates 2 representative samples with LOH of Tfap4 in tumors. (C) Diagram showing the detection of LOH using Tfap4-mC reporter knock-in mice. (D) Detection of TFAP4-mC fusion protein in peripheral blood B cells from healthy 4-week old Eμ-Myc Tfap4^mC/+ and Eμ-Myc Tfap4^mC/– mice (upper panel). Loss of TFAP4-mC expression in Eμ-Myc Tfap4^mC/– tumor B cells with LOH or CD11b⁺ cells as internal mC^– control (lower panel). The numbers to the right represent unique mouse IDs. chr16, chromosome 16; ex, exon; w/o, without.