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Letters to the Editor
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Figure 1. In vitro induction of MLL rearrangements in embryonic, neonatal and adult human CD34+ hematopoietic stem and progenitor cells following acute and chronic exposure to etoposide, permethrin and chlorpyrifos. (A) Experimental design to assess the induction of MLL breaks in human undifferentiated embryonic stem cells (hESC) and CD34+ hematopoietic stem and progenitor cells (HSPC) after 24 h single-pulse exposure to the indicated treatments (etoposide, ETO; permethrin, PER; and chlorpyrifos, CPF). (B) Representative interphase fluorescence in situ hybridization (iFISH) images showing MLL germline and rearranged (MLLr) human CD34+ cells. (C) Frequency of MLL breaks in undifferentiated hESC and embryonic, neonatal and adult CD34+ HSPC after 24 h sin- gle-pulse exposure to the indicated treatments (n=3 independent experiments for each cell type). Asterisks indicate statistically significant differences of a given treatment as compared with dimethylsulfoxide (DMSO, vehicle treatment) *P<0.05, **P<0.01. Dotted lines in the graphs show the percentage of MLL breaks in the DMSO-treated control groups. A minimum of 500 nuclei were analyzed except in some samples for which 80-400 nuclei were analyzed. (D) Experimental design to analyze the frequency of MLL breaks and gross chromosomal damage in hESC after continuous exposure to PER and CPF. (E) Frequency of MLL breaks detected by iFISH 45 days after chronic treatment with either PER or CPF (n=3 independent experiments). A minimum of 400 nuclei was analyzed per experi- ment. (F) Representative image of a G-banding karyotype 45 days after chronic treatment with either PER, CPF or DMSO (n=3). (G) Representative image of DNA copy number variation profiling by comparative genomic hybridization array analysis 45 days after chronic treatment with either PER or CPF. CGH: comparative genomic hybridization; AMP: amplification; DEL: deletion; LOH: loss of heterozygosity.
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