FISH analyses of normal control and MM-derived cell lines carrying the t(4;14)(p16.3;q32) using the IGH costant regions (green) and the YAC 764-H1 (red) as probes. (A) and (B) Metaphase and interphase nuclei hybridization of normal lymphocytes; arrowheads indicate chromosome 14 and the X indicates chromosome 4. (C) and (D) Metaphase and interphase nuclei hybridization from the KMS-11 cell line. The arrow indicates the colocalized signals on der(14). As shown, the IGH probe recognizes an apparently normal chromosome 14 and an altered, unidentified chromosome; consistent with these findings, there is an additional green signal in the interphase nuclei (D). There are two chromosomes 4 (X) with different long arms; we have previously demonstrated that the longest is the der(4) on the basis of the absence of the FGFR3 locus.13 (E) and (F) Metaphase and interphase nuclei hybridization from the OPM2 cell line. There are two der(14) chromosomes with colocalized signals (arrows). The IGHprobe hybridized to a putative isochromosome and an unidentified, structurally altered chromosome. Three chromosomes 4 were detected (X). Consistent with this pattern, the OPM2 interphase nuclei show five green and five red spots, two of which are overlapping (yellow signal) and indicated by arrows. The FGFR3 locus was found to be localized on both der(14) (data not shown).