Structural heterogeneity of hsr(11) in the MDA-MB-134 mammary carcinoma cell line

The MDA-MB-134 cell line was characterized by the presence of two homogeneously staining region (hsr) carrier chromosomes containing sequences from 8p11-p12, 11q13, and 8q24. Using fluorescence in situ hybridization, a detailed study of the organization of this chromosome has been performed. The hsr carrier chromosomes are shown to be identical and to derive from a chromosome 11, on which large segments of the long arm of chromosome 8 are translocated, forming its short arm. The hsr segment is inserted in the long arm, distally to C1NH gene. It is formed by sequences from both chromosomes 8 and 11. For the genes investigated by both methods the number of copies detected by in situ hybridization is compatible with that expected by quantification of Southern blots. In spite of its complexity, a possible mechanism of formation is proposed.