Genome organization and the role of centromeres in evolution of the erythroleukaemia cell line HEL.

BACKGROUND AND OBJECTIVES: The human erythroleukaemia (HEL) cell line has a highly rearranged genome. We matched whole chromosome analysis with cytogenomic microarray data to build a detailed description of these rearrangements. METHODOLOGY: We used a combination of single nucleotide polymorphism array and multiple fluorescence in situ hybridization approaches, and compared our array data with publicly available data for different sublines of HEL. B allele frequencies revealed the fate of each homologue for most chromosomes. RESULTS: At least two instances of the breakage-fusion-bridge cycle appear to have facilitated amplification of oncogenes and deletion of tumour suppressor genes. Because our study included centromere identification, we found that some abnormal chromosomes had centromeres that did not match the identity of the rest of the chromosome. CONCLUSIONS AND IMPLICATIONS: This study highlights the variety of complementary methods required to understand remodelling of the genome in cancer and uncover some of the mechanisms involved. We present evidence of centromere capture as a means of preserving broken chromosome segments. Testing for another highly repetitive DNA region, the nucleolus organizer region, helped identify the steps involved in chromosome 9 copy number aberrations. Increased use of techniques for identifying centromeres and other repetitive DNA regions will add to our understanding of genome remodelling and evolution. The pattern of chromosome 20 aberration in HEL supports an association of 20q11.21 amplification with erythroleukaemia (acute myeloid leukaemia subtype M6) in the context of 20q12 deletion. The differences between the karyotypes in different HEL sublines highlight the constantly evolving genomes of cultured cell lines.

Detection of chromosome abnormalities using cytoplasmic immunoglobulin staining and FISH in myeloma.

The low proliferation rate of myeloma cells in vitro can result in a normal cytogenetic karyotype with the abnormal cell population not being detected. Because plasma cell myeloma is a patchy disease, conventional FISH is also hampered by normal cell contamination. Identification of plasma cells by cytoplasmic immunoglobulin staining in combination with FISH (cIg FISH) can ensure that only the cells of interest are analyzed, and thus the results obtained are a more accurate reflection of the plasma cell population karyotype. Current literature suggests that probes for t(4;14), t(14;16), and del(17)(p13) should be used in routine diagnostic testing; however, this technique can be used for any probes of interest. In this chapter, we present the techniques and methods used in our laboratory for the detection of abnormalities in plasma cells by cIg staining in conjunction with FISH.

Abnormal cytogenetics in orbital lipoma.

Orbital lipoma is a rare entity with only a small number of cases previously described. The authors describe a case of orbital lipoma in a 56-year-old man, which was treated with surgical excision. Cytogenetic analysis of the lesion demonstrated abnormalities of chromosome 12, consistent with chromosomal abnormalities in lipomas found elsewhere in the body. Therefore, cytogenetic analysis may be useful to differentiate lipomatous tumors from normal orbital fat.