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PubMed1987

Lipomas have characteristic structural chromosomal rearrangements of 12q13-q14.

Cytogenetic analysis was performed in 10 consecutive lipomas; 6 had typical benign histology whereas four had foci of atypia. Three tumors had supernumerary ring chromosomes, 6 had different balanced rearrangements, and one had a normal karyotype. Chromosome 12 was involved in 5 of the balanced rearrangements and, although less certainly, in all the ring chromosomes, with breakpoints localized to 12q13 or q14. The other rearranged chromosomes were numbers 2, 3, 7, 8, 11, 17 and 22. These results demonstrate the non-random involvement of chromosomal region 12q13-q14 in benign lipogenic tumors. The combined data from this and previous studies on benign and malignant lipogenic tumors indicate that different levels of cytogenetic specificity exist within this group of neoplasms. We suggest that myxoid liposarcoma development requires the recombination of 2 specific chromosomal bands (12q13 and 16pII), whereas for some types of benign lipogenic tumors structural changes in 12q13-q14 may be sufficient for neoplastic growth.

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PubMed1987

(dC-dA)n.(dG-dT)n sequences have evolutionarily conserved chromosomal locations in Drosophila with implications for roles in chromosome structure and function.

In situ hybridization of (dC-dA)n.(dG-dT)n to the polytene chromosomes of Drosophila melanogaster reveals a clearly non-random distribution of chromosomal sites for this sequence. Sites are distributed over most euchromatic regions but the density of sites along the X chromosome is significantly higher than the density over the autosomes. All autosomes show approximately equal levels of hybridization except chromosome 4 which has no detectable stretches of (dC-dA)n.(dG-dT)n. Another striking feature is the lack of hybridization of the beta-heterochromatin of the chromocenter. The specific sites are conserved between different strains of D. melanogaster. The same overall chromosomal pattern of hybridization is seen for the other Drosophila species studied, including D. simulans, a sibling species with a much lower content of middle repetitive DNA, and D. virilis, a distantly related species. The evolutionary conservation of the distribution of (dC-dA)n.(dG-dT)n suggests that these sequences are of functional importance. The distribution patterns seen for D. pseudoobscura and D. miranda raise interesting speculations about function. In these species a chromosome equivalent to an autosomal arm of D. melanogaster has been translocated onto the X chromosome and acquired dosage compensation. In each species the new arm of the X also has a higher density of (dC-dA)n.(dG-dT)n similar to that seen on other X chromosomes. In addition to correlations with dosage compensation, the depletion of (dC-dA)n.(dG-dT)n in beta-heterochromatin and chromosome 4 may also be related to the fact that these regions do not normally undergo meiotic recombination.

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