Human centromeres have been extensively studied over the past two decades. Consequently, more is known of centromere structure and organization in humans than in any other higher eukaryote species. Recent advances in the construction of a human (or mammalian) artificial chromosome have fostered increased interest in determining the structure and function of fully functional human centromeres. Here, we present an overview of currently identified human centromeric repetitive DNA families: their discoveries, molecular characterization, and organization with respect to other centromeric repetitive DNA families. A brief examination of some functional based studies is also included.

Human centromeric DNAs

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A survey of the genomic distribution of alpha satellite dna on all the human chromosomes, and derivation of a new consensus sequence

Merkel cell carcinoma (MCC) is a rare aggressive neuroendocrine tumor of the skin. Cytogenetic studies have indicated that deletions and unbalanced translocations involving chromosome 1 short arm material occur in 40% of the investigated cases. Recurrent chromosomal imbalances detected by comparative genomic hybridization (CGH) analysis were loss of 3p, 10q, 13q and 17p and gains of 1q, 3q, 5p and 8q. In order to study genomic aberrations occurring in MCC in further detail, we combined karyotyping, CGH and multiplex-fluorescence in situ hybridization (M-FISH), a strategy that proved to be successful in the analysis of other malignancies. Analysis of 6 MCC cell lines and 1 MCC tumor revealed mostly near-diploid karyotypes with an average of 5 chromosomal rearrangements. The observed karyotypic changes were heterogeneous, with 3–27 breakpoints per case, leading to imbalance of the involved chromosomal regions that was confirmed by CGH. Chromosomal rearrangements involving the short arm of chromosome 1, the long arm of chromosome 3 and gain of 5p material were the most frequently observed abnormalities in our study. In keeping with previous observations, this series of MCCs showed no evidence for high-level amplification. We provid a detailed description of chromosomal translocations occurring in MCC that could be useful to direct future intensive investigation of these chromosomal regions. © 2002 Wiley-Liss, Inc.

Combined karyotyping, CGH and M-FISH analysis allows detailed characterization of unidentified chromosomal rearrangements in Merkel cell carcinoma.

The methylation profile of ten α-satellites was investigated in normal individuals and in ICF (Immunodeficiency, Centromeric instability, Facial abnormalities) patients. Two out of three ICF patients showed modified methylation of these sequences, reproducing a placental profile. CENP-B boxes, the binding sites of centromeric protein B, were always skewed toward nonmethylation. Unexpected results were observed in normal individuals: in somatic adult tissues the methylation pattern of α-satellite DNA varied between chromosomes, and in fetal tissues these satellites were homogeneously undermethylated. Detailed methylation analysis of CENP-B boxes revealed that unmethylated α-satellite units coexist with thoroughly methylated regions. These observations showed that the two major components of constitutive heterochromatin are differently methylated in normal somatic and fetal tissues, since classical satellites are consistently methylated. The definite changes in the methylation profile of heterochromatin in somatic chromosomes and the asynchronous timing of methylation of classical and α-satellites during development may reflect specific roles of highly repeated sequences in genomic organization.

α-Satellite DNA methylation in normal individuals and in ICF patients: heterogeneous methylation of constitutive heterochromatin in adult and fetal tissues

BACKGROUND AND PURPOSE: Extensive metabolic impairments have been reported in association with mesial temporal lobe epilepsy (mTLE). We investigated whether proton MR spectroscopy (1H-MRS) depicts metabolic changes beyond the hippocampus in cases of mTLE and whether these changes help lateralize the seizure focus. METHODS: MR imaging and 1H-MRS were performed in 15 patients with mTLE with a postoperative diagnosis of mesial temporal sclerosis and in 12 control volunteers. Point-resolved spectroscopy and multisection 1H-MRS measured N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) in the hippocampus, temporal opercular and lateral cortices, insula and cerebellum, and frontal, parietal, and occipital lobes. Metabolites were assessed as ratios to Cr and in absolute units. RESULTS: Twelve patients had ipsilateral hippocampal atrophy; three had negative imaging results. In the ipsilateral hippocampus, absolute NAA (|NAA|) was 27.3% lower in patients compared with that in control volunteers (P CONCLUSION: Multisection 1H-MRS depicts interictal reductions of NAA in the ipsilateral temporal lobe beyond the hippocampus and accurately lateralizes seizure foci.

http://www.ajnr.org/content/ajnr/23/8/1359.full.pdf

Multisection Proton MR Spectroscopy for Mesial Temporal Lobe Epilepsy

Starting from a chromosome-specific DNA library, we have isolated a human chromosome-specific satellite DNA sequence. This sequence of 635 base pairs (bp) consists of 3.7 alpha DNA monomers of 170-171 bp. Under high stringency it hybridizes to the centromere of chromosome 3 in a region composed of 2,750 bp tandem repeats characterized by the regular spacing of Hind III and TaqI restriction enzyme recognition sites. It has diverged and undergone amplification after the human speciation. The amplification allows an easy monitoring of the chromosome 3 centromere by in situ hybridization with a nonradioactive probe.

C. Brossard

Papers

Studies on the human chromosome 3 centromere with a newly cloned alphoid DNA probe.

Isolation and characterization of an alphoid DNA sequence recently amplified on human chromosome 3.