Chromosomal mapping of repetitive DNAs in the beetle Dichotomius geminatus provides the first evidence for an association of 5S rRNA and histone H3 genes in insects, and repetitive DNA similarity between the B chromosome and A complement.

Chromosomal banding techniques and repetitive DNA mapping are useful tools in comparative analysis and in the elucidation of genome organization of several groups of eukaryotes. In this study, we contributed to the knowledge of Coleoptera genomes by reporting the chromosomal organization of repetitive DNA sequences, as well as the presence and characteristics of a B chromosome in two natural populations of Dichotomius geminatus (Coleoptera; Scarabaeidae) using classical, chromosomal banding and molecular cytogenetic techniques. As in other coleopteran species, the heterochromatin was mainly concentrated in pericentromeric regions and the B chromosome was composed almost entirely of heterochromatin. Physical mapping using double fluorescent in situ hybridization was performed for the first time in Coleoptera; using DNA probes for 5S and 18S ribosomal RNA (rRNA) and histone H3 genes, we showed that ribosomal 18S rDNAs are located in chromosomes 3 and 4, whereas 5S rRNA and histone H3 genes are colocalized in chromosomal pair 2 and show an apparently interspersed organization. Moreover, these genes are not present in the B chromosome, suggesting that the B chromosome did not originate from chromosomal pairs 2, 3 or 4. On the other hand, mapping of the C(0)t-1 DNA fraction showed that the B chromosome is enriched in repetitive DNA elements, also present in the standard complement, indicating an intraspecific origin of this element in D. geminatus. These results will contribute to our understanding of genome organization and evolution of repetitive elements in Coleoptera and other insects regarding both A and B chromosomes.

Familial calcium crystal diseases: what have we learned?

The spectrum of heterotopic calcification or ossification is expanding because of the reports of several kindreds with calcium pyrophosphate deposition disease, apatite deposition disease, and others with less common syndromes associated with extracellular matrix calcification, such as fibrodysplasia ossificans progressiva and related syndromes. Genomic DNA studies in both humans and mice provide a shortcut to understanding the genetic basis of promotion and prevention of ECM calcification. Mutation in the COL2A1 gene has been identified in one family with spondyloepiphyseal dysplasia and calcium pyrophosphate and apatite crystalline deposits. In another kindred with precocious osteoarthritis without spondyloepiphyseal dysplasia, the phenotype was linked to markers of chromosome 8. In four other kindreds, the phenotypes were linked to an area of chromosome 5p. Two genes located in this region, which are expressed in articular cartilage, are being investigated as possible calcium pyrophosphate deposition disease genes. The results of linkage studies in three kindreds with articular/periarticular ADD with the COL2A1 gene were noninformative. Two different mouse mutations, the ank/ank and the ttw/ttw mice, are associated with intra-articular and ligament apatite deposits caused by a decrease in extracellular pyrophosphate concentrations, mimicking human arthritis caused by apatite deposition disease. Mutations in the matrix GLA protein, both in mice and in humans, are also associated with vascular and articular calcification. These mouse mutations provide cutting-edge information in the investigation of the mechanisms of apatite deposition in humans.

Dense mapping of chromosome 12q13.12-q23.3 and linkage to asthma and atopy

BACKGROUND: Asthma is a complex disease characterized by a high prevalence of allergic diathesis and the almost ubiquitous presence of upper airway disease (eg rhinitis). Previously, we observed linkage of asthma among Afro-Caribbean families to markers in chromosome 12q, which contains a number of genes encoding for products closely related to allergic airway inflammation and disease. OBJECTIVE: To identify susceptibility loci in chromosome 12q contributing to the genetics of upper and lower airway diseases and to expand the region to include genes encoding IFN- ã(IFNG) and one of the signal transducers and activators of transcription (STAT6), we conducted further linkage studies among 33 multiplex families. METHODS: We characterized 528 subjects from Barbados for asthma; 82 percent were characterized for allergic rhinitis. Two-point and multipoint linkage analysis of 22 microsatellite markers (spanning ~79 centimorgan) was performed. RESULTS: Affected sib-pair analysis revealed significant evidence for linkage to asthma over approximately 30 cM (P < .05 to .002), with the best evidence for linkage at a CA repeat polymorphism in the first intron of IFNG in 12q21.1 (P = .002). Evidence of linkage to allergic rhinitis was observed in the same region (D12S313, P = .006, and IFNGCA, P = .01. respectively). Multipoint linkage analysis also provided evidence for linkage to asthma, with the best nonparametric linkage analysis score at D12S326 (nonparametric linkage score = 3.8, P = .0008). Modest evidence for linkage to allergic rhinitis was observed next to D12S326 at D12S1052 (p = .036) CONCLUSIONS: Our findings suggest that (1) one or more loci in the chromosome 12q13.12-q23.3 region are contributing to the expresstion of the clinical phenotype asthma and the strongest evidence for linkage is in a region near the gene encoding IFNG and (2) a susceptibility locus for both asthma and allergic rhinitis maps to this region.