Dicentric chromosomes and the inactivation of the centromere

Summary The origin and behavior of human dicentric chromosomes are reviewed. Most dicentrics between two non-homologous or two homologous chromosomes (isodicentrics), which are permanent members of a chromosome complement, probably originate from segregation of an adjacent quadriradial; such configurations are the result of a chromatid translocation between two nonhomologous chromosomes, or they represent an adjacent counterpart of a mitotic chiasma. The segregation of such a quadriradial may also give rise to a cell line monosomic for the chromosome concerned (e.g., a 45,X line). Contrary to the generally held opinion, isodicentrics rarely result from an isolocal break in two chromatids followed by rejoining of sister chromatids. In this case the daughter centromeres go to opposite poles in the next anaphase, and the resulting bridge breaks at a random point. This mechanism, therefore, leads to the formation of an isodicentric chromosome only if the two centromeres are close together, or if one centromere is immediately inactivated. Observations on the origin of dicentrics in Bloom syndrome support these conclusions. One centromere is permanently inactivated in most dicentric chromosomes, and even when the dicentric breaks into two chromosomes, the centromere is not reactivated. The appearance and behavior of the acentric X chromosomes show that their centromeres are similarly inactivated and not prematurely divided. Two Bloom syndrome lymphocytes, one with an extra chromosome 2 and the other with an extra chromosome 7, each having an inactivated centromere, show that this can also happen in monocentric autosomes.     

The spectrum of mitochondrial DNA mutations in families with Leber hereditary optic neuroretinopathy

The mitochondrial complex I genes were sequenced in seven Leber hereditary optic neuroretinopathy (LHON) families without the ND4/11778 and ND1/3460 mutations. Four replacement mutations restricted only to LHON families were found, one in the ND1 gene at nt 4025, and three in the ND5 gene at nt 12811, 13637, and 13967. The mutations did not change evolutionarily conserved amino acids suggesting that they are not primary LHON mutations in these families. They may be considered as secondary LHON mutations serving as exacerbating factors in an appropriate genetic background. A complex III mutation, cyt b/15257, has been suggested to be one of the primary mutations causing LHON. Its presence was determined for 23 Finnish LHON families, and it was detected in two families harboring the ND4/11778 mutation. Similarly, complex IV mutation COI/7444 was screened in Finnish LHON families, and it was found in one family carrying the ND1/3460 mutation.     

Species,Guilds, and Functional Groups: Taxonomy and Behavior in Nematophagous Arthropods

Phylogenetic relationship is an indication of shared abilities, or at least of shared constraints, on morphology, physiology, and behavior; but is phylogenetic relationship a sufficient criterion for predicting ecological function? Ecologists have assumed that the function of invertebrates in soil systems can be predicted at a low level of taxonomic resolution, but our research indicates that critical functional parameters -- e.g., feeding behavior, developmental rate, and reproductive mode -- are rarely predictable above the generic level. Since morphology is more strongly conserved than behavior, feeding guilds or functional groups based on broad taxonomic relationship or untested assumptions about correlations between trophic morphology and feeding behavior have little meaning for nematophagous arthropods from grassland soils in Colorado.     

Human telomeric 6; 19 translocation chromosome with a tendency to break at the fusion point

The behavior of a translocation chromosome t(6; 19) in the lymphocytes of a mentally retarded woman with other anomalies has been analyzed. The two chromosomes were attached at the telomeres of their short arms without any apparent deletion. The centromere of chromosome 19 was marked by a primary constriction and the site of the centromere of chromosome 6 by a C-band, but no constriction. The translocation chromosome showed two primary constrictions once in 8,800 metaphases, probably resulting from mitotic crossing-over. One or both chromatids of the translocation chromosome were broken at the attachment point with a frequency of 1/733 cells. In addition, the chromosome was often bent at this point and the translocated chromosomes 19 and 6 showed a differential spiralization. In this characteristic as well as the weakness of the fusion point, this chromosome differed from other translocations; the fusion obviously was not as firm as in translocations in general. The broken-off chromosome 6 did not regain a primary constriction, but had the appearance of a large acentric fragment. The segregation of the translocation chromosome and the fragment gave rise to a complicated mosaicism with various levels of ploidy for the fragment lacking a functional centromere. The data are in quantitative agreement with the equilibrium expectations under the assumption that each fragment goes to either pole at random in mitosis and that cells divide at the same rate regardless of ploidy. The high rate of nondisjunction of the fragment showed that the inactivated centromere of the translocation chromosome did not regain its activity when chromosome 19 with the functional centromere became separated from it. — The fragility and the behavior of the translocation chromosome and the production of telomeric associations are briefly discussed.     

Influence of oxygen transfer rate on vinegar production by Acetobacter aceti in submerged fermentation

Summary A study was carried out on the influence of oxygen transfer rate on bacterial growth and acid production in submerged vinegar fermentation by an industrial culture of Acetobacter aceti. The production rate grew as did growth rate even if no increment in cellular mass was noticed when oxygen transfer rate was increased. The relationship between growth and production followed a mixed growth associated model.     

The origin of telocentric chromosomes in man: A girl with tel(Xq)

Summary A mentally retarded girl with several Turner symptoms had the chromosome constitution 46,X,tel(Xq). The abnormal X chromosome appeared to be completely telocentric and stable. It was late-replicating and formed a smaller than normal Barr body. The origin of telocentric chromosomes is discussed.     

Redistribution of rat renal allograft-responding leukocytes during rejection: 1. Model

We describe a model that enables us to trace the traffic of allograft-responding inflammatory leukocytes to and from the graft without handling of these cells in vitro. At different times after transplantation, the kidney transplant pedicle—including the artery, vein, and draining lymphatics—is clamped. The allograft-responding leukocytes are labeled by a [³H]thymidine pulse either in situ or in the systemic lymphoid organs of the recipient. Fifteen minutes later the pulse is chased with a 1000-fold excess of cold thymidine, and the clamp is opened. The animals are sacrificed 18 hr later, when a balance between the synthesis of new labeled leukocytes from the originally labeled ones and dilution of intracellular label has been achieved. This model was used to analyze the allograft-responding inflammatory cell traffic to and from a renal transplant performed across the major histocompatibility complex in the rat. A sizable traffic was observed to both directions: After systemic injection of label only 0.008 × 10⁶ labeled cells × hr^?1 were found to emigrate into a kidney allograft (control). Already on the third day after transplantation—when the in situ inflammatory response is still at its beginning—more than 0.3 × 10⁶ labeled cells × hr^?1 migrated from the host to the allograft and 1.6 × 10⁶ labeled cells × hr^?1 left the allograft to the recipient spleen. The first figure is several-fold higher than any previous estimate. The findings emphasize the systemic nature of the antiallograft inflammatory response.     

Characterization of Cyanobacteria by SDS-PAGE of whole-cell proteins and PCR/RFLP of the 16S rRNA gene

Planktonic, filamentous cyanobacterial strains from different genera, both toxic and nontoxic strains, were characterized by SDS-PAGE of whole-cell proteins and PCR/RFLP of the 16S rRNA gene. Total protein pattern analysis revealed the mutual relationships at the genus level. Restriction fragment length polymorphism (RFLP) of the 16S rRNA gene with reference strains proved to be a good method for the cyanobacterial taxonomy. The nonheterocystous strains outgrouped from the nitrogen-fixing ones. With both methods, Aphanizomenon clustered with Anabaena, and Nodularia with Nostoc. In the RFLP study of Anabaena, the neurotoxic strains were identical, but the hepatotoxic ones formed a heterogeneous group. Genetic distances found in the RFLP study were short, confirming that close genotypic relationships underlie considerable diversity among cyanobacterial genera. Received: 16 December 1996 / Accepted: 14 May 1997     

An increased frequency of chromosomal changes and SCE's in cultured blood lymphocytes of 12 subjects vaccinated against smallpox

Summary An increased frequency of chromosomal changes and sister chromatid exchanges was detected in 10 women 7 days after smallpox vaccination.