Visceral gout in a rough legged hawk (Buteo lagopus)

Visceral gout is reported for the first time in a rough legged hawk (Buteo lagopus). Urate crystals were present on the pericardium, thoracic and abdominal air sacs, and the ventral surface of the liver. The liver and spleen also had urate crystals throughout the parenchyma. There was no indication of articular or renal involvement. The immediate cause of death in this hawk was not identified, but appeared to result from multiple factors, including the visceral gout.     

Effect of telomere length on telomeric gene expression.

Telomeres gradually shorten as human somatic cells divide and a correlation has been observed between the average telomere length and cell senescence. It has been proposed that the genes responsible for cell senescence are located near the telomere and are activated when telomere length reaches a critical point. This is consistent with evidence from Saccharomyces cerevisiae, in which genes are regulated differently depending on their distance from the telomere. We investigated the possibility that differential gene expression is conferred by telomere length in human cells. A plasmid containing the neomycin phosphotransferase (neo) gene was transfected into the SV40-transformed human fibroblast cell line LM217. In one transfectant the plasmid was integrated at the telomere of chromosome 13. Subclones of this cell line that had various lengths of telomeric repeat sequences on the end of this chromosome were isolated. No effect on neo gene expression was found when the length of the telomere varied between 25 and 0.5 kb, as demonstrated by colony forming ability, growth rates and RNA blot analysis. These results therefore suggest that putative chromatin structural differences conferred by telomere length do not affect the expression of genes located near telomeres.     

Telomere dynamics in an immortal human cell line.

The integration of transfected plasmid DNA at the telomere of chromosome 13 in an immortalized simian virus 40-transformed human cell line provided the first opportunity to study polymorphism in the number of telomeric repeat sequences on the end of a single chromosome. Three subclones of this cell line were selected for analysis: one with a long telomere on chromosome 13, one with a short telomere, and one with such extreme polymorphism that no distinct band was discernible. Further subcloning demonstrated that telomere polymorphism resulted from both gradual changes and rapid changes that sometimes involved many kilobases. The gradual changes were due to the shortening of telomeres at a rate similar to that reported for telomeres of somatic cells without telomerase, eventually resulting in the loss of nearly all of the telomere. However, telomeres were not generally lost completely, as shown by the absence of polymorphism in the subtelomeric plasmid sequences. Instead, telomeres that were less than a few hundred base pairs in length showed a rapid, highly heterogeneous increase in size. Rapid changes in telomere length also occurred on longer telomeres. The frequency of this type of change in telomere length varied among the subclones and correlated with chromosome fusion. Therefore, the rapid changes in telomere length appeared occasionally to result in the complete loss of telomeric repeat sequences. Rapid changes in telomere length have been associated with telomere loss and chromosome instability in yeast and could be responsible for the high rate of chromosome fusion observed in many human tumor cell lines.     

Formation of extrachromosomal circular DNA in HeLa cells by nonhomologous recombination.

Extrachromosomal circular DNA (eccDNA) generated from chromosomal DNA is found in all mammalian cells and increases with cell stress or aging. Studies of eccDNA structure and mode of formation provide insight into mechanisms of instability of the mammalian genome. Previous studies have suggested that eccDNA is generated through a process involving recombination between repetitive sequences. However, we observed that approximately one half of the small eccDNA fragments cloned from HeLa S3 cells were composed entirely of nonrepetitive or low-copy DNA sequences. We analyzed four of these fragments by polymerase chain reaction and nucleotide sequencing and found that they were complete eccDNAs. We then screened a human genomic library with the eccDNAs to isolate the complementary chromosomal sequences. Comparing the recombination junctions within the eccDNAs with the chromosomal sequences from which they were derived revealed that nonhomologous recombination was involved in their formation. One of the eccDNAs was composed of two separate sequences from different parts of the genome. These results suggest that rejoining of ends of fragmented DNA is responsible for the generation of a substantial portion of the eccDNAs found in HeLa S3 cells.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Analysis of rat serum apolipoproteins by isoelectric focusing. I. Studies on the middle molecular weight subunits.

Analytical isoelectric focusing (IEF) has been applied to the study of the apolipoprotein components of rat serum high density and very low density lipoproteins. The apolipoproteins were separated on 7.5% polyacrylamide gels containing 6.8% urea, with a pH gradient of 4-6. The middle molecular weight range apolipoproteins were identified on IEF gels by the use of apolipoproteins purified by electrophoresis on gels containing sodium dodecyl sulfate (SDS). The A-1 protein focused as 4 to 5 bands from pH 5.46 to 5.82; the A-IV protein and the arginine-rich protein each focused as 4 to 6 bands from pH 5.31 to 5.46. The low molecular weight proteins focused from pH. 4.43 to 4.83 and are the subject of a separate communication. Comparisons of the IEF method with SDS gel electrophoresis, polyacrylamide gel electrophoresis in urea, and Sephadex chromatography are also reported. Additional studies were also carried out that tend to rule out carbamylation or incomplete unfolding of the proteins in the presence of urea as the causes of the observed heterogeneity.     

Localization of dystrophin relative to acetylcholine receptor domains in electric tissue and adult and cultured skeletal muscle

Two high-affinity mAbs were prepared against Torpedo dystrophin, an electric organ protein that is closely similar to human dystrophin, the gene product of the Duchenne muscular dystrophy locus. The antibodies were used to localize dystrophin relative to acetylcholine receptors (AChR) in electric organ and in skeletal muscle, and to show identity between Torpedo dystrophin and the previously described 270/300-kD Torpedo postsynaptic protein. Dystrophin was found in both AChR-rich and AChR-poor regions of the innervated face of the electroplaque. Immunogold experiments showed that AChR and dystrophin were closely intermingled in the AChR domains. In contrast, dystrophin appeared to be absent from many or all AChR-rich domains of the rat neuromuscular junction and of AChR clusters in cultured muscle (Xenopus laevis). It was present, however, in the immediately surrounding membrane (deep regions of the junctional folds, membrane domains interdigitating with and surrounding AChR domains within clusters). These results suggest that dystrophin may have a role in organization of AChR in electric tissue. Dystrophin is not, however, an obligatory component of AChR domains in muscle and, at the neuromuscular junction, its roles may be more related to organization of the junctional folds.