DNA sequence analysis of spontaneous mutations at the aprt locus of hamster cells.

To determine the nature of spontaneous mutational events in cellular genes in hamster cells, mutant adenine phosphoribosyltransferase (aprt) genes were cloned and the regions to which we mapped alterations were sequenced. A variety of nucleotide changes were found to occur in the 12 mutant genes analyzed. Most mutations were simple base-pair substitutions-transitions (both G X C----A X T and A X T----G X C) and transversions. The only multiple mutation was a simple transition next to a single-base-pair insertion. Of the 12 mutations, 4 were more complex, involving small deletions or duplications. Two of these were similar to previously described deletions in that they occurred between short direct sequence repeats. No hot spots were detected. Three independent mutations were characterized at one restriction endonuclease site, although no other mutations were detected in the nucleotides surrounding this site in other mutant strains. At a functional level, sequence changes were either in exons (resulting in missense and, in one instance, nonsense mutations) or at splicing sites.     

Transient Inability to Manage Proteobacteria Promotes Chronic Gut Inflammation in TLR5-Deficient Mice

Colitis results from breakdown of homeostasis between intestinal microbiota and the mucosal immune system, with both environmental and genetic influencing factors. Flagellin receptor TLR5-deficient mice (T5KO) display elevated intestinal proinflammatory gene expression and colitis with incomplete penetrance, providing a genetically sensitized system to study the contribution of microbiota to driving colitis. Both colitic and noncolitic T5KO exhibited transiently unstable microbiotas, with lasting differences in colitic T5KO, while their noncolitic siblings stabilized their microbiotas to resemble wild-type mice. Transient high levels of proteobacteria, especially enterobacteria species including E.?coli, observed in close proximity to the gut epithelium were a striking feature of colitic microbiota. A Crohn's disease-associated E.?coli strain induced chronic colitis in T5KO, which persisted well after the exogenously introduced bacterial species had been eliminated. Thus, an innate immune deficiency can result in unstable gut microbiota associated with low-grade inflammation, and harboring proteobacteria can drive and/or instigate chronic colitis.     

Alzheimer's disease: current knowledge,management and research

Alzheimer''s disease is a common neurological condition, appearing as early as age 40 but increasing dramatically in incidence over age 85. Different genetic factors are at play, modified by events over a lifetime. Clinical diagnosis is possible through careful history taking with a reliable informant and a minimum number of laboratory tests. A relatively predictable natural history can be observed, with progression through stages of cognitive loss, functional impairment and behavioural disinhibition or apathy. New medications such as donepezil offer hope for improving or stabilizing symptoms. Such treatment can be administered by primary care physicians with experience in the diagnosis and management of Alzheimer''s disease. Disease stabilization, or even prevention, may be possible in the future.     

Spontaneous deletion formation at the aprt locus of hamster cells: the presence of short sequence homologies and dyad symmetries at deletion termini.

To examine the factors governing the generation of DNA sequence rearrangements in mammalian somatic cells, we have cloned and sequenced novel junctions produced by six spontaneous deletion mutations at the aprt locus of Chinese hamster ovary cells. Our analyses indicate that these rearrangements were produced by non-homologous recombinational events occurring between short (2-7 bp) sequence repeats at the two termini of the deletion which leave one copy of the repeat in the mutant gene. Certain tri- and tetranucleotides recur at the deletion termini, suggesting that these may possibly be a recognition sequence for an enzyme involved in the event. No other gene structural alterations were found at the novel junctions or in neighbouring sequences. The deletions are not randomly distributed over the aprt gene; four termini clustered in a 40-bp sequence. This region of aprt is unusual as it contains both significant stretches of dyad symmetry which could potentially form stable DNA secondary structures and short direct repeats. Regions of dyad symmetry were also found at at least one terminus of all the deletions. In view of the similar properties of this set of deletions, possible mechanisms for the formation of this type of gene rearrangement are considered.     

DNA amplification--deletion in a spontaneous mutation of the hamster aprt locus: structure and sequence of the novel joint.

In a collection of spontaneous mutants of Chinese hamster ovary cells selected for deficiency in adenine phosphoribosyl transferase (aprt) activity, one was detected having not only a deletion of aprt coding sequences but also an apparent amplification of remaining sequences. The HindIII fragment bearing the novel joint was cloned and sequenced revealing a complex gene rearrangement. A deletion of at least 9 kb extending upstream from the aprt locus is accompanied by an inverted duplication of flanking sequences 672 bp downstream from the novel joint. This unit is amplified three to four times with the net result of some sequences being increased as much as eight fold in copy number because of the duplication. The fidelity of the sequences involved is preserved. We propose a model which could account for this inverted duplication.     

Investigation of expression of HOX 2C and HOX 4B homeobox genes in human colorectal cancer by using an RT-PCR method

Investigation of expression of both HOX 2C and HOX 4B homeobox genes in the same patient with colorectal cancer was proposed by using an RT-PCR method. In order to conduct this investigation, PCR products of 445 bp of HOX 2C and 301 bp of HOX 4B were amplified in both tumor and normal samples of ten patients. Expressions of HOX 2C gene were observed in both tumor and normal samples of four patients and in only a tumor sample of one patient, while the expression was not observed in both tumor and normal samples of five patients. Expressions of HOX 4B gene were not observed in both tumor and normal samples of ten patients.In the present study, it was found that individuality seems to be important. The results of these two genes, observed in patients with colorectal cancer, should be taken into consideration for further researches.