Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the...Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the E.coli wild type and mutator strains, the mutant frequencies suggest that base substitutions in rpoB gene are induced by the N + implantation. A highly conserved region is selected to get the direct evidence for base substitutions by sequence of the high fidelity PCR amplification products in mutants. Most of the mutants (90.9%, 40/44) have at least one base substitution in the amplification region. The evidences for CG to TA (55%, 22/40), AT to GC (20%, 8/40) and TA to CG (5%, 2/40) transitions are identified. The transversions are AT to TA (15%, 6/40) and GC to CG (5%, 2/40). It is suggested that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N + implantation by analysis of the mutant frequencies of mutator strains.展开更多
Background. The point mutations occurring in codons 12 and 13 of the Ki-ras gene are useful genetic markers to identify intratumoral heterogeneity. A single tumor crypt, which consists of monoclonal cells, can be obta...Background. The point mutations occurring in codons 12 and 13 of the Ki-ras gene are useful genetic markers to identify intratumoral heterogeneity. A single tumor crypt, which consists of monoclonal cells, can be obtained using the crypt isolation method. Ki-ras gene mutations have been examined using the crypt isolation method to determine whether multiclonarity is present within the same tumor. Methods. Ki-ras gene mutations were analyzed using a crypt isolation technique coupled with polymerase chain reaction and direct sequencing in 21 sporadic colorectal carcinomas. The specimens were divided into two groups: a representative sample, which was composed of more than 50 tumor crypts, and a single tumor crypt sample. The latter consisted of 10 single tumor crypts, which were obtained from the same tumor separately. Results. Ki-ras gene mutations were found in 11 of 21 representative samples and in 12 of 21 single tumor crypt samples. In the 11 samples with Ki-ras mutation, Ki-ras mutations were also found in most single tumor crypts. Among the 12 base substitutions found, G:C to A:T transitions were the most commonly observed. There were no differences between the two samples in the types of Ki-ras mutations found. One Ki-ras mutation that was not detected in the representative sample was observed in only a single tumor crypt. Conclusions. Most carcinomas appear to have a homogeneous composition that may result from the successful progression of one of the clones having a Ki-ras mutation. Additional mutations in the Ki-ras gene were rarely observed in colorectal carcinomas.展开更多
文摘Ever since the low energy N + ion beam has been accepted, the mutations of ionizing radiation are attributable mainly to avoidance of DNA damages repair. Evidences based on in vivo proof results are limited. Using the E.coli wild type and mutator strains, the mutant frequencies suggest that base substitutions in rpoB gene are induced by the N + implantation. A highly conserved region is selected to get the direct evidence for base substitutions by sequence of the high fidelity PCR amplification products in mutants. Most of the mutants (90.9%, 40/44) have at least one base substitution in the amplification region. The evidences for CG to TA (55%, 22/40), AT to GC (20%, 8/40) and TA to CG (5%, 2/40) transitions are identified. The transversions are AT to TA (15%, 6/40) and GC to CG (5%, 2/40). It is suggested that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N + implantation by analysis of the mutant frequencies of mutator strains.
文摘Background. The point mutations occurring in codons 12 and 13 of the Ki-ras gene are useful genetic markers to identify intratumoral heterogeneity. A single tumor crypt, which consists of monoclonal cells, can be obtained using the crypt isolation method. Ki-ras gene mutations have been examined using the crypt isolation method to determine whether multiclonarity is present within the same tumor. Methods. Ki-ras gene mutations were analyzed using a crypt isolation technique coupled with polymerase chain reaction and direct sequencing in 21 sporadic colorectal carcinomas. The specimens were divided into two groups: a representative sample, which was composed of more than 50 tumor crypts, and a single tumor crypt sample. The latter consisted of 10 single tumor crypts, which were obtained from the same tumor separately. Results. Ki-ras gene mutations were found in 11 of 21 representative samples and in 12 of 21 single tumor crypt samples. In the 11 samples with Ki-ras mutation, Ki-ras mutations were also found in most single tumor crypts. Among the 12 base substitutions found, G:C to A:T transitions were the most commonly observed. There were no differences between the two samples in the types of Ki-ras mutations found. One Ki-ras mutation that was not detected in the representative sample was observed in only a single tumor crypt. Conclusions. Most carcinomas appear to have a homogeneous composition that may result from the successful progression of one of the clones having a Ki-ras mutation. Additional mutations in the Ki-ras gene were rarely observed in colorectal carcinomas.
