Four novel single nucleotide polymorphisms within the promoter region of p53 gene and their associations with uterine leiomyoma

Dysregulated p53 expression has been implicated as a major contributor to numerous tumorigenesis. Single nucleotide polymorphisms (SNPs) within the functional consequence of the novel p53 promoter region remains obscure. Herein, we aimed to establish the extent of genetic variability within the promoter region of p53 gene as well as their association with leiomyoma susceptibility. Women were divided into two groups, leiomyoma (n = 160) and nonleiomyoma controls (n = 200). Total DNA was isolated from the peripheral blood of subjects. The DNA fragment containing p53 promoter regions (+64 approximately -404 bp) were obtained by amplification of polymerase chain reaction. The variations of DNA fragments were detected by DNA sequencing or restriction fragment length polymorphism (RFLP). Sequence alignment was used to identify sequence variations in p53 promoter regions. Genotypes were analyzed by method of RFLP. Genotypes/allelic frequencies in the leiomyoma and control groups were compared. A total of 15 sequence variations within p53 promoter region were identified, including -408 T/C, -382 A/G, -359 A/G, -325 T/C, -250 A/G, -216 T/C, -205 G/A, -198 G/A, -177 T/C, -103 A/G, -81 G/A, -71 G/A, -51 T/A, -33 A/G, and -17 T/C. Among these variations, four SNPs (-250 A/G, -216 T/C, -103 A/G, and -33 A/G) were established. Allele frequencies of -250*G/-216*C/-103*G/-33*G in the leiomyoma group and control group 6.9/5.0/5.9/3.8% and 3.8/1.8/2.3/4.0%, respectively. Two of them (-216*C and -103*G) are associated with higher leiomyoma susceptibility. We concluded that some sequence variations were observed within the promoter region of p53 gene. The SNPs of -216*C and -103*G among the identical sequence variations are associated with leiomyoma development.     

Identification of three SNPs in the porcine myostatin gene (MSTN)

Thirteen pairs of primers were designed for the entire porcine MSTN gene to enable PCR amplification for the detection of single nucleotide polymorphisms (SNPs) by a PCR-SSCP approach. Altogether 96.5% (1089/1128) of the encoding regions and 971 bp of the non-coding regions were screened. A total of three polymorphisms were identified with PCR-SSCP. They were located in the promoter, intron one and exon three regions of the gene. These polymorphisms were then confirmed to be point mutations (T --> A transversion, G --> A transition and C --> T transition respectively) by sequencing. Allele frequencies were determined for all three SNPs in several different pig breed populations. The polymorphisms were found to be rare in Western breeds, but much more common in Chinese breeds. Whether they have any relationship with the marked difference in lean meat mass between Western and Chinese breeds requires further study.     

Cloning, partial sequence, and single-nucleotide polymorphism of the ryanodine receptor gene of the Pacific white shrimp Litopenaeus vannamei (Penaeidae)

Ryanodine receptor/calcium release channel is a large protein that plays an essential role in muscle contraction; mutations in the ryanodine receptor gene affect sensitivity to stress. As a first step towards investigating the relationship between the ryanodine receptor and shrimp cramped muscle syndrome, we cloned, partially sequenced, and examined single-nucleotide polymorphisms (SNPs) of the ryanodine receptor gene of the Pacific white shrimp (Litopenaeus vannamei). The nucleotide sequence of a 15.06-kb L. vannamei genomic DNA segment containing a partial ryanodine receptor gene sequence was determined (deposited in GenBank nucleotide database: HM367069). Direct sequencing of PCR-amplified ryanodine receptor exons with their intron-flanking regions in 10 cramped muscle syndrome shrimp and 10 healthy shrimp, revealed seven SNPs. Five of them (1713A/G, 1749T/C, 1755T/C, 3965G/A, and 8737C/T) are located in exons; however, they appear to be neutral (synonymous), since they do not alter the encoded amino acid. The other SNPs (1553C/T and 13337A/G) are in introns. The SNPs identified in the ryanodine receptor gene could be useful for association studies aimed at determining the physiological role of the ryanodine receptor in cramped muscle syndrome of shrimp.     

The complementary neighborhood patterns and methylation-to-mutation likelihood structures of 15,110 single-nucleotide polymorphisms in the bovine genome

Bayesian analysis was performed to examine the single-nucleotide polymorphism (SNPs) neighborhood patterns in cattle using 15,110 SNPs, each with a flanking sequence of 500 bp. Our analysis confirmed three well-known features reported in plants and/or other animals: (1) the transition is the most abundant type of SNPs, accounting for 69.8% in cattle; (2) the transversion occurs most frequently (38.56%) in cattle when the A + T content equals two at their immediate adjacent sites; and (3) C <--> T and A <--> G transitions have reverse complementary neighborhood patterns and so do A <--> C and G <--> T transversions. Our study also revealed several novel SNP neighborhood patterns that have not been reported previously. First, cattle and humans share an overall SNP pattern, indicating a common mutation system in mammals. Second, unlike C <--> T/A <--> G and A <--> C/G <--> T, the true neighborhood patterns for A <--> T and C <--> G might remain mysterious because the sense and antisense sequences flanking these mutations are not actually recognizable. Third, among the reclassified four types of SNPs, the neighborhood ratio between A + T and G + C was quite different. The ratio was lowest for C <--> G, but increased for C <--> T/A <--> G, further for A <--> C/G <--> T, and the most for A <--> T. Fourth, when two immediate adjacent sites provide structures for CpG, it significantly increased transitions compared to the structures without the CpG. Finally, unequal occurrence between A <--> G and C <--> T in five paired neighboring structures indicates that the methylation-induced deamination reactions were responsible for approximately 20% of total transitions. In addition, conversion can occur at both CpG sites and non-CpG sites. Our study provides new insights into understanding molecular mechanisms of mutations and genome evolution.     

A role for DNA polymerase V in G --> T mutations from the major benzo[a]pyrene N2-dG adduct when studied in a 5'-TGT sequence in E. coli

Benzo[a]pyrene (B[a]P), a potent mutagen/carcinogen, is metabolically activated to (+)-anti-B[a]PDE, which induces a full spectrum of mutations (e.g. GC --> TA, GC --> AT, etc.) principally via its major adduct [+ta]-B[a]P-N2-dG. Recent findings suggest that different lesion bypass DNA polymerases may be involved in different mutagenic pathways, which is the subject of this report. [+ta]-B[a]P-N2-dG built into a plasmid in a 5'-TGT sequence gives approximately equal numbers of G --> T and G --> A mutations when host E. coli are UV irradiated prior to transformation, so this sequence context was chosen to investigate what DNA polymerases are involved in G --> T versus G --> A mutations. G --> T mutations decline (>10-fold) if E. coli either are not UV-irradiated or are deficient in DNA polymerase V ((delta)umuD/C), demonstrating a role for damage-inducible DNA Pol V in a G --> T pathway. G --> T mutations are not affected by transformation into E. coli deficient in either DNA polymerases II or IV. While the work herein was in progress, Lenne-Samuel et al. [Mol. Microbiol. 38 (2000) 299] built the same adduct into a plasmid in a 5'-GGA sequence, and showed that the frequency of G --> T mutations was similar in UV-irradiated and unirradiated host E. coli cells, suggesting no involvement by damage-inducible, lesion bypass DNA polymerases (i.e., not II, IV or V); furthermore, a role for DNA Pol V was explicitly ruled out. The easiest way to reconcile the findings of Lenne-Samuel et al. with the findings herein is if two G --> T mutagenic pathways exist for [+ta]-B[a]P-N2-dG, where sequence context dictates which pathway is followed. In contrast to the G --> T mutations, herein G --> A mutations from [+ta]-B[a]P-N2-dG in the 5'-TGT sequence context are shown not to be affected by UV-irradiation of host E. coli, and are not dependent on DNA Pol V, or Pol II, Pol IV, or the damage-inducible, but SOS-independent UVM system. Published studies, however, have shown that G --> A mutations are usually enhanced by UV-irradiation of host E. coli prior to the introduction of plasmids either site-specifically modified with [+ta]-B[a]P-N2-dG or randomly adducted with (+)-anti-B[a]PDE; both findings imply the involvement of a lesion-bypass DNA polymerase. These disparate results suggest the existence of two G --> A mutagenic pathways for [+ta]-B[a]P-N2-dG as well, although confirmation of this awaits further study. In conclusion, a comparison between the evidence presented herein and published findings suggests the existence of two distinct mutagenic pathways for both G --> T and G --> A mutations from [+ta]-B[a]P-N2-dG, where in each case one pathway is not damage-inducible and not dependent on a lesion-bypass DNA polymerase, while the second pathway is damage-inducible and dependent on a lesion-bypass DNA polymerase. Furthermore, DNA sequence context appears to dictate which pathway (as defined by the involvement of different DNA polymerases) is followed in each case.     

Modeling genetic imprinting effects of DNA sequences with multilocus polymorphism data

Single nucleotide polymorphisms (SNPs) represent the most widespread type of DNA sequence variation in the human genome and they have recently emerged as valuable genetic markers for revealing the genetic architecture of complex traits in terms of nucleotide combination and sequence. Here, we extend an algorithmic model for the haplotype analysis of SNPs to estimate the effects of genetic imprinting expressed at the DNA sequence level. The model provides a general procedure for identifying the number and types of optimal DNA sequence variants that are expressed differently due to their parental origin. The model is used to analyze a genetic data set collected from a pain genetics project. We find that DNA haplotype GAC from three SNPs, OPRKG36T (with two alleles G and T), OPRKA843G (with alleles A and G), and OPRKC846T (with alleles C and T), at the kappa-opioid receptor, triggers a significant effect on pain sensitivity, but with expression significantly depending on the parent from which it is inherited (p = 0.008). With a tremendous advance in SNP identification and automated screening, the model founded on haplotype discovery and statistical inference may provide a useful tool for genetic analysis of any quantitative trait with complex inheritance.     

Novel SNPs in <Emphasis Type="Italic">HSP70A1A</Emphasis> gene and the association of polymorphisms with thermo tolerance traits and tissue specific expression in Chinese Holstein cattle

Heat stress induces heat shock proteins (HSPs) expression and HSP70 family is one of them that have been reported to involve in cellular protection against heat stress. But whether there is any association of genetic variation in the HSP70A1A gene with thermo tolerance is unknown. PCR-SSCP and DNA sequencing were used to detect possible SNPs in HSP70A1A gene in 890 Chinese Holstein cattle. Three fragments were amplified and five novel mutations were found in HSP70A1A gene in Chinese Holstein cattle. G/A mutation was found at nucleotide 1524 in coding region that resulting two genotypes of AA and AB. T/C mutation was found at nucleotide 3494 in 3′-UTR resulting three genotypes of CC, CD and DD. The other three point mutations, G/C at nucleotide 6400, C/T at nucleotide 6600 and G/A at nucleotide 6601 were also found in 3′-UTR resulting six genotypes of EE, EF, FF, EG, FG and GG. Linkage disequilibrium (LD) analysis showed that the nucleotide 6400, 6600 and 6601 were in strong LD (D > 0.75). Association analysis indicated that AB, DD and FF genotype were the thermo tolerance genotype. SBYE Green I was used to quantify HSP70A1A mRNA expression in different tissues through quantitative real-time PCR assay. The results of the real-time PCR showed that the expression of HSP70A1A mRNA in the heart was significantly higher than that in the other tissues (P < 0.05). We presume that these mutations could be used in marker assisted selection for anti-heat stress cows in our breeding program.     

Identification of functional DNA variants in the constitutive promoter region of MDM2

Although mutations in the oncoprotein murine double minute 2 (MDM2) are rare, MDM2 gene overexpression has been observed in several human tumors. Given that even modest changes in MDM2 levels might influence the p53 tumor suppressor signaling pathway, we postulated that sequence variation in the promoter region of MDM2 could lead to disregulated expression and variation in gene dosage. Two promoters have been reported for MDM2; an internal promoter (P2), which is located near the end of intron 1 and is p53-responsive, and an upstream constitutive promoter (P1), which is p53-independent. Both promoter regions contain DNA variants that could influence the expression levels of MDM2, including the well-studied single nucleotide polymorphism (SNP) SNP309, which is located in the promoter P2; i.e., upstream of exon 2. In this report, we screened the promoter P1 for DNA variants and assessed the functional impact of the corresponding SNPs. Using the dbSNP database and genotyping validation in individuals of European descent, we identified three common SNPs (?1494?G?>?A; indel 40?bp; and ?182?C?>?G). Three major promoter haplotypes were inferred by using these three promoter SNPs together with rs2279744 (SNP309). Following subcloning into a gene reporter system, we found that two of the haplotypes significantly influenced MDM2 promoter activity in a haplotype-specific manner. Site-directed mutagenesis experiments indicated that the 40?bp insertion/deletion variation is causing the observed allelic promoter activity. This study suggests that part of the variability in the MDM2 expression levels could be explained by allelic p53-independent P1 promoter activity.     

Sequence variants in the FcepsilonRI alpha chain gene.

There is a relationship between IgE levels and expression of high-affinity IgE receptors (FcepsilonRI). Because the alpha chain is the only portion of the receptor that binds directly to IgE, we reasoned that sequence variants in the FcepsilonRI alpha gene may exist that alter these binding events. We screened all of the exons and the promoter region of the FcepsilonRI alpha chain gene with genomic DNA from 389 asthmatic and 341 normal control subjects for mutations by using single-stranded conformational polymorphism analysis. No nonsynonomous single nucleotide polymorphisms (SNPs) were identified in the coding region. Three SNPs were found in the promoter region: an A/C transversion at -770 from the translation start site; a G/A transition at -664; and a T/C transition at -335. No differences in allele frequencies were detected between asthmatic subjects and controls. Homozygosity for the C variant at locus -335 was more common in Caucasian asthmatic patients with IgE levels in the lower quartile than in the upper quartile (P = 0.032). An analysis of highly polymorphic SNPs indicated that this association is unlikely to be due to population substructure. We conclude that homozygosity for the C allele of FcepsilonRI alpha chain variant is associated with lower IgE levels.     

Changes in primary DNA sequence complexity influence the phenotypic consequences of mutations in human gene regulatory regions

No general rules have been proposed to account for the functional consequences of gene regulatory mutations. In a first attempt to establish the nature of such rules, an analysis was performed of the DNA sequence context of 153 different single base-pair substitutions in the regulatory regions of 65 different human genes underlying inherited disease. Use of a recently proposed measure of DNA sequence complexity (taking into account the level of structural repetitiveness of a DNA sequence, rather than simply the oligonucleotide composition) has served to demonstrate that the concomitant change in local DNA sequence complexity surrounding a substituted nucleotide is related to the likelihood of a regulatory mutation coming to clinical attention. Mutations that led to an increase in complexity exhibited higher odds ratios in favour of pathological consequences than mutations that led to a decrease or left complexity unchanged. This relationship, however, was discernible only for pyrimidine-to-purine transversions. Odds ratios for other types of substitution were not found to be significantly associated with local changes in sequence complexity, even though a trend similar to that observed for Y-->R transversions was also apparent for transitions. These findings suggest that the maintenance of a defined level of DNA sequence complexity, or at least the avoidance of an increase in sequence complexity, is a critical prerequisite for the function of gene regulatory regions.     

Mutational specificity of gamma-radiation-induced guanine-thymine and thymine-guanine intrastrand cross-links in mammalian cells and translesion synthesis past the guanine-thymine lesion by human DNA polymerase eta

Comparative mutagenesis of gamma- or X-ray-induced tandem DNA lesions G[8,5-Me]T and T[5-Me,8]G intrastrand cross-links was investigated in simian (COS-7) and human embryonic (293T) kidney cells. For G[8,5-Me]T in 293T cells, 5.8% of progeny contained targeted base substitutions, whereas 10.0% showed semitargeted single-base substitutions. Of the targeted mutations, the G --> T mutation occurred with the highest frequency. The semitargeted mutations were detected up to two bases 5' and three bases 3' to the cross-link. The most prevalent semitargeted mutation was a C --> T transition immediately 5' to the G[8,5-Me]T cross-link. Frameshifts (4.6%) (mostly small deletions) and multiple-base substitutions (2.7%) also were detected. For the T[5-Me,8]G cross-link, a similar pattern of mutations was noted, but the mutational frequency was significantly higher than that of G[8,5-Me]T. Both targeted and semitargeted mutations occurred with a frequency of approximately 16%, and both included a dominant G --> T transversion. As in 293T cells, more than twice as many targeted mutations in COS cells occurred in T[5-Me,8]G (11.4%) as in G[8,5-Me]T (4.7%). Also, the level of semitargeted single-base substitutions 5' to the lesion was increased and 3' to the lesion decreased in T[5-Me,8]G relative to G[8,5-Me]T in COS cells. It appeared that the majority of the base substitutions at or near the cross-links resulted from incorporation of dAMP opposite the template base, in agreement with the so-called "A-rule". To determine if human polymerase eta (hpol eta) might be involved in the mutagenic bypass, an in vitro bypass study of G[8,5-Me]T in the same sequence was carried out, which showed that hpol eta can bypass the cross-link incorporating the correct dNMP opposite each cross-linked base. For G[8,5-Me]T, nucleotide incorporation by hpol eta was significantly different from that by yeast pol eta in that the latter was more error-prone opposite the cross-linked Gua. The incorporation of the correct nucleotide, dAMP, by hpol eta opposite cross-linked T was 3-5-fold more efficient than that of a wrong nucleotide, whereas incorporation of dCMP opposite the cross-linked G was 10-fold more efficient than that with dTMP. Therefore, the nucleotide incorporation pattern by hpol eta was not consistent with the observed cellular mutations. Nevertheless, at and near the lesion, hpol eta was more error-prone compared to a control template. The in vitro data suggest that translesion synthesis by another Y-family DNA polymerase and/or flawed participation of an accessory protein is a more likely scenario in the mutagenesis of these lesions in mammalian cells. However, hpol eta may play a role in correct bypass of the cross-links.