Axis inhibition protein 2 (AXIN2) polymorphisms may be a risk factor for selective tooth agenesis

Selective tooth agenesis is the most common developmental abnormality of the human dentition. To date, this abnormality has been associated only with mutations in MSX1 and PAX9 mutations, however it has recently been suggested that mutations of axis inhibition protein 2 (AXIN2) may also contribute to this complex anomaly. The protein product of this gene is a negative regulator of the Wnt-signaling pathway. We searched for AXIN2 variants in a group of patients with tooth agenesis who did not have mutations of MSX1 and PAX9. Using multi-temperature single-stranded conformational polymorphism and sequencing analysis, we identified three novel AXIN2 gene variants: c.956+16A > G, c.1060-17C > T and c.2062C > T. We also observed that individuals carrying the c.956+16G and c.2062T alleles exhibited an increased risk of tooth agenesis. The calculated odds ratio was 2.94 (95% CI 1.104-7.816; p = 0.026; p(corr) = 0.234) and 4.01 (95% CI 1.563-10.301; p = 0.002; p(corr) = 0.018), respectively. Moreover, we found that the c.2062C > T transition may change exon splice enhancer-specific binding sites of the protein splicing regulators SC35 and SF2/ASF. This alternation may negatively affect the splicing process and cellular concentration of AXIN2 protein. Our findings suggest that AXIN2 polymorphic variants may be associated with both hypodontia and oligodontia.

[Genetic polymorphisms of GSTM1 and GSTT1 in mothers of children with isolated cleft lip with or without cleft palate]

Orofacial clefts are one of the most common developmental malformations (OMIM #119530, #119540), which aetiology is very complex and associated with both genetic and environmental factors. One of the main environmental factors increasing the risk of having a child with an oral cleft is maternal cigarette smoking. The effect of maternal smoking may be modified by genes involved in biotransformation of toxic compounds derived from tobacco. Very important role in this process is played by S-glutathione transferase M1 (GSTM1) and S-glutathione transferase T1 (GSTT1) which conjugate glutathione with xenobiotics and promote their removal from human body. The aim of this study was frequency analysis of homozygous deletion of GSTM1 and GSTT1 genes in women having infants with ororfacial clefts and in control group. In this case-control study we used DNA isolated from peripheral blood lymphocytes of 121 mothers having children with isolated cleft lip with or without cleft palate and from 80 control mothers. The common deletions of GSTM1 and GSTT1 were determined by polymerase chain reaction and agarose gel separation. The prevalence of genotype GSTM1(-)/GSTT1(-) was higher in mothers of children with cleft (6.6%) compared to controls (3.7%, p>0.05). Among multiparous mothers of children with cleft (one child with birth defect and at least 2 healthy children, mean number of children - 4) the prevalence of genotype GSTM1(+)/GSTTI(+) was significantly reduced (31.0% vs. 58.7%, p=0.011). A significantly increased risk of giving birth to a child with cleft was found in multiparous subgroup of mothers with GSTM1(-)/GSTT1(-) and GSTM1(-)/ GSTT1(+) genotypes as compared to those with GSTM1(+)IGSTT1(+) genotype (OR 6.96; 95%CI: 1.33-36.57, p<0.01 i 3.05; 95%CI: 1.153-8.05, p<0.02 respectively). We did not observe a significant correlation between smoking status, GSTM1/GSTT1 genotypes and risk of orofacial clefts. Our results suggest that homozygous deletions of GSTM1 and GSTT1 in mother genome might increase the risk of having child with cleft lip with or without cleft palate.

Monitoring the mitochondrial transmembrane potential with the JC-1 fluorochrome in programmed cell death during mesophyll leaf senescence

Analysis of the mitochondrial transmembrane potential (Delta Psi(m)) with the help of the JC-1 fluorochrome (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide) during mesophyll leaf senescence was performed in order to determine whether a reduction of Delta Psi(m) takes place during mesophyll senescence and whether plant mitochondria, like mammalian ones, might be involved in the induction of programmed cell death. Fluorescence analysis of mesophyll protoplasts of Pisum sativum in a confocal microscope, fluorescent spectra analysis and time dependence of fluorescence intensity of monomers and of J-aggregates revealed that JC-1 is incorporated and accumulated specifically in plant mitochondria. Analysis of Delta Psi(m) during mesophyll protoplast senescence revealed that two subpopulations of mitochondria which differ in Delta Psi(m) exist in all analyzed stages of leaf senescence. The first subpopulation contains mitochondria with red fluorescence of J-aggregates due to an unperturbed high Delta Psi(m). The second subpopulation comprises mitochondria with green fluorescence of monomers due to a low Delta Psi(m), proving total depolarization of mitochondrial membranes. Fluorescence analysis demonstrated that even in the latest analyzed stages of leaf senescence, mitochondria with a high Delta Psi(m) still exist. Fluorometric measurements revealed that the fluorescence intensity of J-aggregates decreases with the age of plants, which indicates that a reduction of Delta Psi(m) during the mesophyll senescence process takes place; however, it does not take place within the whole population of mitochondria of the same protoplast. The reason of this can be due to a dramatic reorganization of mitochondria in mesophyll cells and the appearance of large mitochondria with local heterogeneity of Delta Psi(m) in the oldest analyzed stages. All mitochondria in every stage of senescence maintained their membrane organization even when their size, distribution, and spatial organization in protoplasts changed dramatically. We stated that the reduction of Delta Psi(m) does not directly induce programmed cell death in mesophyll cells, as opposed to animal apoptosis.

Expression of modified Cry1Ac gene of Bacillus thuringiensis in transgenic tobacco plants

Several mutations were introduced into the Cry1Ac toxin gene, resulting in four variants with altered sequences that were responsible for low expression of the toxin in transgenic plants. These variants were as follows: V1, with modified three A/T-rich regions, including the first signal of transcription termination; V2, with modified five putative polyadenylation signals (polyadenylation signals PAS) and the second signal of transcription termination; V3, with four initial AUUUA motifs; V4, with modification of six PASs, four AUUUA motifs, as well as the first and the second signals of transcription termination. The modified variants and the initial WT gene were cloned into the binary vector pBI121 and introduced into tobacco plants (Nicotiana tabacum) by Agrobacterium tumefaciens-mediated transformation. The presence of transgenes in the tobacco plants was confirmed by the polymerase chain reaction (PCR) method. The expression of particular variants of the Cry1Ac gene in tobacco was assayed using Western blotting with antibodies against the domain II of the Cry1Ac toxin. The average expression of WT was estimated to be 0.0025% of soluble proteins, and the expression levels of modified variants were 0.004%, 0.0098%, 0.0125%, and 0.0043% for V1, V2, V3, and V4, respectively. In this article we described the construction of a variant of the Cry1Ac gene (V3) with 12 point mutations leading to an average level of expression in transgenic plants five times higher than that observed in the case of the WT gene. Our results have shown for the first time that the modification of AUUUA sequences has a significant effect on the expression of the Cry1Ac gene in transgenic plants.

Molecular basis of non-syndromic tooth agenesis: mutations of MSX1 and PAX9 reflect their role in patterning human dentition

Tooth agenesis constitutes the most common anomalies of dental development in man. Despite this, little is known about the genetic defects responsible for this complex condition. To date, the only genes associated with the non-syndromic form of tooth agenesis are MSX1 and PAX9, which encode transcription factors that play a critical role during tooth development. This paper aims to review current literature about the molecular mechanisms responsible for selective tooth agenesis in humans.

Novel mutation in the paired box sequence of PAX9 gene in a sporadic form of oligodontia

Tooth development is regulated through a series of reciprocal interactions between the dental epithelium and mesenchyme and requires protein products of a number of genes. It has been reported that selective tooth agenesis is associated with mutations in human MSX and PAX9 genes. Mutational analysis of the two genes was performed in 25 individuals with familial or sporadic form of permanent tooth agenesis. Single-stranded conformational polymorphism analysis revealed no mutations in the entire coding sequence of the MSX1 gene. In PAX9, a novel, heterozygous G151A transition in the sequence encoding the paired domain of the PAX9 protein was detected in a patient with agenesis of third molars, second premolars and incisors, but not in her parents, the remaining patients or 162 individuals with normal dentition. This is the first de novo mutation described in PAX9. Our results support the view that mutations in PAX9 could constitute a causative factor of oligodontia. We hypothesize that the G151A transition in PAX9 might be responsible for the sporadic form of tooth agenesis in this patient.

The novel polymorphic variants within the paired box of the PAX9 gene are associated with selective tooth agenesis

It has been reported that two genes MSX1 and PAX9, which encode transcription factors, are associated with selective tooth agenesis. Expression of these genes specifically marks the regions of the mesenchyme where the tooth buds are formed. A mutation in the MSX1 gene, detected in a single family, resulting in an Arg-->Pro substitution in the homeodomain of the protein product of this gene has previously been associated with the deficiency of second premolars and third molars. However, mutations of the MSX1 gene were excluded in the patients with agenesis of the other type of teeth. In a single family with the lack of first and second molars, a mutation in the PAX9 gene was found. In our group of patients with the deficiency of various teeth, in 20% of the patients and their relatives sequence analysis revealed a C-->T transition in the coding sequence of the PAX9 gene. However, this polymorphism does not alter amino acid sequence of the protein product of this gene.