Search tips
Search criteria

Results 1-9 (9)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
1.  Transcriptome analysis of chestnut (Castanea sativa) tree buds suggests a putative role for epigenetic control of bud dormancy 
Annals of Botany  2011;108(3):485-498.
Background and Aims
Recent papers indicated that epigenetic control is involved in transitions in bud dormancy, purportedly controlling gene expression. The present study aimed to identify genes that are differentially expressed in dormant and non-dormant Castanea sativa buds.
Two suppression subtractive hybridization cDNA libraries were constructed to characterize the transcriptomes of dormant apical buds of C. sativa, and buds in which dormancy was released.
Key Results
A total of 512 expressed sequence tags (ESTs) were generated in a forward and reverse subtractive hybridization experiment. Classification of these ESTs into functional groups demonstrated that dormant buds were predominantly characterized by genes associated with stress response, while non-dormant buds were characterized by genes associated with energy, protein synthesis and cellular components for development and growth. ESTs for a few genes involved in different forms of epigenetic modification were found in both libraries, suggesting a role for epigenetic control in bud dormancy different from that in growth. Genes encoding histone mono-ubiquitinase HUB2 and histone acetyltransferase GCN5L were associated with dormancy, while a gene encoding histone H3 kinase AUR3 was associated with growth. Real-time RT-PCR with a selection of genes involved in epigenetic modification and stress tolerance confirmed the expression of the majority of investigated genes in various stages of bud development, revealing a cyclical expression pattern concurring with the growth seasons for most genes. However, senescing leaves also showed an increased expression of several of the genes associated with dormancy, implying pleiotropy. Furthermore, a comparison between these subtraction cDNA libraries and the poplar bud dormancy transcriptome and arabidopsis transcriptomes for seed dormancy and non-dormancy indicated a common basis for dormancy in all three systems.
Bud dormancy and non-dormancy in C. sativa were characterized by distinct sets of genes and are likely to be under different epigenetic control.
PMCID: PMC3158698  PMID: 21803738
Bud dormancy; Castanea sativa; epigenetic modification; gene expression; leaf development; seed dormancy; senescence; subtraction library
2.  Evolution and management of de novo neoplasm post-liver transplantation: a 20-year experience from a single European centre 
Hepatology International  2010;5(2):707-715.
Survival post-liver transplantation (LT) has improved; however, patients are considered at the, risk of malignancy due to prolonged immunosuppression. The long-term outcome of patients developing de novo neoplasm (DN) at our centre was evaluated.
Between October 1988 and December 2007, 800 LT were performed in 742 patients. Patients were divided into two study periods according to the time of LT; first: October 1988–December 1995; second: January 1996–December 2007.
After a mean follow-up of 5 ± 4.6 years, 71 DN (9.5%) were detected in 742 patients. The cumulative risk of DN development increased with the time from LT although no differences at 3, 5, and 10 years were found when first and second periods were compared (3, 7, 16% vs. 2, 4, 11%, respectively; p = 0.4). DN incidence was higher in the first compared with the second period (10.7 vs. 7.8%; p < 0.04); no significant differences were observed in mortality rate (50 vs. 27%; p = 0.052). Actuarial patient survival post-DN at 1, 3, and 5 years: 67, 48, 45% versus 82, 71, 65%, in the first versus second period, respectively, p < 0.04.
DN incidence has decreased in recent years; however, as survival post-LT increases, so does the incidence of DN. Surveillance programmes are necessary to diagnose DN at early stages.
PMCID: PMC3090551  PMID: 21484107
De novo neoplasms; Immunosuppression; Surveillance; Survival
3.  An unsupervised strategy for biomedical image segmentation 
Many segmentation techniques have been published, and some of them have been widely used in different application problems. Most of these segmentation techniques have been motivated by specific application purposes. Unsupervised methods, which do not assume any prior scene knowledge can be learned to help the segmentation process, and are obviously more challenging than the supervised ones. In this paper, we present an unsupervised strategy for biomedical image segmentation using an algorithm based on recursively applying mean shift filtering, where entropy is used as a stopping criterion. This strategy is proven with many real images, and a comparison is carried out with manual segmentation. With the proposed strategy, errors less than 20% for false positives and 0% for false negatives are obtained.
PMCID: PMC3170003  PMID: 21918628
segmentation; mean shift; unsupervised segmentation; entropy
4.  Dynamics of DNA methylation and Histone H4 acetylation during floral bud differentiation in azalea 
BMC Plant Biology  2010;10:10.
The ability to control the timing of flowering is a key strategy for planning production in ornamental species such as azalea, however it requires a thorough understanding of floral transition. Floral transition is achieved through a complex genetic network and regulated by multiple environmental and endogenous cues. Dynamic changes between chromatin states facilitating or inhibiting DNA transcription regulate the expression of floral induction pathways in response to environmental and developmental signals. DNA methylation and histone modifications are involved in controlling the functional state of chromatin and gene expression.
The results of this work indicate that epigenetic mechanisms such as DNA methylation and histone H4 acetylation have opposite and particular dynamics during the transition from vegetative to reproductive development in the apical shoots of azalea. Global levels of DNA methylation and histone H4 acetylation as well as immunodetection of 5-mdC and acetylated H4, in addition to a morphological study have permitted the delimitation of four basic phases in the development of the azalea bud and allowed the identification of a stage of epigenetic reprogramming which showed a sharp decrease of whole DNA methylation similar to that is defined in other developmental processes in plants and in mammals.
The epigenetic control and reorganization of chromatin seem to be decisive for coordinating floral development in azalea. DNA methylation and H4 deacetylation act simultaneously and co-ordinately, restructuring the chromatin and regulating the gene expression during soot apical meristem development and floral differentiation.
PMCID: PMC2923518  PMID: 20067625
6.  Comparison of BGM and PLC/PRC/5 Cell Lines for Total Culturable Viral Assay of Treated Sewage▿  
The objective of this study was to compare PLC/PRF/5 and BGM cell lines for use in a total culturable viral assay (TCVA) of treated sewage effluents. Samples were collected before and after chlorination from an activated sludge wastewater treatment plant and from the effluent of a high-rate enhanced flocculation system, followed by UV light disinfection. Cell monolayers were observed for cytopathic effect (CPE) after two passages of 14 days each. Monolayers exhibiting viral CPE were tested for the presence of adenoviruses and enteroviruses by PCR or reverse transcription-PCR. Eight percent of the samples exhibited CPE on BGM cells, and 57% showed CPE on PLC/PRF/5 cells. Only enteroviruses were detected on the BGM cells, while 30% and 52% of the samples were positive for enteroviruses and adenoviruses, respectively, on the PLC/PRF/5 cells. Thirty percent of the samples were positive for both adenoviruses and enteroviruses in chlorinated activated sludge effluent. Thirty percent of the samples were positive for adenoviruses in the UV treatment effluent, but no enteroviruses were detected. In conclusion, the PLC/PRF/5 cells were more susceptible than BGM cells to viruses found in treated sewage. The use of BGM cells for TCVA may underestimate viral concentration in sewage effluent samples. The PLC/PRF/5 cells were more susceptible to adenoviruses, which is important in the evaluation of UV disinfection systems because adenoviruses are highly resistant to UV inactivation.
PMCID: PMC2394896  PMID: 18326686
7.  Promoter DNA Hypermethylation and Gene Repression in Undifferentiated Arabidopsis Cells 
PLoS ONE  2008;3(10):e3306.
Maintaining and acquiring the pluripotent cell state in plants is critical to tissue regeneration and vegetative multiplication. Histone-based epigenetic mechanisms are important for regulating this undifferentiated state. Here we report the use of genetic and pharmacological experimental approaches to show that Arabidopsis cell suspensions and calluses specifically repress some genes as a result of promoter DNA hypermethylation. We found that promoters of the MAPK12, GSTU10 and BXL1 genes become hypermethylated in callus cells and that hypermethylation also affects the TTG1, GSTF5, SUVH8, fimbrin and CCD7 genes in cell suspensions. Promoter hypermethylation in undifferentiated cells was associated with histone hypoacetylation and primarily occurred at CpG sites. Accordingly, we found that the process specifically depends on MET1 and DRM2 methyltransferases, as demonstrated with DNA methyltransferase mutants. Our results suggest that promoter DNA methylation may be another important epigenetic mechanism for the establishment and/or maintenance of the undifferentiated state in plant cells.
PMCID: PMC2556100  PMID: 18827894
8.  Binarization of medical images based on the recursive application of mean shift filtering : Another algorithm 
Binarization is often recognized to be one of the most important steps in most high-level image analysis systems, particularly for object recognition. Its precise functioning highly determines the performance of the entire system. According to many researchers, segmentation finishes when the observer’s goal is satisfied. Experience has shown that the most effective methods continue to be the iterative ones. However, a problem with these algorithms is the stopping criterion. In this work, entropy is used as the stopping criterion when segmenting an image by recursively applying mean shift filtering. Of this way, a new algorithm is introduced for the binarization of medical images, where the binarization is carried out after the segmented image was obtained. The good performance of the proposed method; that is, the good quality of the binarization, is illustrated with several experimental results. In this paper a comparison was carried out among the obtained results with this new algorithm with respect to another developed by the author and collaborators previously and also with Otsu’s method.
PMCID: PMC3169934  PMID: 21918602
image segmentation; mean shift; algorithm; entropy; Otsu’s method
9.  Statistical Analyses: Possible Reasons for Unreliability of Source Tracking Efforts 
Analyses for the presence of indicator organisms provide information on the microbiological quality of water. Indicator organisms recommended by the United States Environmental Protection Agency for monitoring the microbiological quality of water include Escherichia coli, a thermotolerant coliform found in the feces of warm-blooded animals. These bacteria can also be isolated from environmental sources such as the recreational and pristine waters of tropical rain forests in the absence of fecal contamination. In the present study, E. coli isolates were compared to E. coli K12 (ATCC 29425) by restriction fragment length polymorphism using pulsed-field gel electrophoresis. Theoretically, genomic DNA patterns generated by PFGE are highly specific for the different isolates of an organism and can be used to identify variability between environmental and fecal isolates. Our results indicate a different band pattern for almost every one of the E. coli isolates analyzed. Cluster analysis did not show any relations between isolates and their source of origin. Only the discriminant function analysis grouped the samples with the source of origin. The discrepancy observed between the cluster analysis and discriminant function analysis relies on their mathematical basis. Our validation analyses indicate the presence of an artifact (i.e., grouping of environmental versus fecal samples as a product of the statistical analyses used and not as a result of separation in terms of source of origin) in the classification results; therefore, the large genetic heterogeneity observed in these E. coli populations makes the grouping of isolates by source rather difficult, if not impossible.
PMCID: PMC1183283  PMID: 16085864

Results 1-9 (9)