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Model-based multifacet clustering with high-dimensional omics applications.

High-dimensional omics data often contain intricate and multifaceted information, resulting in the coexistence of multiple plausible sample partitions based on different subsets of selected features. Conventional clustering methods typically yield only one clustering solution, limiting their capacity to fully capture all facets of cluster structures in high-dimensional data. To address this challenge, we propose a model-based multifacet clustering (MFClust) method based on a mixture of Gaussian mixture models, where the former mixture achieves facet assignment for gene features and the latter mixture determines cluster assignment of samples. We demonstrate superior facet and cluster assignment accuracy of MFClust through simulation studies. The proposed method is applied to three transcriptomic applications from postmortem brain and lung disease studies. The result captures multifacet clustering structures associated with critical clinical variables and provides intriguing biological insights for further hypothesis generation and discovery.

Humans↗

Multiple methylation-free islands flank a small breakpoint cluster region on 11p13 in the t(11;14)(p13;q11) translocation.

The t(11;14)(p13;q11) translocation is one of the most frequent chromosomal abnormalities in T-cell acute lymphoblastic leukemia (ALL). Ten different leukemias carrying this translocation have been analysed and all 10 breakpoints fall within a region of less than 25 kb on chromosome band 11p13. We have used PFGE and cosmid cloning to assess the presence of potential genes by analysing methylation-free islands in the vicinity. Four methylation-free islands, within 270 kb, flank the t(11;14)-associated breakpoint cluster region (T-ALLbcr), one occurring about 25 kb on the telomeric side and one about 100 kb on the centromeric side of the T-ALLbcr. Evidence for eight further methylation-free islands on both sides of the T-ALLbcr region is also presented. Thus multiple methylation-free islands exist on 11p13 flanking the t(11;14)(p13;q11) translocation-associated breakpoint cluster region, representing multiple potential transcription units whose chromosomal environment is altered by chromosome translocation.

Chromosomes, Human, Pair 11↗

Differential profiles of verbal learning in traumatic brain injury.

Several recent investigations have utilized cluster analytic procedures to elucidate profiles of verbal learning on the California Verbal Learning Test following traumatic brain injury (TBI). Although the results of these studies have contributed to our understanding of verbal learning following TBI, limitations in sample composition and methodology render the results difficult to evaluate. The current study provides an analysis of verbal learning clusters in the most comprehensive sample (n = 160) of TBI patients reported thus far. Results obtained from multiple hierarchical agglomerative clustering procedures suggested the presence of two distinct clusters, the first consisting of performance patterns falling within normal limits and the second consisting of moderate-to-severe impairment. Two iterative partitioning analyses further suggested a reliable solution with better-than-chance agreement (kappa coefficients >.85, p <.001). Thus, it is concluded that a two-cluster classification solution provides a parsimonious understanding of verbal learning profiles after TBI.

Adult↗

Microswitch clusters to enhance non-spastic response schemes with students with multiple disabilities.

PURPOSE: The study explored whether the use of microswitch clusters could enhance the performance of correct (non-spastic) response schemes by two students with multiple disabilities. METHOD: The study started with baseline on the two responses selected for each student. Then, intervention was implemented on the first response. This was followed by new baseline and intervention on the second response. Subsequently, intervention sessions on the two responses were alternated. Post-intervention checks were carried out over periods of 4 and 2.5 months. RESULTS AND CONCLUSIONS: Both students had an increase in correct response schemes and, conversely, a decline in spastic response schemes. The importance and practicality of microswitch clusters to enhance appropriate responding in students with multiple disabilities were discussed.

Adolescent↗

BOLD-fMRI of PTZ-induced seizures in rats.

PURPOSE: To develop a non-invasive method for exploring seizure initiation and propagation in the brain of intact experimental animals. METHODS: We have developed and applied a model-independent statistical method--Hierarchical Cluster Analysis (HCA)--for analyzing BOLD-fMRI data following administration of pentylenetetrazol (PTZ) to intact rats. HCA clusters voxels into groups that share similar time courses and magnitudes of signal change, without any assumptions about when and/or where the seizure begins. RESULTS: Epileptiform spiking activity was monitored by EEG (outside the magnet) following intravenous PTZ (IV-PTZ; n=4) or intraperitoneal PTZ administration (IP-PTZ; n=5). Onset of cortical spiking first occurred at 29+/-16 s (IV-PTZ) and 147+/-29 s (IP-PTZ) following drug delivery. HCA of fMRI data following IV-PTZ (n=4) demonstrated a single dominant cluster, involving the majority of the brain and first activating at 27+/-23s. In contrast, IP-PTZ produced multiple, relatively small, clusters with heterogeneous time courses that varied markedly across animals (n=5); activation of the first cluster (involving cortex) occurred at 130+/-59 s. With both routes of PTZ administration, the timing of the fMRI signal increase correlated with onset of EEG spiking. CONCLUSIONS: These experiments demonstrate that fMRI activity associated with seizure activity can be analyzed with a model-independent statistical method. HCA indicated that seizure initiation in the IV- and IP-PTZ models involves multiple regions of sensitivity that vary with route of drug administration and that show significant variability across animal subjects. Even given this heterogeneity, fMRI shows clear differences that are not apparent with typical EEG monitoring procedures, in the activation patterns between IV and IP-PTZ models. These results suggest that fMRI can be used to assess different models and patterns of seizure activation.

Animals↗

A Bayesian approach for joint modeling of cluster size and subunit-specific outcomes.

In applications that involve clustered data, such as longitudinal studies and developmental toxicity experiments, the number of subunits within a cluster is often correlated with outcomes measured on the individual subunits. Analyses that ignore this dependency can produce biased inferences. This article proposes a Bayesian framework for jointly modeling cluster size and multiple categorical and continuous outcomes measured on each subunit. We use a continuation ratio probit model for the cluster size and underlying normal regression models for each of the subunit-specific outcomes. Dependency between cluster size and the different outcomes is accommodated through a latent variable structure. The form of the model facilitates posterior computation via a simple and computationally efficient Gibbs sampler. The approach is illustrated with an application to developmental toxicity data, and other applications, to joint modeling of longitudinal and event time data, are discussed.

Animals↗

Automatic sorting of multiple unit neuronal signals in the presence of anisotropic and non-Gaussian variability.

Neuronal noise sources and systematic variability in the shape of a spike limit the ability to sort multiple unit waveforms recorded from nervous tissue into their single neuron constituents. Here we present a procedure to efficiently sort spikes in the presence of noise that is anisotropic, i.e., dominated by particular frequencies, and whose amplitude distribution may be non-Gaussian, such as occurs when spike waveforms are a function of interspike interval. Our algorithm uses a hierarchical clustering scheme. First, multiple unit records are sorted into an overly large number of clusters by recursive bisection. Second, these clusters are progressively aggregated into a minimal set of putative single units based on both similarities of spike shape as well as the statistics of spike arrival times, such as imposed by the refractory period. We apply the algorithm to waveforms recorded with chronically implanted micro-wire stereotrodes from neocortex of behaving rat. Natural extension of the algorithm may be used to cluster spike waveforms from records with many input channels, such as those obtained with tetrodes and multiple site optical techniques.

Action Potentials↗

Hierarchical clustering analysis of tissue microarray immunostaining data identifies prognostically significant groups of breast carcinoma.

Prognostically relevant cluster groups, based on gene expression profiles, have been recently identified for breast cancers, lung cancers, and lymphoma. Our aim was to determine whether hierarchical clustering analysis of multiple immunomarkers (protein expression profiles) improves prognostication in patients with invasive breast cancer. A cohort of 438 sequential cases of invasive breast cancer with median follow-up of 15.4 years was selected for tissue microarray construction. A total of 31 biomarkers were tested by immunohistochemistry on these tissue arrays. The prognostic significance of individual markers was assessed by using Kaplan-Meier survival estimates and log-rank tests. Seventeen of 31 markers showed prognostic significance in univariate analysis (P < or = 0.05) and 4 markers showed a trend toward significance (P < or = 0.2). Unsupervised hierarchical clustering analysis was done by using these 21 immunomarkers, and this resulted in identification of three cluster groups with significant differences in clinical outcome. chi2 analysis showed that expression of 11 markers significantly correlated with membership in one of the three cluster groups. Unsupervised hierarchical clustering analysis with this set of 11 markers reproduced the same three prognostically significant cluster groups identified by using the larger set of markers. These cluster groups were of prognostic significance independent of lymph node metastasis, tumor size, and tumor grade in multivariate analysis (P=0.0001). The cluster groups were as powerful a prognostic indicator as lymph node status. This work demonstrates that hierarchical clustering of immunostaining data by using multiple markers can group breast cancers into classes with clinical relevance and is superior to the use of individual prognostic markers.

Adult↗

PHOG-BLAST--a new generation tool for fast similarity search of protein families.

BACKGROUND: The need to compare protein profiles frequently arises in various protein research areas: comparison of protein families, domain searches, resolution of orthology and paralogy. The existing fast algorithms can only compare a protein sequence with a protein sequence and a profile with a sequence. Algorithms to compare profiles use dynamic programming and complex scoring functions. RESULTS: We developed a new algorithm called PHOG-BLAST for fast similarity search of profiles. This algorithm uses profile discretization to convert a profile to a finite alphabet and utilizes hashing for fast search. To determine the optimal alphabet, we analyzed columns in reliable multiple alignments and obtained column clusters in the 20-dimensional profile space by applying a special clustering procedure. We show that the clustering procedure works best if its parameters are chosen so that 20 profile clusters are obtained which can be interpreted as ancestral amino acid residues. With these clusters, only less than 2% of columns in multiple alignments are out of clusters. We tested the performance of PHOG-BLAST vs. PSI-BLAST on three well-known databases of multiple alignments: COG, PFAM and BALIBASE. On the COG database both algorithms showed the same performance, on PFAM and BALIBASE PHOG-BLAST was much superior to PSI-BLAST. PHOG-BLAST required 10-20 times less computer memory and computation time than PSI-BLAST. CONCLUSION: Since PHOG-BLAST can compare multiple alignments of protein families, it can be used in different areas of comparative proteomics and protein evolution. For example, PHOG-BLAST helped to build the PHOG database of phylogenetic orthologous groups. An essential step in building this database was comparing protein complements of different species and orthologous groups of different taxons on a personal computer in reasonable time. When it is applied to detect weak similarity between protein families, PHOG-BLAST is less precise than rigorous profile-profile comparison method, though it runs much faster and can be used as a hit pre-selecting tool.

Algorithms↗

Antimicrobial resistance islands: resistance gene clusters in Salmonella chromosome and plasmids.

Genes conferring simultaneous resistance to different classes of antimicrobials, confer a selective advantage to the host, particularly when those corresponding antibiotics are administered. Multiple resistance genes clustered within the same genetic locus (resistance island) can be transferred en bloc to other organisms. In this chapter we review novel multidrug resistance islands recently described in Salmonella.

Anti-Bacterial Agents↗

Clustered damages and total lesions induced in DNA by ionizing radiation: oxidized bases and strand breaks.

Ionizing radiation induces both isolated DNA lesions and clustered damages-multiple closely spaced lesions (strand breaks, oxidized purines, oxidized pyrimidines, or abasic sites within a few helical turns). Such clusters are postulated to be difficult to repair and thus potentially lethal or mutagenic lesions. Using highly purified enzymes that cleave DNA at specific classes of damage and electrophoretic assays developed for quantifying isolated and clustered damages in high molecular length genomic DNAs, we determined the relative frequencies of total lesions and of clustered damages involving both strands, and the composition and origin of such clusters. The relative frequency of isolated vs clustered damages depends on the identity of the lesion, with approximately 15-18% of oxidized purines, pyrimidines, or abasic sites in clusters recognized by Fpg, Nth, or Nfo proteins, respectively, but only about half that level of frank single strand breaks in double strand breaks. Oxidized base clusters and abasic site clusters constitute about 80% of complex damages, while double strand breaks comprise only approximately 20% of the total. The data also show that each cluster results from a single radiation (track) event, and thus clusters will be formed at low as well as high radiation doses.

DNA↗

Improved rosenbluth monte carlo scheme for cluster counting and lattice animal enumeration

We describe an algorithm for the Rosenbluth Monte Carlo enumeration of clusters and lattice animals. The method may also be used to calculate associated properties such as moments or perimeter multiplicities of the clusters. The scheme is an extension of the Rosenbluth method for growing polymer chains and is a simplification of a scheme reported earlier by one of the authors. The algorithm may be used to obtain a Monte Carlo estimate of the number of distinct lattice animals on any lattice topology. The method is validated against exact and Monte Carlo enumerations for clusters up to size 50, on a two dimensional square lattice and three dimensional simple cubic lattice. The method may be readily adapted to yield Boltzmann weighted averages over clusters.

Journal Article↗

Diffuse panbronchiolitis with multiple tumorlets. A quantitative study of the Kultschitzky cells and the clusters.

An autopsy case of diffuse panbronchiolitis with incidentally observed multiple tumorlets was reported. Quantitative study revealed the distribution and number of single Kultschitzky cell and its cluster. These cells were more frequently observed in the present case than in 20 control cases, and moreover, they tended to occur more frequently in the pulmonary segment in which tumorlets were found and there was an apparent transition of them into tumorlets. Immunohistochemically, gastrin-releasing peptide, calcitonin, and serotonin were demonstrable in the cells which consisted of both tumorlets and Kultschitzky cell clusters. It is suggested that the Kultschitzky cell is a precursor cell of the tumorlet and that tumorlet is benign, being hyperplastic in nature.

Bronchial Neoplasms↗

Further evaluation of microswitch clusters to enhance hand response and head control in persons with multiple disabilities.

This study was a further evaluation of microswitch clusters (combinations of two microswitches) to improve adaptive responding together with correct head position in two persons with multiple disabilities. The two participants were 19.7 and 6.6 yr. old and had profound intellectual disabilities, spastic tetraparesis, and visual impairment. They were initially taught an adaptive hand response that activated a pressure microswitch and produced favorite stimulation. Thereafter, their performance of the hand response produced favorite stimulation only when it was combined with a correct head position (detected through a mercury microswitch). Analysis showed that both participants increased the frequency of the hand response and, subsequently, the percentage of times they emitted this response in combination with correct (upright) head position. In essence, they were able to coordinate constructive occupation with exercise of appropriate posture. Performance was maintained at a 2-mo. postintervention check.

Adult↗

Macrolide inactivation gene cluster mphA-mrx-mphR adjacent to a class 1 integron in Aeromonas hydrophila isolated from a diarrhoeic pig in Oklahoma.

OBJECTIVES: To characterize a multidrug-resistant Aeromonas hydrophila isolate (CVM861) that possesses a high-level macrolide inactivation gene cluster (mphA-mrx-mphR), previously only reported in Escherichia coli. METHODS: PCR fragment length mapping, gene sequencing and Southern blotting were used to map the mphA-mrx-mphR gene cluster and flanking elements in CVM861. Conjugation experiments were done to determine whether the multidrug resistance genetic element was mobile. RESULTS: The mphA-mrx-mphR gene cluster mapped downstream of a class 1 integron and upstream of an aph(3') gene, and was present on a Tn21-like element. The gene order determined by sequencing was intI1-dhfrXII-orfF-aadA2-qacDeltaE-sul1-orf5Delta178-tnpA-mphR-mrx-mphA. Horizontal transmission of high-level macrolide resistance from CVM861 to E. coli 47011 was inconsistent; however, a composite plasmid possessing the mphA gene cluster was transferred at a conjugation frequency of 2.02 x 10(-5) per recipient. CONCLUSIONS: An mphA-mrx-mphR gene cluster was present downstream of the In2 integron located on a Tn21-like transposon in an A. hydrophila isolate. Whether this recombination event resulted in the truncation of the orf5 sequence is unknown. The presence of other resistance genes downstream of the mphA-mrx-mphR gene cluster suggests that multiple recombination events have occurred on this genetic element. This is the first known report of the mphA-mrx-mphR gene cluster carried by A. hydrophila and the first known isolation of this cluster in the United States.

Aeromonas hydrophila↗

Proposed involvement of a soluble methane monooxygenase homologue in the cyclohexane-dependent growth of a new Brachymonas species.

High-throughput mRNA differential display (DD) was used to identify genes induced by cyclohexane in Brachymonas petroleovorans CHX, a recently isolated beta-proteobacterium that grows on cyclohexane. Two metabolic gene clusters were identified multiple times in independent reverse transcription polymerase chain reactions (RT-PCR) in the course of this DD experiment. These clusters encode genes believed to be required for cyclohexane metabolism. One gene cluster (8 kb) encodes the subunits of a multicomponent hydroxylase related to the soluble butane of Pseudomonas butanovora and methane monooxygenases (sMMO) of methanotrophs. We propose that this butane monooxygenase homologue carries out the oxidation of cyclohexane into cyclohexanol during growth. A second gene cluster (11 kb) contains almost all the genes required for the oxidation of cyclohexanol to adipic acid. Real-time PCR experiments confirmed that genes from both clusters are induced by cyclohexane. The role of the Baeyer-Villiger cyclohexanone monooxygenase of the second cluster was confirmed by heterologous expression in Escherichia coli.

Adipates↗

Ancient genomic architecture for mammalian olfactory receptor clusters.

BACKGROUND: Mammalian olfactory receptor (OR) genes reside in numerous genomic clusters of up to several dozen genes. Whole-genome sequence alignment nets of five mammals allow their comprehensive comparison, aimed at reconstructing the ancestral olfactory subgenome. RESULTS: We developed a new and general tool for genome-wide definition of genomic gene clusters conserved in multiple species. Syntenic orthologs, defined as gene pairs showing conservation of both genomic location and coding sequence, were subjected to a graph theory algorithm for discovering CLICs (clusters in conservation). When applied to ORs in five mammals, including the marsupial opossum, more than 90% of the OR genes were found within a framework of 48 multi-species CLICs, invoking a general conservation of gene order and composition. A detailed analysis of individual CLICs revealed multiple differences among species, interpretable through species-specific genomic rearrangements and reflecting complex mammalian evolutionary dynamics. One significant instance involves CLIC #1, which lacks a human member, implying the human-specific deletion of an OR cluster, whose mouse counterpart has been tentatively associated with isovaleric acid odorant detection. CONCLUSION: The identified multi-species CLICs demonstrate that most of the mammalian OR clusters have a common ancestry, preceding the split between marsupials and placental mammals. However, only two of these CLICs were capable of incorporating chicken OR genes, parsimoniously implying that all other CLICs emerged subsequent to the avian-mammalian divergence.

Animals↗