chipenrich: Run ChIP-Enrich on narrow genomic regions
In chipenrich: Gene Set Enrichment For ChIP-seq Peak Data

Description Usage Arguments Value ChIP-Enrich Method Choosing A Method Randomizations See Also Examples

ChIP-Enrich is designed for use with 1,000s or 10,000s of narrow peaks which results in fewer gene loci containing a peak overall. For example, ChIP-seq experiments for transcription factors. For more details, see the 'ChIP-Enrich Method' section below. For help choosing a method, see the 'Choosing A Method' section below, or see the vignette.

chipenrich(peaks, out_name = "chipenrich", out_path = getwd(),
  genome = supported_genomes(), genesets = c("GOBP", "GOCC", "GOMF"),
  locusdef = "nearest_tss", method = "chipenrich",
  mappability = NULL, fisher_alt = "two.sided", qc_plots = TRUE,
  min_geneset_size = 15, max_geneset_size = 2000,
  num_peak_threshold = 1, randomization = NULL, n_cores = 1)

`peaks`	Either a file path or a `data.frame` of peaks in BED-like format. If a file path, the following formats are fully supported via their file extensions: .bed, .broadPeak, .narrowPeak, .gff3, .gff2, .gff, and .bedGraph or .bdg. BED3 through BED6 files are supported under the .bed extension. Files without these extensions are supported under the conditions that the first 3 columns correspond to 'chr', 'start', and 'end' and that there is either no header column, or it is commented out. If a `data.frame` A BEDX+Y style `data.frame`. See `GenomicRanges::makeGRangesFromDataFrame` for acceptable column names.
`out_name`	Prefix string to use for naming output files. This should not contain any characters that would be illegal for the system being used (Unix, Windows, etc.) The default value is "chipenrich", and a file "chipenrich_results.tab" is produced. If `qc_plots` is set, then a file "chipenrich_qcplots.png" is produced containing a number of quality control plots. If `out_name` is set to NULL, no files are written, and results then must be retrieved from the list returned by `chipenrich`.
`out_path`	Directory to which results files will be written out. Defaults to the current working directory as returned by `getwd`.
`genome`	One of the `supported_genomes()`.
`genesets`	A character vector of geneset databases to be tested for enrichment. See `supported_genesets()`. Alternately, a file path to a a tab-delimited text file with header and first column being the geneset ID or name, and the second column being Entrez Gene IDs. For an example custom gene set file, see the vignette.
`locusdef`	One of: 'nearest_tss', 'nearest_gene', 'exon', 'intron', '1kb', '1kb_outside', '1kb_outside_upstream', '5kb', '5kb_outside', '5kb_outside_upstream', '10kb', '10kb_outside', '10kb_outside_upstream'. For a description of each, see the vignette or `supported_locusdefs`. Alternately, a file path for a custom locus definition. NOTE: Must be for a `supported_genome()`, and must have columns 'chr', 'start', 'end', and 'gene_id' or 'geneid'. For an example custom locus definition file, see the vignette.
`method`	A character string specifying the method to use for enrichment testing. Must be one of ChIP-Enrich ('chipenrich') (default), or Fisher's exact test ('fet').
`mappability`	One of `NULL`, a file path to a custom mappability file, or an `integer` for a valid read length given by `supported_read_lengths`. If a file, it should contain a header with two column named 'gene_id' and 'mappa'. Gene IDs should be Entrez IDs, and mappability values should range from 0 and 1. For an example custom mappability file, see the vignette. Default value is NULL.
`fisher_alt`	If method is 'fet', this option indicates the alternative for Fisher's exact test, and must be one of 'two-sided' (default), 'greater', or 'less'.
`qc_plots`	A logical variable that enables the automatic generation of plots for quality control.
`min_geneset_size`	Sets the minimum number of genes a gene set may have to be considered for enrichment testing.
`max_geneset_size`	Sets the maximum number of genes a gene set may have to be considered for enrichment testing.
`num_peak_threshold`	Sets the threshold for how many peaks a gene must have to be considered as having a peak. Defaults to 1. Only relevant for Fisher's exact test and ChIP-Enrich methods.
`randomization`	One of `NULL`, 'complete', 'bylength', or 'bylocation'. See the Randomizations section below.
`n_cores`	The number of cores to use for enrichment testing. We recommend using only up to the maximum number of physical cores present, as virtual cores do not significantly decrease runtime. Default number of cores is set to 1. NOTE: Windows does not support multicore enrichment.

A list, containing the following items:

`opts`	A data frame containing the arguments/values passed to `chipenrich`.
`peaks`	A data frame containing peak assignments to genes. Peaks which do not overlap a gene locus are not included. Each peak that was assigned to a gene is listed, along with the peak midpoint or peak interval coordinates (depending on which was used), the gene to which the peak was assigned, the locus start and end position of the gene, and the distance from the peak to the TSS. The columns are: peak_id an ID given to unique combinations of chromosome, peak start, and peak end. chr the chromosome the peak originated from. peak_start start position of the peak. peak_end end position of the peak. peak_midpoint the midpoint of the peak. gene_id the Entrez ID of the gene to which the peak was assigned. gene_symbol the official gene symbol for the gene_id (above). gene_locus_start the start position of the locus for the gene to which the peak was assigned (specified by the locus definition used.) gene_locus_end the end position of the locus for the gene to which the peak was assigned (specified by the locus definition used.) nearest_tss the closest TSS to this peak (for any gene, not necessarily the gene this peak was assigned to.) nearest_tss_gene the gene having the closest TSS to the peak (should be the same as gene_id when using the nearest TSS locus definition.) nearest_tss_gene_strand the strand of the gene with the closest TSS.
`peaks_per_gene`	A data frame of the count of peaks per gene. The columns are: gene_id the Entrez Gene ID. length the length of the gene's locus (depending on which locus definition you chose.) log10_length the log10(locus length) for the gene. num_peaks the number of peaks that were assigned to the gene, given the current locus definition. peak whether or not the gene is considered to have a peak, as defined by `num_peak_threshold`.
`results`	A data frame of the results from performing the gene set enrichment test on each geneset that was requested (all genesets are merged into one final data frame.) The columns are: Geneset.ID the identifier for a given gene set from the selected database. For example, GO:0000003. Geneset.Type specifies from which database the Geneset.ID originates. For example, "Gene Ontology Biological Process." Description gives a definition of the geneset. For example, "reproduction." P.Value the probability of observing the degree of enrichment of the gene set given the null hypothesis that peaks are not associated with any gene sets. FDR the false discovery rate proposed by Bejamini \& Hochberg for adjusting the p-value to control for family-wise error rate. Odds.Ratio the estimated odds that peaks are associated with a given gene set compared to the odds that peaks are associated with other gene sets, after controlling for locus length and/or mappability. An odds ratio greater than 1 indicates enrichment, and less than 1 indicates depletion. N.Geneset.Genes the number of genes in the gene set. N.Geneset.Peak.Genes the number of genes in the genes set that were assigned at least one peak. Geneset.Avg.Gene.Length the average length of the genes in the gene set. Geneset.Peak.Genes the list of genes from the gene set that had at least one peak assigned.

The ChIP-Enrich method uses the presence of a peak in its model for enrichment: peak ~ GO + s(log10_length). Here, GO is a binary vector indicating whether a gene is in the gene set being tested, peak is a binary vector indicating the presence of a peak in a gene, and s(log10_length) is a binomial cubic smoothing spline which adjusts for the relationship between the presence of a peak and locus length.

The following guidelines are intended to help select an enrichment function:

broadenrich():: is designed for use with broad peaks that may intersect multiple gene loci, and cumulatively cover greater than 5% of the genome. For example, ChIP-seq experiments for histone modifications.
chipenrich():: is designed for use with 1,000s or 10,000s of narrow peaks which results in fewer gene loci containing a peak overall. For example, ChIP-seq experiments for transcription factors.
polyenrich():: is also designed for narrow peaks, for experiments with 100,000s of peaks, or in cases where the number of binding sites per gene affects its regulation. If unsure whether to use chipenrich or polyenrich, then we recommend hybridenrich.
hybridenrich():: is a combination of chipenrich and polyenrich, to be used when one is unsure which is the optimal method.

Randomization of locus definitions allows for the assessment of Type I Error under the null hypothesis. The randomization codes are:

NULL:: No randomizations, the default.
'complete':: Shuffle the gene_id and symbol columns of the locusdef together, without regard for the chromosome location, or locus length. The null hypothesis is that there is no true gene set enrichment.
'bylength':: Shuffle the gene_id and symbol columns of the locusdef together within bins of 100 genes sorted by locus length. The null hypothesis is that there is no true gene set enrichment, but with preserved locus length relationship.
'bylocation':: Shuffle the gene_id and symbol columns of the locusdef together within bins of 50 genes sorted by genomic location. The null hypothesis is that there is no true gene set enrichment, but with preserved genomic location.

The return value with a selected randomization is the same list as without. To assess the Type I error, the alpha level for the particular data set can be calculated by dividing the total number of gene sets with p-value < alpha by the total number of tests. Users may want to perform multiple randomizations for a set of peaks and take the median of the alpha values.

Other enrichment functions: broadenrich

# Run ChipEnrich using an example dataset, assigning peaks to the nearest TSS,
# and on a small custom geneset
data(peaks_E2F4, package = 'chipenrich.data')
peaks_E2F4 = subset(peaks_E2F4, peaks_E2F4$chrom == 'chr1')
gs_path = system.file('extdata','vignette_genesets.txt', package='chipenrich')
results = chipenrich(peaks_E2F4, method='chipenrich', locusdef='nearest_tss',
			genome = 'hg19', genesets=gs_path, out_name=NULL)

# Get the list of peaks that were assigned to genes.
assigned_peaks = results$peaks

# Get the results of enrichment testing.
enrich = results$results