JBrowse is freely available without logging in to navigate through the genome and view tracks.
Navigating the Genome
Once the JBrowse page for an organism is loaded for the first time, you will see a blank viewer with number lines and navigation controls at the top of the page. The upper number line represents coordinates of an entire chromosome, and has a red rectangle showing the specific location of the current view. The lower number line represents the chromosomal coordinates of the current view. Arrow buttons allow panning left and right, and zoom levels can be adjusted using the plus and minus icons. To the right of the zoom buttons is a pulldown menu to select a chromosome or scaffold, and a box to enter chromosome coordinates. Rather than selecting a chromosome and entering coordinates, you can enter an identifier for an Ensembl or RefSeq transcript to navigate directly to the its genome location.
Use the "Select Tracks" tab in the upper left corner of the browser to access the Faceted Track Selector which allows you to find tracks based on data type and various other attributes. Highlighting one or more categories on the left panel filters rows in the table on the right, which provides metadata, such as tissue, SRA experiment accession, SRA run accession, BioSample accession, BioProject, and sample attributes such as sex, age, and breed. The table is further searchable by entering text in the “Contains text” search box above the table. Tracks are selected for viewing by clicking boxes to the left of the table.
Chip-seq Peak Tracks
ChIP-seq Peak tracks are currently available only in the horse genome browser. Tissue-specific ChIP-seq peaks for histone modification marks (H3K27ac, H3K27me3, H3K4me1, H3K4me3) appear as thick bars. Each track is a result of merging peaks for two individual samples (Kingsley et al. 2019). Right clicking an individual mark shows more information, including the “Score”, which is the number of reads in that peak. The corresponding RNA-seq for the two individual samples can be identified in the Faceted Track Selector by first noting the BioSample ids in the BioSample column for the ChIP-seq track, and then filtering the desired RNA-seq track type for those BioSample ids (one at a time).
Gene Prediction Tracks
Gene prediction tracks are provided for RefSeq and Ensembl genes, and display transcripts, including protein-coding, long non-coding and other RNA. Protein-coding gene tracks are configured to show untranslated regions (UTR) in dark blue. The coding portions of the exons are slightly thicker than the UTR, and appear in different colors representing reading frames. An arrow at one end of the transcript indicates coding direction, pointing right for coding on the plus strand, and left for coding on the minus strand. When zoomed out, gene prediction tracks appear as histograms depicting gene density, while zooming in allows the visualization of predicted introns and exons. Right clicking a transcript feature provides more information, which may include gene symbol, description and database cross references.
Gene Prediction Problem Tracks
Ensembl Protein-coding Split/Merge tracks show Ensembl protein-coding genes that are either split or merged compared to RefSeq genes.
RefSeq Protein-coding Split/Merge tracks show RefSeq protein-coding genes that are either split or merged compared to Ensembl genes.
"PE" or "SE" in the track category name refers to paired-end or single-end sequencing.
RNAseq Combined Density tracks provide heatmaps representing gene expression levels in log scale for all RNA-seq experiments of a particular BioProject. Mousing over the legend on the left side of the browser, appearing as a green vertical bar, shows the tissue and accession of an individual experiment.
BAM dense tracks are useful for checking the suitability of a RNA-seq experiment for solving a particular gene prediction problem prior to zooming in with a more computationally intensive draggable BAM track. Right clicking an individual read alignment reveals additional information such as the read sequence and quality, alignment score, and details about matches, mismatches and indels in CIGAR format.
BAM draggable tracks are very computationally intensive, and require a sufficient zoomed-in level to avoid an error message, but provide a particularly useful feature when inspecting splice sites. After clicking an exon in a gene prediction track, red lines will appear at matching boundaries among all the read alignments in the BAM track. If red lines do not appear in the draggable BAM track, one would suspect a predicted splice site is incorrect. The name “draggable” refers to an Apollo feature, in that you can drag a single read alignment to the Editing Area to initiate an annotation. Right clicking an individual read alignment reveals additional information such as the read sequence and quality, alignment score, and details about matches, mismatches and indels in CIGAR format.
RNAseq junctions (arcs) tracks collapse junctions from individual reads for viewing when zoomed out to see entire genes or regions between genes. Arc thickness is related to the number of reads supporting the splice junction.
RNAseq junctions (flat) tracks collapse junctions from individual reads into a single bar, and provide the number of reads that support the junction as the “Score” when viewing details about the feature.
StringTie tracks show transcripts models created by assembling RNA-seq read alignments, and can reveal the possibility of new isoforms. The tracks are similar in appearance to gene prediction tracks, but they do not distinguish UTR from coding regions. Similar to gene prediction tracks, StringTie tracks appear as histograms depicting density when zoomed out, and as intron/exon structures when zoomed in.
XYPlot tracks show read depth in log scale, and are used to identify regions of high or low expression.
RepeatMasker tracks were created using RepeatMasker (Smit, AFA, Hubley, R & Green, P. RepeatMasker Open-4.0. 2013-2015). Repeat features are labeled with a name, and right clicking the feature shows the repeat class and family.
dbSNP tracks show SNP that were originally from dbSNP, and now downloadable from Ensembl Variation. Right clicking a SNP id reveals the location of the SNP relative to genes, and the alternate and reference alleles.
QTL tracks show QTL from AnimalQTLdb. QTL features are labeled with traits, and right clicking reveals additional information such as the breed, flanking markers, peak centimorgans, test statistics, model tested, test base, and PubMed ids. The QTL id provided in the information panel allows you to look for more information at AnimalQTLdb.