shazam - The shazam package
Dramatic improvements in high-throughput sequencing technologies now enable
large-scale characterization of Ig repertoires, defined as the collection of transmembrane
antigen-receptor proteins located on the surface of T and B lymphocytes. The
package provides tools for advanced analysis of somatic hypermutation (SHM) in
immunoglobulin (Ig) sequences. The key functions in
shazam, broken down topic, are
shazam provides tools to quantify the extent and nature of SHM within
full length V(D)J sequences as well as sub-regions (eg, FWR and CDR).
Quantification of expected mutational loaded, under specific SHM targeting
models, can also be performed along with model driven simulations of SHM.
- collapseClones: Build clonal consensus sequences.
- consensusSequence: Build a single consensus sequence.
- observedMutations: Compute observed mutation counts and frequencies.
- expectedMutations: Compute expected mutation frequencies.
- shmulateSeq: Simulate mutations in a single sequence.
- shmulateTree: Simulate mutations over a lineage tree.
SHM targeting models¶
Computational models and analyses of SHM have separated the process into two independent components:
- A mutability model that defines where mutations occur.
- A nucleotide substitution model that defines the resulting mutation.
Collectively these are what form the targeting model of SHM.
provides empirically derived targeting models for both humans and mice,
along with tools to build these mutability and substitution models from data.
- createTargetingModel: Build a 5-mer targeting model.
- plotMutability: Plot 5-mer mutability rates.
- HH_S5F: Human 5-mer SHM targeting model.
- MK_RS5NF: Mouse 5-mer SHM targeting model.
Quantification of selection pressure¶
Bayesian Estimation of Antigen-driven Selection in Ig Sequences is a
novel method for quantifying antigen-driven selection in high-throughput
Ig sequence data. Targeting models created using
shazam can be used
to estimate the null distribution of expected mutation frequencies used
by BASELINe, providing measures of selection pressure informed by known
AID targeting biases.
- calcBaseline: Calculate the BASELINe probability density functions (PDFs).
- groupBaseline: Combine PDFs from sequences grouped by biological or experimental relevance.
- summarizeBaseline: Compute summary statistics from BASELINe PDFs.
- testBaseline: Perform significance testing for the difference between BASELINe PDFs.
- plotBaselineDensity: Plot the probability density functions resulting from selection analysis.
- plotBaselineSummary: Plot summary stastistics resulting from selection analysis.
Mutational distance calculation¶
shazam provides tools to compute evolutionary distances between
sequences or groups of sequences, which can leverage SHM targeting
models. This information is particularly useful in understanding and
defining clonal relationships.
- findThreshold: Identify clonal assignment threshold based on distances to nearest neighbors.
- distToNearest: Tune clonal assignment thresholds by calculating distances to nearest neighbors.
- calcTargetingDistance: Construct a nucleotide distance matrix from a 5-mer targeting model.
- Hershberg U, et al. Improved methods for detecting selection by mutation analysis of Ig V region sequences. Int Immunol. 2008 20(5):683-94.
- Uduman M, et al. Detecting selection in immunoglobulin sequences. Nucleic Acids Res. 2011 39(Web Server issue):W499-504. (Corrections at http://selection.med.yale.edu/baseline/correction/)
- Yaari G, et al. Quantifying selection in high-throughput immunoglobulin sequencing data sets. Nucleic Acids Res. 2012 40(17):e134.
- Yaari G, et al. Models of somatic hypermutation targeting and substitution based on synonymous mutations from high-throughput immunoglobulin sequencing data. Front Immunol. 2013 4:358.
- Cui A, Di Niro R, Vander Heiden J, Briggs A, Adams K, Gilbert T, O’Connor K, Vigneault F, Shlomchik M and Kleinstein S (2016). A Model of Somatic Hypermutation Targeting in Mice Based on High-Throughput Ig Sequencing Data. The Journal of Immunology, 197(9), 3566-3574.