Compressively-accelerated read mapping framework for next-generation sequencing
A method of compressive read mapping. A high-resolution homology table is created for the reference genomic sequence, preferably by mapping the reference to itself. Once the homology table is created, the reads are compressed to eliminate full or partial redundancies across reads in the dataset. Preferably, compression is achieved through self-mapping of the read dataset. Next, a coarse mapping from the compressed read data to the reference is performed. Each read link generated represents a cluster of substrings from one or more reads in the dataset and stores their differences from a locus in the reference. Preferably, read links are further expanded to obtain final mapping results through traversal of the homology table, and final mapping results are reported. As compared to prior techniques, substantial speed-up gains are achieved through the compressive read mapping technique due to efficient utilization of redundancy within read sequences as well as the reference.
1. A method of accelerating processing of a dataset of genomic data, comprising:
during a pre-processing phase:
generating a homology table for a reference genomic sequence by mapping the reference genomic sequence to itself, the homology table storing similarity information of homologous or similar regions of the reference genomic sequence of a specified length within a given distance;
during a read mapping phase that is distinct from the pre-processing phase:
compressing reads in the dataset to generate compressed read data;
applying a coarse mapping from the compressed read data to the reference genomic sequence to generate a set of read links, each read link being a pointer to the homology table and representing a cluster of substrings from one or more reads in the dataset; and
processing the set of read links through traversal of the homology table to obtain a final mapping result set;
wherein processing the set of read links using the homology table provides sublinear-time read mapping of the dataset and without requiring decompression of the compressed read data.
2. The method as described in claim 1 wherein the reads are compressed by mapping the reads to themselves.
3. The method as described in claim 1 wherein the homology table contains all homologous pairs of loci in the reference genomic sequence for a given homology block length and above a similarity threshold.
4. The method as described in claim 3 wherein the given homology block length is between 32-64 base pairs and the similarity threshold is a Hamming distance 0-3.
5. The method as described in claim 1 wherein the homology table represents pointers for each position in the reference genomic sequence indicating all of its neighboring k-mers, wherein a k-mer refers to all the possible substrings, of length k, that are contained in the reference genomic sequence.
6. The method as described in claim 1 further including re-using the homology table against a second dataset that is distinct from the dataset.
7. The method as described in claim 1 wherein given the reference genomic sequence as DNA sequence R, a substring length k, and a mismatch error threshold s, the homology table H(R, k, s) is a compact data structure that stores the read links among all similar k-base substrings (k-mers) of R up to s mismatches under reverse complementation.
8. The method as described in claim 1 wherein the homology table is one of: an exact homology table, an inexact homology table, and a combination of the exact homology table and the inexact homology table.
9. The method as described in claim 1 wherein prior to applying the coarse mapping the method further includes executing a split collapsing scheme wherein each read is first split into two consecutive substrings of a same length, wherein each consecutive substring is thereafter processed during the read mapping phase individually.
10. The method as described in claim 9 wherein after applying the coarse mapping the method further includes reorganizing collapsed substrings into the read prior to producing the final mapping result set.
11. The method as described in claim 1 further including implementing a memorization scheme wherein for at least one read link that represents more than a certain number of substrings in compressed form, the homology table is traversed once and inferred genomic positions for the read link are saved in a lookup table, and wherein for each of the substrings within the at least one read link, the look-up table is used for further processing instead of re-computing genomic neighbors using the homology table.