snco: single nucleus crossover analysis

snco is a set of tools for identifying recombination events at the single nucleus/cell level, using read alignments and/or SNP data from single nucleus sequencing experiments of recombinant haploid gametes. Reads alignments or SNPs are summarised into a per-cell barcode "marker" dataset which can then be used to perform crossover analysis with a hidden Markov model. snco also provides commands for generating per-barcode summary statistics, plotting marker and crossover profiles, and simulating ground truth datasets using marker distributions from real data.

snco is still under active development, so expect some bugs and changes! If in doubt about the behaviour of snco or how it might change, feel free to reach out by opening an issue!

Installation:

The easiest way to install snco is using the conda yaml provided:

git clone https://github.com/schneebergerlab/snco.git
cd snco
conda env create -f snco.yml

alternatively, you can install it using pip:

pip install git+https://github.com/schneebergerlab/snco.git

snco requires torch and pomegranate>=1.0 for performing crossover detection, pysam and joblib for bam file manipulation and numpy, pandas, scipy and matplotlib for general marker analysis and plotting. The command line interface is build using click. For some of the provided helper scripts, parasail is also required.

Quickstart:

snco divides the analysis into several subcommands for modular and flexible workflows. There are currently two different methods provided for loading markers into the format used for crossover prediction. These are:

• snco loadbam: read a bam file aligned with cell barcode and haplotype alignment tags. Currently the best way to generate this is to run STAR solo in Diploid alignment mode. This is a mode of STAR where reads can be aligned to two different haploid genomes at once. See the STAR manual and detailed snco loadbam documentation (coming soon) for further information.
• snco loadcsl: read a matrix market + vcf file describing biallelic SNP counts for individual cells, generated by cellsnp-lite. The reference allele is assumed to derive from haplotype 1, and the alternative allele from haplotype 2.

The output of both load commands is a json file containing marker information, which can be fed into the downstream clean, predict, stats and plot commands.

If you would like to perform the full analysis in a single step, then the core analysis pipeline, load(+clean)+predict, can be run together as a single command using snco bam2pred or snco csl2pred.

Please see the documentation pages (coming soon...) for a full list of commands and their options.

Python API

snco also provides an API with some helpful classes for working with output marker and predictions datasets in python. These are the MarkerRecords and PredictionRecords classes:

from snco import MarkerRecords, PredictionRecords

co_markers = MarkerRecords.read_json('markers.json')
co_preds = PredictionRecords.read_json('pred.json')

co_markers.barcodes[:5]

    ['TGGTTAGGTAGATTGA',
     'ACGTAGTTCATCAGTG',
     'GACCAATCAACAAAGT',
     'CTATAGGGTTACCTTT',
     'AGAGAATCAGACAATA']

Plotting functions can also accessed both from the command line using snco plot and also in python using the snco.plot module or built in methods of MarkerRecords/PredictionRecords

co_markers.plot_barcode('TGGTTAGGTAGATTGA', co_preds=co_preds, max_yheight=10);