GISTIC2 for Canine CanFam3.1 genome

Changes to original code by

• Emmanuel Martinez
• Samir B. Amin

For canine (canFam3.1), gistic2 run needs a few changes. You will need matlab to change code and recompile top level executable module or script, gp_gistic2_from_seg. I am using v2.0.22 from ftp://ftp.broadinstitute.org/pub/GISTIC2.0/

PS: If you are unable to re-compile (so as we) matlab script using updated GISTIC2 version, try using pre-compiled matlab script, gp_gistic2_from_seg_upd. For this to work, you will need to use canfam3_1_order.mat and may require to downgrade Matlab runtime to MCR/8.0 and gistic2 to v2.0.22. Please note that our pre-compiled matlab script is based on relatively older reference genome annotations and cytoband information for CanFam 3.1 (~2011). You can browser gistic_run.sh for details on how to run GISTIC2 using CanFam3.1 based reference genome. Please make sure to manually verify GISTIC2 peaks by loading input copy-number segments into genome browser like IGV or JBrowse.

Recompile gp_gistic2_from_seg

Following are a few changes I made after getting input from a colleague, Emmanuel Martinez.

• Make a refgene.file in .mat format containing three objects You can check valid format by opening hg19.mat in matlab.

1. cyto (1x40): containing cytoband. Since canFam has basic cytoband, it will not have detailed (1p11.1, 1p22, etc.) band info as with hg19.mat. canine cytoband can be fetched from UCSC table browser or ftp. https://link.sbamin.com/2ztpbWM or http://hgdownload.soe.ucsc.edu/goldenPath/canFam3/database/cytoBandIdeo.txt.gz

2. rg (1x<number_of_genes>): gene metadata based on canFam refGene/Ensemble gtf file

3. rg_info (1x1): is additional metadata

Save these three objects as canfam3.1.mat

• Now, extract GITIC2 v2.0.22 tarball. Structure would be something similar as noted here: ftp://ftp.broadinstitute.org/pub/GISTIC2.0/README.txt Now, we edit source/RefGeneInfo.m file, line 15 to change nchr from 24 to 40, and at line 29, add corresponding canine chromosomes c(25:38, 'MT', 'X').

RGI.chr.symb = {'1','2','3','4','5','6','7','8','9','10',...
                '11','12','13','14','15','16','17','18',...
                '19','20','21','22','23','24','25','26',...
                '27','28','29','30','31','32','33','34',...
                '35','36','37','38','MT','X'};

Please make sure to have chr sequence order identical to one in cyto object, which was specified under canfam3.1.mat.

• Also, edit line 42 to 44 to match number of chromosomes: This may vary whether or not you like to add/remove autosomes, sex and MT chr.

RGI.txt2num('39') = 39;
RGI.txt2num('40') = 40;
RGI.chr.autosomal = (1:40)<39;

• That's it! Recompile gp_gistic2_from_seg module which is the main executable under gistic2 shell wrapper.
• Here is guide to package matlab application. For the first step under an option, add main file, provide path to gp_gistic2_from_seg.m, add relevant details, keep LICENSE unchanged, i.e., it is copyrighted software by Mermel et al., Broad Institute, Cambridge, MA, USA.
• I will push gistic2 code for canine sometime soon at https://github.com/sbamin Just fixing some of canfam3.1.mat issues to better annotate gistic plots. Feel free to comment/edit here for improvements/bugs.

Segment file

• View make_segments.R for example script.

• I use following script to generate segment file. It is well-defined at ftp://ftp.broadinstitute.org/pub/GISTIC2.0/

## read each segment file, convert non-integer chromosome names to integers.

## create marker column based on the original window size used for making mappability bigwig file, i.e.,
## generateMap.pl -w 100 -i bowtie_index/CanFam3_1.fa "${REF_FASTA}" -o bigwigs/CanFam3_1.map.ws100bp.bw

convert log2 cn to log2-1 cn for GISTIC, so as log2(2) -1 == 0

Note: HMMcopy derived values are already log2 copy ratio, i.e., log2(T/N) = log2(T) - log2(N) = log2(T) - 1. So, it does not require substraction by 1, as I wrongly stated earlier. Read more on format at ftp://ftp.broadinstitute.org/pub/GISTIC2.0/GISTICDocumentation_standalone.htm and https://www.biostars.org/p/174382/#175590

gistic2_seg_file = dplyr::bind_rows(lapply(1:length(segfiles), function(i) {
    aux_data <- read_tsv(segfiles[i], col_types = "cddid") %>%
                filter(!chr == "MT") %>%
                mutate(chri = match(chr, info_chr$X1),
                       start = as.integer(start),
                       end = as.integer(end),
                       markers = as.integer((end - start + 1)/100),
                       segvalue = median,
                       Sample = sampleids[i]) %>%
                dplyr::arrange(chri) %>%
                dplyr::select(one_of(c("Sample", "chr", "start", "end", 
                                "markers", "segvalue")))
    return(aux_data)
    }))

head(gistic2_seg_file)
colnames(gistic2_seg_file) <- c("Sample", "Chromosome", "Start Position", "End Position", "Num markers", "Seg.CN")

write_tsv(gistic2_seg_file, path = sprintf("%s/%s.tsv", getwd(), outfile))

Marker file

• marker file is not required since GISTIC v2.023 but we are using v2.022
• Following a post by Ming Tang to get marker file.

## marker file:

sed '1d' gistic2_segments.tsv | cut -f2,3 > markers.txt
sed '1d' gistic2_segments.tsv | cut -f2,4 >> markers.txt

## sort the files by chromosome, take the unique ones and number the markers.

cat markers.txt | sort -V -k1,1 -k2,2nr | uniq | nl > markers_gistic.txt
rm markers.txt

Example run

View gistic_run.sh file for details.

Samir