Last updated: 2020-10-25

Checks: 6 1

Knit directory: Comparative_eQTL/analysis/

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Overview

Original reviewer point:

Did the authors test directly whether eQTLs were enriched in genes with a high dispersion? I could not find this going back through the paper. This seems almost trivially likely to be true. I may have missed this result? Or did the authors worry this is too likely to be confounded with cell type? Either way, this seems like a result that may be useful to show even if the authors did acknowledge that it was likely to be confounded.

What we have shown already, is that chimp specific eGenes have more dispersion in chimp than in human (vice versa). But the reviewer is asking something slightly different. Let’s look into it…

Analysis

First, load necessary libraries… and read in data

library(tidyverse)
library(knitr)
source("../code/CustomFunctions.R")


Overdispersion <- read.delim("../output/Final/TableS3.tab")
Chimp.eGenes <- read.delim("../output/Final/TableS8.tab")
Human.eGenes <- read.delim("../data/GTEX_v8_eGenes/Heart_Left_Ventricle.v8.egenes.txt.gz")
GeneNames <- read.delim("../data/Biomart_export.Hsap.Ptro.orthologs.txt.gz") %>%
  distinct(Gene.stable.ID, .keep_all = T) %>%
  filter(Chimpanzee.homology.type=="ortholog_one2one")

head(Overdispersion) %>% kable()
gene HGNC.symbol Chimp.Mean.Expression Human.Mean.Expression Chimp.Overdispersion Human.Overdispersion Chimp.Mean.Adjusted.Dispersion Human.Mean.Adjusted.Dispersion Chimp.SE Human.SE P q.value
ENSG00000186891 TNFRSF18 -20.04475 -22.72507 2.1055309 0.6147549 2.3121799 0.0805422 0.3799365 1.2023115 0.0054 0.0317946
ENSG00000186827 TNFRSF4 -18.77917 -19.33208 0.6203152 0.8582437 1.6405781 1.9529450 0.2157222 0.3020914 0.3439 0.3126680
ENSG00000078808 SDF4 -17.25701 -17.12363 0.0583115 0.0420739 -0.5386575 -0.8183559 0.2215974 0.2267717 0.3624 0.3210003
ENSG00000176022 B3GALT6 -18.54108 -18.71933 0.0921186 0.0543682 -0.2006514 -0.6565939 0.2894171 0.2657152 0.3434 0.3124612
ENSG00000184163 C1QTNF12 -20.22992 -20.96884 0.9431169 0.3705950 1.4085703 0.3109663 0.3138983 0.4147022 0.0662 0.1329230
ENSG00000160087 UBE2J2 -18.96377 -18.91956 0.0832274 0.0533650 -0.4256215 -0.7154168 0.2888279 0.3411127 0.4752 0.3657044
head(Chimp.eGenes) %>% kable()
BestSNP gene beta statistic pvalue FDR BF TESTS
ID.19.305637.C.G ENSPTRG00000010141 1.1665064 3.021675 0.0057314 0.7342957 1 459
ID.19.305637.C.G ENSPTRG00000010142 0.7623738 3.247842 0.0033040 0.6614980 1 546
ID.19.330232.T.G ENSPTRG00000049019 0.4123193 2.958944 0.0066627 0.7592049 1 931
ID.19.464214.CAG.C ENSPTRG00000010153 -0.4969125 -2.946400 0.0068655 0.7628932 1 931
ID.19.476671.G.A ENSPTRG00000010155 -0.3514492 -3.420594 0.0021534 0.5970544 1 991
ID.19.624908.C.T ENSPTRG00000049419 1.7797750 3.025529 0.0056785 0.7335257 1 981
head(Human.eGenes) %>% kable()
gene_id gene_name gene_chr gene_start gene_end strand num_var beta_shape1 beta_shape2 true_df pval_true_df variant_id tss_distance chr variant_pos ref alt num_alt_per_site rs_id_dbSNP151_GRCh38p7 minor_allele_samples minor_allele_count maf ref_factor pval_nominal slope slope_se pval_perm pval_beta qval pval_nominal_threshold log2_aFC log2_aFC_lower log2_aFC_upper
ENSG00000227232.5 WASH7P chr1 14410 29553 - 1364 1.01157 280.800 282.379 0.0000008 chr1_665098_G_A_b38 635545 chr1 665098 G A 1 rs114979547 91 94 0.1217620 1 0.0000002 0.403338 0.0756735 0.0003000 0.0002128 0.0003112 0.0002359 0.697958 0.513705 0.873141
ENSG00000240361.1 OR4G11P chr1 62948 63887 + 1520 1.01235 326.604 289.739 0.0035926 chr1_665098_G_A_b38 602150 chr1 665098 G A 1 rs114979547 91 94 0.1217620 1 0.0023564 -0.259344 0.0845860 0.6927340 0.6864840 0.2863100 0.0002033 -0.775033 -1.281557 -0.473808
ENSG00000186092.4 OR4F5 chr1 69091 70008 + 1541 1.01869 326.003 287.455 0.0000906 chr1_807641_T_C_b38 738550 chr1 807641 T C 1 rs3964475 171 195 0.2525910 1 0.0000405 0.291123 0.0699246 0.0263974 0.0270163 0.0250127 0.0002079 0.932644 0.649848 1.331262
ENSG00000268903.1 RP11-34P13.15 chr1 135141 135895 - 1863 1.03811 353.346 282.101 0.0006611 chr1_986007_G_A_b38 850112 chr1 986007 G A 1 rs115014500 8 8 0.0103627 1 0.0003129 -0.900366 0.2470360 0.1963520 0.1934770 0.1206300 0.0002038 -6.643856 -6.643856 -6.643856
ENSG00000269981.1 RP11-34P13.16 chr1 137682 137965 - 1868 1.05087 334.272 277.796 0.0002781 chr1_1028281_C_T_b38 890316 chr1 1028281 C T 1 rs13303147 28 29 0.0375648 1 0.0001057 -0.587608 0.1496360 0.0744926 0.0768662 0.0598632 0.0002240 -1.615290 -6.094829 -1.119854
ENSG00000279457.4 RP11-34P13.18 chr1 185217 195411 - 2234 1.04471 378.207 275.991 0.0003427 chr1_665098_G_A_b38 469687 chr1 665098 G A 1 rs114979547 91 94 0.1217620 1 0.0001272 0.340850 0.0878486 0.1064890 0.1086650 0.0785110 0.0001944 0.401163 0.248050 0.612973
head(GeneNames) %>% kable()
Gene.stable.ID Transcript.stable.ID Chimpanzee.gene.stable.ID Chimpanzee.gene.name Chimpanzee.protein.or.transcript.stable.ID Chimpanzee.homology.type X.id..target.Chimpanzee.gene.identical.to.query.gene X.id..query.gene.identical.to.target.Chimpanzee.gene dN.with.Chimpanzee dS.with.Chimpanzee Chimpanzee.orthology.confidence..0.low..1.high.
ENSG00000198888 ENST00000361390 ENSPTRG00000042641 MT-ND1 ENSPTRP00000061407 ortholog_one2one 94.6541 94.6541 0.0267 0.5455 1
ENSG00000198763 ENST00000361453 ENSPTRG00000042626 MT-ND2 ENSPTRP00000061406 ortholog_one2one 96.2536 96.2536 0.0185 0.7225 1
ENSG00000210127 ENST00000387392 ENSPTRG00000042642 MT-TA ENSPTRT00000076396 ortholog_one2one 100.0000 100.0000 NA NA NA
ENSG00000198804 ENST00000361624 ENSPTRG00000042657 MT-CO1 ENSPTRP00000061408 ortholog_one2one 98.8304 98.8304 0.0065 0.5486 1
ENSG00000198712 ENST00000361739 ENSPTRG00000042660 MT-CO2 ENSPTRP00000061402 ortholog_one2one 97.7974 97.7974 0.0106 0.5943 1
ENSG00000228253 ENST00000361851 ENSPTRG00000042653 MT-ATP8 ENSPTRP00000061400 ortholog_one2one 94.1176 94.1176 0.0325 0.3331 1

Plot dispersion of chimp eGenes vs non eGenes

Chimp.Data.To.Plot <- Chimp.eGenes %>%
  inner_join(GeneNames, by=c("gene"="Chimpanzee.gene.stable.ID")) %>%
  inner_join(Overdispersion, by=c("Gene.stable.ID"="gene")) %>%
  dplyr::select(Chimp.Mean.Adjusted.Dispersion, q.value=FDR, Gene.stable.ID) %>%
  mutate(eGene=q.value<0.1)

wilcox.test(Chimp.Mean.Adjusted.Dispersion~eGene, data=Chimp.Data.To.Plot)

    Wilcoxon rank sum test with continuity correction

data:  Chimp.Mean.Adjusted.Dispersion by eGene
W = 994733, p-value = 4.682e-05
alternative hypothesis: true location shift is not equal to 0
ggplot(Chimp.Data.To.Plot, aes(x=Chimp.Mean.Adjusted.Dispersion, color=eGene)) +
  stat_ecdf() +
  theme_bw()

Same for human eGenes vs non eGenes

Human.Data.To.Plot <- Human.eGenes %>%
  mutate(gene=str_remove(gene_id, "\\.\\d+$")) %>%
  inner_join(Overdispersion, by=c("gene")) %>%
  dplyr::select(Human.Mean.Adjusted.Dispersion, q.value=qval, Gene.stable.ID=gene) %>%
  mutate(eGene=q.value<0.1)

wilcox.test(Human.Mean.Adjusted.Dispersion~eGene, data=Human.Data.To.Plot)

    Wilcoxon rank sum test with continuity correction

data:  Human.Mean.Adjusted.Dispersion by eGene
W = 20851189, p-value = 0.1276
alternative hypothesis: true location shift is not equal to 0
ggplot(Human.Data.To.Plot, aes(x=Human.Mean.Adjusted.Dispersion, color=eGene)) +
  stat_ecdf() +
  theme_bw()

Hmm, this is again an example of assymetrical results may be a result of analyzing eGenes with vastly different power. Let’s use the same approach I used in the manuscript, and just consider the top 500 human eGenes…

EgenesTested <- TsvToCombinedEgenes(Chimp.tsv = "../output/ChimpEgenes.eigenMT.txt.gz", Human.tsv = "../data/GTEX_v8_eGenes/Heart_Left_Ventricle.v8.egenes.txt.gz", SysToID.tsv = "../data/Biomart_export.Hsap.Ptro.orthologs.txt.gz", HumanTsvType = "GTEx")
EgenesTested.grouped <- AddGroups(EgenesTested, HumanEgeneCount=500)

Chimp.Data.To.Plot <- EgenesTested.grouped %>%
  inner_join(Overdispersion, by=c("H.gene"="gene")) %>%
  mutate(eGene=group %in% c("both", "chimp"))

Chimp.Test <- wilcox.test(Chimp.Mean.Adjusted.Dispersion~eGene, data=Chimp.Data.To.Plot)
Chimp.Test

    Wilcoxon rank sum test with continuity correction

data:  Chimp.Mean.Adjusted.Dispersion by eGene
W = 989832, p-value = 4.14e-05
alternative hypothesis: true location shift is not equal to 0
ggplot(Chimp.Data.To.Plot, aes(x=Chimp.Mean.Adjusted.Dispersion, color=eGene)) +
  stat_ecdf() +
  theme_bw()

Human.Data.To.Plot <- EgenesTested.grouped %>%
  inner_join(Overdispersion, by=c("H.gene"="gene")) %>%
  mutate(eGene=group %in% c("both", "human"))

Human.Test <- wilcox.test(Human.Mean.Adjusted.Dispersion~eGene, data=Human.Data.To.Plot)
Human.Test

    Wilcoxon rank sum test with continuity correction

data:  Human.Mean.Adjusted.Dispersion by eGene
W = 2062701, p-value = 3.351e-05
alternative hypothesis: true location shift is not equal to 0
ggplot(Human.Data.To.Plot, aes(x=Human.Mean.Adjusted.Dispersion, color=eGene)) +
  stat_ecdf() +
  theme_bw()

So, there is a modest, but very significant trend as the reviewer suspected: eGenes have higher dispersion (or at least, the top eGenes do, since with sufficient power near every gene is an eGene).

Let’s save out a figure to show this

Tests <- data.frame(species=c("Chimp", "Human"), P=c(Chimp.Test$p.value, Human.Test$p.value)) %>%
  mutate(label=paste0("P=", format.pval(P, digits = 2)))
Tests
  species            P     label
1   Chimp 4.139519e-05 P=4.1e-05
2   Human 3.351107e-05 P=3.4e-05
PlotToSave <- EgenesTested.grouped %>%
  inner_join(Overdispersion, by=c("H.gene"="gene")) %>%
  mutate(Chimp=group %in% c("both", "chimp")) %>%
  mutate(Human=group %in% c("both", "human")) %>%
  dplyr::select(Chimp,Human,H.gene, Human.Mean.Adjusted.Dispersion, Chimp.Mean.Adjusted.Dispersion) %>%
  gather(key="species", value="eGene", Chimp, Human)  %>%
  gather(key="Dispersion.species", value="Dispersion", Human.Mean.Adjusted.Dispersion, Chimp.Mean.Adjusted.Dispersion) %>%
  mutate(Dispersion.species=recode(Dispersion.species, Human.Mean.Adjusted.Dispersion="Human", Chimp.Mean.Adjusted.Dispersion="Chimp")) %>%
  filter(species==Dispersion.species) %>%
  mutate(eGene=if_else(eGene, "eGene", "non eGene")) %>%
  ggplot(aes(x=Dispersion)) +
  stat_ecdf(aes(color=eGene)) +
  geom_text(
  data    = Tests,
  mapping = aes(x = Inf, y = -Inf, label = label),
  hjust   = 1.1,
  vjust   = -1
) +
  ylab("ecdf") +
  facet_wrap(~species) +
  xlim(c(-3,3)) +
  theme_bw() +
  theme(legend.position="bottom", legend.title = element_blank())
PlotToSave

Write out the plot

ggsave("../figures/OriginalArt/ResponseToReviewers.Point8_eGenesAndDispersion.pdf", PlotToSave, height=2.5, width=4)

sessionInfo()
R version 3.6.1 (2019-07-05)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Catalina 10.15.5

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRblas.0.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] cowplot_1.0.0   gridExtra_2.3   edgeR_3.26.8    limma_3.40.6   
 [5] MASS_7.3-53     knitr_1.26      forcats_0.4.0   stringr_1.4.0  
 [9] dplyr_1.0.2     purrr_0.3.3     readr_1.3.1     tidyr_1.0.0    
[13] tibble_3.0.3    ggplot2_3.3.2   tidyverse_1.3.0

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.5       locfit_1.5-9.1   lubridate_1.7.9  lattice_0.20-38 
 [5] assertthat_0.2.1 rprojroot_1.3-2  digest_0.6.23    R6_2.4.1        
 [9] cellranger_1.1.0 backports_1.1.5  reprex_0.3.0     evaluate_0.14   
[13] httr_1.4.1       highr_0.8        pillar_1.4.6     rlang_0.4.7     
[17] readxl_1.3.1     rstudioapi_0.10  rmarkdown_1.18   labeling_0.3    
[21] munsell_0.5.0    broom_0.7.0      compiler_3.6.1   httpuv_1.5.2    
[25] modelr_0.1.5     xfun_0.11        pkgconfig_2.0.3  htmltools_0.4.0 
[29] tidyselect_1.1.0 workflowr_1.5.0  fansi_0.4.0      crayon_1.3.4    
[33] dbplyr_1.4.2     withr_2.1.2      later_1.0.0      grid_3.6.1      
[37] jsonlite_1.6     gtable_0.3.0     lifecycle_0.2.0  DBI_1.0.0       
[41] git2r_0.26.1     magrittr_1.5     scales_1.1.1     cli_2.0.0       
[45] stringi_1.4.3    farver_2.0.3     fs_1.3.1         promises_1.1.0  
[49] xml2_1.2.2       ellipsis_0.3.0   generics_0.0.2   vctrs_0.3.4     
[53] tools_3.6.1      glue_1.4.2       hms_0.5.2        yaml_2.2.0      
[57] colorspace_1.4-1 rvest_0.3.5      haven_2.2.0