Ensembl Biomart
The Ensembl Biomart database enables users to retrieve a vast diversity of annotation data for specific organisms. Initially, Steffen Durinck and Wolfgang Huber provide an powerful interface between the R language and Ensembl Biomart by providing the R package biomaRt. However, the biomartr
package extends the functionality of the biomaRt package and introduces a more organism centered annotation retrieval concept.
The following sections will introduce users to the functionality and data retrieval precedures of biomartr
and will show how biomartr
extends the functionality of the initial biomaRt package.
biomartr
This query methodology provided by Ensembl Biomart
and the biomaRt
package is a very well defined approach for accurate annotation retrieval. Nevertheless, when learning this query methodology it (subjectively) seems non-intuitive from the user perspective. Therefore, the biomartr
package provides another query methodology that aims to be more organism centric.
Taken together, the following workflow allows users to perform fast BioMart queries for attributes using the biomart()
function implemented in this biomartr
package:
get attributes, datasets, and marts via : organismAttributes()
choose available biological features (filters) via: organismFilters()
specify a set of query genes: e.g. retrieved with getGenome()
, getProteome()
or getCDS()
specify all arguments of the biomart()
function using steps 1) - 3) and perform a BioMart query
Note that dataset names change very frequently due to the update of dataset versions. So in case some query functions do not work properly, users should check with organismAttributes(update = TRUE)
whether or not their dataset name has been changed. For example, organismAttributes("Homo sapiens", topic = "id", update = TRUE)
might reveal that the dataset ENSEMBL_MART_ENSEMBL
has changed.
The getMarts()
function allows users to list all available databases that can be accessed through BioMart interfaces.
# load the biomartr package
library(biomartr)
# list all available databases
getMarts()
Now users can select a specific database to list all available datasets that can be accessed through this database. In this example we choose the ENSEMBL_MART_ENSEMBL
database.
head(getDatasets(mart = "ENSEMBL_MART_ENSEMBL") , 5)
Now you can select the dataset hsapiens_gene_ensembl
and list all available attributes that can be retrieved from this dataset.
tail(getDatasets(mart = "ENSEMBL_MART_ENSEMBL") , 38)
Now that you have selected a database (hsapiens_gene_ensembl
) and a dataset (hsapiens_gene_ensembl
), users can list all available attributes for this dataset using the getAttributes()
function.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# list all available attributes for dataset: hsapiens_gene_ensembl
head( getAttributes(mart = "ENSEMBL_MART_ENSEMBL",
dataset = "hsapiens_gene_ensembl"), 10 )
Finally, the getFilters()
function allows users to list available filters for a specific dataset that can be used for a biomart()
query.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# list all available filters for dataset: hsapiens_gene_ensembl
head( getFilters(mart = "ENSEMBL_MART_ENSEMBL",
dataset = "hsapiens_gene_ensembl"), 10 )
In most use cases, users will work with a single or a set of model organisms. In this process they will mostly be interested in specific annotations for this particular model organism. The organismBM()
function addresses this issue and provides users with an organism centric query to marts
and datasets
which are available for a particular organism of interest.
Note that when running the following functions for the first time, the data retrieval procedure will take some time, due to the remote access to BioMart. The corresponding result is then saved in a *.txt
file named _biomart/listDatasets.txt
within the tempdir()
folder, allowing subsequent queries to be performed much faster. The tempdir()
folder, however, will be deleted after a new R session was established. In this case the inital call of the subsequent functions again will take time to retrieve all organism specific data from the BioMart database.
This concept of locally storing all organism specific database linking information available in BioMart into an internal file allows users to significantly speed up subsequent retrieval queries for that particular organism.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# retrieving all available datasets and biomart connections for
# a specific query organism (scientific name)
organismBM(organism = "Homo sapiens")
The result is a table storing all marts
and datasets
from which annotations can be retrieved for Homo sapiens. Furthermore, a short description as well as the version of the dataset being accessed (very useful for publications) is returned.
Users will observe that 3 different marts
provide 6 different datasets
storing annotation information for Homo sapiens.
Please note, however, that scientific names of organisms must be written correctly! For ex. “Homo Sapiens” will be treated differently (not recognized) than “Homo sapiens” (recognized).
Similar to the biomaRt
package query methodology, users need to specify attributes
and filters
to be able to perform accurate BioMart queries. Here the functions organismAttributes()
and organismFilters()
provide useful and intuitive concepts to obtain this information.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# return available attributes for "Homo sapiens"
head(biomartr::organismAttributes("Homo sapiens"), 20)
Users will observe that the organismAttributes()
function returns a data.frame storing attribute names, datasets, and marts which are available for Homo sapiens
. After the ENSEMBL release 87 the ENSEMBL_MART_SEQUENCE
service provided by Ensembl does not work properly and thus the organismAttributes()
function prints out warning messages to make the user aware when certain marts provided bt Ensembl do not work properly, yet.
An additional feature provided by organismAttributes()
is the topic
argument. The topic
argument allows users to to search for specific attributes, topics, or categories for faster filtering.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for attribute topic "id"
head(organismAttributes("Homo sapiens", topic = "id"), 20)
Now, all attribute names
having id
as part of their name
are being returned.
Another example is topic = "homolog"
.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for attribute topic "homolog"
head(organismAttributes("Homo sapiens", topic = "homolog"), 20)
Or topic = "dn"
and topic = "ds"
for dn
and ds
value retrieval.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for attribute topic "dn"
head(organismAttributes("Homo sapiens", topic = "dn"))
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for attribute topic "ds"
head(organismAttributes("Homo sapiens", topic = "ds"))
Analogous to the organismAttributes()
function, the organismFilters()
function returns all filters that are available for a query organism of interest.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# return available filters for "Homo sapiens"
head(organismFilters("Homo sapiens"), 20)
The organismFilters()
function also allows users to search for filters that correspond to a specific topic or category.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for filter topic "id"
head(organismFilters("Homo sapiens", topic = "id"), 20)
The short introduction to the functionality of organismBM()
, organismAttributes()
, and organismFilters()
will allow users to perform BioMart queries in a very intuitive organism centric way. The main function to perform BioMart queries is biomart()
.
For the following examples we will assume that we are interested in the annotation of specific genes from the Homo sapiens proteome. We want to map the corresponding refseq gene id to a set of other gene ids used in other databases. For this purpose, first we need consult the organismAttributes()
function.
# show all elements of the data.frame
options(tibble.print_max = Inf)
head(organismAttributes("Homo sapiens", topic = "id"))
# show all elements of the data.frame
options(tibble.print_max = Inf)
# retrieve the proteome of Homo sapiens from refseq
file_path <- getProteome( db = "refseq",
organism = "Homo sapiens",
path = file.path("_ncbi_downloads","proteomes") )
Hsapiens_proteome <- read_proteome(file_path, format = "fasta")
# remove splice variants from id
gene_set <- unlist(sapply(strsplit(Hsapiens_proteome@ranges@NAMES[1:5], ".",fixed = TRUE), function(x) x[1]))
result_BM <- biomart( genes = gene_set,
mart = "ENSEMBL_MART_ENSEMBL",
dataset = "hsapiens_gene_ensembl",
attributes = c("ensembl_gene_id","ensembl_peptide_id"),
filters = "refseq_peptide")
result_BM
The biomart()
function takes as arguments a set of genes (gene ids specified in the filter
argument), the corresponding mart
and dataset
, as well as the attributes
which shall be returned.
The biomartr
package also enables a fast and intuitive retrieval of GO terms and additional information via the getGO()
function. Several databases can be selected to retrieve GO annotation information for a set of query genes. So far, the getGO()
function allows GO information retrieval from the Ensembl Biomart database.
In this example we will retrieve GO information for a set of Homo sapiens genes stored as hgnc_symbol
.
The getGO()
function takes several arguments as input to retrieve GO information from BioMart. First, the scientific name of the organism
of interest needs to be specified. Furthermore, a set of gene ids
as well as their corresponding filter
notation (GUCA2A
gene ids have filter
notation hgnc_symbol
; see organismFilters()
for details) need to be specified. The database
argument then defines the database from which GO information shall be retrieved.
# show all elements of the data.frame
options(tibble.print_max = Inf)
# search for GO terms of an example Homo sapiens gene
GO_tbl <- getGO(organism = "Homo sapiens",
genes = "GUCA2A",
filters = "hgnc_symbol")
GO_tbl
Hence, for each gene id the resulting table stores all annotated GO terms found in Ensembl Biomart.