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Description | Resource with controlled vocabulary to describe the function of genes and gene products |
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Website | geneontology |
The Gene Ontology (GO) is a major bioinformatics initiative to unify the representation of gene and gene product attributes across all species. More specifically, the project aims to: 1) maintain and develop its controlled vocabulary of gene and gene product attributes; 2) annotate genes and gene products, and assimilate and disseminate annotation data; and 3) provide tools for easy access to all aspects of the data provided by the project, and to enable functional interpretation of experimental data using the GO, for example via enrichment analysis. GO is part of a larger classification effort, the Open Biomedical Ontologies, being one of the Initial Candidate Members of the OBO Foundry.
Whereas gene nomenclature focuses on gene and gene products, the Gene Ontology focuses on the function of the genes and gene products. The GO also extends the effort by using markup language to make the data (not only of the genes and their products but also of curated attributes) machine readable, and to do so in a way that is unified across all species (whereas gene nomenclature conventions vary by biological taxon).
Terms and ontology
From
a practical view, an ontology is a representation of something we know
about. "Ontologies" consist of representations of things that are
detectable or directly observable, and the relationships between those
things.
There is no universal standard terminology in biology and related
domains, and term usages may be specific to a species, research area or
even a particular research group. This makes communication and sharing
of data more difficult. The Gene Ontology project provides an ontology of defined terms representing gene product properties. The ontology covers three domains:
- cellular component, the parts of a cell or its extracellular environment;
- molecular function, the elemental activities of a gene product at the molecular level, such as binding or catalysis;
- biological process, operations or sets of molecular events with a defined beginning and end, pertinent to the functioning of integrated living units: cells, tissues, organs, and organisms.
Each GO term within the ontology has a term name, which may be a word
or string of words; a unique alphanumeric identifier; a definition with
cited sources; and an ontology indicating the domain to which it
belongs. Terms may also have synonyms, which are classed as being
exactly equivalent to the term name, broader, narrower, or related;
references to equivalent concepts in other databases; and comments on
term meaning or usage. The GO ontology is structured as a directed acyclic graph, and each term has defined relationships
to one or more other terms in the same domain, and sometimes to other
domains. The GO vocabulary is designed to be species-neutral, and
includes terms applicable to prokaryotes and eukaryotes, single and multicellular organisms.
GO is not static, and additions, corrections and alterations are
suggested by, and solicited from, members of the research and annotation
communities, as well as by those directly involved in the GO project.
For example, an annotator may request a specific term to represent a
metabolic pathway, or a section of the ontology may be revised with the
help of community experts (e.g.). Suggested edits are reviewed by the ontology editors, and implemented where appropriate.
The GO ontology and annotation files are freely available from the GO website in a number of formats, or can be accessed online using the GO browser AmiGO. The Gene Ontology project also provides downloadable mappings of its terms to other classification systems.
Example term
- id: GO:0000016
- name: lactase activity
- ontology: molecular_function
- def: "Catalysis of the reaction: lactose + H2O=D-glucose + D-galactose." [EC:3.2.1.108]
- synonym: "lactase-phlorizin hydrolase activity" BROAD [EC:3.2.1.108]
- synonym: "lactose galactohydrolase activity" EXACT [EC:3.2.1.108]
- xref: EC:3.2.1.108
- xref: MetaCyc:LACTASE-RXN
- xref: Reactome:20536
- is_a: GO:0004553 ! hydrolase activity, hydrolyzing O-glycosyl compounds
Annotation
Genome annotation
encompasses the practice of capturing data about a gene product, and GO
annotations use terms from the GO ontology to do so. Annotations from
GO curators are integrated and disseminated on the GO website, where
they can be downloaded directly or viewed online using AmiGO. In addition to the gene product identifier and the relevant GO term, GO annotations have at least the following data:
The reference used to make the annotation (e.g. a journal article);
An evidence code denoting the type of evidence upon which the annotation is based;
The date and the creator of the annotation
Supporting information, depending on GO term and evidence used and supplementary information, such as the conditions the function is observed under, may also be included in a GO annotation.
The evidence code comes from a controlled vocabulary of codes, the Evidence Code Ontology, covering both manual and automated annotation methods. For example, Traceable Author Statement
(TAS) means a curator has read a published scientific paper and the
metadata for that annotation bears a citation to that paper; Inferred from Sequence Similarity
(ISS) means a human curator has reviewed the output from a sequence
similarity search and verified that it is biologically meaningful.
Annotations from automated processes (for example, remapping annotations
created using another annotation vocabulary) are given the code Inferred from Electronic Annotation
(IEA). In 2010, over 98% of all GO annotations were inferred
computationally, not by curators, but as of July 2, 2019, only about 30%
of all GO annotations were inferred computationally.
As these annotations are not checked by a human, the GO Consortium
considers them to be marginally less reliable and they are commonly to
higher level, less detailed terms. Full annotation data sets can be
downloaded from the GO website. To support the development of
annotation, the GO Consortium provides workshops and mentors new groups
of curators and developers.
Many machine learning algorithms have been designed and implemented to predict Gene Ontology annotations.
Example annotation
- Gene product: Actin, alpha cardiac muscle 1, UniProtKB:P68032
- GO term: heart contraction ; GO:0060047 (biological process)
- Evidence code: Inferred from Mutant Phenotype (IMP)
- Reference: PMID 17611253
- Assigned by: UniProtKB, June 6, 2008
Tools
There are a large number of tools available
both online and to download that use the data provided by the GO
project. The vast majority of these come from third parties; the GO
Consortium develops and supports two tools, AmiGO and OBO-Edit.
AmiGO
is a web-based application that allows users to query, browse and
visualize ontologies and gene product annotation data. It also has a BLAST tool, tools allowing analysis of larger data sets, and an interface to query the GO database directly.
AmiGO can be used online at the GO website to access the data
provided by the GO Consortium, or can be downloaded and installed for
local use on any database employing the GO database schema (e.g.). It is free open source software and is available as part of the go-dev software distribution.
OBO-Edit
is an open source, platform-independent ontology editor developed and
maintained by the Gene Ontology Consortium. It is implemented in Java, and uses a graph-oriented
approach to display and edit ontologies. OBO-Edit includes a
comprehensive search and filter interface, with the option to render
subsets of terms to make them visually distinct; the user interface can
also be customized according to user preferences. OBO-Edit also has a reasoner
that can infer links that have not been explicitly stated, based on
existing relationships and their properties. Although it was developed
for biomedical ontologies, OBO-Edit can be used to view, search and edit
any ontology. It is freely available to download.
Consortium
The Gene Ontology Consortium is the set of biological databases and research groups actively involved in the gene ontology project. This includes a number of model organism databases and multi-species protein databases, software development groups, and a dedicated editorial office.
History
The Gene Ontology was originally constructed in 1998 by a consortium of researchers studying the genomes of three model organisms: Drosophila melanogaster (fruit fly), Mus musculus (mouse), and Saccharomyces cerevisiae (brewer's or baker's yeast). Many other Model Organism Databases
have joined the Gene Ontology Consortium, contributing not only
annotation data, but also contributing to the development of the
ontologies and tools to view and apply the data. Many major plant,
animal and microorganism databases make a contribution towards this
project. As of July 2019, the GO contains 44,945 terms; there are 6,408,283 annotations to 4,467 different biological organisms. There is a significant body of literature on the development and use of the GO, and it has become a standard tool in the bioinformatics
arsenal. Their objectives have three aspects: building gene ontology,
assigning ontology to gene/gene products and developing software and
databases for the first two objects.
Several analyses of the Gene Ontology using formal,
domain-independent properties of classes (the metaproperties) are also
starting to appear. For instance, an ontological analysis of biological
ontologies see.