Bioconductor Annotationhub

AnnotationHub — Comprehensive Skill Guide

Domain: Annotation / Genomics Bioconductor: AnnotationHub Paper: Morgan M et al. (2021). Bioconductor package.

Access a large collection of biologically relevant annotation resources (genome sequences, chain files, GTF, OrgDbs, TxDbs) directly from within R via the Bioconductor AnnotationHub.

Dependencies & Environment

Package-intrinsic requirements from the Bioconductor landing page — reproduce in any R environment.

• Version: 4.2.0 · Bioconductor: 3.23 · R: ≥ 4.6
• Depends: BiocGenerics, BiocFileCache
• Imports: RSQLite, BiocManager, BiocVersion, curl, rappdirs, AnnotationDbi, S4Vectors, httr2, yaml, dplyr, BiocBaseUtils
• Install: BiocManager::install("AnnotationHub")

When to Use

• Download organism annotation databases (OrgDb, TxDb, EnsDb)
• Get GTF/GFF files, chain files, FASTA sequences for any organism
• Access reference genome resources without manual downloads

Alternatives: GenomicFeatures::makeTxDbFromGFF(), biomaRt, BSgenome

Do NOT Use When

• Custom/proprietary genome builds not in Ensembl or UCSC.
• Real-time annotation updates — hub resources are versioned snapshots.

Data Requirements

Installation

if (!require("BiocManager", quietly=TRUE))
    install.packages("BiocManager")
BiocManager::install("AnnotationHub")
library(AnnotationHub)

Workflows

Query and retrieve Bioconductor annotation resources

Find and load genome annotations, ortholog mappings, and database snapshots

Connect and search AnnotationHub

library(AnnotationHub)
ah <- AnnotationHub()       # connects to Bioconductor AnnotationHub cloud

# Search by species and data type
query(ah, c("Homo sapiens", "EnsDb"))
query(ah, c("Mus musculus", "TxDb"))
query(ah, c("GRCh38", "gtf"))

Retrieve a specific resource

# Fetch Ensembl 108 database for human
edb <- ah[["AH98047"]]       # EnsDb.Hsapiens.v108 equivalent
genes(edb)                   # returns GRanges of all genes

# Fetch GENCODE GTF as GRanges
gr <- ah[["AH49556"]]

Use OrgDb for gene-symbol mapping

# Load human OrgDb
org_hs <- ah[["AH114084"]]   # org.Hs.eg.db snapshot
library(AnnotationDbi)
mapIds(org_hs, keys=c("BRCA1","TP53"), column="ENTREZID", keytype="SYMBOL")

Key Functions & Parameters

AnnotationHub()()

Create an AnnotationHub connection

query()()

Search the hub for resources

ah[[id]]()

Download and load a resource by its AH identifier (e.g. 'AH12345')

mcols()()

View metadata for all resources in a filtered hub

display()()

Interactive Shiny browser for AnnotationHub records

Scientific Assumptions

The method assumes the following about your data and experiment:

• Hub resources are pre-curated and versioned — use the same resource ID for reproducibility.

Result Interpretation

• Each resource has a unique AH identifier (e.g. AH98047) — record this for reproducibility.
• EnsDb objects: use genes(), exons(), transcripts() to extract annotation tables.
• TxDb objects: use makeTxDbFromEnsembl() alternatively for more control.

Best Practices

• Use query(ah, c('Homo sapiens', 'EnsDb', '109')) to find species + resource type + version.
• Save downloads locally with saveRDS() to avoid re-downloading in each session.
• Set options(timeout=300) before downloading large resources.
• Use ah$species and ah$rdataclass columns to filter results before downloading.

When to Choose This vs Alternatives

Benchmark Evidence

AnnotationHub is infrastructure rather than a statistical method; formal benchmarks compare it against manual download pipelines.

• Morgan M, Shepherd L (2022). Bioconductor Annotation Infrastructure. Bioconductor Workflows AnnotationHub reduces annotation retrieval from hours to seconds; reproducible snapshots improve cross-study comparability vs. manual genome downloads.

• Gentleman RC et al. (2004). Genome Biol 5:R80. PMID:15461798 Foundational Bioconductor paper establishing annotation infrastructure that AnnotationHub extends; cited for the broader ecosystem providing interoperability guarantees.

Common Errors & Troubleshooting

Error in .AnnotationHub_cache: cache invalid or corrupt

Cause: Partial download or corrupted cache

Fix: Remove cache: removeCache(ah); ah <- AnnotationHub()

Additional Notes from Official Documentation

Extracted from the AnnotationHub Bioconductor vignette(s)

Contents

2 Troubleshooting 2.1 Accessing Behind A Proxy 2.1 Accessing Behind A Proxy 3 Other configuration options for resource downloading 3.1 Invalid Cache 3.2 Corrupt Cache 3.2.1 sqlite file 3.2.2 index file 3.2.3 resource path 3.2.4 resource id 3.3 Corrupt Database 3.4 Cannot retrieve resource 3.5 Offline localHub usage 3.1 Invalid Cache 3.2 Corrupt Cache 3.2.1 sqlite file 3.2.2 index file 3.2.3 resource path 3.2.4 resource id 3.2.1 sqlite file 3.2.2 index file 3.2.3 resource path 3.2.4 resource id 3.3 Corrupt Database 3.4 Cannot retrieve resource 3.5 Offline localHub usage 4 Group Hub/Cache Access 5 Lock file Troubleshooting 5.1 Permissions 5.2 Cannot lock file / no lock available 5.1 Permissions 5.2 Cannot lock file / no lock available 6 Default Caching Location Update 6.1 Option 1: Move cac

1 Overview

In spring 2019 the Hubs ( AnnotationHub / ExperimentHub ) upgraded their backend to utilize BiocFileCache . This upgrade changed how resources were downloaded and saved. While the Hub code itself ensures validity, it is possible to access the BiocFileCache of resources directly without the Hub front ends, which opens up the possibility of having caching problems. This document will touch on some troubleshooting for these issues as well as any other frequently asked issues. If the question or answer cannot be found here please ask on the Bioconductor Support Site or on the mailing list bioc-devel@r-project.org

2.1 Accessing Behind A Proxy

The ExperimentHub and AnnotationHub use CRAN package httr2 functions for accessing and downloading web resources. This can be problematic if operating behind a proxy. You can pass proxy information for Hubs by setting the options like the following: Unfortunately unlike the previously used httr::set_config , there is no option to globally set the proxy for httr2 requests. To get around this you can also set a system wide environment variable “ANNOTATION_HUB_PROXY” for AnnotationHub, “EXPERIMENT_HUB_PROXY” for ExperimentHub, or “HUB_PROXY” that will work across all Hub classes (e.g. AnnotationHub and ExperimentHub)}

proxy <- "http://my_user:my_password@myproxy:8080"
AnnotationHub::setAnnotationHubOption("PROXY", proxy)
## or 
ExperimentHub::setExperimentHubOption("PROXY", proxy)

3 Other configuration options for resource downloading

As mentioned previously, There is no global option like httr::set_config to set configuration options when using httr2. A config argument may be passed to [[ and cache functions. This argument is a R list object that will be passed to httr2::req_options . The names of the items should be valid curl options as defined in curl::curl_options .

ssl_opts <- list(verbose = 1L,ssl_verifypeer = 0L, ssl_verifyhost = 0L)

3.1 Invalid Cache

An invalid cache ERROR results from a missing sqlite or index file in the Hub’s BiocFileCache. The Hub code needs these files in order to operate correctly. Rerun the Hub constructor ( AnnotationHub() or ExperimentHub() ) again. If you were trying to run the constructor with localHub=TRUE , you will have to run localHub=FALSE at least once to redownload the Hub sqlite file.

3.2 Corrupt Cache

A corrupt cache ERROR results from multiple entries in the BiocFileCache matching a query for a particular file. This will involve removing one, multiple, or all entries for a file. Please see specific section below although all follow the same principles.

3.2.1 sqlite file

If the sqlite file is the problematic file you should see something like the following (maybe be experimenthub.sqlite3 respectively) You will need to investigate the underlying BiocFileCache for the Hub and remove some or all of the files so that there is only a single entry for the filename. Call the BiocFileCache constructor with the path listed as cache in the ERROR message. Now we can query the BiocFileCache using the filename of the ERROR message. This shows the number of entries for the filename. There should only be one row You will need to deterime if you can validate which entry should remain by evaluating the entries in the cache; [dplyr package][] methods may be useful for parsing the tibble res object. If you can identify which entry should be kept - remove the other entries i

> ah = AnnotationHub()
Error: Corrupt Cache: sqlite file
  See AnnotationHub's TroubleshootingTheHubs vignette section on corrupt cache
  cache: /home/lori/.cache/AnnotationHub
  filename: annotationhub.sqlite3

library(BiocFileCache)
bfc <- BiocFileCache("/home/lori/.cache/AnnotationHub")

3.2.1.1 redownload of sqlite file

A force redownload of the sqlite hub file can be achieved through the refreshHub function. To specify which of the Bioconductor Hubs to redownload use the hubClass argument with either AnnotationHub or ExperimentHub.

ah2 = refreshHub(hubClass="AnnotationHub")

Resources

• Bioconductor page: https://bioconductor.org/packages/release/bioc/html/AnnotationHub.html
• Vignette: https://bioconductor.org/packages/release/bioc/html/AnnotationHub.html
• GitHub:
• Bioconductor support forum: https://support.bioconductor.org/
• Paper: Morgan M et al. (2021). Bioconductor package.

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