Seasonal gene expression in a migratory songbird

Abstract

The annual migration of a bird can involve thousands of kilometres of nonstop flight, requiring accurately timed seasonal changes in physiology and behaviour. Understanding the molecular mechanisms controlling this endogenous programme can provide functional and evolutionary insights into the circannual biological clock and the potential of migratory species to adapt to changing environments. Under naturally timed photoperiod conditions, we maintained captive Swainson's thrushes (Catharus ustulatus) and performed RNA sequencing (RNA-Seq) of the ventral hypothalamus and optic chiasma to evaluate transcriptome-wide gene expression changes of individuals in migratory condition. We found that 188 genes were differentially expressed in relation to migratory state, 86% of which have not been previously linked to avian migration. Focal hub genes were identified that are candidate variables responsible for the occurrence of migration (e.g. CRABP1). Numerous genes involved in cell adhesion, proliferation and motility were differentially expressed (including RHOJ, PAK1 and TLN1), suggesting that migration-related changes are regulated by seasonal neural plasticity.

Timing avian long-distance migration: from internal clock mechanisms to global flights

“…Likewise, we expect that the interpretation of field data can be guided by growing insights into timing mechanisms gathered from captive studies. A particularly promising avenue are genetic approaches 5,116,141,[165][166][167][168][169] . These are increasingly used to identify mechanistic processes, specific features, and evolutionary consequences of migration.…”

“…These are increasingly used to identify mechanistic processes, specific features, and evolutionary consequences of migration. For example, several recent studies compared gene expression, either globally or for candidate genes, between migrants and non-migrants, or between migrants during and outside migration phases 141,[165][166][167][168] . These studies give important leads to identifying the physiological organization of the timing of migration and the interactive roles of different physiological systems.…”

Hypothalamic and liver transcriptome from two crucial life‐history stages in a migratory songbird

“…Specifically, there was an increased expression of genes associated with lipid transport and fatty acid catabolic processes in the muscle and with a ribosomal structure that indicated protein synthesis in the blood of the migrant ( J. h. hyemalis ) compared with the resident ( J. h. carolinensis ) juncos (Fudickar et al., ). Furthermore, Johnston, Paxton, Moore, Wayne, and Smith () performed RNA‐Seq of brain tissue, and found that genes involved in focal adhesion, proliferation and motility had higher expression during the migratory state than during the non‐migratory state in the ventral hypothalamus of captive Swainson's thrushes ( Catharus ustulatus ). In contrast, a study of the blood transcriptome on partial migratory European blackbirds ( Turdus merula ) reported only four differentially expressed genes that are possibly associated with the hyperphagia, moulting and enhanced DNA replication in blackbirds (Franchini et al., ).…”

Avian transcriptomics: opportunities and challenges

“…Using comparative gene expression, we can get a better understanding of how the genome is regulated at different stages of bird migration (Box 2). Johnston et al (2016), using RNA-seq data, found 188 genes that were differentially expressed in the brain of captive Swainson's Thrushes Catharus ustulatus during different migratory states. A large number of these genes were associated with functions such as cell adhesion, proliferation and motility, and the authors hence suggested that migration-related changes might be regulated by seasonal neural plasticity (Johnston et al 2016).…”

“…Johnston et al (2016), using RNA-seq data, found 188 genes that were differentially expressed in the brain of captive Swainson's Thrushes Catharus ustulatus during different migratory states. A large number of these genes were associated with functions such as cell adhesion, proliferation and motility, and the authors hence suggested that migration-related changes might be regulated by seasonal neural plasticity (Johnston et al 2016). However, migration is a complex behaviour, which certainly involves hundreds of genes, some of them with known functions (these can be identified by annotation with other known genes) and others, for which a function still needs to be explored.…”