Hypothalamic and liver transcriptome from two critical life-history stages in a migratory songbird

Abstract

Very little is understood about genetic mechanisms underlying the onset of spring migration in latitudinal avian migrants. To gain insight into genetic architecture of the hypothalamus and liver tissues of a long-distance migrant, we examined and compared the transcriptome profile of captive night-migratory blackheaded buntings (Emberiza melanocephala) between photoperiodically-induced winter non-migratory (WnM) and spring migratory (SM) life-history states (LHSs) under short and long days, respectively. High-throughput 454 pyrosequenced transcripts were mapped initially with reference to the genome of two phylogenetically close species, Taeniopygia guttata and Ficedula albicollis. The F. albicollis genome gave higher annotation results, and was used for further analysis. A total of 216 (78 in hypothalamus; 138 in liver) genes were found to be differentially expressed between the WnM and SM LHSs. These genes were enriched for physiological pathways, which may be involved in regulating seasonal migrations in birds. For example, genes that enriched for ATP binding pathway in the hypothalamus were expressed at a significantly higher level in SM than in the WnM LHS. Similarly, upregulated genes associated with myelin sheath and focal adhesion were enriched in the hypothalamus, and those with cell-to-cell junction, intracellular protein transport, calcium ion transport and small GTPase-mediated signal transduction were enriched in the liver. Many of these genes are a part of physiological pathways potentially involved in regulating seasonal migration in birds. These results show molecular changes at the regulatory and metabolic levels associated with seasonal transitions in a long-distance migrant, and provide bases for future studies aimed at unravelling the genetic control of migration in birds.

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