Background:
Migrant birds prepare differently to fly north for breeding in spring and for the flight to lower latitudes during autumn avoiding the cold and food shortages of the north hemisphere's harsh winter. The molecular events associated with these fundamental stages in the life history of migrants include the differential gene expression in different tissues. Semipalmated sandpipers (Calidris pusilla) are Artic breeding shorebirds that migrate to the coast of South America during non-breeding season. Thus, the adaptive molecular changes in the brain of these birds at lower latitudes have not yet been investigated in detail.
Results:
Here, we searched for differential gene expression in the brain of semipalmated sandpiper, of recent arrived birds (RA) from autumnal migration and that of individuals in the premigratory period (PM) in the spring. All individuals were collected in the tropical coastal of northern Brazil. We generated a De novo neurotranscriptome for C. pusilla individuals and compared gene expression across libraries for neurotranscriptome. To that end we mapped RNA-seq reads to the C. pusilla neurotranscriptome in a total of 4 brain samples each group. A total of 266,414 transcripts were reconstructed that yielded 615 differentially expressed genes in the brain of both groups.
Conclusions:
The present report revealed a remarkable differential gene expression in the brain of recently arrived and premigratory individuals. It also revealed molecular brain changes associated with the recovering of the 4 to 5 days long-distance uninterrupted flight across Atlantic Ocean and preparation for the long-distance multiple stopover spring migration.
Migrant birds prepare differently to fly north for breeding in the spring and for the flight to lower latitudes during autumn, avoiding the cold and food shortages of the Northern Hemisphere’s harsh winter. The molecular events associated with these fundamental stages in the life history of migrants include the differential gene expression in different tissues. Semipalmated sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that migrate to the coast of South America during the non-breeding season. In a previous study, we demonstrated that between the beginning and the end of the wintering period, substantial glial changes and neurogenesis occur in the brain of C. pusilla. These changes follow the epic journey of the autumn migration when a 5-day non-stop transatlantic flight towards the coast of South America and the subsequent preparation for the long-distance flight of the spring migration takes place. Here, we tested the hypothesis that the differential gene expressions observed in the brains of individuals captured in the autumn and spring windows are consistent with the previously described cellular changes. We searched for differential gene expressions in the brain of the semipalmated sandpiper, of recently arrived birds (RA) from the autumnal migration, and that of individuals in the premigratory period (PM) in the spring. All individuals were collected in the tropical coastal of northern Brazil in the mangrove region of the Amazon River estuary. We generated a de novo neurotranscriptome for C. pusilla individuals and compared the gene expressions across libraries. To that end, we mapped an RNA-Seq that reads to the C. pusilla neurotranscriptome in four brain samples of each group and found that the differential gene expressions in newly arrived and premigratory birds were related with neurogenesis, metabolic pathways (ketone body biosynthetic and the catabolic and lipid biosynthetic processes), and glial changes (astrocyte-dopaminergic neuron signaling, astrocyte differentiation, astrocyte cell migration, and astrocyte activation involved in immune response), as well as genes related to the immune response to virus infections (Type I Interferons), inflammatory cytokines (IL-6, IL-1β, TNF, and NF-κB), NLRP3 inflammasome, anti-inflammatory cytokines (IL-10), and cell death pathways (pyroptosis- and caspase-related changes).
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