Transcriptomic analysis of changes in gene expression of immune proteins of gill tissue in response to low environmental temperature in fathead minnows (Pimephales promelas).

In the face of ongoing climate change, it is imperative to understand better the effects of temperature on immune function in freshwater teleosts. It is unclear whether previously observed changes were caused by temperature per se. We studied changes in the gill transcriptome of fathead minnows (Pimephales promelas) at low temperature to understand better the effects of temperature on immune function. De novo assembly of the transcriptome using Trinity software resulted in 73,378 assembled contigs. Annotation using the Trinotate package yielded 58,952 Blastx hits (accessions). Expression of 194 unique mRNA transcripts changed in gill tissue of fathead minnows acclimatized to 5° compared to controls at 22 °C. At 5 °C mRNAs coding for proteins involved in innate immune responses were up-regulated. Those included proteins that block early-stage viral replication and macrophage activation. Expression of mRNAs coding for pro-inflammatory molecules and mucus secretion were also enhanced. Messenger RNAs coding for proteins associated with adaptive immune responses were down-regulated at 5 °C. Those included antigen-presenting proteins and proteins involved in immunoglobin production. Messenger RNAs coding for proteins that stimulate the cell cycle were also down-regulated at 5 °C. Histological comparison revealed that gills of cold acclimated fish had fewer mucus cells but cells contained larger mucus droplets. We conclude that decreased temperature modifies the immune systems of freshwater teleosts, leading to genome-wide upregulation of innate immunity and down regulation of adaptive immunity. Such acclimation likely evolved as an adaptive strategy against seasonal changes in infectious insults.