Brain transcriptomes of harbor seals demonstrate gene expression patterns of animals undergoing a metabolic disease and a viral infection.

Stephanie M Rosales,Rebecca L Vega Thurber

doi:10.7717/peerj.2819

Abstract

Diseases of marine mammals can be difficult to diagnose because of their life history and protected status. Stranded marine mammals have been a particularly useful resource to discover and comprehend the diseases that plague these top predators. Additionally, advancements in high-throughput sequencing (HTS) has contributed to the discovery of novel pathogens in marine mammals. In this study, we use a combination of HTS and stranded harbor seals (Phoca vitulina) to better understand a known and unknown brain disease. To do this, we used transcriptomics to evaluate brain tissues from seven neonatal harbor seals that expired from an unknown cause of death (UCD) and compared them to four neonatal harbor seals that had confirmed phocine herpesvirus (PhV-1) infections in the brain. Comparing the two disease states we found that UCD animals showed a significant abundance of fatty acid metabolic transcripts in their brain tissue, thus we speculate that a fatty acid metabolic dysregulation contributed to the death of these animals. Furthermore, we were able to describe the response of four young harbor seals with PhV-1 infections in the brain. PhV-1 infected animals showed a significant ability to mount an innate and adaptive immune response, especially to combat viral infections. Our data also suggests that PhV-1 can hijack host pathways for DNA packaging and exocytosis. This is the first study to use transcriptomics in marine mammals to understand host and viral interactions and assess the death of stranded marine mammals with an unknown disease. Furthermore, we show the value of applying transcriptomics on stranded marine mammals for disease characterization.

Highlights

The combination of high-throughput sequencing (HTS) and stranded marine mammals for disease discoveryThe health of wild marine mammal populations is difficult to assess because of their unknown population sizes, large distributions, and protected status
Each library was aligned to the harbor seal de novo transcriptome with alignments ranging from 17.1% to 28.05% and there were no significant differences between PhV-1com and unknown cause of death (UCD) alignments (Welch Two Sample t -test, p-value = 0.2825)
In our previous work on this data set, we found that there was a significant abundance of Burkholderia transcripts in UCD animals and our new results indicate that these same animals exhibit high fatty acid metabolic process gene expression (Fig. 3)

Summary

Introduction

The combination of high-throughput sequencing (HTS) and stranded marine mammals for disease discoveryThe health of wild marine mammal populations is difficult to assess because of their unknown population sizes, large distributions, and protected status. The combination of high-throughput sequencing (HTS) and stranded marine mammals for disease discovery. In 2007, it was reported that only 56% of marine mammal mortality events had a known cause of death (Gulland & Hall, 2007), leaving the pathogens and physiological causes of many diseases to be discovered. The introduction of high-throughput sequencing (HTS) has led to the identification of many more marine mammal pathogens, such as seal and California sea lion anellovirus, phocine herpesvirus 7, and seal parvovirus (Ng et al, 2009; Ng et al, 2011; Bodewes et al, 2013; Kuiken et al, 2015). The combination of stranded animals and HTS are vital resources for the discovery of marine mammal diseases

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