Immunologic Profiling of the Atlantic Salmon Gill by Single Nuclei Transcriptomics

Area of Science:

• Physiology
• Cell Biology
• Genomics

Background:

• Anadromous salmonids undergo smoltification for seawater adaptation.
• Gill remodeling is crucial for osmoregulation and immunity during seawater migration.
• Previous studies suggested extensive gill changes, but cellular details remained limited.

Purpose of the Study:

• To comprehensively characterize cytological and gene expression changes in Atlantic salmon gills during smoltification using single-nuclei RNA sequencing.
• To identify novel gill cell types and quantify smoltification-associated cellular alterations.
• To investigate the impact of smoltification on gill immune cell populations.

Main Methods:

• Single-nuclei RNA sequencing (snRNA-seq) of Atlantic salmon gills.
• Bioinformatic analysis to identify distinct cell clusters and gene expression patterns.
• Comparative analysis of gill cellular composition before and after smoltification and seawater transfer.

Main Results:

• Identification of 20 distinct cell clusters in the salmon gill, including novel cell types.
• Quantification of smoltification-associated gene expression changes specific to each cell cluster.
• Observed an increase in seawater mitochondrion-rich cells, alongside a significant reduction in several immune-related cell types.

Conclusions:

• Smoltification induces extensive cellular remodeling in Atlantic salmon gills beyond previously appreciated levels.
• The observed reduction in immune cells suggests a potential immune reprogramming during seawater adaptation.
• These findings provide novel insights into the cellular complexity and immune adaptations of gills during the freshwater-to-seawater transition.