Proteomic Analysis of Chinook Salmon Ovarian Fluid Composition

Secretory epithelia in the ovaries and filtered blood plasma of the Salmonidae family are responsible for the production of ovarian, or coelomic, fluid. Approximately 10–30% of spawned egg mass is coelomic fluid. Previous studies have shown that the fluid itself affects important functions in the reproductive process—among them, those linked to sperm motility and speed.

Using mass spectrometric protein analysis, Johnson et al. recently characterized the coelomic fluid of mature, three-year-old Chinook salmon.¹ They collected coelomic fluid from 25 Chinook and initially performed one-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis (1D SDS-PAGE). This process excluded five salmon from the remainder of the experiments, as they showed unusually strong protein bands that indicated contamination with albumin and other plasma proteins. In the remaining 20 samples, the investigators found five regions (up to 10 kDa,10–18 kDa, 20–55 kDa, 55–90 kDa, and 90–260 kDa) that they excised, performing in-gel trypsin digestion. Johnson et al. then analyzed the samples in an UltiMate 3000 nanoflow uHPLC system coupled in-line to the nanospray source of an LTQ Orbitrap XL hybrid ion trap-Orbitrap mass spectrometer (Thermo Scientific). They selected the five strongest signals for collision-induced dissociation (CID)–tandem mass spectrometry in the LTQ Orbitrap XL mass analyzer.

Mass spectrometric data identified 174 proteins in the salmon coelomic fluid samples. When classified according to biological process, the research team identified six gene ontology (GO) categories within the coelomic fluid: response to chemical stimulus, response to hypoxia, response to estradiol, response to bacterium, the formation of somites in the developing embryo, and epiboly involved in gastrulation. The investigators further note that they found no homology to known sperm attraction or sperm-activating peptides among the 174 proteins. Of the proteins assigned to the GO pathway “response to chemical stimulus,” the complement components produced by the immune system particularly stood out as potentially important in affecting sperm performance traits. Studies of the complement system in humans and some species of trout have shown these to be significant in the events leading up to fertilization. Additionally, numerous forms of vitellogenin were identified in salmon ovarian fluid; the authors suggest these could be important in mediating sperm motility.

This study is the first to characterize Chinook salmon coelomic fluid. The investigators identified 174 different proteins, with the potential to identify more if the salmon genome is fully sequenced. Further research may elucidate factors influencing successful egg production and fertilization in Chinook salmon.

References

1. Johnson, S.L, et al. (2014, August) “Proteomic Analysis of Chinook Salmon (Oncorhynchus tshawytscha) Ovarian Fluid,” PLOS ONE, doi: 10.1371/journal.pone.0104155.

Post Author: Miriam Pollak. Miriam specialised in neuroscience as an undergraduate but traded in lab work for a post graduate degree in science communication.

She has since had a career that has spanned science communication, science education and communications management.

However, Miriam has found her bliss balancing her love of writing and disseminating medical research with managing a multimillion dollar research budget for a childhood cancer charity in Australia.

Oh, and because she’s a sucker for punishment… she’s just started a Masters in Human Nutrition…

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