The Zebrafish Perivitelline Fluid Provides Maternally-Inherited Defensive Immunity

Abstract

In the teleost egg, the embryo is immersed in an extraembryonic fluid that fills the space between the embryo and the chorion and partially isolates it from the external environment, called the perivitelline fluid (PVF). The exact composition of the PVF remains unknown in vertebrate animals. The PVF allows the embryo to avoid dehydration, to maintain a safe osmotic balance and provides mechanical protection; however, its potential defensive properties against bacterial pathogens has not been reported. In this work, we determined the global proteomic profile of PVF in zebrafish eggs and embryos, and the maternal or zygotic origin of the identified proteins was studied. In silico analysis of PVF protein composition revealed an enrichment of protein classes associated with non-specific humoral innate immunity. We found lectins, protease inhibitors, transferrin, and glucosidases present from early embryogenesis until hatching. Finally, in vitro and in vivo experiments done with this fluid demonstrated that the PVF possessed a strong agglutinating capacity on bacterial cells and protected the embryos when challenged with the pathogenic bacteria Edwardsiella tarda. Our results suggest that the PVF is a primitive inherited immune extraembryonic system that protects the embryos from external biological threats prior to hatching.

A New Bioassay for the Detection of Paralytic and Amnesic Biotoxins Based on Motor Behavior Impairments of Zebrafish Larvae

“…On the other hand, the LMA of 5 dpf individuals is not affected by small incubation volume ranging from 50 to 100 µL (Figure 1d), but it is significantly higher when the incubation volume is 200 µL. This is important since a small incubation volume allows the testing by immersion of expensive compounds, as is the case of marine biotoxin standards, difficult to obtain extracts such as the fish egg's perivitelline fluid [40] or others, using small amounts of test substances or samples without compromising the reproducibility of the results and the robustness of the statistical analysis by the reduction of technical replicates.…”

Developing Inside a Layer of Germs—A Potential Role for Multiciliated Surface Cells in Vertebrate Embryos

“…Zebrafish embryos have an active innate immune response with macrophages and neutrophils maturing early in development [55,56], while adaptive immune responses mature after hatching [57]. Recent work using proteomics has revealed enhanced innate immune functions in perivitelline fluid in zebrafish embryos over three stages of development [58]. Peptide mass spectrometry revealed candidate lectins, glucosidases, alpha-macroglobulin protease inhibitors, and chitinase modifying enzymes inherited from the mother as well as iron co-factor chelation by zygotic transferrin-a.…”

Microbiome composition and function within the Kellet’s whelk perivitelline fluid

“…In this study, we explored the diversity and functional role of the microbiome in the perivitelline fluid (PVF) in egg capsules of Kellet’s whelk, Kelletia kelletii , a coastal marine, predatory gastropod, and commercial fisheries species along the North American West Coast ( 13 ). Similar to some other marine invertebrates [e.g., near-shore squid ( Doryteuthis opalescens ), Apple Snail ( Pomacea maculata ), and Horseshoe crab ( Tachypleus tridentatus )], Kellet’s whelk exhibits a bi-partite life history (dispersive larvae, relatively sessile adults) and females lay egg capsules on hard substrate (e.g., reef) in the coastal marine environment, each containing hundreds to potentially more than 1,000 eggs that develop (prior to dispersal) for 35–45 days while suspended in a PVF consisting of a polysaccharide and protein matrix ( 14 – 17 ). This PVF most likely originates from an albumen exocrine gland within the mother ( 18 ).…”

“…The PVF secreted by these glands have been reported to nourish and protect developing eggs. For example, in Zebrafish ( Danio rerio ) and the sea hare ( Aplysia kurodai ), the PVF contains immune defense proteins and antibacterial factors that protect embryos from pathogenic infection ( 15 , 19 ), and the PVF of the Apple Snail produces plant-like defenses that deter predation and pathogenic infection ( 20 – 23 ); for both species, the defense mechanisms are believed to be maternally inherited. The PVF may also contain functional microbiomes that can be vertically transferred to the PVF of egg capsules.…”