Neofunctionalization of zona pellucida proteins enhances freeze-prevention in the eggs of Antarctic notothenioids

Abstract

The mechanisms by which the eggs of the Antarctic notothenioid fishes avoid freezing are not fully understood. Zona pellucida proteins (ZPs) are constituents of the chorion which forms a protective matrix surrounding the egg. Here we report occurrence of freezing temperature-related gene expansion and acquisition of unusual ice melting-promoting (IMP) activity in a family of Antarctic notothenioid ZPs (AnnotoZPs). Members of AnnotoZPs are shown to bind with ice and non-colligatively depress the melting point of a solution in a range of 0.26 to 0.65 °C at a moderate concentration. Eggs of zebrafishes expressing an AnnotoZP transgene show improved melting point depression and enhanced survival in freezing conditions. Mutational analyses in a representative AnnotoZP indicate the ZP domain and patches of acidic residues are essential structures for the IMP activity. AnnotoZPs, therefore, represent a group of macromolecules that prevent freezing by a unique ZP–ice interaction mechanism distinct from the known antifreeze proteins.

The sterlet sturgeon genome sequence and the mechanisms of segmental rediploidization

“…A total of 116 zp genes were annotated in sterlet (Supplementary Table 18 and Supplementary Note 11). A similar expansion was noted in cold-adapted teleosts and explained as a protection mechanism from physical forces for the developing embryo 61,62 . The biological reason for the zp gene family expansion in sturgeon is unclear.…”

Antarctic blackfin icefish genome reveals adaptations to extreme environments

“…A low-coverage Illumina-based draft assembly of the C. aceratus genome annotated 4 copies of AFGP genes 38 , whereas our results revealed 11 copies of AFGP genes adjacent to 10 tandem copies of trypsinogen genes and 2 copies of trypsinogen-like protease genes. Antarctic fish embryos do not appear to express AFGP genes 12,39 , which raises the question of how these embryos resist freezing 12 . Zona pellucida egg-coat proteins play roles in fertilization and preventing polyspermy in mammals 40 , and provide thickness and hardness to fish eggshells 41 .…”

“…Ancestral notothenioids were red-blooded but had no myoglobin in their skeletal muscle; they lived on the ocean floor and lacked a buoyancy-generating swim bladder. As Antarctica cooled, finally reaching −1.9 °C in the high Antarctic about 10-14 million years ago (Ma) 8 , ecological niches opened into which notothenioids radiated due to adaptive changes for cold tolerance 9 , including antifreeze glycoproteins (AFGPs) in larvae and adults 10,11 , and ice-resistant egg chorion proteins surrounding embryos 12 . Notothenioids, living in constant cold, evolved a substantially non-conventional heat-shock response 13,14 .…”

Fasting enhances cold resistance in fish through stimulating lipid catabolism and autophagy

“…), and generation of antifreeze proteins in freezing environments (Devries, ; Cao et al . ). Moreover, several transcriptomic studies have indicated that numerous genes involved in energy metabolism are changed significantly in several fishes under cold stress (Gracey et al .…”

“…Viewed as either an economic or a research interest, studying the mechanisms of cold resistance in fish is fascinating. Several mechanisms related to cold adaptation in fish have been reported, including the alteration of cell-membrane fluidity (Johnston & Roots, 1964), recruitment of different muscle fibres (Gerlach et al 1990), synthesis of molecular chaperones (Fader et al 1994;Donaldson et al 2008), and generation of antifreeze proteins in freezing environments (Devries, 1971;Cao et al 2016). Moreover, several transcriptomic studies have indicated that numerous genes involved in energy metabolism are changed significantly in several fishes under cold stress (Gracey et al 2004;Mininni et al 2014), and a transgenic zebrafish (Danio rerio) strain expressing carp muscle-specific form III of creatine kinase showed enhanced cold resistance .…”