Comparative ultrastructure and proteomics of two economic species (common carp and grass carp) egg envelope

Abstract

Progressive morphological and cytochemical processes occur in the egg after fertilization in which the egg envelope changes dramatically. However, the biochemical and structural alterations of egg envelope between common carp adhesive eggs and grass carp semi-buoyant eggs remain poorly understand. Here, this study found that compared with grass carp semi-buoyant eggs, common carp adhesive eggs possess a smaller egg diameter and a thicker egg envelope, and the difference was most significant at 1 h postfertilization. After fertilization, an adhesive layer was found and gradually thickened in common carp eggs, especially at 1 h postfertilization. The surface of fertilized adhesive egg of common carp was covered by a dense adhesive layer which gradually grew to be thickened after fertilization. While grass carp semi-buoyant eggs did not possess an adhesive layer after fertilization and the surface of grass carp semi-buoyant egg was smoother. Moreover, proteomic changes of egg envelopes between common carp adhesive eggs and grass carp semi-buoyant eggs at 1 h postfertilization showed that a rapid fold change of cytoskeleton-associated proteins (including actin, filamin-A, α-actinin, cytoskeleton-associated protein 5, and ezrin) was observed in common carp egg envelope after fertilization, which might be conductive to maintaining cell morphology and fish egg morphology. Significant upregulation of proteins such as a coagulation factor XIII A protein, zona pellucida proteins and cystatin in the fertilized egg of common carp might be responsible for inducing the process of egg envelope hardening in order to the protection of embryonic development. Obviously up-regulated level of alpha-2-macroglobulin-like protein in the fertilized egg of common carp could reflect the potentials of the effective immune defense in fertilized adhesive eggs of common carp. In conclusion, this study is the first to present the ultrastructure and protein composition in the egg envelope of common carp adhesive eggs and grass carp semi-buoyant eggs. Extensive changes in the abundance of proteins of egg envelope would throw some new lights on the biochemical processes underlying the early developmental processes after fertilization.