A Unique Seminal Plasma Protein, Zona Pellucida 3-Like Protein, has Ca2+ -Dependent Sperm Agglutination Activity

Identification of seminal proteins provides a means of investigating their roles. Despite their importance in the study of protein function, such as regulation of sperm motility, it is difficult to select candidates from the large number of proteins. Analyzing the rate of molecular evolution is a useful strategy for selecting candidates, and expressing the protein allows the examination of its function. In the present study, we investigated seminal plasma proteins of the cichlid Oreochromis mossambicus, which exhibits a unique mode of fertilization and a rapidly evolving gene that encodes a seminal plasma protein, zona-pellucida 3-like (ZP3-like), which does not belong to the same molecular family as other ZPs. Seminal plasma proteins of O. mossambicus were separated by two-dimensional electrophoresis, and 19 major proteins were identified by mass spectrometry (MALDI-Tof Mass). Because proteins that are under positive selection often impact sperm function, the rates of molecular evolution of these proteins were analyzed in terms of non-synonymous/synonymous substitutions (ω). Among the 19 proteins, positive selection was supported for five genes; functional assays were carried out on four of the proteins encoded by these genes. Of the four positively selected proteins, only ZP3-like protein agglutinated sperm in a dose- and Ca²⁺ -dependent manner. The other three proteins did not affect sperm motility. Because of the unique fertilization type, in which fertilization occurs in the buccal cavity, the need to retain sperm within the cavity during spawning, and the agglutination of sperm, which may be partly assisted by ZP3-like protein, may contribute to fertilization success. Fertilization in the buccal cavity may be related to its rapid molecular evolution.

Enhanced dietary formulation to mitigate winter thermal stress in gilthead sea bream (Sparus aurata): a 2D-DIGE plasma proteome study

Low water temperatures during winter are common in farming of gilthead sea bream in the Mediterranean. This causes metabolic disorders that in extreme cases can lead to a syndrome called "winter disease." An improved immunostimulatory nutritional status might mitigate the effects of this thermal metabolic stress. A trial was set up to assess the effects of two different diets on gilthead sea bream physiology and nutritional state through plasma proteome and metabolites. Four groups of 25 adult gilthead sea bream were reared during winter months, being fed either with a control diet (CTRL) or with a diet called "winter feed" (WF). Proteome results show a slightly higher number of proteins upregulated in plasma of fish fed the WF. These proteins are mostly involved in the immune system and cell protection mechanisms. Lipid metabolism was also affected, as shown both by plasma proteome and by the cholesterol plasma levels. Overall, the winter feed diet tested seems to have positive effects in terms of fish condition and nutritional status, reducing the metabolic effects of thermal stress.

Characterization, expression and antibacterial properties of apolipoproteins A from carp (Cyprinus carpio L.) seminal plasma

Apolipoproteins A are multifunctional proteins that, in addition to contributing to lipid metabolism and transport, are associated with the innate immune system in fish. Using a three step isolation procedure consisting of affinity chromatography on Blue-Sepharose, delipidation and reverse phase HPLC we isolated apolipoproteins from carp seminal plasma and identified them as ApoA-I and Apo-14 kDa. Moreover, we provided the full-length cDNA sequence of ApoA-I encoding 257 amino acids including a 18 amino acid signal peptide and a 4 amino acid propeptide. Apolipoproteins corresponded to the most abundant proteins in carp seminal plasma. Both ApoA-I and Apo-14 kDa were represented by several proteoforms that differ both in molecular mass and isoelectric point. The proteoforms of ApoA-I characteristic for seminal plasma were distinguished from those of blood. Carp seminal plasma ApoA-I and Apo-14 kDa showed a high immunologic similarity to their counterparts in carp blood and seminal plasma of other Cyprinid species. The mRNA expression analysis and immunohistochemical study suggest synthesis and secretion of ApoA-I and Apo-14 kDa in the fish reproductive tract and suggest a role in spermatogenesis and the stabilization of sperm membrane. Moreover, ApoA-I displayed bactericidal activity against Escherichia coli and bacteriostatic activity against Aeromonas hydrophila which suggests that ApoA-I is associated with innate immune system of the fish reproductive tract.

Sperm and seminal fluid proteomes of the field cricket Teleogryllus oceanicus: identification of novel proteins transferred to females at mating

Reproductive proteins are amongst the most evolutionarily divergent proteins known, and research on genetically well-characterized species suggests that postcopulatory sexual selection might be important in their evolution; however, we lack the taxonomic breadth of information on reproductive proteins that is required to determine the general importance of sexual selection for their evolution. We used transcriptome sequencing and proteomics to characterize the sperm and seminal fluid proteins of a cricket, Teleogryllus oceanicus, that has been widely used in the study of postcopulatory sexual selection. We identified 57 proteins from the sperm of these crickets. Many of these had predicted function in glycolysis and metabolism, or were structural, and had sequence similarity to sperm proteins found across taxa ranging from flies to humans. We identified 21 seminal fluid proteins, some of which resemble those found to be involved in postmating changes to female reproduction in other species. Some 27% of sperm proteins and 48% of seminal fluid proteins were of unknown function. The characterization of seminal fluid proteins in this species will allow us to explore their adaptive significance, and to contribute comparative data that will facilitate a general appreciation of the evolution of reproductive proteins within and among animal taxa.