14 As for the SP, availability of seminal material has not been an issue because volumes are sufficient for analyses for either human or animal studies. Moreover, sampling methods can be refined for examination of other portions than the bulk ejaculate, Ceritinib mouse such as specific fractions or even specific accessory glands (for instance after massage expression of prostate, seminal vesicles, etc.). Neither does the protein content matter, because proteins are a major component, throughout species. Major SP proteins belong to one of three main groups: proteins carrying fibronectin type II (Fn-2) modules, spermadhesins

or cysteine-rich secretory proteins (CRISPs).30 However, differences in type

and source of proteins are present among species, owing BMS-777607 to the already named differences in glands and/or the sequence they are emptied or the type of ejaculate they have. In most species, proteins are mainly of vesicular gland origin, and in ungulate mammals (boar, stallion, bull, buck), most proteins are Fn2 and/or spermadhesins.30,31 Spermadhesins have been most thoroughly studied in pig SP, as a family built by the following three members: the Alanine–Glutamine–Asparagine proteins AQN (−1 and −3), the Alanine–Tryptophan–Asparagine proteins (AWNs) and the porcine seminal plasma proteins I and II (PSP-I and PSP-II).32 Spermadhesins are multifunctional 12- to 16-kDa glycoproteins whose biological activities depend on their sequence, grade of glycosylation or aggregation state, as well as on their ability to bind heparin [AQN-1, AQN-3 and AWN, grouped as O-methylated flavonoid heparin-binding proteins (HBPs)] or not (PSPs), as they attach in varying

degree, to the sperm plasma membrane, from the testis to the ejaculate. Collectively, they have been related to multiple effects on spermatozoa including membrane stabilization, capacitation and interplay between sperm–oviductal lining or sperm-ZP. The HBPs seem to stabilize the plasma membrane over the acrosome prior to capacitation.33 Detection of AWN epitopes on boar spermatozoa bound in vivo to the ZP strongly suggests that the protein mediates sperm–ZP interaction.34 While HBPs do not seem to promote sperm survival, at least in vitro,35 the non-heparin-binding PSP-I and PSP-II,36,37 which accounts for >50% of all SP proteins and forms a glycosylated heterodimer,38 binds to the sperm surface and displays protective action on highly extended and processed spermatozoa.39,40 The PSPs depict, moreover, clear immunostimulatory activities in vitro and in vivo, presumably in relation to specific cytokines.