Identification and characterisation of siglec expression on sperm and in the male reproductive tract

The sialic acids (Sias) are a uniquely diverse group of sugars that are ubiquitous on a wide range of glycoproteins and glycolipids. They are peripherally located on the glycan structures that these molecules display: presenting salient features for molecular interactions. Sialosides have recently been identified in both human and bovine cervical mucins (Andersch- Björkman et al. 2007; Pluta et al. 2012; Tharmalingam et al. unpublished) and are modulated during the oestrous cycle in cows (Tharmalingam et al. unpublished) suggesting a dynamic and responsive role in regulating the environment within the female reproductive tract (FRT). Recent proteomic and transcriptional studies have identified Siglecs, protein that bind specifically to Sias, in both human and bovine sperm (Lalancette et al. 2008; Peddinti et al. 2008; Ma et al. 2012; Amaral et al. 2013) and these are possible sperm surface Sialic acid (SA) binding proteins.In this study, Siglec proteins have been identified at specific locations on bovine, human and ovine sperm. They are also widely expressed on the epithelium of the bovine male reproductive tract (MRT) and the glandular components of the male accessory glands. In associated work, soluble or shed Siglec isoforms have also been provisionally identified as components of epididymal and seminal fluid (Hazem AlMhanna, personal communication). The influence of Sias on sperm mucus penetration was investigated and an unconjugated form of SA (Neu5Ac) increased mucus penetration in a dose dependent manner indicating a specific SA-mediated effect interaction between sperm and cervical mucus. At higher levels a reduction in sperm motility and mucus penetration was evident suggesting a toxic or regulatoryeffect. It is possible that this effect may be mediated via Siglec proteins on sperm. Based on these related and connected studies, it is hypothesised that Siglecs on sperm play a role in mediating sperm function (development, maturation, storage, motility, FRT transit and fertilisation (oocyte binding)) within the MRT and FRT.