N-linked mannose glycoconjugates on shrimp thrombospondin, pmTSP-II, and their involvement in the sperm acrosome reaction

Molecular evolution of the Thrombospondin superfamily

Thrombospondins (TSPs) are multidomain, calcium-binding glycoproteins that have wide-ranging roles in vertebrates in cell interactions, extracellular matrix (ECM) organisation, angiogenesis, tissue remodelling, synaptogenesis, and also in musculoskeletal and cardiovascular functions. Land animals encode five TSPs, which assembly co-translationally either as trimers (subgroup A) or pentamers (subgroup B). The vast majority of research has focused on this canonical TSP family, which evolved through the whole-genome duplications that took place early in the vertebrate lineage. With benefit of the growth in genome- and transcriptome-predicted proteomes of a much wider range of animal species, examination of TSPs throughout metazoan phyla has revealed extensive conservation of subgroup B-type TSPs in invertebrates. In addition, these searches established that canonical TSPs are, in fact, one branch within a TSP superfamily that includes other clades designated mega-TSPs, sushi-TSPs and poriferan-TSPs. Despite the apparent simplicity of poriferans and cnidarians as organisms, these phyla encode a greater diversity of TSP superfamily members than vertebrates. We discuss here the molecular characteristics of the TSP superfamily members, current knowledge of their expression profiles and functions in invertebrates, and models for the evolution of this complex ECM superfamily.

Shrimp thrombospondin (TSP): presence of O-β1,4 N-acetylglucosamine polymers and its function in TSP chain association in egg extracellular matrix

We characterized the existence of O-β(1,4)-GlcNAc polymers (β1,4GNP) that were anchored on the O-linked glycosylation sites of shrimp thrombospondin (pmTSP-II). There were five putative β1,4GNP linkages on the epithelial growth factor-like domain of pmTSP-II. Antibody against O-β-GlcNAc (CTD110.6) was used to prove the existence of linear and complex β1,4GNP. The antibody well reacted with linear chito-triose, -tetraose and -pentaose conjugated with phosphatidylethanolamine lipid. The immunoreactivity could also be detected with a complex β1,4GNP within pmTSP-II (at MW > 250 kDa). Upon denaturing the protein with SDS-PAGE buffer, the size of pmTSP-II was shifted to be 250 kDa, approximately 2.5 folds larger than the deduced molecular mass of pmTSP-II (110 kDa), suggesting additional association of pmTSP-II apart from its known disulfide bridging. This was confirmed by chitinase digestion on pmTSP-II protein leading to the subsequent smaller protein bands at 110–170 kDa in time- and concentration-dependent manners. These bands well reacted with CTD110.6 antibody and disappeared after extensive chitinase hydrolysis. Together, we believe that β1,4GNP on pmTSP-II serve the function in an inter-chain association to provide structural architecture of egg extracellular matrix, a novel function of pmTSP-II in reproductive biology.

Different expression pattern of thrombospondin gene in the presence and absence of β-glucan fed Penaeus monodon challenged with white spot syndrome virus

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Thrombospondin (TSP) gene expression in response to WSSV infection in shrimp, Penaeus monodon.

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Expression pattern of TSP gene in the presence and absence of β-glucan fed shrimp.

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High-level expression of TSP gene in various tissues of WSSV-challenged shrimp at 2 h.

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Altered gene expression pattern in WSSV-challenged shrimp, fed with and without β-glucan.

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TSP could play a role as an acute inducible phase response protein to WSSV infection.

Thrombospondins (TSPs) are extracellular, calcium-binding glycoproteins that play an essential role in cell homeostasis and development, wound-healing, angiogenesis, connective tissue organization, immune response etc. and it conserves from sea sponges to mammals. However, their role in shrimp immunity is poorly understood. In the present study, the differential expression profiling of TSP transcripts in Penaeus monodon tissues such as gills, lymphoid organs, hepatopancreas, and hemolymph challenged with white spot syndrome virus (WSSV), were studied by quantitative real-time PCR. Further, shrimps fed with the immunostimulant (β-glucan) when challenged with WSSV showed significant upregulation of TSP expression in gills, hepatopancreas, and lymphoid organ at the early phase of WSSV infection. The results suggest that TSP may be an inducible acute phase response protein to WSSV infection. The possibility of differences in mRNA expression pattern seen in immunostimmulated shrimp after the viral challenge, possibility due to altered immune mechanisms getting triggered during immunostimulant administration and virus infections in the host.

Mannosylated glycoconjugates on the surface of activated sperm in the giant freshwater prawn are crucial for sperm binding with the egg vitelline envelop

The unusual morphology and poorly defined acrosome-like structure in the mature sperm of the giant freshwater prawn Macrobrachium rosenbergii has led to difficulties in identifying the state of sperm activation. Mature distal vas deferens sperm (dVSp) can be activated by the calcium ionophore A23187 to show acrosome reaction-like enzymatic activities that increase their binding and penetration capabilities. However, these short-lived enzymatic activities limit their usefulness as a marker of sperm activation for further qualitative and quantitative analyses, leading to our examining the alterations in the exposure of sperm surface glycoconjugates both as markers of sperm activation and for their role in gamete interaction. Our results showed that after A23187 treatment, there was an increased exposure of mannosylated glycoconjugates on the sperm surface revealed by significant Concanavalin A (Con A) staining. Furthermore, sodium metaperiodate pre-treatment, Con A pre-incubation, or co-incubation with α-mannose monosaccharides all significantly reduced A23187-induced dVSp binding to the egg vitelline envelop, demonstrating the importance of sperm surface mannosylated glycoconjugates in the binding process. These same pre-treatments of sperm also resulted in the inhibition of the binding of soluble vitelline envelop proteins (MrVE) to both the sperm surface and to mannosylated dVSp protein bands. Therefore, the present study demonstrated the importance of the exposure of mannosylated glycoconjugates on the surface of activated dVSp, both as a reliable marker of sperm activation and as a binding factor in the gamete interaction process. Furthermore, these findings allow for a better understanding of the surface glycoconjugate-mediated interaction process between gametes in this species of prawn.