Viral communities associated with healthy and bleaching corals

The coral holobiont is the integrated assemblage of the coral animal, its symbiotic algae, protists, fungi and a diverse consortium of Bacteria and Archaea. Corals are a model system for the study of symbiosis, the breakdown of which can result in disease and mortality. Little is known, however, about viruses that infect corals and their symbionts. Here we present metagenomic analyses of the viral communities associated with healthy and partially bleached specimens of the Caribbean reef-building coral Diploria strigosa. Surprisingly, herpes-like sequences accounted for 4–8% of the total sequences in each metagenome; this abundance of herpes-like sequences is unprecedented in other marine viral metagenomes. Viruses similar to those that infect algae and plants were also present in the coral viral assemblage. Among the phage identified, cyanophages were abundant in both healthy and bleaching corals and vibriophages were also present. Therefore, coral-associated viruses could potentially infect all components of the holobiont – coral, algal and microbial. Thus, we expect viruses to figure prominently in the preservation and breakdown of coral health

Regulation of Sperm Capacitation and the Acrosome Reaction by PIP 2 and Actin Modulation

Actin polymerization and development of hyperactivated (HA) motility are two processes that take place during sperm capacitation. Actin polymerization occurs during capacitation and prior to the acrosome reaction, fast F-actin breakdown takes place. The increase in F-actin during capacitation depends upon inactivation of the actin severing protein, gelsolin, by its binding to phosphatydilinositol-4, 5-bisphosphate (PIP 2 ) and its phosphorylation on tyrosine-438 by Src. Activation of gelsolin following its release from PIP 2 is known to cause F-actin breakdown and inhibition of sperm motility, which can be restored by adding PIP 2 to the cells. Reduction of PIP 2 synthesis inhibits actin polymerization and motility, while increasing PIP 2 synthesis enhances these activities. Furthermore, sperm demonstrating low motility contained low levels of PIP 2 and F-actin. During capacitation there was an increase in PIP 2 and F-actin levels in the sperm head and a decrease in the tail. In spermatozoa with high motility, gelsolin was mainly localized to the sperm head before capacitation, whereas in low motility sperm, most of the gelsolin was localized to the tail before capacitation and translocated to the head during capacitation. We also showed that phosphorylation of gelsolin on tyrosine-438 depends upon its binding to PIP 2 . Stimulation of phospholipase C, by Ca 2 + -ionophore or by activating the epidermal-growth-factor-receptor, inhibits tyrosine phosphorylation of gelsolin and enhances enzyme activity. In conclusion, these data indicate that the increase of PIP 2 and/or F-actin in the head during capacitation enhances gelsolin translocation to the head. As a result, the decrease of gelsolin in the tail allows the maintenance of high levels of F-actin in this structure, which is essential for the development of HA motility

Zn2+-stimulation of sperm capacitation and of the acrosome reaction is mediated by EGFR activation

AbstractExtracellular zinc regulates cell proliferation via the MAP1 kinase pathway in several cell types, and has been shown to act as a signaling molecule. The testis contains a relatively high concentration of Zn2+, required in both the early and late stages of spermatogenesis. Despite the clinical significance of this ion, its role in mature sperm cells is poorly understood. In this study, we characterized the role of Zn2+ in sperm capacitation and in the acrosome reaction. Western blot analysis revealed the presence of ZnR of the GPR39 type in sperm cells. We previously demonstrated the presence of active epidermal growth factor receptor (EGFR) in sperm, its possible transactivation by direct activation of G-protein coupled receptor (GPCR), and its involvement in sperm capacitation and in the acrosome reaction (AR). We show here that Zn2+ activates the EGFR during sperm capacitation, which is mediated by activation of trans-membrane adenylyl cyclase (tmAC), protein kinase A (PKA), and the tyrosine kinase, Src. Moreover, the addition of Zn2+ to capacitated sperm caused further stimulation of EGFR and phosphatydil-inositol-3-kinase (PI3K) phosphorylation, leading to the AR. The stimulation of the AR by Zn2+ also occurred in the absence of Ca2+ in the incubation medium, and required the tmAC, indicating that Zn2+ activates a GPCR. The AR stimulated by Zn2+ is mediated by GPR39 receptor, PKA, Src and the EGFR, as well as the EGFR down-stream effectors PI3K, phospholipase C (PLC) and protein kinase C (PKC). These data support a role for extracellular zinc, acting through the ZnR, in regulating multiple signaling pathways in sperm capacitation and the acrosome reaction

Dissociation between AKAP3 and PKARII promotes AKAP3 degradation in sperm capacitation.

Ejaculated spermatozoa must undergo a series of biochemical modifications called capacitation, prior to fertilization. Protein-kinase A (PKA) mediates sperm capacitation, although its regulation is not fully understood. Sperm contain several A-kinase anchoring proteins (AKAPs), which are scaffold proteins that anchor PKA. In this study, we show that AKAP3 is degraded in bovine sperm incubated under capacitation conditions. The degradation rate is variable in sperm from different bulls and is correlated with the capacitation ability. The degradation of AKAP3 was significantly inhibited by MG-132, a proteasome inhibitor, indicating that AKAP3 degradation occurs via the proteasomal machinery. Treatment with Ca(2+)-ionophore induced further degradation of AKAP3; however, this effect was found to be enhanced in the absence of Ca(2+) in the medium or when intracellular Ca(2+) was chelated the degradation rate of AKAP3 was significantly enhanced when intracellular space was alkalized using NH4Cl, or when sperm were treated with Ht31, a peptide that contains the PKA-binding domain of AKAPs. Moreover, inhibition of PKA activity by H89, or its activation using 8Br-cAMP, increased AKAP3 degradation rate. This apparent contradiction could be explained by assuming that binding of PKA to AKAP3 protects AKAP3 from degradation. We conclude that AKAP3 degradation is regulated by intracellular alkalization and PKARII anchoring during sperm capacitation