Ca2+ spikes in the flagellum control chemotactic behavior of sperm. (1/14)

The events that occur during chemotaxis of sperm are only partly known. As an essential step toward determining the underlying mechanism, we have recorded Ca2+ dynamics in swimming sperm of marine invertebrates. Stimulation of the sea urchin Arbacia punctulata by the chemoattractant or by intracellular cGMP evokes Ca2+ spikes in the flagellum. A Ca2+ spike elicits a turn in the trajectory followed by a period of straight swimming ('turn-and-run'). The train of Ca2+ spikes gives rise to repetitive loop-like movements. When sperm swim in a concentration gradient of the attractant, the Ca2+ spikes and the stimulus function are synchronized, suggesting that precise timing of Ca2+ spikes controls navigation. We identified the peptide asterosap as a chemotactic factor of the starfish Asterias amurensis. The Ca2+ spikes and swimming behavior of sperm from starfish and sea urchin are similar, implying that the signaling pathway of chemotaxis has been conserved for almost 500 million years.  (+info)

Yolk granule tethering: a role in cell resealing and identification of several protein components. (2/14)

Homotypic fusion among echinoderm egg yolk granules has previously been reconstituted in vitro, and shown to be a rapid, Ca2+-triggered reaction that can produce extremely large (>10 microm diameter) fusion products. We here show that, prior to Ca2+-triggered fusion, yolk granules in vitro, if isolated in an appropriate buffer, became tethered to one another, forming large aggregates of more than 100 granules. Granule washing with mildly chaotropic salt abolished this tethering reaction, and prevented Ca2+-triggered formation of the large fusion products characteristic of tethered granules. Protein factors present in the wash restored tethering activity and these factors could be substantially enriched by anion exchange chromatography. The enriched fraction behaved under native conditions as a high molecular weight (approximately 670 kDa), multisubunit complex of at least seven proteins. Monoclonal antibodies directed against this complex of proteins were capable of immunodepleting tethering activity, confirming the role of the complex in granule tethering. These antibodies selectively stained the surface of yolk granules in the intact egg. We therefore propose a new role for tethering: it can promote the formation of large vesicular fusion products, such as those required for successful resealing. We have, moreover, identified several proteins that may be critical to this tethering mechanism.  (+info)

Acrosome reaction is subfamily specific in sea star fertilization. (3/14)

In the fertilization process of sea stars, sperm is activated to go through the acrosome reaction before cell fusion. We focused on induction of the acrosome reaction as a key process in fertilization. Six species of sea stars were used in this study: Asterias amurensis, Asterias rubens, Asterias forbesi, Aphelasterias japonica, Distolasterias nipon, and Asterina pectinifera. Acrosome reaction assays indicate that the acrosome reaction can be induced across species within Asteriinae subfamily. However, cross-fertilization assays indicate that sea stars have species specificity in fertilization. Therefore, steps after the acrosome reaction are responsible for the species specificity. To explain acrosome reaction subfamily specificity at the molecular level, the sugar components of egg jelly were examined and analyzed by principal component analysis. A. amurensis and A. forbesi belong to the same induction group of the acrosome reaction. D. nipon and An. pectinifera are in a unique group. Enzyme-linked immunosorbent assays indicate that Asteriinae subfamily share a common glycan structure, the Fragment 1 of Acrosome Reaction-Inducing Substance from A. amurensis. Fragment 1 plays an important role in the subfamily specificity of acrosome reaction induction. In addition, A. amurensis sperm activating peptide was recognized by sperm from the same superorder. These results demonstrate that the specificity of acrosome reaction induction is present at the subfamily level in sea stars.  (+info)

Coelomocytes and post-traumatic response in the common sea star Asterias rubens. (4/14)

Coelomocytes are recognized as the main cellular component of the echinoderm immune system. They are the first line of defense and their number and type can vary dramatically during infections or following injury. Sea stars have been used as a model system to study the regeneration process after autotomy or predation. In the present study we examined the cellular and biochemical responses of coelomocytes from the European sea star Asterias rubens to traumatic stress using immunochemical and biochemical approaches. In terms of trauma and post-traumatic stress period, here we consider the experimental arm amputation and the repair phase involved in the first 24 hours post-amputation, which mimicked a natural predation event. Four cell morphotypes were distinguishable in the coelomic fluid of both control and post-traumatic-stressed animals (phagocytes, amoebocytes, vibratile cells, hemocytes), but phagocytes were the major components, accounting for about 95% of the total population. Thus, the effects measured relate to the overall population of coelomocytes. A modest increase in the total number of freely circulating coelomocytes was observed 6 hours post-amputation. Interestingly, a monoclonal antibody (McAb) to a sea urchin embryo adhesion protein (toposome) cross-reacted with isolated sea star coelomocytes and stained the coelomic epithelium of control animals with an increase in trauma-stressed arms. In addition, coelomocytes from trauma-stressed animals showed a time-dependent increase in Hsp70 levels, as detected by both immunocytochemistry and immunoblotting within 24 hours after arm tip amputation, with a peak at 6 hours after amputation. Our findings indicate a clear role for coelomocytes and classic stress molecules in the post-traumatic stress associated with the early repair phase of regeneration.  (+info)

Can salinity-induced mortality explain larval vertical distribution with respect to a halocline? (5/14)

For the larvae of two echinoderm species that coexist in Atlantic Canada (bipinnaria of the sea star Asterias rubens and 4- and 6-arm echinoplutei of the sea urchin Strongylocentrotus droebachiensis), we examined the effect of short- and long-term exposure to salinity (ranging from 18 to 35) on the probability of larval survival in laboratory experiments. We also related larval vertical distributions in response to sharp haloclines generated in the laboratory to survival probability in the salinity of different layers in the water column. For both species and developmental stages, survival probability decreased with decreasing salinity, and a salinity range of 24-27 emerged as the critical threshold for larval tolerance. The relationship between the proportion of larvae that crossed a halocline into the top water layer and the survival probability of larvae in the salinity of that layer was significant for both species. Interestingly, the shape of this response was species-specific but not stage-specific for S. droebachiensis. Our findings suggest that larval avoidance of low-salinity water layers may be an adaptive behavior that increases survival and indirectly influences larval distribution.  (+info)

Glycosylceramides obtain from the starfish Asterias amurensis Lutken. (6/14)

Complex lipids in the starfish Asterias amurensis were characterized and the influence of sphingoid bases on human colon carcinoma Caco-2 cells was also investigated. Lipid content of gonad and viscera were 3.3% and 6.8%, respectively, in wet basis. The main lipid class in gonad was ceramide monohexoside (CMH) while triglyceride (TG) was predominant in the viscera. The most abundant fatty acid in the polar lipid was eicosapentaenoic acid (EPA, C20:5n-3), with the gonad and viscera samples having the highest proportion of 41.5% and 32.7%, respectively, of total fatty acids. Starfish internal organ contained enormous amount (0.7% in wet base) of glycosylceramide. Sphingoid bases of the glycosylceramide were mainly consisted of d22:2, d22:1 and d18:3. This sphingoid base exerted an apoptotic activity on Caco-2 cells. Thus, starfish could be used as a potential source of precious and useful complex lipids.  (+info)

Induced cell proliferation in putative haematopoietic tissues of the sea star, Asterias rubens (L.). (7/14)

 (+info)

Kistimonas asteriae gen. nov., sp. nov., a gammaproteobacterium isolated from Asterias amurensis. (8/14)

 (+info)

• 1
• 2