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Activation state of sperm motility named 'hyperactivation' enables mammalian sperm to progress through the oviductal matrix, although a similar state of sperm motility is unknown in non-mammalian vertebrates at fertilization. Here, we found a high motility state of the sperm in the newt Cynops pyrrhogaster. It was predominantly caused in egg jelly extract ( JE) and characterized by a high wave velocity of the undulating membrane ( UM) that was significantly higher at the posterior midpiece. An insemination assay suggested that the high motility state might be needed for sperm to penetrate the egg jelly, which is the accumulated oviductal matrix. Specific characteristics of the high motility state were completely abrogated by a high concentration of verapamil, which blocks the L-type and T-type voltage-dependent Ca2+ channels ( VDCCs). Mibefradil, a dominant blocker of T-type VDCCs, suppressed the wave of the UM at the posterior midpiece with separate wave propagation from both the anterior midpiece and the posterior principal piece. In addition, nitrendipine, a dominant L-type VDCC blocker, weakened the wave of the UM, especially in the anterior midpiece. Live Ca2+ imaging showed that, compared with the intact sperm in the JE, the relative intracellular Ca2+ level changed especially in the anterior and posterior ends of the midpiece of the blocker-treated sperm. These suggest that different types of Ca2+ channels mediate the intracellular Ca2+ level predominantly in the anterior and posterior ends of the midpiece to maintain the high motility state of the newt sperm. [ABSTRACT FROM AUTHOR]

Sperm chemotaxis occurs widely in animals and plants and plays an important role in the success of fertilization. Several studies have recently demonstrated that Ca2+ influx through specific Ca2+ channels is a prerequisite for sperm chemotactic movement. However, the regulator that modulates flagellar movement in response to Ca2+ is unknown. Here we show that a neuronal calcium sensor, calaxin, directly acts on outer-arm dynein and regulates specific flagellar movement during sperm chemotaxis. Calaxin inhibition resulted in significant loss of sperm chemotactic movement, despite normal increases in intracellular calcium concentration. Using a demembranated sperm model, we demonstrate that calaxin is essential for generation and propagation of Ca2+-induced asymmetric flagellar bending. An in vitro motility assay revealed that calaxin directly suppressed the velocity of microtubule sliding by outer-arm dynein at high Ca2+ concentrations. This study describes the missing link between chemoattractant-mediated Ca2+ signaling and motor-driven microtubule sliding during sperm chemotaxis. [ABSTRACT FROM AUTHOR]

As part of its growth strategy, Bangladesh instituted a trade liberalization process in the early 1990s which gained momentum in later years. Trade grew from 24.4 to 45% of GDP between 1980-81 and 2007-08, an indicator of increased liberalization as well as the growing importance of the external sector in Bangladesh. Apart from its unilateral liberalization, Bangladesh participates in three different regional trade agreements (RTAs): the South Asian Free Trade Agreement (SAFTA), the Asia Pacific Trade Agreement (APTA) and the Bay of Bengal Initiative for Multisectoral Technical and Economic Cooperation Free Trade Area (BIMSTEC FTA). In addition, Bangladesh signed preferential trade agreements (PTAs) with the member countries of the Developing 8 (D8). Because of the growing importance of RTAs, this study investigates their contribution to the export flows from Bangladesh using the gravity model that has become the primary tool for estimating the trade effects of regional integration. Regression results of bilateral exports for 40 countries from 1992-2009 indicate two crucial aspects. Firstly, all the RTAs consistently maintained statistically significant negative signs, except the BIMSTEC FTA and SAFTA, which showed insignificantly positive and insignificantly negative effects respectively. Secondly, the intensity of negative effects and the level of significance have shown a declining trend as the status of those blocs has changed from political or economic cooperation agreements to preferential agreements and from preferential agreements to free trade agreements. Thus, the intensity of tariff liberalization and the degree of sectoral coverage seem to be the important determinants of the RTAs' performance. Therefore, experts expect that full-fledged implementation of FTA provisions and the elimination of all tariff and non-tariff barriers might result in a higher degree of integration. [ABSTRACT FROM AUTHOR]

Many hermaphroditic organisms possess a self-incompatibility system to avoid self-fertilization. Recently, we identified the genes responsible for self-sterility in a hermaphroditic primitive chordate (ascidian), Ciona intestinalis: sperm-side polycystin 1-like receptors s-Themis-A/B and egg-side fibrinogen-like ligands on the vitelline coat (VC) ν-Themis-A/B. Here, we investigated the sperm behavior and intracellular Ca2+ concentration ([Ca2+]i) in response to self/nonself-recognition. We found that sperm motility markedly decreased within 5 min after attachment to the VC of self-eggs but not after attachment to the VC of nonself-eggs and that the apparent decrease in sperm motility was suppressed in low Ca2+ seawater. High-speed video analysis revealed that sperm detached from the self-VC or stopped motility within 5 min after binding to the self-VC. Because s-Themis-B contains a cation channel domain in its C terminus, we monitored sperm [Ca2+]i by real-time [Ca2+]i imaging using Fluo-8H-AM (AAT Bioquest, Inc.). Interestingly, we found that sperm [Ca2+]i rapidly and dramatically increased and was maintained at a high level in the head and flagellar regions when sperm interacted with the self-VC but not when the sperm interacted with the nonself-VC. The increase in [Ca2+]i was also suppressed by low-Ca2+ seawater. These results indicate that the sperm self-recognition signal triggers [Ca2+]i increase and/or Ca2+ influx, which elicits a self-incompatibility response to reject self-fertilization in C. intestinalis. [ABSTRACT FROM AUTHOR]