为改善拖曳线列阵声呐的尾向探测能力,降低拖船噪声对半波长间距阵尾向探测性能的制约,本文关注四分之一波长间距阵对连续波信号和带限噪声的响应。研究表明,四分之一波长间距阵具有非对称的端向指向性,与半波长间距阵相比有约20 d B的...为改善拖曳线列阵声呐的尾向探测能力,降低拖船噪声对半波长间距阵尾向探测性能的制约,本文关注四分之一波长间距阵对连续波信号和带限噪声的响应。研究表明,四分之一波长间距阵具有非对称的端向指向性,与半波长间距阵相比有约20 d B的空间抑制能力,能有效抑制拖船辐射噪声干扰。本文还提出用零陷权组合传感器构成四分之一波长间距阵,理论上其抗拖船噪声干扰的效果比四分之一波长间距阵更好。展开更多
LEF1/TCFs are high mobility group box-containing transcriptional factors mediating canonical Wnt/β-catenin signaling during early embryogenesis and tumorigenesis. β-Catenin forms a complex with LEF 1/TCFs and transa...LEF1/TCFs are high mobility group box-containing transcriptional factors mediating canonical Wnt/β-catenin signaling during early embryogenesis and tumorigenesis. β-Catenin forms a complex with LEF 1/TCFs and transactivates LEF1/TCF-mediated transcriptions during dorsalization. Although LEF-mediated transcription is also implicated in ventralization, the underlying molecular mechanism is not well understood. Using the vertebrate Xenopus laevis model system, we found that Xom, which is a ventralizing homeobox protein with dual roles of transcriptional activation and repression, forms a complex with LEF 1/TCF through its homeodomain and transactivates LEF 1/TCF-mediated transcription through its N-terminal transactivation domain （TAD）. Our data show that Xom lacking the N-terminal TAD fails to transactivate ventral genes, such as BMP4 and Xom itself, but retains the ability to suppress transcriptional activation of dorsal gene promoters, such as the Goosecoid promoter, indicating that transactivation and repression are separable functions of Xom. It has been postulated that Xom forms a positive re-enforcement loop with BMP4 to promote ventral- ization and to suppress dorsal gene expression. Consistent with an essential role of Xom transactivation of LEF1/TCFs during early embryogenesis, we found that expression of the dominant-negative Xom mutant that lacks the TAD fails to re-enforce the ventral signaling of BMP4 and causes a catastrophic effect during gastrulation. Our data suggest that the functional interaction of Xom and LEF 1/TCF-factors is essential for ventral cell fate determination and that LEF 1/TCF factors may function as a point of convergence to mediate the combined signaling of Wnt/β-catenin and BMP4/Xom pathways during early embryogenesis.展开更多
Smad family proteins are identified as intracellular signal mediators of the TGF-β superfamily.In this study,we identified two novel members of the Smad family,termed as AmphiSmad1/5/8 and AmphiSmad4,from Chinese amp...Smad family proteins are identified as intracellular signal mediators of the TGF-β superfamily.In this study,we identified two novel members of the Smad family,termed as AmphiSmad1/5/8 and AmphiSmad4,from Chinese amphioxus.Both AmphiSmad1/5/8 and AmphiSmad4 showed a typical domain structure of Smad proteins consisting of conserved MH1 and MH2 domains.Phylogenetic analysis placed AmphiSmad1/5/8 in the Smad1,5 and 8 subgroup of the R-Smad subfamily,and AmphiSmad4 in the Co-Smad subfamily.The spatial and temporal gene expression patterns of AmphiSmad1/5/8 and AmphiSmad4 showed that they may be involved in the embryonic development of notochord,myotome and alimentary canal,and may help to establish the specification of dorsal-ventral axis of amphioxus.Moreover,AmphiSmad1/5/8 and AmphiSmad4 showed extensive distribution in all adult tissues examined,suggesting that these two genes may play important roles in the morphogenesis of a variety of tissues especially notochord and gonad.展开更多
Supramolecular chemistry is based on non-covalent interactions that enable molecular recognition.By weak interactions,a large number of structures,such as rotaxane[1-2]and catenane[3-4],as well as more complex structu...Supramolecular chemistry is based on non-covalent interactions that enable molecular recognition.By weak interactions,a large number of structures,such as rotaxane[1-2]and catenane[3-4],as well as more complex structures[5-6]have been assembled.展开更多
文摘为改善拖曳线列阵声呐的尾向探测能力,降低拖船噪声对半波长间距阵尾向探测性能的制约,本文关注四分之一波长间距阵对连续波信号和带限噪声的响应。研究表明,四分之一波长间距阵具有非对称的端向指向性,与半波长间距阵相比有约20 d B的空间抑制能力,能有效抑制拖船辐射噪声干扰。本文还提出用零陷权组合传感器构成四分之一波长间距阵,理论上其抗拖船噪声干扰的效果比四分之一波长间距阵更好。
文摘LEF1/TCFs are high mobility group box-containing transcriptional factors mediating canonical Wnt/β-catenin signaling during early embryogenesis and tumorigenesis. β-Catenin forms a complex with LEF 1/TCFs and transactivates LEF1/TCF-mediated transcriptions during dorsalization. Although LEF-mediated transcription is also implicated in ventralization, the underlying molecular mechanism is not well understood. Using the vertebrate Xenopus laevis model system, we found that Xom, which is a ventralizing homeobox protein with dual roles of transcriptional activation and repression, forms a complex with LEF 1/TCF through its homeodomain and transactivates LEF 1/TCF-mediated transcription through its N-terminal transactivation domain （TAD）. Our data show that Xom lacking the N-terminal TAD fails to transactivate ventral genes, such as BMP4 and Xom itself, but retains the ability to suppress transcriptional activation of dorsal gene promoters, such as the Goosecoid promoter, indicating that transactivation and repression are separable functions of Xom. It has been postulated that Xom forms a positive re-enforcement loop with BMP4 to promote ventral- ization and to suppress dorsal gene expression. Consistent with an essential role of Xom transactivation of LEF1/TCFs during early embryogenesis, we found that expression of the dominant-negative Xom mutant that lacks the TAD fails to re-enforce the ventral signaling of BMP4 and causes a catastrophic effect during gastrulation. Our data suggest that the functional interaction of Xom and LEF 1/TCF-factors is essential for ventral cell fate determination and that LEF 1/TCF factors may function as a point of convergence to mediate the combined signaling of Wnt/β-catenin and BMP4/Xom pathways during early embryogenesis.
基金supported by the National Basic Research Program of China(Grant No. 2007CB815800)the National High Technology Research and Development Program of China(Grant No. 2006330004104456)the National Natural Science Foundation of China(Grant Nos. 30300264,30270693 and 30570967)
文摘Smad family proteins are identified as intracellular signal mediators of the TGF-β superfamily.In this study,we identified two novel members of the Smad family,termed as AmphiSmad1/5/8 and AmphiSmad4,from Chinese amphioxus.Both AmphiSmad1/5/8 and AmphiSmad4 showed a typical domain structure of Smad proteins consisting of conserved MH1 and MH2 domains.Phylogenetic analysis placed AmphiSmad1/5/8 in the Smad1,5 and 8 subgroup of the R-Smad subfamily,and AmphiSmad4 in the Co-Smad subfamily.The spatial and temporal gene expression patterns of AmphiSmad1/5/8 and AmphiSmad4 showed that they may be involved in the embryonic development of notochord,myotome and alimentary canal,and may help to establish the specification of dorsal-ventral axis of amphioxus.Moreover,AmphiSmad1/5/8 and AmphiSmad4 showed extensive distribution in all adult tissues examined,suggesting that these two genes may play important roles in the morphogenesis of a variety of tissues especially notochord and gonad.
基金supported by the Archival Projects of the Department of Education of Heilongjiang Province,China(No.1352MSYYB010)the National Topic Cultivation Project of Mudanjiang Normal University,China(No.GP2020001)the Key Project of Department of Education of Heilongjiang Province,China(No.1355ZD003).
文摘Supramolecular chemistry is based on non-covalent interactions that enable molecular recognition.By weak interactions,a large number of structures,such as rotaxane[1-2]and catenane[3-4],as well as more complex structures[5-6]have been assembled.
