Neural tube defects （NTDs） are severe congenital malformation diseases, which occur in 1 out of 1000 births in human. In Xenopus, several tissue movements are involved in the neural tube closure process. Immediately...Neural tube defects （NTDs） are severe congenital malformation diseases, which occur in 1 out of 1000 births in human. In Xenopus, several tissue movements are involved in the neural tube closure process. Immediately after the neural tube fusion, the neural crest cells get monopolar protrusion toward dorsal midline and migrate to form the roof of the neural tube. At the same time, radial intercalation takes place from the ventral neural tube and forces it to be single-layered. Here, we physically block the neural tube closure to test the cell movements and the following patterning in Xenopus laevis explants. The results show that the single-layered neural tube fails to form and the neural crest cells remain at the lateral regions in the explants with NTDs. However, the patterning of the neural tube is not affected as indicated by the normal expression of the preneural genes. These results indicate a requirement of the neural tube fusion for the radial intercalation and the dorsal midline directed neural crest migration, but not for the dorsal-ventral patterning of the neural tube.展开更多
In his commentary on the Platonic Parmenides, the Neoplatonist philosopher Proclus （ca. 411-485） offers a systematic defense of the objective existence of the Forms by means of the use of distinctive arguments, four...In his commentary on the Platonic Parmenides, the Neoplatonist philosopher Proclus （ca. 411-485） offers a systematic defense of the objective existence of the Forms by means of the use of distinctive arguments, four of which are ontological. In contrast with Aristotle, Proclus clearly accepts that the Forms exist as principles of the world and not as posterior concepts describing the common elements of the sensible entities. Thus, he argues first that the ontological presuppositions of the sensible beings are placed in the area of the self-subsistent beings, which correspond to the categories of the Second Hypothesis of the Parmenides. The Forms belong to this area as well. In this respect, Proclus refers to the way of production of the sensible beings, aiming at a strict definition of this process. Secondly, he proves that the existence of the Forms, which possess ontological completeness, is prior to the existence of the sensible things. This is possible since the Forms are generated by the Demiurge of the whole world, by means of an internal reflection upon himself. Thirdly, in order to prove that the sensible world cannot be attributed to mere chance, he argues that the external activity, i.e., the creation of the world, depends on the internal activity, i.e., the development of the Forms in the divine intellect. Fourthly, he implements the concept of hierarchy in the realm of the Forms, through an extensive reference to the ontological priority of the imparticipable over the participable. Thus, he shows how the existence of the primary and intelligible Forms is prior to that of the substantiated Forms. Interestingly enough, the above-mentioned arguments exercised considerable influence on the commentaries of the members of the school of Ammonius, son of Hermias.展开更多
基金supported by grants from the National Natural Science Foundation of China (30425011 30530380)the Innovation Project of the Chinese Academy of Sciences (KSCX2-YW-R-090)~~
文摘Neural tube defects （NTDs） are severe congenital malformation diseases, which occur in 1 out of 1000 births in human. In Xenopus, several tissue movements are involved in the neural tube closure process. Immediately after the neural tube fusion, the neural crest cells get monopolar protrusion toward dorsal midline and migrate to form the roof of the neural tube. At the same time, radial intercalation takes place from the ventral neural tube and forces it to be single-layered. Here, we physically block the neural tube closure to test the cell movements and the following patterning in Xenopus laevis explants. The results show that the single-layered neural tube fails to form and the neural crest cells remain at the lateral regions in the explants with NTDs. However, the patterning of the neural tube is not affected as indicated by the normal expression of the preneural genes. These results indicate a requirement of the neural tube fusion for the radial intercalation and the dorsal midline directed neural crest migration, but not for the dorsal-ventral patterning of the neural tube.
文摘In his commentary on the Platonic Parmenides, the Neoplatonist philosopher Proclus （ca. 411-485） offers a systematic defense of the objective existence of the Forms by means of the use of distinctive arguments, four of which are ontological. In contrast with Aristotle, Proclus clearly accepts that the Forms exist as principles of the world and not as posterior concepts describing the common elements of the sensible entities. Thus, he argues first that the ontological presuppositions of the sensible beings are placed in the area of the self-subsistent beings, which correspond to the categories of the Second Hypothesis of the Parmenides. The Forms belong to this area as well. In this respect, Proclus refers to the way of production of the sensible beings, aiming at a strict definition of this process. Secondly, he proves that the existence of the Forms, which possess ontological completeness, is prior to the existence of the sensible things. This is possible since the Forms are generated by the Demiurge of the whole world, by means of an internal reflection upon himself. Thirdly, in order to prove that the sensible world cannot be attributed to mere chance, he argues that the external activity, i.e., the creation of the world, depends on the internal activity, i.e., the development of the Forms in the divine intellect. Fourthly, he implements the concept of hierarchy in the realm of the Forms, through an extensive reference to the ontological priority of the imparticipable over the participable. Thus, he shows how the existence of the primary and intelligible Forms is prior to that of the substantiated Forms. Interestingly enough, the above-mentioned arguments exercised considerable influence on the commentaries of the members of the school of Ammonius, son of Hermias.
