SOME FEATURES OF THE SUBMICROSCOPIC MORPHOLOGY OF SYNAPSES IN FROG AND EARTHWORM

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.     

Expression of {beta}-galactoside {alpha}2,6 sialyltransferase blocks synthesis of polysialic acid in Xenopus embryos

Polysialic acid is a developmentally regulated carbohydratestructure found on neural cell adhesion molecules (NCAM). Expressionof ß-galactoside 2,6-sialyltransferase in Xenopusembryos, by injection of mRNA, prevents the polysialylationof NCAM, presumably by introducing a different type of sugarlinkage that terminates chain elongation. Abnormalities in neuraldevelopment result from this treatment, but in general the bodyplan of the injected embryos is not severely affected. The resultsprovide evidence that the mis-expression of glycosyltransferasescan be used to interfere with the normal pattern of glycosylationin whole organisms. glycosylation NCAM polysialic acid Xenopus development     

Molecular nature of Spemann's organizer: the role of the Xenopus homeobox gene goosecoid.

This study analyzes the function of the homeobox gene goosecoid in Xenopus development. First, we find that goosecoid mRNA distribution closely mimics the expected localization of organizer tissue in normal embryos as well as in those treated with LiCl and UV light. Second, goosecoid mRNA accumulation is induced by activin, even in the absence of protein synthesis. It is not affected by bFGF and is repressed by retinoic acid. Lastly, microinjection of goosecoid mRNA into the ventral side of Xenopus embryos, where goosecoid is normally absent, leads to the formation of an additional complete body axis, including head structures and abundant notochordal tissue. The results suggest that the goosecoid homeodomain protein plays a central role in executing Spemann's organizer phenomenon.     

MORPHOGENESIS OF THE RETINAL RODS : AN ELECTRON MICROSCOPE STUDY

The morphogenesis of the retinal rods has been studied with the electron microscope in white mice from birth up to the 16th day of age. Observations have been mainly concentrated on specimens of the 8th and 12th days and on the differentiation of the inner and outer segments of the retinal rods. In the morphogenesis of the outer segment three main stages have been considered. The first stage consists in the development of a primitive cilium projecting from a bulge of protoplasm which constitutes the primordium of the inner segment. A basal body, nine pairs of peripheral filaments, a surface membrane, and a matrix filled with a fine vesicular material have been recognized as components of the primitive cilium. The vesicles are called "morphogenetic material" because it is believed that they represent the macromolecular primordium of the rod sacs of the future outer segment. The second stage corresponds to the great enlargment of the apical region of the primitive cilium due to the rapid building up of the lamellar material of the rod sacs. The primitive rod sacs appear to be connected with the ciliary filaments. The basal portion of the primitive cilium remains undifferentiated and constitutes the connecting cilium of the adult rod (1). The third stage consists in the remodelling and reorientation of the rod sacs into their permanent transverse disposition. This process starts in the middle portion of the outer segments and proceeds towards both extremities which can be considered as zones of growth of the outer segment. The inner segment is at the beginning a bulge of protoplasm containing unoriented mitochondria, a basal body, a small Golgi zone, and numerous dense particles. Then this region becomes elongated and the different components assume the stratified disposition found in the adult (1). The demonstration that the entire outer segment of the rod cell is the result of the differentiation of a primitive cilium is discussed in view of the conflicting interpretations found in the literature. The possible macromolecular mechanisms that may be involved in the submicroscopic morphogenesis of the rod sacs are discussed and the possible role of the morphogenetic material is considered. The results described in this paper confirm and extend the interpretation of the submicroscopic morphology of the adult rod cell as presented in a previous paper (1).     

NEUROCHEMICAL AND STRUCTURAL STUDIES ON THE MECHANISM OF ACTION OF HEMICHOLINIUM-3 IN CENTRAL CHOLINERGIC SYNAPSES

—The action of hemicholinium-3 (HC-3) on the cerebral cortex of the rat was studied after subarachnoidal administration. There was a marked decrease of content of ACh in nerve endings and especially in the fraction containing synaptic vesicles, despite the fact that the number of synaptic vesicles was not reduced, as judged by electron microscopy, by the rate of incorporation of ortho [³²P]phosphate, and by the phosphorus content of the phospholipids of the isolated synaptic vesicles. There was a close association of [^l4C]HC-3 and of monoaminoxidase, which indicated that the drug was preferentially bound to mitochondria. Experiments indicating that HC-3 could be acetylated suggested that this drug may compete with choline not only for entry but also for acetylation.