Biomedical subjects

Stefan Catsicas

Publications and source records attributed to Stefan Catsicas.

5 recordsLinked to original sources

PubMed2003

Morphological and molecular heterogeneity in release sites of single neurons.

We have previously shown that labelling intensities for synaptic proteins vary strongly among synaptic boutons. Here we addressed the questions as to whether there are heterogeneous levels of integral membrane synaptic vesicle proteins at distinct active release sites of single neurons and if these sites possess the ultrastructural features of synapses. By double-immunostaining with specific antibodies against synaptophysin, synaptotagmin I, VAMP1 and VAMP2, we identified different relative levels of these integral membrane proteins of synaptic vesicles in comparison to boutons of the same rat cortical neuron. This heterogeneity could also be observed between the two isoforms VAMP1 and VAMP2. By studying pairs of these proteins implicated in neurotransmitter release, including both VAMP isoforms, we also show that the sites that contained predominantly one protein were nevertheless functional, as they internalized and released FM1-43 upon potassium stimulation. Using electron microscopy, we show that these active sites could have either synaptic specializations, or the features of vesicle-containing varicosities without a postsynaptic target. Different varicosities of the same neuron showed different intensities for synaptic vesicle proteins; some varicosities were capable of internalizing and releasing FM1-43, while others were silent. These results show that integral membrane synaptic vesicle proteins are differentially distributed among functional release sites of the same neuron.

Animals↗

PubMed2002

Developmental and spatial expression pattern of syntaxin 13 in the mouse central nervous system.

Vesicular transport involves SNARE (soluble- N-ethylmaleimide-sensitive-factor-attachment-protein-receptor) proteins on transport vesicles and on target membranes. Syntaxin 13 is a SNARE enriched in brain, associated with recycling endosomes; its overexpression in PC12 cells promotes neurite outgrowth. This suggests an important role for receptor recycling during neuronal differentiation. Here we describe the spatiotemporal pattern of syntaxin 13 expression during mouse brain development. During early embryogenesis (E12-E15), it was found in the forebrain ventricular zone and in primary motor and sensory neurons in the brainstem, spinal cord and sensory ganglia. In the forebrain at E15, syntaxin 13 was not detected in neuroblasts in the intermediate zone of the embryonic hemispheric wall, while there was labeling in cortical neurons in deeper layers starting at E15-18, and progressively in later-generated neurons up to layer II around P6. Syntaxin 13 reached maximal expression in all brain divisions at about P7, followed by a decrease, with heterogeneous neuron populations displaying various staining intensities in adult brain. While usually restricted to the soma of neurons, we transiently detected syntaxin 13 in dendrites of pyramidal neurons during the first postnatal week. In conclusion, the developmentally regulated syntaxin 13 expression in various neuronal populations is consistent with its involvement in endocytic trafficking and neurite outgrowth.

Aging↗

PubMed2002

Modulation of receptor cycling by neuron-enriched endosomal protein of 21 kD.

Although correct cycling of neuronal membrane proteins is essential for neurite outgrowth and synaptic plasticity, neuron-specific proteins of the implicated endosomes have not been characterized. Here we show that a previously cloned, developmentally regulated, neuronal protein of unknown function binds to syntaxin 13. We propose to name this protein neuron-enriched endosomal protein of 21 kD (NEEP21), because it is colocalized with transferrin receptors, internalized transferrin (Tf), and Rab4. In PC12 cells, NEEP21 overexpression accelerates Tf internalization and recycling, whereas its down-regulation strongly delays Tf recycling. In primary neurons, NEEP21 is localized to the somatodendritic compartment, and, upon N-methyl-d-aspartate (NMDA) stimulation, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor subunit GluR2 is internalized into NEEP21-positive endosomes. NEEP21 down-regulation retards recycling of GluR1 to the cell surface after NMDA stimulation of hippocampal neurons. In summary, NEEP21 is a neuronal protein that is localized to the early endosomal pathway and is necessary for correct receptor recycling in neurons.

Androstadienes↗

PubMed2000

Presynaptic Heterogeneity: Vive la difference.

Since individual synapses of the same neuron may have different molecular composition, an important question in neurobiology is how the properties of individual synapses are established and maintained. Recent technical advances allow assay of activity at individual synapses and investigation of the relationship between function and molecular composition at the synapse.

Journal Article↗

PubMedDate not supplied

Large fluctuations in the disassembly rate of microtubules revealed by atomic force microscopy.

Atomic force microscopy (AFM) in situ has been used to observe the cold disassembly dynamics of microtubules at a previously unrealised spatial resolution. Microtubules either electrostatically or covalently bound to aminosilane surfaces disassembled at room temperature under buffer solutions with no free tubulin present. This process was followed by taking sequential tapping-mode AFM images and measuring the change in the microtubule end position as a function of time, with an spatial accuracy down to +/-20nm and a temporal accuracy of +/-1s. As well as giving average disassembly rates on the order of 1-10 tubulin monomers per second, large fluctuations in the disassembly rate were revealed, indicating that the process is far from smooth and linear under these experimental conditions. The surface bound rates measured here are comparable to the rates for GMPCPP-tubulin microtubules free in solution, suggesting that inhibition of tubulin curvature through steric hindrance controls the average, relatively low disassembly rate. The large fluctuations in this rate are thought to be due to multiple pathways in the kinetics of disassembly with differing rate constants and/or stalling due to defects in the microtubule lattice. Microtubules that were covalently bound to the surface left behind the protofilaments covalently cross-linked to the aminosilane via glutaraldehyde during the disassembly process. Further work is needed to quantitatively assess the effects of surface binding on protofibril disassembly rates, reveal any differences in disassembly rates between the plus and minus ends and to enable assembly as well as disassembly to be imaged in the microscope fluid cell in real-time.

Aluminum Silicates↗