Biomedical subjects

Roberto Zoncu

Publications and source records attributed to Roberto Zoncu.

4 recordsLinked to original sources

PubMed2006

Two synaptojanin 1 isoforms are recruited to clathrin-coated pits at different stages.

Phosphoinositides are thought to play an important role in clathrin-coated pit (CCP) dynamics. Biochemical and structural studies have shown a direct interaction of phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] with endocytic clathrin adaptors, whereas functional studies using cell-free systems or intact cells have demonstrated the importance of PI(4,5)P2 synthesis and dephosphorylation in clathrin coating and uncoating, respectively. Furthermore, genetic manipulations of kinases and phosphatases involved in PI(4,5)P2 metabolism result in major defects in synaptic vesicle recycling and other forms of clathrin-dependent endocytosis. However, live imaging studies of these enzymes at CCPs have not been conducted. We have used multicolor total internal reflection fluorescence microscopy (TIRFM) to visualize the spatial-temporal recruitment of synaptojanin 1 (SJ1), a polyphosphoinositide phosphatase, and its binding partner endophilin to CCPs. Strikingly, we observed differential temporal recruitment of the two major SJ1 splice variants to CCPs. The 145-kDa isoform, the predominant isoform expressed in the brain, was rapidly recruited as a "burst," together with endophilin, at a late stage of CCP formation. In contrast, the nonneuronal ubiquitously expressed 170-kDa isoform of SJ1 was present at all stages of CCP formation. These results raise the possibility that dynamic phosphoinositide metabolism may occur throughout the lifetime of a CCP.

Acyltransferases↗

PubMed2006

Overlapping events with application to image sequences.

Counting spatially and temporally overlapping events in image sequences and estimating their shape-size and duration features are important issues in some applications. We propose a stochastic model, a particular case of the nonisotropic 3D Boolean model, for performing this analysis: the temporal Boolean model. Some probabilistic properties are derived and a methodology for parameter estimation from time-lapse image sequences is proposed using an explicit treatment of the temporal dimension. We estimate the mean number of germs per unit area and time, the mean grain size and the duration distribution. A wide simulation study in order to assess the proposed estimators showed promising results. The model was applied on biological image sequences of in-vivo cells in order to estimate new parameters such as the mean number and duration distribution of endocytic events. Our results show that the proposed temporal Boolean model is effective for obtaining information about dynamic processes which exhibit short-lived, but spatially and temporally overlapping events.

Algorithms↗

PubMed2002

Recruitment and regulation of phosphatidylinositol phosphate kinase type 1 gamma by the FERM domain of talin.

Membrane phosphoinositides control a variety of cellular processes through the recruitment and/or regulation of cytosolic proteins. One mechanism ensuring spatial specificity in phosphoinositide signalling is the targeting of enzymes that mediate their metabolism to specific subcellular sites. Phosphatidylinositol phosphate kinase type 1 gamma (PtdInsPKI gamma) is a phosphatidylinositol-4-phosphate 5-kinase that is expressed at high levels in brain, and is concentrated at synapses. Here we show that the predominant brain splice variant of PtdInsPKI gamma (PtdInsPKI gamma-90) binds, by means of a short carboxy-terminal peptide, to the FERM domain of talin, and is strongly activated by this interaction. Talin, a principal component of focal adhesion plaques, is also present at synapses. PtdInsPKI gamma-90 is expressed in non-neuronal cells, albeit at much lower levels than in neurons, and is concentrated at focal adhesion plaques, where phosphatidylinositol-4,5-bisphosphate has an important regulatory role. Overexpression of PtdInsPKI gamma-90, or expression of its C-terminal domain, disrupts focal adhesion plaques, probably by local disruption of normal phosphoinositide balance. These findings define an interaction that has a regulatory role in cell adhesion and suggest new similarities between molecular interactions underlying synaptic junctions and general mechanisms of cell adhesion.

3T3 Cells↗

PubMed2002

Origin of GABAergic neurons in the human neocortex.

The mammalian neocortex contains two major classes of neurons, projection and local circuit neurons. Projection neurons contain the excitatory neurotransmitter glutamate, while local circuit neurons are inhibitory, containing GABA. The complex function of neocortical circuitry depends on the number and diversity of GABAergic (gamma-aminobutyric-acid-releasing) local circuit neurons. Using retroviral labelling in organotypic slice cultures of the embryonic human forebrain, we demonstrate the existence of two distinct lineages of neocortical GABAergic neurons. One lineage expresses Dlx1/2 and Mash1 transcription factors, represents 65% of neocortical GABAergic neurons in humans, and originates from Mash1-expressing progenitors of the neocortical ventricular and subventricular zone of the dorsal forebrain. The second lineage, characterized by the expression of Dlx1/2 but not Mash1, forms around 35% of the GABAergic neurons and originates from the ganglionic eminence of the ventral forebrain. We suggest that modifications in the expression pattern of transcription factors in the forebrain may underlie species-specific programmes for the generation of neocortical local circuit neurons and that distinct lineages of cortical interneurons may be differentially affected in genetic and acquired diseases of the human brain.

Basic Helix-Loop-Helix Proteins↗