Biomedical subjects

Frédéric Jaskolski

Publications and source records attributed to Frédéric Jaskolski.

5 recordsLinked to original sources

PubMed2005

Co-assembly of two GluR6 kainate receptor splice variants within a functional protein complex.

Kainate receptors (KAR) are composed of several distinct subunits and splice variants, but the functional relevance of this diversity remains largely unclear. Here we show that two splice variants of the GluR6 subunit, GluR6a and GluR6b, which differ in their C-terminal domains, do not show distinct functional properties, but coassemble as heteromers in vitro and in vivo. Using a proteomic approach combining affinity purification and MALDI-TOF mass spectrometry, we found that GluR6a and GluR6b interact with two distinct subsets of cytosolic proteins mainly involved in Ca(2+) regulation of channel function and intracellular trafficking. Guided by these results, we provide evidence that the regulation of native KAR function by NMDA receptors depends on the heteromerization of GluR6a and GluR6b and interaction of calcineurin with GluR6b. Thus, GluR6a and GluR6b bring in close proximity two separate subsets of interacting proteins that contribute to the fine regulation of KAR trafficking and function.

Alternative Splicing↗

PubMed2005

An automated method to quantify and visualize colocalized fluorescent signals.

The most commonly used method to analyze colocalization of fluorescent signal in paired images is based on superimposition of images ("merging") and visual inspection. A method based on the comparison of the mean deviation of fluorescent signal intensity has recently been proposed to quantify colocalization within a user-defined area [Li Q, Lau A, Morris TJ, Guo L, Fordyce CB, Stanley EF. A syntaxin 1, Galpha(o), and N-type calcium channel complex at a presynaptic nerve terminal: analysis by quantitative immunocolocalization. J Neurosci 2004;24:4070-81]. Unfortunately, the latter quantification method does not provide a spatial representation of the correlation between the two fluorescent signals. Here we propose a new method that combines quantification and imaging of colocalization. We describe an algorithm based on edge detection and calculation of signal intensity deviation. The method is illustrated and validated on both simulated images and experimental data. This new and automated method calculates a correlation index (I(corr)) and generates an image of the correlated signals from the two original images. In addition to help in comparing and quantifying colocalization between two fluorescent stainings, this method can be adapted to measure the distribution of ions, proteins, organelles and cells in a large array of techniques.

Algorithms↗

PubMed2005

Differential trafficking of GluR7 kainate receptor subunit splice variants.

Kainate receptors (KARs) are heteromeric ionotropic glutamate receptors that play a variety of roles in the regulation of synaptic network activity. The function of glutamate receptors (GluRs) is highly dependent on their surface density in specific neuronal domains. Alternative splicing is known to regulate surface expression of GluR5 and GluR6 subunits. The KAR subunit GluR7 exists under different splice variant isoforms in the C-terminal domain (GluR7a and GluR7b). Here we have studied the trafficking of GluR7 splice variants in cultured hippocampal neurons from wild-type and KAR mutant mice. We have found that alternative splicing regulates surface expression of GluR7-containing KARs. GluR7a and GluR7b differentially traffic from the ER to the plasma membrane. GluR7a is highly expressed at the plasma membrane, and its trafficking is dependent on a stretch of positively charged amino acids also found in GluR6a. In contrast, GluR7b is detected at the plasma membrane at a low level and retained mostly in the endoplasmic reticulum (ER). The RXR motif of GluR7b does not act as an ER retention motif, at variance with other receptors and ion channels, but might be involved during the assembly process. Like GluR6a, GluR7a promotes surface expression of ER-retained subunit splice variants when assembled in heteromeric KARs. However, our results also suggest that this positive regulation of KAR trafficking is limited by the ability of different combinations of subunits to form heteromeric receptor assemblies. These data further define the complex rules that govern membrane delivery and subcellular distribution of KARs.

Alternative Splicing↗

PubMed2005

Subcellular localization and trafficking of kainate receptors.

Glutamate receptors of the kainate type have been identified recently as key players in the modulation of neuronal-network activity. The role of kainate receptors depends on their precise subcellular localization in presynaptic, postsynaptic and extrasynaptic domains. Subcellular localization of kainate receptors has been inferred mainly from electrophysiological studies with the help of selective pharmacological tools and kainate receptor mutant mice. These studies, combined with recent ultrastructural data, highlight the diversity of subcellular localizations of kainate receptors. It is important to understand the molecular mechanisms that underlie the polarized trafficking of kainate receptors in distinct neuronal domains. In this article, we review recent data that shed light on the trafficking and membrane delivery of kainate receptor isoforms, and on the identification of proteins that interact with kainate receptors and might regulate this trafficking.

Animals↗

PubMed2004

Subunit composition and alternative splicing regulate membrane delivery of kainate receptors.

Kainate receptors (KARs) are heteromeric ionotropic glutamate receptors (GluRs) that play various roles in the regulation of synaptic transmission. The KAR subunits GluR5 and GluR6 exist under different splice variant isoforms in the C-terminal domain (GluR5a, GluR5b, GluR5c, GluR6a, GluR6b). The differential role of KAR subunit splice variants is presently unknown. In transfected COS-7 cells and neurons from wild-type and GluR5 x GluR6 mice, we have found that the subcellular localization and membrane delivery differed between these splice variants. GluR6a was highly expressed at the plasma membrane. GluR6b, GluR5a, and GluR5b were detected at lower levels in the plasma membrane and mainly colocalized with calreticulin in the endoplasmic reticulum (ER). GluR5c was strongly retained in the ER by an RXR motif. GluR6a acted as a key subunit splice variant promoting surface expression of ER-retained subunit splice variants when assembled in heteromeric KARs. Surface expression of GluR6a was independent of its PDZ (postsynaptic density-95/discs large/zona occludens-1) binding motif and was promoted by a stretch of four basic amino acid residues at its C terminus. Overall, splice variants and subunit composition of KARs regulate receptor trafficking from the endoplasmic reticulum to the plasma membrane.

Alternative Splicing↗