Mice, Molecules and Synapse Formation
Principal Investigator: Fekrije SELIMI, DR2 Cnrs (ATIP-AVENIR)
The brain is composed of many different types of neuronal populations that form functional networks by establishing very specific synapses. The complex process of synapse formation involves both target recognition, through a putative "molecular code", and activity-dependent stabilization/elimination of synapses. The goal of our team is to provide new insights on the formation of functional neural networks in vivo, in particular on the molecular basis of synapse specificity and synapse remodeling, and its contribution to neurological diseases.
The mouse is a perfect model system to perform this type of research, since its genome has now been sequenced, and it is accessible to genetic, biochemical, physiological and behavioral studies. In particular, the use of the BAC (Bacterial Artificial Chromosome) modification strategy to generate transgenic mice provides drivers to target expression of any transgene in specific types of neurons in the brain. Our project takes advantage of two new methods that use the BAC modification strategy: 1) The bacTRAP method (Translating Ribosome Affinity Purification) allows the gene expression profiling of specific neuronal populations in the mouse in vivo (in collaboration with the laboratory of Pr. Nathaniel Heintz, The Rockefeller University, USA). 2) The synapse protein profiling strategy enables the identification of the protein content of specific synapses in a given neuronal population (cf. figure 1).
Bottom : Protein profiling of the parallel fiber/Purkinje cell synapse (A) Electron micrograph of purified synaptic structures ; (B) Coomassie staining of purified proteins from the parallel fiber/Purkinje cell synapses ; (C) Mass spectrometry identification of 65 proteins from the parallel fiber/Purkinje cell synapses
Our team is combining these innovative strategies to address the question of the control of synapse specificity and elimination using the olivo-cerebellar network as a model system (figure 2). This network is composed of a limited number of cell types connected in a very precise and stereotyped manner. Each of these neuronal types can be specifically targeted in genetically modified mice using BAC drivers already described in the GENSAT database (www.gensat.org). Purkinje cells (PCs), the sole output of the cerebellar cortex, receive two types of excitatory inputs, one from the granule cells through the parallel fibers (PF), and one from the inferior olivary neurons, through the climbing fibers (CF). These two types of excitatory synapses have clear differences in terms of their physiology and form on separate dendritic territories on Purkinje cells. In addition, the climbing fiber/Purkinje cell synapse is one of the best examples of developmental synapse remodeling in the central nervous system, making it an ideal model to find the molecular controls of this important step in neuronal network formation.
Climbing fibers (green) make synapses with Purkinje cells (blue) on their primary dendrites, whereas parallel fibers (pink) make synapses on distal dendrites.
Synaptic protein profiling of the climbing fiber/Purkinje cell synapse:
We have used the bacTRAP method to identify genes expressed in inferior olivary neurons. Using comparative analysis of gene expression profiles in the olivo-cerebellar network, we are now screening for genes that code ligand/receptor couples potentially specific to the climbing fiber/Purkinje cell synapse. We will then use one of these proteins to apply the synapse protein profiling approach and identify the proteins localized at the climbing fiber/Purkinje cell synapse. This will allow the first comparison of the composition of two excitatory synapses established on the same target-neuron: the parallel fiber/Purkinje cell synapse and the climbing fiber/Purkinje cell synapse.
New synaptic signaling pathways:
Our group has used the synaptic protein profiling strategy to identify the proteins located at the parallel fiber/Purkinje cell synapse. We are now using a combination of knockdown experiments, genetically modified mice, biochemistry and mass spectrometry to identify the function and signaling pathway of some of the newly identified synaptic proteins in vivo. For example, the BAI (Brain Angiogenesis Inhibitor) receptors are members of the adhesion-GPCRs subgroup, which has been little studied despite GPCRs' potential as important signaling molecules and therapeutic targets. The proteins BAI2 and BAI3 were found in our biochemical preparations of parallel fiber/Purkinje cell synapses. Expression data show that the brain is the highest site of expression for these receptors from early stages of development (www.genepaint.org; http://mouse.brain-map.org/). We are currently analyzing the role of BAI3 in the development of the olivo-cerebellar system.
- Sigoillot, S.M., Monk, K.R., Piao, X., Selimi, F. & Harty, B.L., (2016), Adhesion GPCRs as Novel Actors in Neural and Glial Cell Functions: From Synaptogenesis to Myelination. Handb Exp Pharmacol 234, 275–298.
- Usardi, A., Iyer, K., Sigoillot, S.M., Dusonchet, A. & Selimi, F. (2016), The immunoglobulin-like superfamily member IGSF3 is a developmentally regulated protein that controls neuronal morphogenesis. Dev Neurobiol. Jun 21.
- Sigoillot S.M., Iyer K., Binda F., González-Calvo I., Talleur M., Vodjdani G., Isope P. & Selimi F. (2015), The Secreted Protein C1QL1 and Its Receptor BAI3 Control the Synaptic Connectivity of Excitatory Inputs Converging on Cerebellar Purkinje Cells. Cell Reports, vol. 10, issue 5, 10, pp 820-832.
- Proville RD., Spolidoro M., Guyon N., Dugué GP., Selimi F., Isope P., Popa D., Léna C. (2014), Cerebellum involvement in cortical sensorimotor circuits for the control of voluntary movements, Nat Neurosci. Jul 27.
- Chaumont J., Guyon N., Valera A., Dugué G.P., Popa D., Marcaggi P., Gautheron V., Reibel-Foisset S., Dieudonné S., Stephan A., Barrot M., Cassel J.C., Dupont J.L., Doussau F., Poulain B., Selimi F.*, Léna C.* & Isope P.*(2013), Clusters of cerebellar Purkinje cells control their afferent climbing fiber discharge. Proc. Natl. Acad. Sci. USA, Oct 1;110(40):16223-16228 (*equal contribution).
- Lanoue V., Usardi A., Sigoillot S., Talleur M., Iyer K., Mariani J., Isope P., Vodjdani G., Heintz N. & Selimi F. (2013), The adhesion‐GPCR BAI3, a gene linked to psychiatric disorders, regulates dendrite morphogenesis in neurons. Mol Psychiatry 18(8):943-50.
- Heller E.A., Zhang W., Selimi F., Earnheart J.C., Slimak M.A., Santos-Torres J., Ibañez-Tallon I., Aoki C., Chait B.T. & Heintz N. (2012), The biochemical anatomy of cortical inhibitory synapses. PLoS One. 7(6):e39572.
- Selimi F., Cristea I.M., Heller E., Chait B.T. & Heintz N. (2009), Proteomic studies of a single CNS synapse type: specific regulatory components of the parallel fiber/Purkinje cell synapse. PloS Biology 7(4): e83.
- Zanjani S. H., Selimi F., Vogel M.W., Haeberlé A.-M., Boeuf J., Mariani J. & Bailly Y.J. (2006), Survival of interneurons and of parallel fiber synapses in a cerebellar cortex deprived of Purkinje cells: studies in the double mutant mouse Grid2 Lc/+;Bax-/-. J. Comp. Neurol. 497(4):622-35.
- F. Selimi & N. Heintz (2005), How do neurons keep in touch ? Nature neuroscience, 8(11):1417-8
- Selimi F., Lohof A.M., Heitz S., Lalouette A., Jarvis C.I., Bailly Y. & Mariani J. (2003), Lurcher GRID2 induced death and depolarization can be dissociated in cerebellar Purkinje cells. Neuron 37(5):813-9.
- Yue Z., Horton A., Bravin M., DeJager P.L., Selimi F. & Heintz N. (2002), A novel protein complex linking the d2 glutamate receptor and autophagy: implications for neurodegeneration in Lurcher mice. Neuron 35: 921-933.
- Selimi F., Vogel M.W. & Mariani J. (2000), Bax inactivation in Lurcher mutants rescues cerebellar granule cells, but not Purkinje cells nor inferior olivary neurons. Journal of Neuroscience 20: 5339-5345
- Selimi F., Doughty M.L., Delhaye-Bouchaud N. & Mariani J. (2000), Target-related and intrinsic neuronal death in Lurcher mutant mice involve different apoptotic pathways, but are both mediated by caspase-3 activation. Journal of Neuroscience 20: 992-1000
- Doughty M.L., Lohof A., Selimi F., Delhaye-Bouchaud N. & Mariani J. (1999), Afferent-target cell interactions in the cerebellum: negative effect of granule cells on Purkinje cell development in Lurcher mice. Journal of Neuroscience 19: 3448-3456.
Selimi Fekrije, DR2 CNRS
Postdoctoral fellows & PhD Students:
Gonzalez-calvo Ines, PhD student
Adeline Boyreau IE CDF
Albert Mélanie, CDD AI CNRS