Temporally distinct demands for classic cadherins in synapse formation and maturation

Abstract

Classic cadherins are synaptic adhesion proteins that have been implicated in synapse formation and targeting. Brief inactivation of classic cadherin function in young neurons appears to abrogate synapse formation when examined acutely. It remains unknown whether such abrogation is unique to young neurons, whether it occurs by stalling neuronal maturation or by directly interfering with the process of synapse assembly, and whether synapse targeting is altered. Here we asked whether sustained pan-cadherin blockade would prevent or alter the progression of axonal and dendritic outgrowth, synaptogenesis and the stereotypic distribution of excitatory and inhibitory synapses on cultured hippocampal neurons. While pre-and postsynaptic cadherins are required for synapse assembly in young neurons, we find that in neurons older than 10 days, classic cadherins are entirely dispensable for joining and aligning presynaptic vesicle clusters with molecular markers of the postsynaptic density. Further, we find the proportion and relative distributions of excitatory and inhibitory terminals on single neurons is not altered. However, synapse formation on neurons in which cadherin function is blocked are smaller; such synapses exhibit decreased synaptic vesicle recycling and a decreased frequency of spontaneous EPSCs. Moreover, such synapses fail to acquire resistance to F-actin depolymerization, a hallmark of mature, stable contacts. These data provide new evidence that cadherins are required to promote synapse stabilization and structural and functional maturation, but dispensable for the correct subcellular distribution of excitatory and inhibitory synapses.

Essential cooperation of N-cadherin and neuroligin-1 in the transsynaptic control of vesicle accumulation

“…In agreement to our results, expression of a dominant-negative mutant N-cadherin led to a reduction in the number of vesicle clusters that was most pronounced in immature neurons (16,20). In addition, β-catenin-(19) and p120catenin-deficient (17) hippocampal neurons showed a reduced clustering of presynaptic vesicles.…”

“…In addition to its important postsynaptic roles (4,(16)(17)(18), N-cadherin has been suggested to be involved in the formation of presynaptic vesicle clusters (4,16,19,20). However, these findings could not yet be confirmed in N-cadherin knockout neurons (21,22), and expression of N-cadherin in nonneuronal cells does not induce clustering of synaptic vesicles in contacting axons (3,9).…”

β-Catenin regulates excitatory postsynaptic strength at hippocampal synapses

“…Accordingly, impairing the adhesive activity of cadherins by deletion of ␤-catenin or N-cadherin reduces the number of reserve pool synaptic vesicles at the presynaptic terminal, resulting in enhanced synaptic depression during repetitive stimulation (21,22). Moreover, overexpressing an N-cadherin mutant lacking the extracellular domain or ␤-catenin mutants with an altered phosphorylation site alters spine morphology and synaptic efficacy (23)(24)(25)(26). Analysis of ␣N-catenin knockout mice has also revealed a requirement for the cadherin link to the actin cytoskeleton in regulating spine dynamics (27).…”

Expression of classical cadherins in the cerebellar anlage: Quantitative and functional aspects

“…Their role in postmigratory synaptogenesis, (e.g. Bozdagi et al, 2004;Bamji, 2005) is thus clearly beyond its reach. In contrast, limitations arising from the fact that the current study is restricted to a subset of the multiple cell-cell and cell-substrate contact-mediating proteins differentially expressed in the cerebellar anlage (e.g., protocadherins, tetraspanins, integrins, ephrins; Hirano et al, 1999;Frank et al, 2005;Rogers et al, 1999;Juenger et al, 2005) may be overcome in the future.…”

“…Radice et al, 1997;Lele et al, 2002) to synaptogenesis (e.g., Poskanzer et al, 2003;Bozdagi et al, 2004), and possibly regeneration (Obst-Pernberg and Redies, 1999;Liu et al, 2004). Both classical and the more recently described group of protocadherins are widely expressed in the nervous system, and their expression patterns may be perceived as a reflection of molecular diversity, and possibly functional specificity within discrete central nervous circuits (e.g., Redies and Puelles, 2001;Esumi et al, 2005;Frank et al, 2005).…”