Thus, it is possible that the Pcdh-s will posses the same reelin-binding activity as the Pcdh-s. may be exchanged among synapses and intracellular compartments. Our results show that although Pcdh-s can be synaptic molecules, synapses form lacking Pcdh-s. Thus, Pcdh-s and their relatives may be late additions to the classical cadherin-based synaptic adhesive scaffold; their presence in intracellular compartments suggests a role in modifying synaptic physiology or stability. splicing of mRNA generated from promoters upstream from each Pcdh gene (Tasic et al., 2002; Wang et al., 2002a). Thus, a diversity of molecules are produced, presumably with different specificity, that can bind to the same submembranous elements at the synapse. Consistent with a role in neural recognition, neurons of the same type and cellular layer express different repertoires of Pcdh-s (Wang et al., 2002b; M. Frank and D. R. Colman, unpublished Nelfinavir Mesylate observations). Pcdh extracellular domains exhibit characteristics of calcium-dependent adhesion molecules (Obata et al., 1995; Kohmura et al., Nelfinavir Mesylate 1998; Wu and Maniatis, 1999), but their cytoplasmic domains bear no similarity to those of classical cadherins. Classical cadherins form an intracellular complex with the catenins that links cadherins to the actin cytoskeleton (Aberle et al., 1996) and to other synaptic proteins (Nishimura et al., 2002). Blockade of the interaction between the cadherin cytoplasmic domain and catenins disrupts the formation and alignment of presynaptic and postsynaptic components in cultured hippocampal neurons (Togashi et al., 2002). Thus, although it is possible that the Pcdhs are adhesive molecules (Obata et al., 1995), the Pcdh- and – constant cytoplasmic Nelfinavir Mesylate domains must connect to different submembranous components, suggesting a role distinct from that of the classical cadherins. We asked whether Pcdh-s exhibit properties consistent with a role in adhesion/recognition during synaptogenesis. Pcdh-s were expressed in a subset of neurons in culture, interneuronal cells and some pyramidal-like neurons, whereas many pyramidal-like neurons forming excitatory synapses did not express appreciable levels of these molecules. In the subset of Pcdh–positive pyramidal-like cells, Pcdh-s were found at certain excitatory synapses. Immunoelectron microscopy showed Pcdh-s in the presynaptic and postsynaptic membranes of some synapses and nonsynaptic membranes, as well as within intracellular tubulovesicular organelles. Our results show that Pcdh-s are likely to mediate trans-synaptic interactions but are not required for initial events in synaptogenesis as are classical cadherins. We suggest a model in which Pcdhs modify existing synaptic adhesive scaffolds only at synapses formed between two neurons that express the same Pcdh. Materials and Methods (DIV) and processed for immunocytochemistry. For analysis of Pcdh- expression in mature neurons, cultures were fixed after 30 d in culture and processed. for 20 min. The supernatant was reserved, and the pellet was resuspended in water. A small aliquot of the pellet was as the synaptic junctional fraction. To the remainder of the pellet, an equal volume of 20 mm Tris, pH 8, 1% Triton X-100 was added. The junctions were extracted on ice for 20 min and centrifuged at 15,000 for 20 min. The supernatant (fraction enriched in presynaptic material) and pellet (postsynaptic densities) were recovered. All fractions were brought to 5% SDS by adding 0.25 volume of 20% SDS. Protein determination was performed by the BCA method (Pierce). Five micrograms of each fraction were electrophoresed, transferred to nitrocellulose, and probed with the indicated antibodies. Specific bands were visualized using an alkaline phosphatase secondary antibody and color reaction. and and is the same. Scale bar: (in and test; 0.001). The increased recruitment of Pcdh-s to synapses in Pcdh–positive cell pairs is exemplified in Figure 4. Pcdh- labeling in isolated neurons (Fig. 4, green channel), albeit punctate, mostly did not colocalize PSD-95 (Fig. 4, red channel), although Pcdh–positive synapses were occasionally noted (Fig. 4and are shown below. In the solitary neuron, colocalization of Pcdh-s and PSD-95 was less than that observed in the Pcdh–positive neuron pair. with the extracellular matrix protein reelin (Senzaki et al., 1999). The binding site for reelin was localized Nelfinavir Mesylate within a 29 amino acid region of the first extracellular domain (EC1) of Pcdh-s that is almost completely conserved among all Pcdh- family members. Within an analogous region of the Pcdh- EC1 domain, there is also a highly conserved region that bears some similarity to the reelin binding site within the Pcdh-s (Wu and Maniatis, 1999). Thus, it KMT3A is possible that the Pcdh-s will posses the same reelin-binding activity as the Pcdh-s. Coincidentally, both reelin and Pcdh-s.