How clustered protocadherin binding specificity is tuned for neuronal self-/nonself-recognition

Abstract

The stochastic expression of fewer than 60 clustered protocadherin (cPcdh) isoforms provides diverse identities to individual vertebrate neurons and a molecular basis for self-/nonself-discrimination. cPcdhs form chains mediated by alternating cis and trans interactions between apposed membranes, which has been suggested to signal self-recognition. Such a mechanism requires that cPcdh cis dimers form promiscuously to generate diverse recognition units, and that trans interactions have precise specificity so that isoform mismatches terminate chain growth. However, the extent to which cPcdh interactions fulfill these requirements has not been definitively demonstrated. Here, we report biophysical experiments showing that cPcdh cis interactions are promiscuous, but with preferences favoring formation of heterologous cis dimers. Trans homophilic interactions are remarkably precise, with no evidence for heterophilic interactions between different isoforms. A new C-type cPcdh crystal structure and mutagenesis data help to explain these observations. Overall, the interaction characteristics we report for cPcdhs help explain their function in neuronal self-/nonself-discrimination.

γ-Protocadherins control synapse formation and peripheral branching of touch sensory neurons

“…Pcdhgs bind strictly homophilically when expressed in cell lines, and can form isoform-specific homophilic trans dimer parallel arrays to generate large two-dimensional structures bridging adjacent membranes (Brasch et al, 2019; Fernandez-Monreal et al, 2009; Frank et al, 2005; Goodman et al, 2022; Obata et al, 1995; Sano et al, 1993). Our finding that Pcdhgc3 functions in somatosensory neurons to promote excitatory synapse formation between sensory neuron axons and spinal cord neurons led us to hypothesize that Pcdhgc3 also functions in spinal cord neurons to promote postsynaptic specialization.…”

Isoform requirement of clustered protocadherin for preventing neuronal apoptosis and neonatal lethality

“… 7 , 8 , 9 , 10 cPcdh proteins form cis -dimers promiscuously, with preferences for heterologous dimers with other isoforms that increase the variety of recognition units. 11 , 12 , 13 cPcdh isoforms then interact strictly homophilically in trans at the cell surface of opposing neurons, such as at synapses, creating interaction specificity. 12 , 13 , 14 , 15 , 16 , 17 Therefore, cPcdh can create cell-surface identity for cell recognition, which leads to the hypothesis that cPcdh works as a synaptic partner-selection molecule.…”

“… 11 , 12 , 13 cPcdh isoforms then interact strictly homophilically in trans at the cell surface of opposing neurons, such as at synapses, creating interaction specificity. 12 , 13 , 14 , 15 , 16 , 17 Therefore, cPcdh can create cell-surface identity for cell recognition, which leads to the hypothesis that cPcdh works as a synaptic partner-selection molecule. However, this has not been proven at the synapse level yet.…”

Gamma-Protocadherins regulate filopodia self-recognition and dynamics to drive dendrite self-avoidance

“…The cPcdh self-avoidance model posits that SACs discriminate self from non-self through homophilic interactions between self dendrites expressing the same cPcdh isoforms (Lefebvre et al 2012). This model is strengthened by recent molecular studies demonstrating the exquisite specificity of cPcdh binding to matching isoforms in trans via zipper-like chains (Nicoludis et al 2015; Rubinstein et al 2015; Brasch et al 2019; Goodman et al 2022; Goodman et al 2016; Thu et al 2014). We propose that the longer self-contacting lifetimes reflect such homophilic interactions.…”

“…The cPcdhs also regulate self-avoidance of olfactory sensory axons, and other aspects of neurite patterning and survival in the CNS (Wang et al 2002; Lefebvre et al 2008; Prasad et al 2008; Garrett et al 2012; Suo et al 2012; Hasegawa et al 2016; Mountoufaris et al 2017; Chen et al 2017; Katori et al 2017; Carriere et al 2020; Mancia Leon et al 2020). The cPcdhs generate extensive recognition specificity through combinatorial expression and homophilic binding of isoforms, providing a molecular basis for neurite self/non-self discrimination in mammals (Esumi et al 2005; Kaneko et al 2006; Schreiner and Weiner 2010; Rubinstein et al 2015; Nicoludis et al 2016; Goodman et al 2016; Goodman et al 2022; Thu et al 2014; Brasch et al 2019).…”