LAR-RPTPs Directly Interact with Neurexins to Coordinate Bidirectional Assembly of Molecular Machineries

Abstract

Neurexins (Nrxns) and LAR-RPTPs (leukocyte common antigen-related protein tyrosine phosphatases) are presynaptic adhesion proteins responsible for organizing presynaptic machineries through interactions with nonoverlapping extracellular ligands. Here, we report that two members of the LAR-RPTP family, PTPr and PTPd, are required for the presynaptogenic activity of Nrxns. Intriguingly, Nrxn1 and PTPr require distinct sets of intracellular proteins for the assembly of specific presynaptic terminals. In addition, Nrxn1a showed robust heparan sulfate (HS)-dependent, high-affinity interactions with Ig domains of PTPr that were regulated by the splicing status of PTPr. Furthermore, Nrxn1a WT, but not a Nrxn1a mutant lacking HS moieties (Nrxn1a DHS), inhibited postsynapse-inducing activity of PTPr at excitatory, but not inhibitory, synapses. Similarly, cis expression of Nrxn1a WT, but not Nrxn1a DHS, suppressed the PTPr-mediated maintenance of excitatory postsynaptic specializations in mouse cultured hippocampal neurons. Lastly, genetics analyses using male or female Drosophila Dlar and Dnrx mutant larvae identified epistatic interactions that control synapse formation and synaptic transmission at neuromuscular junctions. Our results suggest a novel synaptogenesis model whereby different presynaptic adhesion molecules combine with distinct regulatory codes to orchestrate specific synaptic adhesion pathways.

Intact synapse structure and function after combined knockout of PTPδ, PTPσ and LAR

“…Overall, we demonstrate that ablation of LAR-RPTPs from vertebrate synapses does not alter synapse density, vesicle docking, membrane anchoring of active zones, and synaptic vesicle release. This aligns with a parallel study that reported no loss of synaptic puncta and efficient release at excitatory synapses in cultured hippocampal neurons and in acute hippocampal brain slices (Sclip and Südhof, 2020) upon LAR-RPTP knockout, but contrasts RNAi-based studies that led to models in which these RPTPs are major synapse organizers (Dunah et al, 2005; Fukai and Yoshida, 2020; Han et al, 2018, 2020a, 2020b; Kwon et al, 2010; Takahashi and Craig, 2013; Um and Ko, 2013; Yim et al, 2013). LAR-RPTPs belong to the superfamily of RPTPs (Johnson and Van Vactor, 2003), and it is possible that different RPTPs compensate for their loss.…”

“…1L-1O), consistent with enlargements observed in invertebrates (Ackley et al, 2005; Kaufmann et al, 2002). A recent independent study that ablated LAR-RPTPs early also found normal synapse densities (Sclip and Südhof, 2020), contradicting the generalized model that LAR-RPTPs are master synapse organizers (Dunah et al, 2005; Fukai and Yoshida, 2020; Han et al, 2018, 2020a, 2020b; Kwon et al, 2010; Takahashi and Craig, 2013; Um and Ko, 2013; Yim et al, 2013). It remains possible that LAR-RPTPs control assembly of a specific subset of synapses, which may explain why PTPδ ablation causes modest layer-specific impairments of synaptic strength (Park et al, 2020).…”

“…Leukocyte common Antigen-Related Receptor Protein Tyrosine Phosphatases (LAR-RPTPs) are transmembrane proteins often regarded as master presynaptic organizers. Three LAR-RPTPs, PTPδ, PTPσ and LAR, are expressed in the brain, bind to the active zone organizer Liprin-α and to synaptic cell-adhesion proteins, and recruit presynaptic material in artificial synapse formation assays (Bomkamp et al, 2019; Han et al, 2018, 2020a; Johnson and Van Vactor, 2003; Kwon et al, 2010; Pulido et al, 1995; Serra-Pages et al, 1998; Takahashi et al, 2011; Yim et al, 2013). While these data suggest roles in presynaptic assembly (Fukai and Yoshida, 2020; Takahashi and Craig, 2013; Um and Ko, 2013), LAR-RPTP localization and function at neuronal synapses are less clear.…”

“…In invertebrates, loss-of-function mutations in LAR-RPTPs resulted in defects in axon guidance, increased active zone and synapse areas, and impaired neurotransmitter secretion (Ackley et al, 2005; Clandinin et al, 2001; Desai et al, 1997; Kaufmann et al, 2002; Krueger et al, 1996). In mice, RNAi-mediated knockdown of LAR-RPTPs or deletion of PTPσ caused generalized loss of synapse markers and defective synaptic transmission (Dunah et al, 2005; Han et al, 2018, 2020a, 2020b), leading to the model that LAR-RPTPs control synapse formation. Furthermore, mild synaptic and behavioral defects were observed in single gene constitutive knockouts (Elchebly et al, 1999; Horn et al, 2012; Park et al, 2020; Uetani et al, 2000; Wallace et al, 1999).…”

Glypicans and Heparan Sulfate in Synaptic Development, Neural Plasticity, and Neurological Disorders

“…A recent study revealed that HS moiety of Nrxs not only bound to the postsynaptic Nlgns and LRRTMs, but they also formed complexes with the presynaptic synapse organizer, PTPσ ( Figure 1A ) ( Han et al, 2020 ; Roppongi et al, 2020 ). LRRTM4 bound with Nrx through HS, but not with PTPσ.…”