Engineered synaptic tools reveal localized cAMP signaling in synapse assembly

Abstract

The physiological mechanisms driving synapse formation are elusive. Although numerous signals are known to regulate synapses, it remains unclear which signaling mechanisms organize initial synapse assembly. Here, we describe new tools, referred to as “SynTAMs” for synaptic targeting molecules, that enable localized perturbations of cAMP signaling in developing postsynaptic specializations. We show that locally restricted suppression of postsynaptic cAMP levels or of cAMP-dependent protein-kinase activity severely impairs excitatory synapse formation without affecting neuronal maturation, dendritic arborization, or inhibitory synapse formation. In vivo, suppression of postsynaptic cAMP signaling in CA1 neurons prevented formation of both Schaffer-collateral and entorhinal-CA1/temporoammonic-path synapses, suggesting a general principle. Retrograde trans-synaptic rabies virus tracing revealed that postsynaptic cAMP signaling is required for continuous replacement of synapses throughout life. Given that postsynaptic latrophilin adhesion-GPCRs drive synapse formation and produce cAMP, we suggest that spatially restricted postsynaptic cAMP signals organize assembly of postsynaptic specializations during synapse formation.

Essential Role of Latrophilin-1 Adhesion GPCR Nanoclusters in Inhibitory Synapses

“…An important question that remains largely unanswered is how latrophilins function on a molecular level to promote excitatory and inhibitory synapse formation. Recent findings suggest G-protein binding of Latrophilin-3 and localized synaptic cAMP signaling to be essential molecular events for excitatory synapse formation ( Sando et al, 2021 , 2022 ; Wang et al, 2024 ). Neuronal isoforms of Latrophilin-1 bind to multiple G-proteins with a preference for Gs ( Wang et al, 2024 ), which could mean that the inhibitory synapses formed by Lphn1 depend on localized Gs-cAMP signaling cascades but might also include other G-proteins.…”

Orchestration of synaptic functions by WAVE regulatory complex-mediated actin reorganization

“…Intriguingly, the WRC regulatory pathway appears to integrate cues from other signaling pathways encompassing PKA 62 , 63 , 111 . Moreover, a subset of protein kinase pathways, including PKA and postsynaptic cAMP signaling, is essential for compartmentalized signaling at excitatory synapses 112 – 114 , suggesting the fascinating hypothesis that differentially activated WRC pathways determine the strength of intracellular signals in postsynaptic neurons (Fig. 2 ).…”

Trans‐synaptic mechanisms orchestrated by mammalian synaptic cell adhesion molecules

“…[78] A follow-up study showed that Lphn2 and Lphn3 act as constitutive GPCRs and upregulate cyclic adenosine monophosphate (cAMP) levels via binding to G-proteins and arrestins, [30] which is consistent with the idea that compartmentalized intracellular calcium transient levels could dictate synaptic specificity. [14,69] Systematic studies are needed to assess whether the identified functions and mechanisms of Lphns in the hippocampal neural circuits are canonical, given that Lphn2 and Lphn3 appear to have different actions in the cerebellum. [80] Moreover, it is unclear how teneurins and/or FLRTs distinctively cooperate with Lphn2 and Lphn3 to mediate synaptic specificity.…”

“…Excitatory synaptic response & feedforward inhibition (DG → CA3 circuit) [99] LRRTM3 AMPAR-and NMDAR-mediated response (MEC → DG circuit) [88 ] MDGA1 Negative regulation of inhibitory synaptic strength & GABA release (SST + IN → CA1 PN circuit) [62] AMPAR, α-amino-3-hydroxy- showed that compartmentalized postsynaptic signaling is involved in synapse assembly, [14] it remains unclear how the various trans-synaptic signaling pathways contribute to shaping specific properties of neural circuits.…”

“…[ 13 ] These observations collectively suggest that distinct synaptic CAMs contribute to regulating specific synapse properties, such as by transducing trans ‐cellular signals. Although recent studies showed that compartmentalized postsynaptic signaling is involved in synapse assembly, [ 14 ] it remains unclear how the various trans ‐synaptic signaling pathways contribute to shaping specific properties of neural circuits.…”