Abstract
In the central nervous system (CNS), cholinergic transmission induces synaptic plasticity that is required for learning and memory. However, our understanding of the development and maintenance of cholinergic circuits is limited, as the factors regulating the expression and clustering of neuronal nicotinic acetylcholine receptors (nAChRs) remain poorly defined. Recent studies from our group have implicated calpain-dependent proteolytic fragments of menin, the product of the MEN1 tumor suppressor gene, in coordinating the transcription and synaptic clustering of nAChRs in invertebrate central neurons. Here, we sought to determine whether an analogous cholinergic mechanism underlies menin’s synaptogenic function in the vertebrate CNS. Our data from mouse primary hippocampal cultures demonstrate that menin and its calpain-dependent C-terminal fragment (C-menin) regulate the subunit-specific transcription and synaptic clustering of neuronal nAChRs, respectively. MEN1 knockdown decreased nAChR α5 subunit expression, the clustering of α7 subunit-containing nAChRs at glutamatergic presynaptic terminals, and nicotine-induced presynaptic facilitation. Moreover, the number and function of glutamatergic synapses was unaffected by MEN1 knockdown, indicating that the synaptogenic actions of menin are specific to cholinergic regulation. Taken together, our results suggest that the influence of menin on synapse formation and synaptic plasticity occur via modulation of nAChR channel subunit composition and functional clustering.
Highlights
Synapse formation and synaptic plasticity in the central nervous system (CNS) require the coordination of nuclear transcription and site-specific targeting of nascent synaptic proteins in response to extracellular and cell-cell signaling interactions
We performed subcellular fractionation and Western blot (WB) analysis to determine whether differential subcellular distribution of menin and its proteolytic fragments occurs in the mouse CNS
Of the neurons exhibiting an increase in miniature excitatory postsynaptic currents (mEPSCs) frequency in response to nicotine, we found that the mean mEPSC frequency was significantly increased in untreated control (Fig. 8D; P < 0.001, paired t-test; see Table S9) and non-target control (NTC) shRNA-transduced cultures (P < 0.001), but not MEN1 shRNA-transduced cultures (P = 0.130)
Summary
Synapse formation and synaptic plasticity in the central nervous system (CNS) require the coordination of nuclear transcription and site-specific targeting of nascent synaptic proteins in response to extracellular (e.g. neurotrophic factors1) and cell-cell (e.g. neuroligin-neurexin2, 3) signaling interactions. This work posed two important questions regarding menin’s neuronal molecular functions that remained unanswered: (i) does an analogous mechanism of action underlie menin’s synaptogenic function in the vertebrate CNS; and (ii) does menin act ubiquitously as a synaptogenic factor, or are its molecular actions specific to cholinergic synaptogenesis via the regulation of neuronal nAChRs?. It follows that central neurons employ an as-yet unidentified postsynaptic scaffold to cluster nAChRs. Considering our previous observations in Lymnaea that the synaptogenic effects of L-menin are mediated, in part, by the synaptic clustering of L-nAChRs via a calpain-dependent C-terminal proteolytic fragment (C-menin)[6], there exists an intriguing possibility that C-menin may be a candidate molecular scaffold or adaptor for neuronal nAChRs. The mechanisms underlying the synaptogenic function of menin in the vertebrate CNS, have not yet been defined. Our results suggest that menin does not act as a ubiquitous synaptogenic factor, but that it is a specific regulator of neuronal nAChR subunit composition and functional clustering
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
