Neurobeachin, a protein implicated in membrane protein traffic and autism, is required for the formation and functioning of central synapses

Abstract

The development of neuronal networks in the brain requires the differentiation of functional synapses. Neurobeachin (Nbea) was identified as a putative regulator of membrane protein trafficking associated with tubulovesicular endomembranes and postsynaptic plasma membranes. Nbea is essential for evoked transmission at neuromuscular junctions, but its role in the central nervous system has not been characterized. Here, we have studied central synapses of a newly generated gene-trap knockout (KO) mouse line at embryonic day 18, because null-mutant mice are paralysed and die perinatally. Although the overall brain architecture was normal, we identified major abnormalities of synaptic function in mutant animals. In acute slices from the brainstem, both spontaneous excitatory and inhibitory postsynaptic currents were clearly reduced and failure rates of evoked inhibitory responses were markedly increased. In addition, the frequency of miniature excitatory and both the frequency and amplitudes of miniature inhibitory postsynaptic currents were severely diminished in KO mice, indicating a perturbation of both action potential-dependent and -independent transmitter release. Moreover, Nbea appears to be important for the formation and composition of central synapses because the area density of mature asymmetric contacts in the fetal brainstem was reduced to 30% of wild-type levels, and the expression levels of a subset of synaptic marker proteins were smaller than in littermate controls. Our data demonstrate for the first time a function of Nbea at central synapses that may be based on its presumed role in targeting membrane proteins to synaptic contacts, and are consistent with the 'excitatory-inhibitory imbalance' model of autism where Nbea gene rearrangements have been detected in some patients.

Drosophila rugoseIs a Functional Homolog of MammalianNeurobeachinand Affects Synaptic Architecture, Brain Morphology, and Associative Learning

“…Drosophila Rg is neuronally expressed in the larval and adult CNS and localizes to the TGN and endomembranes near the TGN, as does NBEA in mammals (Wang et al, 2000). In contrast to Nbea knock-out mice that die shortly after birth (Su et al, 2004;Medrihan et al, 2009), loss of Rg function results in viable and fertile adults that display an increased number of synaptic boutons at the level of the larval NMJ without affecting basal synaptic transmission. At the level of CNS development, Drosophila rg mutants display gross morphological defects of the Drosophila MB, the fly "learning center," and at the same time rg mutants are impaired in associative odor learning.…”

“…However, Nbea-deficient mice die shortly after birth because of respiratory problems; thus, the role of Nbea in associative learning is as yet untested (Su et al, 2004;Medrihan et al, 2009). To test whether Drosophila rugose functions in learning and memory, we used the well-established olfactory conditioning paradigm (Tully and Quinn, 1985).…”

“…NBEA is a multidomain scaffolding protein with an AKAP (A-kinase anchor protein) domain and is localized near the transGolgi network (TGN) (Wang et al, 2000), supporting a function in vesicle sorting or secretion as demonstrated by experiments performed in Nbea knock-out mice and in vitro (Wang et al, 2000;Su et al, 2004;Medrihan et al, 2009;Castermans et al, 2010;Niesmann et al, 2011). Whereas NBEA is known for its neuronal function and its implication in autism spectrum disorders (Castermans et al, 2003;Volders et al, 2011), the human homolog LRBA has a broad expression pattern, and its function is currently unknown (Wang et al, 2001).…”

Tandem mass spectrometry identifies many mouse brain O -GlcNAcylated proteins including EGF domain-specific O -GlcNAc transferase targets

“…We observed three O-GlcNAcylation sites (T1276, T1796, and T1797) on neurobeachin (Nbea), a protein implicated in membrane protein traffic and autism, and required for the formation and functioning of central synapses (28). This protein is a known phosphoprotein and binds to protein kinase A; however, its O-GlcNAcylation status was previously unknown (29).…”

Gray platelet syndrome and defective thrombo-inflammation in Nbeal2-deficient mice

“…Other members of this family, such as neurobeachin, Nbeal1, Lrba, and Lyst, have been associated with protein trafficking (19,22). In contrast to neuro-beachin, which is prominently expressed in brain tissue and known to be required for the formation and functioning of central synapses in mice (23), NBEAL2 is highly expressed in blood cells, especially during MK maturation, but virtually absent from brain tissue (19).…”