Elucidation of molecular mechanisms that regulate synapse formation is required for the understanding of neural wiring, higher brain functions, and mental disorders. Despite the wealth of in vitro information, fundamental questions about how glutamatergic synapses are formed in the mammalian brain remain unanswered. Glutamate receptor (GluR) delta2 is essential for cerebellar synapse formation in vivo. Here, we show that the N-terminal domain (NTD) of GluRdelta2 interacts with presynaptic neurexins (NRXNs) through cerebellin 1 precursor protein (Cbln1). The synaptogenic activity of GluRdelta2 is abolished in cerebellar primary cultures from Cbln1 knockout mice and is restored by recombinant Cbln1. Knockdown of NRXNs in cerebellar granule cells also hinders the synaptogenic activity of GluRdelta2. Both the NTD of GluRdelta2 and the extracellular domain of NRXN1beta suppressed the synaptogenic activity of Cbln1 in cerebellar primary cultures and in vivo. These results suggest that GluRdelta2 mediates cerebellar synapse formation by interacting with presynaptic NRXNs through Cbln1.

Mental retardation (MR) and autism are highly heterogeneous neurodevelopmental disorders. IL-1-receptor accessory protein-like 1 (IL1RAPL1) is responsible for nonsyndromic MR and is associated with autism. Thus, the elucidation of the functional role of IL1RAPL1 will contribute to our understanding of the pathogenesis of these mental disorders. Here, we showed that knockdown of endogenous IL1RAPL1 in cultured cortical neurons suppressed the accumulation of punctate staining signals for active zone protein Bassoon and decreased the number of dendritic protrusions. Consistently, the expression of IL1RAPL1 in cultured neurons stimulated the accumulation of Bassoon and spinogenesis. The extracellular domain (ECD) of IL1RAPL1 was required and sufficient for the presynaptic differentiation-inducing activity, while both the ECD and cytoplasmic domain were essential for the spinogenic activity. Notably, the synaptogenic activity of IL1RAPL1 was specific for excitatory synapses. Furthermore, we identified presynaptic protein tyrosine phosphatase (PTP) ␦ as a major IL1RAPL1-ECD interacting protein by affinity chromatography. IL1RAPL1 interacted selectively with certain forms of PTP␦ splice variants carrying mini-exon peptides in Ig-like domains. The synaptogenic activity of IL1RAPL1 was abolished in primary neurons from PTP␦ knock-out mice. IL1RAPL1 showed robust synaptogenic activity in vivo when transfected into the cortical neurons of wild-type mice but not in PTP␦ knock-out mice. These results suggest that IL1RAPL1 mediates synapse formation through trans-synaptic interaction with PTP␦. Our findings raise an intriguing possibility that the impairment of synapse formation may underlie certain forms of MR and autism as a common pathogenic pathway shared by these mental disorders.

Interleukin-1 receptor accessory protein (IL-1RAcP

SUMMARY Multi‐storey buildings made of cross‐laminated timber panels (X‐lam) are becoming a stronger and economically valid alternative in Europe compared with traditional masonry or concrete buildings. During the design process of these multi‐storey buildings, also their earthquake behaviour has to be addressed, especially in seismic‐prone areas such as Italy. However, limited knowledge on the seismic performance is available for this innovative massive timber product. On the basis of extensive testing series comprising monotonic and reversed cyclic tests on X‐lam panels, a pseudodynamic test on a one‐storey X‐lam specimen and 1D shaking table tests on a full‐scale three‐storey specimen, a full‐scale seven‐storey building was designed according to the European seismic standard Eurocode 8 and subjected to earthquake loading on a 3D shaking table. The building was designed with a preliminary action reduction factor of three that had been derived from the experimental results on the three‐storey building. The outcomes of this comprehensive research project called ‘SOFIE – Sistema Costruttivo Fiemme’ proved the suitability of multi‐storey X‐lam structures for earthquake‐prone regions. The buildings demonstrated self‐centring capabilities and high stiffness combined with sufficient ductility to avoid brittle failures. The tests provided useful information for the seismic design with force‐based methods as defined in Eurocode 8, that is, a preliminary experimentally based action reduction factor of three was confirmed. Valid, ductile joint assemblies were developed, and their importance for the energy dissipation in buildings with rigid X‐lam panels became evident. The seven‐storey building showed relatively high accelerations in the upper storeys, which could lead to secondary damage and which have to be addressed in future research. Copyright © 2013 John Wiley & Sons, Ltd.

Synapse formation is the key step in the development of neuronal networks. Precise synaptic connections between nerve cells in the brain provide the basis of perception, learning, memory, and cognition. Recently, we have shown that the trans-synaptic interaction of postsynaptic glutamate receptor (GluR) d2 and presynaptic neurexins (NRXNs) through cerebellin precursor protein (Cbln) 1 mediates excitatory synapse formation in the cerebellum (Uemura et al. 2010). This finding raises a question whether GluRd1 regulates synapse formation by trans-synaptic interaction with NRXNs through Cbln subtypes in the forebrain since GluRd1 shares 56% amino acid identity with GluRd2 (Yamazaki et al. 1992;Araki et al. 1993;Lomeli et al. 1993). Previous studies showed that GluRd1 expressed in human embryonic kidney (HEK) 293T cells induced presynaptic differentiation of cultured cerebellar granule cells AbstractGlutamate receptor (GluR) d1 is widely expressed in the developing forebrain, whereas GluRd2 is selectively expressed in cerebellar Purkinje cells. Recently, we found that trans-synaptic interaction of postsynaptic GluRd2 and presynaptic neurexins (NRXNs) through cerebellin precursor protein (Cbln) 1 mediates excitatory synapse formation in the cerebellum. Thus, a question arises whether GluRd1 regulates synapse formation in the forebrain. In this study, we showed that the N-terminal domain of GluRd1 induced inhibitory presynaptic differentiation of some populations of cultured cortical neurons. When Cbln1 or Cbln2 was added to cultures, GluRd1 expressed in HEK293T cells induced preferentially inhibitory presynaptic differentiation of cultured cortical neurons. The synaptogenic activity of GluRd1 was suppressed by the addition of the extracellular domain of NRXN1a or NRXN1b containing splice segment 4. Cbln subtypes directly bound to the N-terminal domain of GluRd1. The synaptogenic activity of GluRd1 in the presence of Cbln subtypes correlated well with their binding affinities. When transfected to cortical neurons, GluRd1 stimulated inhibitory synapse formation in the presence of Cbln1 or Cbln2. These results together with differential interactions of Cbln subtypes with NRXN variants suggest that GluRd1 induces preferentially inhibitory presynaptic differentiation of cortical neurons by interacting with NRXNs containing splice segment 4 through Cbln subtypes.