Contribution of the neural cell recognition molecule NB‐3 to synapse formation between parallel fibers and Purkinje cells in mouse

Abstract

The neural cell recognition molecule NB-3, also referred to as contactin-6, is expressed prominently in the developing nervous system after birth and its deficiency has been shown to cause impairment in motor coordination. Here, we investigated the contribution of NB-3 to cerebellar development, focusing on lobule 3 where NB-3 was expressed in granule cells but not in Purkinje cells. In the developing molecular layer, the neural cell recognition molecules TAG-1, L1, and NB-3 formed distinct expression zones from the external granule cell layer to the internal granule cell layer (IGL), respectively. The NB-3-immunoreactive zone did not overlap with TAG-1-immunoreactive zone. By contrast, the L1-immunoreactive zone overlapped with both the TAG-1- and NB-3-immunoreactive zones. NB-3-positive puncta overlapped with vesicular glutamate transporter 1, a presynaptic marker and were apposed close to metabotropic glutamate receptor 1A, a postsynaptic marker, indicating that NB-3 is localized presynaptically at glutamatergic synapses between parallel fibers and Purkinje cells. In NB-3 knockout mice, L1 immunoreactive signals were increased in the IGL at postnatal day (P) 5, suggesting the increase in the number of immature granule cells of the IGL. In addition, the density of parallel fiber synaptic terminals was reduced in NB-3 knockout mice relative to wild-type mice at P5 to P10. In parallel with these findings, caspase-dependent cell death was significantly increased in the NB- 3-deficient cerebellum at P15. Collectively, our results indicate that NB-3 deficiency affects synapse formation during postnatal cerebellar development.

Adropin Is a Brain Membrane-bound Protein Regulating Physical Activity via the NB-3/Notch Signaling Pathway in Mice

“…NB-3 functions as a membrane-tethered Notch1 ligand and belongs to the contactin family that mediates cell surface interaction during nervous system development (27). NB-3 promotes Notch1 activation and, subsequently, drives the expression of Notch1 target genes such as HES1 and HEY1 (28,29).…”

“…Next, we explored whether the deletion of adropin would affect cerebellum development, as observed in nb3-KO mice (27,33). No gross abnormality in the brain architecture of adrKO mice was observed (data not shown).…”

Developmental role of the cell adhesion molecule Contactin-6 in the cerebral cortex and hippocampus

“…The notion that Cntn6 plays a role in neuronal survival was previously demonstrated by the increased amount of apoptosis in granule cells of the cerebellum and in primary cultures derived from Cntn6 ¡/¡ mouse cortex. 18,20 A selective role of Cntn6 in interneuron function was derived from the observation that the number of PVC interneurons was significantly decreased in Cntn6 ¡/¡ mice, while the number of NPYC interneurons remained unchanged. Cntn6 may serve as a ligand for receptors on PVC interneurons and thereby contribute to migration, guidance or survival or other functions of these interneurons in the visual cortex.…”

“…In particular, Cntn6 ¡/¡ mice exhibited a significant reduction the density of parallel fiber glutamatergic synaptiC-terminals in the cerebellum. 18 Similarly, a significant reduction of glutamatergic synapses was found in the hippocampus of Cntn6 ¡/¡ mice, whereas there was no difference in the amount of GABAergic synapses. 17 Cntn6 was previously found to regulate neurite outgrowth in vitro, 19 and this property was reflected by the delayed formation of the corticospinal tract in Cntn6 ¡/¡ mice.…”

“…24 Defects in migration may cause these dysfunctions. The indication that Cntn6 exerts a number of CAM functions like axon guidance and survival, 18,22 prompted us to examine the migration of GABAergic interneurons. We quantified two non-overlapping populations of interneurons in the visual cortex of wild-type and Cntn6 ¡/¡ mice, namely interneurons positive for parvalbumin (PV) or neuropeptide Y (NPY).…”