Axo-glial communication through neurexin-neuroligin signaling regulates myelination and oligodendrocyte differentiation

Axonal transsynaptic signaling between presynaptic neurexin (NX) and postsynaptic neuroligin (NL) is essential for many properties of synaptic connectivity. Here, we demonstrate the existence of a parallel axo‐glial signaling pathway between axonal NX and oligodendritic (OL) NL3. We show that this pathway contributes to the regulation of myelinogenesis, the maintenance of established myelination, and the differentiation state of the OL using in vitro models. We first confirm that NL3 mRNA and protein are expressed in OLs and in OL precursors. We then show that OLs in culture form contacts with non‐neuronal cells exogenously expressing NL3's binding partners NX1α or NX1β. Conversely, blocking axo‐glial NX‐NL3 signaling by saturating NX with exogenous soluble NL protein (NL‐ECD) disrupts interactions between OLs and axons in both in vitro and ex vivo assays. Myelination by OLs is tied to their differentiation state, and we find that blocking NX‐NL signaling with soluble NL protein also caused OL differentiation to stall at an immature stage. Moreover, in vitro knockdown of NL3 in OLs with siRNAs stalls their development and reduces branching complexity. Interestingly, inclusion of an autism related mutation in the NL blocking protein attenuates these effects; OLs differentiate and the dynamics of OL‐axon signaling occur normally as this peptide does not disrupt NX‐NL3 axo‐glial interactions. Our findings provide evidence not only for a new pathway in axo‐glial communication, they also potentially explain the correlation between altered white matter and autism. GLIA 2015;63:2023–2039 Main Points NL3 is expressed in OLs. Blocking signaling between NX on the axon and NL on OLs using soluble peptides interferes with myelination in vitro and stalls OLs at an immature stage. The presence of an autism mutation in the blocking peptide destroys its functionality.