Figure 1. Transcriptional regulation of synaptic specificity.

a, During early development of nematodes, excitatory motor neurons (blue) on the dorsal side of the embryo make synaptic connections with, and so excite, dorsal muscle and inhibitory dorsal D-type (DD) motor neurons (red). DD neurons innervate, and thus inhibit contraction of, ventral muscle. Howell et al.¹ report that the synaptic inputs and outputs of early DD neurons are controlled by LIN-14. This transcription factor, together with the ubiquitously expressed transcription factor UNC-30, promotes expression of the protein OIG-1, which prevents the formation of synaptic outputs from DD neurons to dorsal muscle cells. b, After the larva’s first moult, LIN-14 is no longer expressed and DD neurons undergo a synaptic inversion — they become innervated by ventral excitatory neurons and themselves innervate dorsal muscle. Ventral D-type (VD) motor neurons (purple) innervate ventral muscle cells and express the transcription factor UNC-55, which, together with UNC-30, promotes OIG-1 expression and prevents VD neurons from forming inhibitory connections to dorsal muscle.