THE GROUCHO-LIKE TRANSCRIPTION FACTOR UNC-37 FUNCTIONS WITH THE NEURAL SPECIFICITY GENE UNC-4 TO GOVERN MOTOR-NEURON IDENTITY IN C-ELEGANS

Groucho and Tup1 are members of a conserved family of WD repeat protei ns that interact with specific transcription factors to repress target genes, Here we show that mutations in WD domains of the Groucho-like protein, UNC-37, affect a motor neuron trait that also depends on UNC- 4, a homeodomain protein that controls neuronal specificity in Caenorh abditis elegans, In unc-4 mutants, VA motor neurons assume the pattern of synaptic input normally reserved for their lineal sister cells, th e VB motor neurons; the loss of normal input to the VAs produces a dis tinctive backward movement defect, Substitution of a conserved residue (H to Y) in the fifth WD repeat in unc-37 (e262) phenocopies the Unc- 4 movement defect, Conversely, an amino acid change (E to K) in the si xth WD repeat of UNC-37 is a strong suppressor of unc-37(e262) and of specific unc-4 missense mutations, We have previously shown that UNC-4 expression in the VA motor neurons specifies the wild-type pattern of presynaptic input, Here we demonstrate that UNC-37 is also expressed in the VAs and that unc-37 activity in these neurons is sufficient to restore normal movement to unc-37(e262) animals. We propose that UNC-3 7 and UNC-4 function together to prevent expression of genes that defi ne the VB pattern of synaptic inputs and thereby generate connections specific to the VA motor neurons, In addition, we show that the WD rep eat domains of UNC-37 and of the human homolog, TLE1, are functionally interchangeable in VA motor neurons which suggests that this highly c onserved protein domain may also specify motor neuron identity and syn aptic choice in more complex nervous systems.