The Journal of Neuroscience, September 1, 2001, 21(17):6810-6819
Conserved Function of Caenorhabditis elegans
UNC-30 and Mouse Pitx2 in Controlling GABAergic Neuron
Differentiation
Joby J.
Westmoreland1,
Jason
McEwen3,
Billie A.
Moore1,
Yishi
Jin3, and
Brian G.
Condie1, 2
1 Institute of Molecular Medicine and Genetics and
2 Departments of Medicine and Cellular Biology and Anatomy,
Medical College of Georgia, Augusta, Georgia 30912, and
3 Department of Molecular, Cellular, and Developmental
Biology, University of California, Santa Cruz, Santa Cruz, California
95064
We are taking a cross-species approach to identify genes that are
required for mammalian GABAergic neuron differentiation. On the basis
of homeodomain similarity, the vertebrate Pitx genes appear to be orthologs of unc-30, a
Caenorhabditis elegans gene necessary for
differentiation of the GABAergic phenotype of type D neurons. One of
the Pitx genes, Pitx2, is expressed in
regions of GABAergic neurogenesis in the mammalian brain. These
observations led us to test the functional conservation of the mouse
Pitx2 and worm unc-30 genes using a
rescue assay. Pitx2 rescues the GABAergic
differentiation defect and partially rescues the axon guidance and
behavioral phenotypes of unc-30 mutants, indicating a
high degree of functional conservation between these evolutionarily related genes. Previous studies show that UNC-30 directly regulates the
unc-25/glutamate decarboxylase gene that encodes the
enzyme for GABA synthesis. We find that the promoter regions of the
mouse and human genes coding for the 67 kDa glutamate decarboxylase (Gad1) also contain binding sites matching the
UNC-30/Pitx2 consensus binding site sequence. We show that these sites
specifically bind to Pitx2 protein in vitro and that in
transfected neuroblastoma cells, the Pitx2 binding sites contribute to
the basal activity of the Gad1 promoter. Furthermore, in
cotransfection experiments, we find that Pitx2 strongly activates the
Gad1 promoter. These results indicate that Pitx2 may
regulate Gad1 expression in mammals, suggesting a new
role for this key developmental transcription factor as a regulator of
GABAergic differentiation during mammalian neural development. Our
results suggest that some of the mechanisms regulating GABAergic
differentiation are evolutionarily conserved.
Key words:
glutamate decarboxylase; neuron differentiation; Gad67; Gad1; unc-30; Pitx2; GABAergic neuron; mouse development; C.
elegans
Copyright © 2001 Society for Neuroscience 0270-6474/01/21176810-10$05.00/0
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