Convergent genetic programs regulate similarities and differences between related motor neuron classes in Caenorhabditis elegans.
How do genetic programs create features common to a specific cell or tissue type while generating modifications necessary for functional diversification? We have addressed this question using the nematode Caenorhabditis elegans. The dorsal D (DD) and ventral D (VD) motorneurons (mns), referred to collectively as the D mns, compose a cross-inhibitory network that contributes to the animal's sinuous locomotion. The D mns share a number of structural and functional features, but are distinguished from one another by their synaptic patterns and the expression of a neuropeptide gene. Our findings suggest that the similarities and differences are generated at the transcriptional level. UNC-30 contains a homeodomain and activates structural and functional genes expressed in both classes. UNC-55 is a nuclear receptor expressed in the VD mns that is necessary for generating features that distinguish the two classes of D mns from one another. In unc-55 mutants, the VD mns adopt the DD mn synaptic pattern and peptide expression profile. Conversely, ectopic expression of unc-55 in the DD mns causes them to adopt VD mn features. The promoter of the neuropeptide gene expressed in the DD mns contains putative binding sites for both UNC-30 and UNC-55; alteration of these sites suggests that UNC-55 represses the ability of UNC-30 to activate a subset of genes that are expressed in the DD mns but not in the VD mns. Thus UNC-55 acts as a switch for the features that distinguish these two functionally related classes of mns.
Shan
Ge
G
Department of Biology, Georgia State University, Atlanta, 30302-4010, USA.
Kim
Kyuhyung
K
Li
Chris
C
Walthall
W W
WW
D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000378:metabolism*; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D009479:Neuropeptides / Q000737:chemistry; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D011401:Promoter Regions, Genetic; D011956:Receptors, Cell Surface / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014158:Transcription, Genetic; D019076:Transgenes
D029742:Caenorhabditis elegans Proteins; D018398:Homeodomain Proteins; D009479:Neuropeptides; D009687:Nuclear Proteins; D010455:Peptides; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C117323:UNC-55 protein, C elegans; C090946:unc-30 protein, C elegans; D049452:Green Fluorescent Proteins