Proper function of the brain requires that neurons adopt different morphologies and connections. In the nematode <i>C. elegans</i>, VA and VB motor neurons arise from a common precursor cell but adopt different morphologies and accept input from separate sets of command interneurons. In <i>unc-4</i> mutants, VA motor neurons are miswired with VB-type inputs. We have proposed that miswiring results when VB genes are ectopically expressed in the VAs in <i>unc-4</i> mutants. Previous work revealed that UNC-4 functions with the UNC-37/Groucho co-repressor protein to repress the VB-specific genes <i>acr-5, del-1, glr-4</i>. However, our genetic data rule out roles for these VB genes in synaptic choice. To identify the missing <i>unc-4</i> target genes, a microarray-based strategy for profiling VA motor neurons was adopted.
A comparison of VA-specific transcripts isolated by mRNA-tagging from wildtype and <i>unc-37</i> mutant animals revealed ~250 upregulated transcripts in <i>unc-37</i> animals. One of these genes, <i>ceh-12</i>, is the <i>C. elegans</i> homolog of HB9, a homeodomain transcription factor with conserved roles in motor neuron fate in flies and vertebrates (Arber et al 1999, Broihier and Skeath 2002). In <i>C. elegans, ceh-12</i>::GFP is exclusively expressed in VB motor neurons in wildtype animals. In <i>unc-4</i> and <i>unc-37</i> mutants, <i>ceh-12</i>::GFP is also expressed in VA motor neurons as suggested by the microarray data. Thus, CEH-12 is a strong candidate for an UNC-4 target gene that regulates synaptic choice.
To test this idea, the <i>unc-4</i> promoter was used to drive CEH-12 expression in wildype VA motor neurons. These animals exhibit an Unc-4 like backward movement defect, as expected for a model in which ectopic CEH-12 is sufficient to impose VB type inputs. In addition, we also showed that <i>ceh-12</i> deletion mutants are partial suppressors of Unc-4 movement, thereby confirming that CEH-12 is also required for the Unc-4 miswiring defect. We conclude the VB-specific gene, <i>ceh-12</i>, is normally repressed in VA motor neurons to prevent the imposition of VB-type inputs. The incomplete suppression of <i>unc-4</i>, however, suggests that UNC-4 also controls other downstream target genes that function in parallel pathways to regulate synaptic choice.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-10262005-161737 |
| Date | 07 November 2005 |
| Creators | Von Stetina, Stephen Edward |
| Contributors | Richard O'Brien, Randy Blakely, David M. Miller, III, David I. Greenstein, Christopher V. E. Wright |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-10262005-161737/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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