Bilateral symmetry of an animal''s body plan is one of the unique features of higher animals. For instance, the nervous system is largely bilaterally symmetric on a morphological level, yet often displays striking degrees of functional left/right (L/R) asymmetry. It remains unclear how functional asymmetries of morphologically bilaterally symmetric structures are established within the nervous system and how they relate to visceral asymmetries. The homeobox genes provide an interesting entry point to study how left/right asymmetries are generated in the nervous system (Chang et al., 2003; Johnston et al., 2006), given that little is understood about cell fate specification after the beginning of gastrulation. Homeobox genes are highly conserved transcription factors that play key roles in the development of humans and animals (Burglin, 2005).
ceh-5, an ortholog to the human VAX genes, shows a unique expression pattern during early embryogenesis. It is strongly expressed in two distinct groups of cells that later would become neurons: one laterally and one anteriorly. Both expressions are chronologically and spatially separated. In addition, a third group of cells also expresses CEH-5 but at a much lower level. This group is in mirror-symmetry to the first expression pattern that is expressed in the lateral group. Therefore, we believe that
ceh-5 displays left/right asymmetry in this manner. We are interested to dissect the promoter region of
ceh-5 to understand how the distinct spatio-temporal expression is generated. We created a series of deletions in the promoter region of
ceh-5 fused to GFP that were used to make transgenic animals, which were monitored using 4D-imaging in live animals lab (please see the two abstracts from J. Hench et al. and J. Henriksson et al. at this meeting). This investigation revealed a 21bp in the promoter region is essential for the regulation of
ceh-5. This motif is highly conserved between different Caenorhabditis species. In order to look for transcription factors involved in regulating the expression of
ceh-5, we screen via RNAi knockdown searching for candidates that would create an altered
ceh-5 expression pattern. Although the screen is far from saturation, a putative transcriptional regulator of
ceh-5 has been identified.