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Comments on Tong, Yong-Guang et al. (2011) International Worm Meeting "A regulatory network of homeobox genes is required for the function of the Caenorhabditis elegans excretory cell." (0)
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Tong, Yong-Guang, Meemon, Krai, & Burglin, Thomas R. (2011). A regulatory network of homeobox genes is required for the function of the Caenorhabditis elegans excretory cell presented in International Worm Meeting. Unpublished information; cite only with author permission.
Homeobox genes play important roles in the development and differentiation of animals. We have previously found that the POU-III class homeobox gene, ceh-6, functions in the excretory cell (Burglin et al. 2001). We have been studying the three C. elegans otd/Otx homeobox genes, ceh-36, ceh-37 and ttx-1 (Tong et al., IWM 2007). Using mutant alleles and RNAi we have found that ceh-37 and ttx-1 act redundantly in the excretory cell (Meemon et al., EWM 2008). Double mutants arrest with excretory cell defects. Furthermore, we have found that the prospero homeobox gene ceh-26 is expressed in the excretory cell and loss of function of ceh-26 causes early larval lethality consistent with excretory cell defects. We further examined the effects of knocking down ceh-6, ceh-26, and ceh-37/ttx-1 in combination by looking at GFP reporters expressed in the excretory cell. For example, knock-down of all genes downregulates the expression of clh-4::GFP in the excretory cell. In contrast, expression of sulp-4::GFP is suppressed in ceh-26(RNAi) and ceh-6(mg6) animals, but not in ceh-37(RNAi)/ttx-1(RNAi) animals. Further, only ceh-6(RNAi) completely abolishes GFP expression of pgp-12, but ceh-26(RNAi) and ceh-37(RNAi)/ttx-1(RNAi) only weakly reduce the level of GFP. We also investigated the regulation of the homeobox genes amongst each other using RNAi and homeobox::GFP integrated lines. ceh-6(RNAi) nearly totally suppresses the GFP expression of both ceh-37 and ceh-26. ceh-26 (RNAi) also abolishes ceh-37::GFP expression. ceh-37/ttx-1(RNAi) of ceh-26::GFP showed that 42%; of the arrested worms still had GFP expression, indicating a partial downregulation, possibly a regulatory feedback loop. Based on our findings, we propose a regulatory hierarchy with ceh-6 at the top, ceh-26 in the middle, and the otd/Otx genes downstream. Yet, not all excretory cell genes depend on this ceh-6 cascade, suggesting the other factors remain to be uncovered.
Affiliation:
- Biosciences & Nutrition, Center for Biosciences, Karolinska Institutet, Huddinge, Sweden