The T-box factor TBX-2 and the SUMO conjugating enzyme UBC-9 are required for ABa-derived pharyngeal muscle in C-elegans

The C. elegans pharynx is produced from the embryonic blastomeres ABa and MS. Pharyngeal fate in the ABa lineage is specified by the combined activities of GLP-1/Notch-mediated signals and the TBX-37 and TBX-38 T-box transcription factors. Here, we show another T-box factor TBX-2 also functions in ABa-derived pharyngeal development. tbx-2 mutants arrest as L1 larvae lacking most or all ABa-derived pharyngeal muscles. In comparison, tbx-2 mutants retain ABa-derived marginal cells and pharyngeal muscles derived from MS. A tbx-2: :gfp translational fusion is expressed in a dynamic pattern in C. elegans embryos beginning near the 100-cell stage. Early expression is limited to a small number of cells, which likely include the ABa-derived pharyngeal precursors, while later expression is observed in body wall muscles and a subset of pharyngeal neurons. TBX-2 contains 2 consensus sumoylation sites, and it interacts in a yeast two-hybrid assay with the UBC-9 and GEI-17 components of the C. elegans SUMO-conjugating pathway. ubc-9(RNAi) has been previously shown to cause variable embryonic and larval arrest, and we find that, like tbx-2 mutants, ubc-9(RNAi) animals lack ABa-derived pharyngeal muscles. ubc-9(RNAi) also alters the subnuclear distribution of TBX-2: :GFP fusion protein, suggesting that UBC-9 and TBX-2 interact in C. elegans. Together, these results indicate that TBX-2 and SUMO-conjugating enzymes are necessary for ABa-derived pharyngeal muscle, and we hypothesize that TBX-2 function requires sumoylation. Sumoylation is increasingly recognized as an important mechanism controlling activity of many nuclear factors, and these results provide the first evidence that T-box factor activity may require sumoylation. (c) 2006 Elsevier Inc. All rights reserved.