Caenorhabditis elegans TBX-2 Directly Regulates Its Own Expression in a Negative Autoregulatory Loop

摘要

T-box genes often exhibit dynamic expression patterns, and their expression levels can be crucial for normal function. Despite the importance of these genes, there is little known about T-box gene regulation. We have focused on the Caenorhabditis elegans gene [tbx-2][1] to understand how T-box gene expression is regulated, and here we demonstrate [TBX-2][1] itself directly represses its own expression in a negative autoregulatory loop. [tbx-2][1] is essential for normal pharyngeal muscle development, and a [tbx-2][1] promoter gfp fusion ( Ptbx-2 :: gfp ) is transiently expressed in the pharynx during embryogenesis and in a small number of head neurons in larvae and adults. Reduced [tbx-2][1] function resulted in ectopic Ptbx-2 :: gfp expression in the seam cells and gut in larvae and adults. Mutation of potential T-box binding sites within the [tbx-2][1] promoter resulted in a similar pattern of ectopic Ptbx-2 :: gfp expression, and chromatin immunoprecipitation analyses show [TBX-2][1] binds these sites in vivo . This pattern of ectopic Ptbx-2 :: gfp expression in [tbx-2][1] mutants was very similar to that observed in mutants affecting the NF-Y complex, and our results comparing [tbx-2][1] and [nfyb-1][2] single- and double mutants suggest [TBX-2][1] and NF-Y function in a single pathway to repress the [tbx-2][1] promoter. The [tbx-2][1] promoter is the first direct target identified for [TBX-2][1], and we used it to ask whether SUMOylation is essential for [TBX-2][1] repression. RNAi knockdown of SUMOylation pathway components led to ectopic Ptbx-2 :: gfp expression in the seam cells and gut. Ectopic Ptbx-2 :: gfp also was observed in the syncytial hypodermis, suggesting either the [tbx-2][1] promoter is repressed by other SUMOylation dependent mechanisms, or that decreased SUMOylation leads to stable changes in seam cell nuclei as they fuse with the syncytial hypodermis. We suggest negative autoregulation is an important mechanism that allows precise control of [tbx-2][1] expression levels and may allow rapid changes in gene expression during development. [1]: http://www.wormbase.org/db/get?name=WBGene00006543;class=Gene [2]: http://www.wormbase.org/db/get?name=WBGene00021132;class=Gene