Cell identity is characterized by a distinct combination of gene expression, cell morphology and cellular function established as progenitor cells divide and differentiate. Following establishment, cell identities can be unstable and require active and continuous maintenance throughout the remaining life of a cell. Mechanisms underlying the maintenance of cell identities are incompletely understood. Here we show that the gene ctbp-1, which encodes the transcriptional corepressor C-terminal binding protein-1 (CTBP-1), is essential for the maintenance of the identities of the two AIA interneurons in the nematode Caenorhabditis elegans. ctbp-1 is not required for the establishment of the AIA cell fate but rather functions cell-autonomously and can act in older worms to maintain proper AIA gene expression, morphology and function. From a screen for suppressors of the ctbp-1 mutant phenotype, we identified the gene egl-13, which encodes a SOX family transcription factor. We found that egl-13 regulates AIA function and aspects of AIA gene expression, but not AIA morphology. We conclude that the CTBP-1 protein maintains AIA cell identity in part by utilizing EGL-13 to repress transcriptional activity in the AIAs. More generally, we propose that transcriptional corepressors like CTBP-1 might be critical factors in the maintenance of cell identities, harnessing the DNA-binding specificity of transcription factors like EGL-13 to selectively regulate gene expression in a cell-specific manner.
The C. elegans Spalt-like protein SEM-4 functions through the SoxC transcription factor SEM-2 to promote a proliferative blast cell fate in the postembryonic mesoderm
