Antagonism Between Transcription Factors Escargot And Scute Controls Intestinal Enteroendocrine Cell Specification

Drosophila intestinal homeostasis is maintained by intestinal stem cells(ISCs).Normally,an ISC divides to produce two daughter cells,one cell maintains stem cell property,and the other differentiates into an Enteroblast cell(EB),which finally differentiates into an EC or ee cell.The Snail family transcription factor escargot(esg)can specifically bind to G/ACAGGTG sequence,which is similar to E box(CANNTG).The proneural genes AS/C complex can bind to E box to promote neurogenesis.In Drosophila intestine,sc,a member of AS/C complex,induces ee cell specification.Our experiments show that knocking down Esg in ISCs promotes ee cell specification,and finally causes ISC loss.And Esg overexpression inhibits the increased ee cell formation caused by Sc overexpression.On the other hand,knocking down Sc represses the increased ee cell specification caused by Esg knockdown.These data suggest that Esg and Sc regulate ee cell specification in parallel.Meanwhile,Pros downregulation also can impair ee cell increasement during Esg knockdown.However,Esg overexpression can not block ISCs loss caused by Pros overexpression.Together with the result that overexpressing Esg in ee cells can repress Pros expression,our studies suggest that Esg controls Pros expression to regulate ee cell specification.Considering that Esg and Sc can bind to the same sequence,and their opposite effect on Pros expression and ee cell specification,we propose that Esg and Sc could compete to regulate Pros to control ee cell specification.Through ChIP assay,a common binding site of Esg and Sc on pros promoter is identified.The LacZ reporter of this site shows its specific expression in ee cells.These data suggest that Esg and Sc bind to pros enhancer to regulate Pros expression.Taken together,we propose a model: Sc activates Pros expression to induce ee cell differentiation,and Esg represses Pros expression directly or through antagonizing Sc to impair ee cell differentiation.So ee cell differentiation depends on the ratio of Sc and Esg.While Notch inactivation,Sc upregulates to increase the ratio of Sc/Esg to activate Pros expression,and finally,induces ee cell differentiation.