Manipulation of gene expression using VP16 fusion and engrailed fusion to a transcription factor? Today, a presenter briefly mentioned that gene expression in sea urchins during development might be manipulated using VP16 and engrailed fusions. On a slide, it said that expression might be increased by mRNA injection or "VP16 fusion to binding domain of TF" and decreased by antisense morpholinos or "engrailed fusion to binding domain of TF". I understand mRNA injection and antisense morpholinos, but I am unclear about the roles of VP16 and engrailed in this context. Can anyone clarify?

VP16 is a herpesvirus derived protein transcription factor, which activates the early genes of the viral infection cycle. The activation domain (AD) which is formed by the 78-amino acids from the C-terminal, can be fused to DNA binding domain of other protein transcription factors, such as GAL4, to make a hybrid protein that constitutively and strongly activates transcription, without the requirement of any ligands. VP16-AD interacts with TBP, TFIID, SAGA histone acetyltransferase complex, and PC4 (transcriptional coactivator positive cofactor 4) to drive transcription.

The _engrailed_ gene, from Drosophila, is a transcriptional repressor. When the repressor domain is fused to transcription factors, the fusion results in trans-dominant negative functions of the transcription factor (phenocopying loss of function mutations in the target genes).