In a paper recently published in Genome Biology, Boris Adryan (Cambridge University) and Sarah Teichmann (LMB) have presented evidence that calls in to question currently-held beliefs about how transcription factors (TFs) coordinate gene expression during development to specify the fates of the different tissues in the body.
It has been assumed that transcription factors are expressed in the manner of a cascade, with one TF turning on the expression of others resulting in groups of TFs acting in a cooperative manner to specify cell fate. In this study, Adryan and Teichmann have analysed gene expression data from Drosophila melanogaster development to investigate when every transcription factor is expressed. 95% of TFs were expressed at some time during embryonic development.
Perhaps the most important finding of the study is the combinatorial complexity of TF expression. The vast majority of the 69,500 possible combinations of pairs of TFs are expressed in at least one tissue at one time. Thus, the co-expression of TFs is extremely plastic. Rather than having tissue-specific TFs dictating the cell fate in different organs, what actually appears to happen is that the specific combination of TFs at a given point is what determines the cells’ fates, with different combinations of the same set of TFs determining different tissue types.
You can read Uwe Ohler’s commentary on the paper, also in Genome Biology, here