MECHANISTIC INSIGHTS INTO THE DEVELOPMENTAL-STAGE SPECIFIC ACTIVITY OF A UBIQUITOUSLY EXPRESSED TRANSCRIPTION FACTOR

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All our cells originate from one single fertilised egg cell which divides many times and gives rise to all the complex cell types in our body. The most fascinating aspect of such developmental processes is the fact that the timing of how different cells form is always the same, thus ensuring that our organs develop in the right order and at the right time. The reason for this synchrony is that all information for our body plan is encoded in our DNA which contains instructions on when our genes should be expressed and when they should be silent. The result is that humans are built with one plan and primates are built by another. However, humans and primates are 99% identical in their DNA, the question therefore arises what is different between the two species. The answer most likely can be found in subtle changes of the order of expression of genes that regulate the expression of other genes, the so-called transcription factors. These proteins can "read" the genetic code and they work together with many other regulator proteins to make sure that a gene is expressed in the right cell and at the right time. In the last years it was found that there are different types of transcription factors: those which are only found in one cell type, and those who are present in many cell types. All types of factors work together to regulate specific genes. When cell-specific factors are missing, usually this cell type does not form. When a factor is missing that is present in every cell, the effects can be dramatic, and often the organism is unable to develop. In this proposal we wish to study a member of the latter class of transcription factors, Sp1. We have shown that without it, blood cell development gets more and more compromised and mature blood cells cannot form. Now we want to know, how Sp1 works, when exactly it is needed and with which other factors it cooperates.However, not only the timing of expression of transcription factors can be different. Also the levels of how much of these regulators is present in a given cell is critical since small changes in the concentration of a factor that regulates other regulators will have a huge effect in further development. An important example of what differences in factor levels can make is seen in people with Down's syndrome who have an extra chromosome in each cell. They have too much of the products of these genes from this chromosome and their development is strongly perturbed. In this grant, we will change the levels of Sp1 and measure, how such changes impact of the expression of its target genes and how this, in turn, then impacts of how many cells of a given type are formed.To this end, we will use a system based on mouse embryonic stem cells that mimics normal development in vitro and where we can generate enough cells to examine many different features. Our work will answer a number of fundamental questions on how transcription factors interact with each other and how the balance and timing of important regulator genes is controlled.