Team:Freiburg/Highlights

6 opportunities with our uniCAS toolkit

We provide 3 different effectors, 2 methods & 1 effector controller! Using our toolkit it's possible to efficiently activate or repress genes in mammalian cells. We also provide devices for effector controling by light. Use our custom-tailored Manual Tool to generate instructions for your own gene regulation experiment. With our toolkit it's possible to target not only one, but multiple genes of interest! We also established uniBAss - our universal Binding Assay for assessing the binding capacity of our fusion proteins. Best of all: It's open source and in iGEM standard!

dCas9 - The Heart of our toolkit

We started by mutating the DNA cleavage site in the Cas9 protein and therefore generated a DNA binding protein. The binding mechanism is relying on a protein-RNA-DNA interaction. By changing the RNA sequence we are now able to determine the DNA binding locus and can direct the protein to any requested DNA target.

This is the heart of our toolkit. A protein that allows multiple and sequence specified DNA binding. By fusing effector domains to dCas9 we created fusion proteins with completely new function. Read more in the next slides.

Activation

We fused dCas9 to the trans-activation domain VP16. This fusion protein is able to activate gene expression. The fusion protein was tested in mammalian cells and used to activate SEAP reporter expression. We achieved up to 30 fold upregulation of gene expression by targeting sequences that are located in front of the promoter (target 1 equals bla target 2 & target 2 equals EMX1). Read more!

Chromatin modification (Repression)

Specific chromatin modification was achieved by fusing the histone methyltransferase G9a to dCas9 and therefore creating an epigenetic biobrick. G9a primarily methylates Histone H3. Different endogenous VEGF loci were targeted in mammalian cells which resulted in an up to 50 % repression (target 3 equals VEGF-8 and target 4 equals VEGF-573). Read more!

Repression

The transcriptional repressor domain KRAB was fused to dCas9. Thus, a transcriptional repressor with the flexibility to target any DNA sequence of interest was created. The device was tested in mammalian cells to target endogenous VEGF loci. An up to 50 % repression was achieved (target 4 equals VEGF-573 & target 5 equals VEGF+343). Read more!

Multiple Targeting

One of the biggest advantages of the CRISPR/Cas9 system is that only one protein is required for targeting several DNA sequences. For a new DNA target there has to be just another guiding RNA. We designed an RNA plasmid, "RNAimer", for inserting this RNA sequence. For multiple targeting different RNAimer inserts can be easily combined using the iGEM BioBrick assembly method. And as the figures show, if one gene is targeted at two loci at a time the activation efficiency shows an additive effect! Read more!

Manual

uniBAss

We developed an ELISA-based method to quantify the binding efficiency of our Cas9 fusion proteins: The uniCAS binding assay uniBAss. It is a powerful tool to assess the DNA binding capacity of dCas9 fusion proteins and our truncated dCas9 versions. Read more!

Summary

In the last months we were able to ...

• ... construct a catalytically inactive version of Cas9 and thus generate a DNA binding protein.
• ... combine this modified dCas9 with different transcriptional effectors.
• ... express this fusion proteins in various mammalian cell lines.
• ... control mammalian gene expression via our modified CRISPR/Cas fusion proteins.
• ... build devices for controling gene expression by light stimulus.
• ... provide an RNA plasmid for easily inserting sequences for crRNAs which target every desired target.
• ... build an online tool that generates customized manuals for using our toolkit
• ... develop a method to assess the DNA binding capacity of our dCas9-fusion proteins.
• ... make our dCas9 accessible to the whole iGEM community by mutating illegal iGEM restriction sites.
• ... In summary, we can now offer a universally applicable toolkit for gene regulation.