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Delighted to share our review article, "Regulation and Consequences of cGAS Activation by Self-DNA", by Christian Zierhut @ChriZieri.
Free article available until Sep 4.
https://authors.elsevier.com/c/1bPjB3QxxSgq3f
Here is a thread on how mitosis researchers bumped into the innate immunity.
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Free article available until Sep 4.
https://authors.elsevier.com/c/1bPjB3QxxSgq3f
Here is a thread on how mitosis researchers bumped into the innate immunity.
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Mitosis is a process to distribute chromosomes to dividing cells. As the nucleosome is the basic structural unit of chromosomes, we wanted to understand function and regulation of nucleosomes in mitosis. Addressing this question in vivo was difficult, however.
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As nucleosomes regulate transcription, even if any mitotic processes are affected upon manipulating nucleosomes, this could be due to a change in mRNA levels of mitotic regulators. Xenopus egg extract is a unique system that can circumvent this problem. 3/
In Xenopus egg extracts, cell cycle regulation, DNA replication, mitotic chromosome condensation and spindle formation can be recapitulated in the absence of de novo transcription, as eggs have a stockpile of RNAs and proteins for early embryonic cell divisions. 4/
If we could specifically deplete histones from egg extracts and complement with recombinant histones, we should be able to assess transcription-independent roles of histones. Due to their high abundance, however, it has been technically difficult to deplete histones
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Luckily, Hiroshi Kimura @Cell_Tokyo_Tech gave us a valuable tool. Collaborating with Naohito Nozaki, Hiroshi generated many mAbs for histone modifications. Hiroshi kindly share these mAbs with us to see if any of them can effectively deplete histones from Xenopus egg extracts. 6/
This approach worked! Christian showed that mAb against histone H4K12ac depleted >95% of the H3-H4 complex from Xenopus egg extracts. Christian made a heroic effort to optimize this method, which is now reproduced in other labs, like @brugueslab! 7/
Using this method, Christian demonstrated that nucleosomes are essential for nuclear pore complex (NPC) formation and spindle assembly, while DNA was sufficient to recruit nuclear membrane.
https://pubmed.ncbi.nlm.nih.gov/24952593/
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https://pubmed.ncbi.nlm.nih.gov/24952593/
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Christian was even able to bypass the requirement of nucleosomes for NPC formation by targeting two critical histone binding proteins (RCC1 and ELYS) to DNA. This suggested that somehow nucleosome-dependent system, rather than DNA-dependent system, was selected by evolution.
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What was the benefit of nucleosome-dependent NPC formation?
In Discussion, we speculated that the nucleosome acts as a hallmark of self-DNA, distinguishing from foreign and aberrant DNAs.
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In Discussion, we speculated that the nucleosome acts as a hallmark of self-DNA, distinguishing from foreign and aberrant DNAs.
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How can we test this hypothesis?
A novel cytoplasmic DNA sensor cGAS, discovered by Zhijian Chen in 2013, caught our eyes.
https://pubmed.ncbi.nlm.nih.gov/23258413/
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A novel cytoplasmic DNA sensor cGAS, discovered by Zhijian Chen in 2013, caught our eyes.
https://pubmed.ncbi.nlm.nih.gov/23258413/
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Upon binding to foreign DNA (e.g., viruses and bacteria) in the cytoplasm, cGAS becomes activated and stimulates inflammation. Genomic DNAs and mitochondrial DNAs are protected from cytoplasmic cGAS by the nuclear envelope and the mitochondrial envelope, respectively.
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When the nuclear envelope breaks down, cytoplasmic cGAS can access to chromosomes. cGAMP, the cyclic nucleotide that is generated by cGAS, is stable in the cytoplasm, so even transient activation of cGAS can be a problem.
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So, what is the mechanism by which cGAS is not normally activated by chromosomal DNA?
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Although we initially predicted that cGAS does not efficiently bind to nucleosomes, Christian showed that cGAS binds to nucleosomes with higher affinity than to naked DNA. However, nucleosomes inhibit DNA-dependent cGAS activation by a competitive mechanism.
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This mechanism explains why cGAS cannot readily be activated by chromosomes, which also have nucleosome-free DNA regions; we assumed that abundant nucleosomes can interfere with binding of cGAS to nucleosome-free DNA.
https://pubmed.ncbi.nlm.nih.gov/31299200/
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https://pubmed.ncbi.nlm.nih.gov/31299200/
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Andrew Jackson, Nicolas Manel @NicolasManelLab and their colleagues also independently reported that nucleosomes are not good activator of cGAS.
https://pubmed.ncbi.nlm.nih.gov/28738408/
https://pubmed.ncbi.nlm.nih.gov/30270045/
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https://pubmed.ncbi.nlm.nih.gov/28738408/
https://pubmed.ncbi.nlm.nih.gov/30270045/
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Nucleosome-based protection is not perfect, though. Christian’s review classifies the processes that make cGAS sense "self-DNA", and how distinct consequences (inflammation, senescences, apoptosis, etc) are indued. Many unsolved questions are highlighted as well.
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Christian will carry on this project in his own lab @ICR_London, opening in this fall.
Christian is a fantastic person with extensive experience on training a number of PhD students and technicians. He will be a great PI in London!
https://www.icr.ac.uk/our-research/researchers-and-teams/dr-christian-zierhut
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Christian is a fantastic person with extensive experience on training a number of PhD students and technicians. He will be a great PI in London!
https://www.icr.ac.uk/our-research/researchers-and-teams/dr-christian-zierhut
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Christian's departure will generate a new postdoc position in the Funabiki lab. Please check out our homepage http://funabikilab.com for details. Ad at jobRxiv is here.
https://twitter.com/jobRxiv/status/1283416318281121793?s=20
Thanks for reading this!
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https://twitter.com/jobRxiv/status/1283416318281121793?s=20
Thanks for reading this!
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