There are scores of papers addressing histone modifications and their impact on epigenetics. It would seem to me that the fact that there are more than 50 variants of the histone proteins present in humans is, if not ignored than at least not very widely researched. The effects of differentially combined histone variants in the nucleosomes could be significant: The lenght of DNA wrapped around differentially composed nucleosomes would be different, different variants will probably be differentially modified by HATs and HMTs etc.. Are there papers around in which this question is adressed? Evidently histone variants are expressed at least in part tissue specific, and some H3 variants are found preferentially bound to sites of former DNA damage. Are there more such examples like specific variants bound to specfic types of genes, promotors etc.? Thanks for all your feedback!
Hi there,
in fact, there are many studies on the subject, even though they focus mostly on two types of histones, H2A.Z and H.3.3. Look at publications by Henikoff S or Felsenfeld G or Gaudreau L, for example.
Hi Oleg,
thanks for pointing those papers out. They actually strengthen the point that different histone variants alter the effects of nucleosomes significantly as shown for the two examples H2A.Z and H3.3 and several others, even without the need for histone-PTMs. I am still wondering for how many other of the more than 50 histone variants similar effects might be found. If the presence of specific histone variants on specific DNA sequences alone is sufficient to regulate expression this adds a complete layer of complexity to DNA-activity regulation.
This question of the roles of histone variants is especially intriguing in plants where the variants of H2A and H2B vary significantly in molecular weight.
Hi Daniel,
Here you can find a few of the many papers that address this question regarding histone H3.3:
Genome-scale profiling of histone H3.3 replacement
patterns - Mito et al. 2005
Distinct Factors Control Histone
Variant H3.3 Localization
at Specific Genomic Regions- Goldberg et al. 2010
Genome-wide analysis of histone H3.1 and H3.3
variants in Arabidopsis thaliana -Stroud et al. 2012
Selective Methylation of Histone H3 variant H3.1 regulates heterochromatin replication - Jacob et al. 2014
And some interesting reviews:
Developmental roles of histone H3
variants and their chaperones - Filipescu et al. 2013
Every amino acid matters: essential
contributions of histone variants to
mammalian development and disease - Maze et al. 2014
It's a very interesting and dynamic field!
Hi Daniel,
I agree with you that the histone variants may be processed in a different way. but I also wanted to remind you that there are a couple of papers where you can see the modifications on the canonical histone as well as histone variant remains same. It is very difficult to address the specific functions related to histone variants owing to their similarity in the amino acid sequence which is a potential problem to raise specific antibodies for the modifications on the histone variants.
You can also look into a recent paper on TH2B (a testicular histoine variant of H2B) and its PTMs (Jorunal of proteome research, Satya krishna et al. 2014)
Compounding the variation in core histones is the variation of the linker histones that modify accessibility to the nucleosomes. There are now 10 different linker histones we know of at the primary sequence level.
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