Basically, heterochromatin is a tightly bounded DNA region. Due to this reason, polymerases cannot access these regions and therefore no transcription. Does that mean heterochromatin region is full of junk DNA? Also, few works have claimed that the heterochromatin has roles in cellular functions like gene regulation... [Spofford JB (1976), Karpen et al. (1988)].
Many thanks in advance.
Basically you have answered your question already. They are not necessarily junk hence might be important on gene regulation. Like transcription factors that are located in that tightly bound regions that affects expression of single or several genes. This tightly bound region are mostly methylated possibly resulted from environmental/external factors.
Basically you have answered your question already. They are not necessarily junk hence might be important on gene regulation. Like transcription factors that are located in that tightly bound regions that affects expression of single or several genes. This tightly bound region are mostly methylated possibly resulted from environmental/external factors.
There Is nothing junk in DNA.they are only regions whose functions not yet known
This Wikipedia article provides a pretty good overview:
https://en.wikipedia.org/wiki/Heterochromatin
If you are still interested, look for a good review. To summarize, some chromosomal regions are always in heterochromatin, including centromeres and telomeres. Other regions may be in heterochromatin or euchromatin depending on the cell type; this is related to permanent repression of certain genes during differentiation. As for junk DNA, very little of the genome contains coding sequences for proteins or known RNA. The majority includes introns, sequences that influence gene expression (promoters, etc), sequences involved in DNA replication or mitosis, possibly coding sequences for unknown RNAs, presumably some does other stuff I haven't thought of, perhaps stuff no one knows about, and finally some may really be "junk" that doesn't do anything. Since the percent of DNA in the last category is not really known, I don't think anyone would claim that it is more common in heterochromatin.
Thank you for your answers. Is there any way to find out the heterochromatin distribution in humans? Would it be possible to find their sequence?
Well basically, outside of telomeres and centromeres (and maybe some repeated sequences), heterochromatin is different for every cell type. It represents compacted chromatin which is associated with unexpressed genes, structural relationships with the nuclear membrane or lamina and boundaries between nuclear domains. For centromeres and telomeres, their sequence are approximatively known, but constituted of repeated sequences, for "varying" heterochromatin, you can map it with ChIP-seq for associated histone marks (H3K9me3 for example), or by looking for wide regions devoid of DNA accessibility (as assessed by DNAse-seq or ATAC-seq). I would really encourage you to read a bunch of good reviews about gene expression regulation and the structure of chromatin. Good luck!
Hello,
In Drosophila melanogaster, constitutive heterochromatin contains about 400 single-copy coding genes and other expressed sequences....
Article Constitutive heterochromatin: A surprising variety of expres...
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