Average 10 Nucleoli per mammalian cell.

There is no source that I have seen that says anything about the size and number of cores in the nucleus

Hi,

I'm developing a method to enumerate and measure the nucleolus. I attach a photo. For anyone interested in developing it, also in article, please contact to me.

Explanatory photo obtained with the method under study on lymphocytes isolated from peripheral blood of a CLL patient CD10 negative.

Dear Zagami Francesco,

Many thanks for sharing the picture with us. We know that chromosomes form the territories inside the nuceli. And some chromosomes are located in the periphery of nucleus and some are located in the center of the nucleus. This also depends on the differentiation state of the stem cell. In the stem cells the chromosomes are uniformly distributed in nuclei while in the more differentiated stem cells, chromosomes are distributed very broadly in different locations.

So, in this context I was interested to know, is thery any way the nucleolus are resposbile for shifting this chromosome organization. So It can be three possibilities, the nucleoli shifting the chromosome postions (i) proportionally, (ii) inverse proportionally, (iii) nucleolus do not relate with chromosome organization.

Do you see any such pattern in chronic lymphocytic leukemia patient?

Thanks!

Dear Ankit Agrawal,

You say right, also in normal human lymphocytes the topology of the chromosomes seem show that gene rich chromosomes (e.g. chromosomes 1, 15, 16, 17, 19, and 22) are preferentially located towards the nuclear interior, whereas gene poor chromosomes (e.g. 2, 3, 4, 5, 13, and 18) are located more towards the periphery. Certain chromosomes (e.g. 15, 16, 17, and 22) contain segmental duplications that are associated with regions of chromosome instability or evolutionary rearrangement. Therefore, one possible explanation for their topological arrangement is for protection, and that the nuclear center is postulated to be an active transcription site, which plays a role in the maintenance of genome stability. The sex chromosomes are localized in the intermediate/peripheral region of the nucleus, in which the X chromosome demonstrating a more interior localization in comparison to the Y chromosome. I think that in the CLL are mostly frequent the genetic abnormalities (65%), that not seem to change the topology of the chromosomes.

Will be a pleasure hear you again!

Dear Francesco,

Thanks for the discussion. If you look the Topologically Associated Domains (TADs) then they form a highly interacting local chromatin structure which stabilize the topology of the chromosomes. This is also evident from the open chromtain structure and DNA methylation data.

So if all these are true that means there is feedback process is going on in the nuclei. A open chromatin local structure (TADs) allow the expression of certain genes and then these genes will change the TADs structure in some other region of the chromatin and process keep goes.

And ofcourese these gene regulation activities are regulated by promoter, enhancer and Transcription Factors.

If chromatin, genes, promoter, enhancers and TFs are enough to describe a cell function then why do we need nucleolus. If I remember correct then nucleolus is formed between acrocentric chromosomes and it is membranless structure. If nucleolus is present then it might have something to do with gene expression and finally with function of cell.

If I understand correct, then CLL patients have some duplication events and hopefully some changes in the nucleoli structure which finally lead to change in the gene expression and at the end will lead to change in function of the cell.

Do you think all these scenario possible?

Dear Ankit,

The link between nucleolar RNA and chromosomes is very strong on which all cellular function depends. I agree with you that changes in the chromosome structure determine a modification in the nucleus-nucleolus communication which leads to a change in the cell in a phenotypic sense (surface markers, functional behaviour)

The data relating to the mitotic process consolidate the existence of this extreme functional symbiosis. A marker of cell proliferation Ki-67, localized in the nucleolus, during interphase appears to be involved in ribosomal biogenesis, while during mitotic prophase, before the nucleolus disassembles, together with the rupture of the nuclear envelope, Ki-67 is released and relocates to the perichromosomal layer of condensed chromosomes. In particular, loss of Ki-67 depletes the mass of the perichromosome layer and causes coalescence of mitotic chromosomes, suggesting that Ki-67 plays a key role in maintaining perichromosome layer integrity.

This process is related to the linkage between the C-terminal Leu-Arg rich (LR) domain, which recognizes chromosomal DNA, and anchors Ki-67 on mitotic chromosomes, while other regions of Ki-67 extend outward to form the perichromosomal layer. Because nuclear proteins associate with small nucleolar RNA (snoRNA) to form RNPs, some snoRNA species, such as U3 snoRNA, are reported to be present at the periphery of the chromosome, and rRNAs are the major RNA species that they associate with condensed chromosomes. These rRNA species are evenly distributed in the perichromosomal layer of each chromosome via interaction with Ki-67. These chromosome-associated rRNAs facilitate chromosome shedding during prometaphase. I think that, during the telophase, the chromosomes begin to decondense, a new nuclear envelope is formed, derived from the vesicles of the endoplasmic reticulum, and the chromosomes, using the rRNA (Ki-67) map, reach their topographic position by simultaneously reforming the nucleoli according to the type or stage of development of the cell.

What do you think?

Dear Francesco,

Many thanks for sharing the nitty gritty details of Ki67. Yes, you are right that in the telophase, nucleoli appears, nuclear envelop form, and chromosome decondensed.

Then the question comes to my brain what is the duration of condensed and decondensed dynamics, and how are such dynamics so robust that they occur every time without an error?

I also read somewhere that LAMIN protein stabilizes the chromosome condensation process. If so, LAMIN proteins, nucleoli, and chromatin all together (maybe with other molecules) play a role in the cell cycle to return from the interphase stage to the mitotic phase. Ki67 gene expression may define such dynamics. If you look ki67 expression across difference cell cycle stage and nucleoli/Lamin density or state then you should be able to see some correlation. I think so...

Dear, Ankit

my knowledge regarding the divisional process and the behaviour of the nucleolus-nucleus in its phases derives from studies of biochemical and cytogenetic literature and therefore they are not data coming from personal experience. However, I feel the matter very close, that's why I wanted to understand the morphological behaviour of the nucleolus in lymphocytes of subjects with CLL. In these cases, there is a strong epigenetic pressure (epigenetic burden) as the DNA methylation, a factor which would seem to assume a fundamental role in increasing or decreasing the possibility of gene mutations, events which could be secondary to the methylome but this remains to be demonstrated. Chicken or egg first. In the meantime, I see the egg (peripheral lymphocytes that are like those of memory) which could give us information on the characteristics of the nucleolus and then we will compare them with the data from the hen (CLL-patients), to evaluate a possible correlation between nucleolus morphology with behaviour of the single CLL-patient.