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Although the anatomy of cellular components is often presented in a simplified manner, these components are extremely intricate in nature. One example of such intricacy is best demonstrated by an organelle predominately only found in eukaryotic cells - the nucleus. It is a highly compartmentalized structure that acts as the control centre for cell regulation, synthesis, and gene expression. (1) The nucleus contains a nuclear envelope (a semi-permeable bilayer membrane consisting of the nuclear pore complex, lamina, rough endoplasmic rectum, ribosomes, and integral proteins) that houses compartments of Cajal bodies, heterochromatin, transcription sites, chromosome territories (CTs), promyelocytic leukemia nuclear bodies (PML), and speckles; it also contains a nucleolus, a concentrated compartment of RNA. (2)
Nonetheless that the nucleus is highly compartmentalized, how do the nuclear components, but more specifically, the chromosomal territories, affect gene expression? To begin, CTs are concentrated and/or localized distinct regions of chromosomes within the nucleus. Each region varies in chromosomal concentration by either gene rich or gene poor. Furthermore, it is not to say that chromosome X is always located in chromosomal territory Y, as each CT is considered to be the most probable likelihood that chromosome X would be evident. (3) Also, each CT is not a continuous blob of chromosomes but rather contains an arrangement of interspersed passageways. Meaburn and Misteli (2) report that these passageways provide access points for chromosome transcription factor binding (activators and repressors).
The exact function of CTs is still undergoing exploration. However, it has been reported that a phenomenon of chromosomal kissing occurs at protruding chromatin loops of a chromosome territory. (4) Chromosomal kissing involves the interaction of different loci (chromatin loops) within the same chromosome or between different chromosomes. (4).
The kissing influences gene expression in the CTs, such that it facilitates gene regulation (activation or silencing) or is the site of chromosome translocations. Additionally, chromosomal translocations often prove to be detrimental and/or lethal to cellular activities. Such translocations are typically viewed as mutations resulting in the loss-of-function, creation of aberrant phenotypes, or complete lethality in the cell should the chromosome breakpoint occur at a regulatory encoding loci. (5)
So far the discussion has been on defining what chromosomal territories are, describing its theoretical function in the nucleus, and those factors influencing gene expression in chromosomal territories. However, what is the comprehensive significance of such information? To answer, a delicate balance between nuclear compartmentalization, in this case chromosomal territories, and gene expression is needed for homeostatic cellular regulation. If the delicate balance is interrupted at the transcription level, it further snowballs by amplifying the coding and/or regulating error in subsequent transcription activities. Such errors would then cause phenotypically abnormalities in the cell and subsequently in the larger organism. These abnormalities would have medical and/or health implications. The Rett's Syndrome (RTT) disorder, found predominantly in young girls, best demonstrates an example of such. RTT results in the prevalence of severe mental and impaired physical symptoms that occur from skewed gene X-inactivation (abnormal gene activation and silencing), deletion, and translocations in the chromosomal territories; such mutations occurring in the CT lead to abnormal transcription effects in the chromatin for gene activation or silencing. (6) For families with RTT children it is devastating, as such gene expression acutely metamorphoses a normal child into one with severe motor and cognitive skill impairment. (6) Although extensive research is underway, the current quality of life for most RTT families are poor, as the exact biological pathway has yet to be reversed. However, breakthrough findings link RTT to mutations occurring in the CTs. (6)
Another example illustrating the medical implications of CTs nuclear compartmentalization and gene expression is through the occurrence of translocations in organisms. The occurrence of deleterious and/or lethal translocations is highly probable, since chromosomal kissing occurs either within or interaction of different CTs. Translocations may cause a break in the section of regulatory coding, which is further amplified into the gene expression of cancerous cells. (3) Subsequently, the organism's health will deteriorate as cancer cells are immortal and undergo angiogenesis, which starve off blood flow to essential organs. (5)
Meaburn and Mistelli (3) suggest that understanding the biological pathways of chromosomal territories and their interactions create another outlet for improved patient care. More specifically, it could lead to better laboratory screening of biopsy samples such that it could provide detailed information, improving and expediting the course of treatment for those with malignancy. Further, the information can be disseminated to the patient for earlier management of lifestyle activities. (3)
In summary, nuclear compartmentalization of chromosomal territories influences gene expression within a cell. Chromosomal territories, condensed regions containing chromosomes inter-chromatin passageways, and protruding loops of chromatin, interact (chromosome kissing) with themselves or other territories creating gene silencing, activation, or translocations. Such gene expressions, if in the regulatory functional regions of the DNA, cause amplified deleterious or lethal affects within the cell. Further, such events will be phenotypically expressed in the organism, which leads to medical illness, disorders, and/or death. Understanding the inter-workings of the CT interaction, cellular compartmentalization, and gene expression have the potential for advances in medical science and practice in patient care management.
Karp G. Chapter 12 - The Cell Nucleus and the Control of Gene Expression. In: Cell and Molecular Biology: Concepts and Experiments. NJ: John Wiley & Sons Inc; 2010. p. 475-532.
This textbook chapter provides general information on the compartmentalization of the nuclear structure, as well as high-level introductory information on how each compartment correlates with gene expression.
Zhao R, Bodnar MS, Spector DL. Nuclear Neighborhoods and Gene Expression. Current Opinion in Genetics & Development [Internet]. 2009 March [cited 2011 Feb 03]; 19:172-179. Available from
The journal provides introductory information and physical sketch of the nuclear envelope, lamina, nuclear pore complex, chromatin, and PML bodies. The diagram demonstrates the compartmentalization aspects of the nuclear components.
Meaburn KJ, Misteli T. Chromosome Territories. Cell Biology [Internet]. 2007 Jan [cited 2011 Feb 03]; 445:379-381. Available from
This study provided specific details on chromosome territories: arrangement, structure, folding, expression, and general discussion on the future of more study on this area of research.
Cremer T, Cremer M, Dietzel S, Muller S, Solovei I, Fakan S. Chromosome Territories - A Functional Nuclear Landscape. Current Opinion in Cell Biology [Internet]. 2006 [cited 2011 Feb 03]; 18:307-316. Available from
This journal discusses the different models on chromosome interactions with respect to chromosomal territories and gene expression: small chromatin loops, large chromatin loops, model controversies, chromatin configurations. Study suggests that laboratory experimentation should be conducted for each model to verify true interactions.
Hartwell LH, Hood L, Goldberg ML, Reynolds AE, Silver LM, Veres RC. Genetics: From Genes to Genomes. 3rd ed. New York: McGraw-Hill Companies Inc; 2008.
This textbook provides information on translocations, cancer genetics, reciprocal translations relating to gene expression, and introductory knowledge on gene activation/ silencing.
Delcuve G, Rastegar M, Davie JR. Epigenetic Control. Journal of Cellular Physiology [Internet]. 2009 Jan [cited 2011 Feb 03]; 219: 243-250. Available from
This journal provides a general overview of chromatin behavior pertaining to compartmentalization. It also links transcriptional chromosomal territories to occurrence of disorders such as Rett's Syndrome and cancer.
Personal Reflection (100 Words or Less)
Problem Summary #01 was challenging, as the first hurdle was to derive a topic for a descriptive-evidence based paper. Also, I had writer's block, as it was my second semester since returning to the University of Calgary after a 13-year hiatus. From a literature review, I found an article linking gene expression, nuclear compartmentalization, and chromosomal territories. It led to the submittal of an outline for feedback, as well as the generation of the first few paragraphs. Feedback was incorporated into the paper. The lesson learned was that the nucleus is a compartmentalized factory that affects gene expression.