Cell Cycle
Introduction
Asymmetric cell division is a situation where a cell divides into parts of two cells that comprise two dissimilar cellular fates. For most part, the term applies and is usually used in referring to cells that are essentially diverse at the point of cytokinesis. Cytokinesis is the term used to describe how the cytoplasm and its organelles divide to form two separate cells. The daughter cell formed contains the same genetic material as the mother cell. This implies that individual daughter cell comprise a diverse physical makeup. This stands to convey the contrast surrounding extrinsically dissimilar cells where individual cell derives a diverse outside stimuli afterwards, which changes its own cellular fate. The retrospective analysis concerning neuroblastomas analyzed concerned with MYCN amplification by Children’s Oncology group was administered. MYCN copy number was derived by counting the amount of signals present in a sample of Interphase nuclei. Tumors containing cells of reasonable copies of HSRs or MYCN that hybridized to MYCN probe were scored in line with amplification. In the cells that were amplified containing dmins, precise scoring was not probable as a result of the fluorescent signals being coalescing. dmins showed and appeared as numerous signals in the entire nucleus, while HSRs were represented by attached signals of cohesive domain.
Cell division cycle
Cell mitosis is a type of cell division that precedes cytokinesis. It involves four phases (Interphase, Prophase, Metaphase, and Telophase) that lead to eventual division of the cellular nucleus. For the formation of two complete daughter cells to occur, cytokinesis must occur. This type of cell division starts when the cell membrane starts indenting inwards along the equatorial line leading to separation of the cytoplasm and its contents (organelles) into two matching daughter cells.
Figure 1: Asymmetric cell division at cytokinesis
Figure 2: Normal cell division and differentiation based on outside stimulus
Interphase an initial phase in cell division, which has several sub phases. It has Gap 0 (G0), which is an inactive stage when the cell division process has stopped. During Gap 1 (G1), cells start increasing in magnitude and preparation for synthesis of DNA occurs. Synthesis (S) is the sub phase that entails DNA duplication, this phase then leads to Gap 2 (G2) when the cell prepares to enter mitosis stage.
Mitosis is the second stage of cell division. Cellular activities during this stage stop and start to mobilize and concentrate energy needed for cell division that leads to formation of daughter cells. Spindle fibers in the cytoplasm attach and direct chromosomes to be aligned at the equator.
During anaphase, which is the third stage in mitosis, centromere divide and sister chromatids follow through. Spindle fibers shorten pulling sister chromatids with them to the opposite ends. A complete state of diploid chromosomes is then achieved at the end of this phase.
The final phase of mitosis is the Telophase, which begins when chromatids have reached the end of the cells. Spindle fibers diminish in length and chromatids become less visible. This phase ends when nuclear membrane starts forming around the chromosomes to form a new-fangled nucleus.
Cytokinesis then follows immediately after mitosis. This process occurs to complete the M phase of cell division cycle. As described above, the cytoplasm and its dissolved substances start curving inwards until two distinct cells with similar nuclei forms. Interphase then follows if the cell is to undergo meiotic division. During meiosis, cells follow similar stages like in normal mitosis only that it is divided into two, meiosis I and meiosis II. Every cells that complete meiosis I and enter meiosis II, are haploid with duplicated chromosomes. On the other hand, the end of meiosis II results in daughter cells that are haploid but with un-replicated chromosomes. Meiosis allows for variation of genes through several ways. One of them is the crossing over concept during metaphase I. This process allows for swapping or transfer of some genetic material between related chromatids. Another way is through no disjunction and independent collection and combination of parent chromosomes.
There exist different kinds of populations of cells that go through asymmetric division at the time of organism’s life cycle. In view, the first, in analyzing the vertebrates, is oocytes for the period of reproduction when main oocyte divides two times to give rise to a mature ovum as well as to a great extend three minor polar bodies.
The other second familiar asymmetric cell division is primarily the mainly cell divisions. Whereas stem cells undergo into either two cell identical or two identical differentiated cells to the parent or main stem cell, majority of stem cell divisions tend to produce a daughter cell similar to the parent as well as a daughter cell that eventually differentiate into a definite cell type. In addition, another fascinating case of asymmetric division primarily in stem cell niches like in the hair follicle where a sequence of asymmetric cell divisions drives to five derived cell kinds as well as a renewal of the usual or original stem cell. There exist a number of diseases involving aberrant asymmetric cell division but the commonly prevalent is found in the cancer. A research has been found out that cancers harbor stem cell, for instance cells that have the behavior similar to that of a stem cell niche.
Cell division is a delicate process that contributes to growth, repair, and maintenance of structure and function tissues. The process therefore, requires strict regulatory mechanisms. If cell division is not well controlled, then irrepressible cellular growth may ensue leading to disease conditions like malignancy (cancer).
The amplification of MYCN carried in neuroblastoma revealed strongly to have correlated and portrayed unfavorable outcome, although little is known concerning the functionality of high expression of MYCN resulting to an aggressive translation of tumor phenotype. Additional aggressive neuroblastomas tend to be generally immature as well as over appearance of exogenous MYCN in other neuronal cell types and cultured neuroblastoma cells have been discovered and reported to inhibit induced differentiation, portraying a link between high an immature phenotype and MYCN expression.
Nevertheless, the demonstration here is that MYCN is articulated in human neuroblasts of sympathetic sequence ganglia at fetal week 8.5, a growth stage at which the neuroblasts demonstrates a variety of sympathetic neuronal differentiation marker genes. Analyses carried for 28 specimens of neuroblastoma tumor as well as 27 cell lines in line with expression of MYCN also a section of neuronal differentiation marker genes showed no close correlation between marker gene expression and MYCN levels. Lastly, a test carried for five individual differentiation protocols revealed that MYCN over expression neuroblastoma cells together with a neuronal phenotype, primarily derived from the known non-MYCN-amplified cell of human neuroblastoma line SK-N-SH, maintain their capability to differentiate in spite of constitutive MYCN over expression. The outcome showed that high MYCN expression along with sympathetic differentiation are compatible, additionally, indirectly the outcome lend support to earlier in print MYCN neuroblastoma tumor data, which implied that in sole MYCN copy neuroblastomas there proved no direct correlation between aggressive behavior of tumor cell and a high protein cellular of MYCN.
Conclusion
Cell division involves a cycle of events that a cell has to go through to give rise to a cell of a similar kind. Mitosis and Meiosis are the terms used to describe the different phases of cell cycle. They produce either a haploid (meiosis) or diploid (mitosis) daughter cells. The most important factor in cell division is the control and regulation of the entire process so that cells do not replicate in large sizes and amounts leading to malignancy or cells do not replicate at a slow rate leading to stunted growth. The MYCN gene is the genetic code that controls the protein responsible for making tissues and organs during uterine growth and development in humans. It is now known that human beings with a high rate of MYCN gene intensification and expression are at a high risk of asymmetrical cell division that may produce indifferent daughter cells, with anomalies like tumors, and in this case, neuroblastoma. On the contrary, individuals with normal expression and amplification of the MYCN gene have a symmetrical cell division
References
Coelho, A. (2007). Asymmetric cell division. Berllin: Springer.
Edsjo, A., Nilsson, H., & Vandesompele, J. (2004, apr 11). Neuroblastoma cells with overexpressed MYCN retain their capacity to undergo neuronal differentiation. Retrievedoct24,2013,frompubmed.gov:
Jacob, J. F., & et, a. (2009, July 18). Name of MYCN expression in human neuroblastoma cells. Retrieved October 21, 2013, from http://www.biomedcentral.com: http://www.biomedcentral.com/1471-2407/9/239
Knoblich, J. A. (2010, 12 11). Asymmetric cell division: recent developments and their implication for tumor biology. Retrieved Oct 24, 2013, from pubmed.gov: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866968/
Pontano, L. L., & Diejl, J. A. (2008). Speeding through cell cycle roadblocks: Nuclear cyclin D1-dependent Kinase and Neoplastic Transformation. Cell Division , 12.
