Findings in Parthenotes Essay

The reason for the halted development is accounted for by a number of interesting findings that have been reported. This has been termed as genetic imprinting. Normally and naturally, the maternal and paternal genomes have been shown to be epigenetically different, and normal and successful development necessitates both the sets of genomes (Watt, 2007, 554-556). on the other hand, in activated eggs, also called parthenotes, the origin of all the genetic material is maternal, this implies that there is no imprinting from the paternal genome. It is a generally accepted fact that parthenotes do not develop a tropoectoderm neither do they develop any of the primitive endoderm and extraembryonic tissue. Therefore they are not compatible with life; they do not develop to term. They resemble ovarian teratodermoids and comprises only of embryonic tissues (Newman-Smith and Werb, 1995, 2069-2077). Calcium and Parthenotes Release of stored calcium ions in precise pulses plays a major role in egg activation. It is a recognized fact that fluctuations in free ionic Calcium concentration serves as chemical signal. (Rhoton-Vlasak, Lu, Barud, Dewald, and Hammitt, 1996, 793-796). Most cell types contain very similar calcium signaling mechanisms and elements. It appears from findings that calcium signals are apparently ubiquitous (Nanassy, Lee, Javor, and Machaty, 2008, 264-274). They can be demonstrated both in the somatic cell lines and also in the germ cell lines too. In view of this, it can be stated that the development from oocyte to early embryo is a pre determined sequence of events that occur concurrently in a linear and irreversible manner. There is no repetition whatsoever (Susko-Parrish, Leibfried-Rutledge, Northey, Schutzkus, and First, 1994, 729-739). Surprisingly, the context of each calcium signal is different in different set of events. There is thus a high probability that the Calcium ion which serve as signals in the oocytes and also, the embryo mirror changes in the state of the cell. They are the landmarks for monitoring the development of this cell. It can be said to represent the predetermined programmed events. (Wang, Wang, Yu, and Xu, 2008, 292-301). The process has not been completely demystified by science but some evidence points to the fact that Calcium ions function as second messengers in the oocyte cytoplasm. The ions cause the intracellular release of some other stored chemical mediators of this process. (Winston, Johnson, Pickering and Braude, 1991, 904-912). The initial release of the calcium ion would lead to the completion of the second meiotic division. Subsequent quantal releases of calcium ion would start up the process of cleavage. The fine details of the mechanisms involved are still not known. However, there are some pointers to the fact that the quantal Calcium ion release may be timed to be released at regular intervals for several hours. This is necessary for the activation of the egg. (Krivokharchenko et al. , 2003, 829-836). A mechanism is proposed: each timed release activates some steps that follow previous events and this also leads to the activation of subsequent steps processes (Niwa et al. , 2004, 1560-1567). Relation with Cell Cycle The cMos gives room for the continuation of meiosis from its arrested state. Oocytes that are deficient of this factor are readily activated. They are not so dependent on the firm regulation of the ionic Calcium. (Bos-Mikich, Whittingham, and Jones, 1997, 172-179). During, meiosis, a half of all the chromosomes in the second metaphase division are all removed as the second polar body. The other remaining chromosomes remain in the nucleus of the oocyte . the nucleus therefore contains only a half of the genome. The oocyte this carries a haploid nucleus. (Gardner and Davies, 2006, 492-502). As stated above, a discrepancy in the formation of the second polar body, which also translates to halving of the genetic material will lead to the persistence of all the shromosomes that are present in the second metaphase division. This in turn gives rise to a diploid cell. Ozil et al. , 2005, 39-54). (An unfertilized egg differs from a fertilized egg. Since this is a change in the state of the cell, the calcium signal is believed to bring in the changes the cell state. It can be stated as evidenced by the animal models that the calcium signal is sufficiently important in bringing about some or even most of the changes that take place. The other role that the sperm serves aside from triggering the transient calcium flux necessary for fertilization and providing a half of the genome is to make available centrosomes (Taylor and Braude, 1994, 2389-2397). The centrosome is increasingly regarded as the initiator of cell cycle. This action gives room for the duality that is required to divide the cell. The events at fertilization can therefore be viewed as events that are specific for fertilization proper including the ones that are related to the regulation of cell cycle (Gao, Czirr, Chung, Han, and Latham, 2004, 1162-1170). Sperm Incorporation When the sperm is incorporated, the following events occur. The cortical granules are extruded, the microvilli get elongated, superoxides are produced, and overall metabolic ctivity is heightened. The zona reaction that occurs in fertilization occurs due to exocytosis of the cortical granules, and this also develops fertilization envelope. These both arrest the entry of supernumerary sperm (Cibelli , Cunniff, and Vrana, 2006, 117- 135). The series of events are initiated directly by the ionic calcium changes present at fertilization. The subsequent events involve the participation of a variety o f proteins that are in control of the division of both unfertilized eggs and oocytes. (Rho, Wu, Kawarsky, Leibo, and Betteridge, 1998, 885-492). Both the normal cells and the oocytes of the various species have their meiotic division arrested at different points of the cycle. All the primitive germ cells have to produce secondary oocytes in order to mature. To be fertilized. The process involves a meiotic division. (Paffoni et al. , 2007, 77-82). This checkpoint mechanism keeps under surveillance the unattached chromosomes. This does not allow the onset of anaphase until all the chromosomes are securely fastened to the microtubules of the kinetochore. Mos, discussed earlier can influence and bypass this checkpoint mechanism, and this results in maintenance of metaphase arrest before fertilization; biochemically thus preventing degradation of the cyclins (Fulka, Jr, First, Fulka1, and Moor, 1999, 1582-1587). The calcium signal of fertilization appears not to immediately interact with the activity of Mos signaling. Rather, it assumes an alternative pathway that bypasses the checkpoint. It does this by stimulating cyclin degradation. This in turn, is mediated by calmodulin kinase II (CaMKII)-mediated stimulation of cyclin ubiquitination. It goes further to stimulate the proteasome degradation machinery (Whitaker, 2006, 25-88). Germinal Vesicle Breakdown There exists a factor which can be transferred from the mature oocyte to the immature one. This leads to the breaking down of the germinal vesicle. This phenomenon is one of the few observations made that led to the discovery of the CDK/Cyclin Kinases. (Jones, 1998, 7). The female germ line cells grow and differentiate in the ovary, and during this time, they briefly pause within the process of meiosis that again with ovulation of the oocytes. The first stopping point of the oocytes in their cell cycle dues not differ from species to species, however, after fertilization, their second stopping points differ indeed vary (Lee and Campbell, 2006, 691-698). Meiosis is initially arrested at the interphase stage with the nuclear envelope (still intact) the structure that is germinal vesicle in the immature oocytes. This is where the exchange of genetic material occurs. Just as I mitosis, the cyclin-dependent kinase CDK1/Cyclin B controls the activities of such intracellular organelles such as the nuclear envelope, spindle apparatus and even the nuclear chromatin. Salamone et al. , 2001, 1761-1768). The With the germinal vesicle breakdown, the activities of the cyclins increase. MAP kinase has a key role to play during meiosis, in addition. MAP kinase maintains the condensation of the chromatin in the interphase that intervenes the two meiotic divisions, where DNA synthesis is suppressed. This provides the cellular and biochemical environment for creation of the mature oocyte that remains haploid (Rogers et al. , 2006, 45-57). Inositol Phosphate The evidence points to a role for the InsP3 signaling system and transient calcium fluxes in the control of GVBD during meiosis. Calcium is a central figure in the control of this process including the fashion in which it progresses. Just as fertilization activates GVBD. (Higgins and Kane, 2003, 111-118). Fertilization calcium responses have been called termed explosions. After the process of fertilization, the oocyte calcium signaling mechanisms revert to a less vigorous mode. Mature follicles spontaneously starts growing as soon as they are removed from the ovarian stroma (Liu, Trimarchi, and Keefe, 2002, 204-210). Moreover, the growing component also becomes expressed on this removal; however, the non viable oocytes will fail to mature. The aforementioned calcium quantal release in exhibited in the mature oocytes, with a frequency of 1 min. this also occurs in growing follicles but the frequency is lower, at 5 min. however, non viable oocytes do not show this quantal relese This implies, cell cycle progression has a link with calcium pulses. (FitzHarris, Larman, Richards, and Carroll, 2005, 4563-4575). It was also demonstrated that immortal stem cells could be manipulated in vitro, providing the opportunity to study early development as well as lineage potential of derived progenitors in