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- كاريوسوم يشير إلى مادة الكروماتين داخل نواة الخلية عندما لا تخضع الخلية للانقسام. (ar)
- Overview The karyosome also known as the karyosphere, are condensed chromatin bundles inside the cell nucleus. These bundles are joint together in a limited nuclear volume, but this only happens when the cell is not undergoing meiotic division. Research suggests that within its bundles there is an absence of RNA synthesis occurring in the karyosphere. This is interesting because RNA is actively being carried out within meiosis, especially throughout the first and second prophase of meiotic division. Formation and Function The formation of karyosomes is a phenomena that occurs in several animal classes and are special for their role in oogenesis. This is important because, oogenesis is a vital process in female gamete development. These gametes can only develop if the mother has oocytes, that are rich in cytoplasm, maternal proteins and contain karyosomes. Karyosomes are known to be very organized. Any mutation that alters the formation and alignment of karyosomes can lead to defects of an oocyte. Defects can also occur with the absence of nucleosomal histone kinase-1. NHK-1 is a kinase that is essential for all karyosomes, for its maintenance and overall formation. NHK-1 is conserved from nematodes to humans. In the absence of NHK-1, karyosome patterns will fall apart within the female's oocyte, and this disruption will lead to problems previously mentioned. There are other causes of mutations, however they are still unknown and misunderstood. The same can be said about the formation of karyosomes., because the phenomena of how they generate is still unclear. It is suggested that NHK-1 substrates, would be the answer to understanding how the karyosome forms during female meiosis. Even though the molecular pathway for this process is still being confirmed, it is known that karyosomes tend to formulate at different stages for different organisms. In fact, for insects this stage is called the diplotene stage. The diplotene stage is a prolonged segment that crosses over genes from two different cells, and aids in the creation of gametes. For example, this occurs within drosophila oocytes aka fruit flies. The formation of karyosomes during this period are based off a ratio. This ratio is dependent on the potential size of an organism, meaning that typically larger organisms will have bigger karyosomes. In other words a typical drosophila oocyte is 20 μm in diameter, then the karyosome is expected to be about 1 μm in diameter. Karyosome Capsule As oogenesis continues, the karyosome is typically covered by a sheath, known as a capsule. These capsules are created from the interaction between nuclear structures, the nuclear membrane and chromosomes. Interestingly enough, karyosomes can form with and without a capsule. Typically karyosomes containing no capsule is seen more with drosophila, but it is not an anomaly. The function and molecular composition of karyosome capsules are quite unknown. It has been suggested that these capsules may be a storage site for nuclear ribonucleoprotein particles. Therefore, the absence of this capsule within certain organisms may demonstrate a reduction in small nuclear proteins and RNA. (en)
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