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You are in the section: Genetic Function of Cytoplasm in an Egg Cell

Function of Cytoplasm in an Egg Cell

Egg cells cytoplasm is liquid containing organelles (mitochondria, Golgi apparatus, cytoplasmic reticulum and others). It intermediates the transfer of information between the individual organelles and assures the insemination process. At first, it has to "dissolve" all sperm structures, except for the genetic material (24 chromosomes, coming from the man) and through cytoplasmic spindles to arrange, in a mirrored way, into pairs with the 24 chromosomes included in the egg cell. Subsequently, the mirrored arranged chromosomes are joined in one full set and then divided into 2, 4, 8… cells with continuous accession of genetic information.

Cytoplasm is significantly engaged in the reproductive processes. Many of its functions, however, have not been described yet. Through its mitochondria it supplies the energy to all reproductive processes. Mitochondria have their own chromosomes (200-500,000 copies of mitochondrial DNA in one cell), which on 37 genes code 13 proteins, 2 ribosomal RNA and 22 transfer RNA.

They exclusively originate in the egg cell (thus they are inherited only through the maternal line). This excludes the correction of potential randomly occurred disorders (mutations) through a set of chromosomes from a man. However, cell division causes "dilution" of this mutation.

If the percentage of mutations at one area of a chromosome exceeds 70%, a disease (disorder) may emerge. A lower percentage may represent a minor disorder (it especially applies to highly energetically demanding processes- i.e. reproduction and cell division).

Possible Corrections to Cytoplasmic and Mitochondrial Disease

  1. Cytoplasmic transfer (of small amount about 10%) from the donor into the recipient's egg cell. It is the simplest method, which does not disturb the cytoplasmic structure of the recipient. Cytoplasm is not removed, just "added"; see the method description in the AR section.
  2. Replacement of a part of cytoplasm of a recipient with cytoplasm of a donor (about 30%). In order to be able to transfer a greater amount of cytoplasm, a part of the original must be removed to prevent an increase in the intracellular pressure, possibly resulting in the damage to the organelles; see the method description in the AR section.
  3. Application of the egg cell genetic material from the recipient (karyoplasm and dividing spindle or polar body) to the egg cell of the donor, devoid of chromosomes. This method is more complicated as it is not easy to identify where the genetic material is placed. It is not directly visible under an optical microscope (this does not apply to polar body). A small percentage of subsequent development after insemination may be expected as the bonds between the genetic material and cytoplasm are disrupted.
  4. Pronuclear transfer. From the donors' early embryo the genetic information is removed and replaced with genetic information (stage 2PN) of the treated couple. This method also disrupts the bonds between pronuclei and cytoplasm. The necessity of chemical inhibition of microtubules and potentiation of genetic material and cytoplasm fusion is described.

 

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