Three ways of cloning

Cloning by embryo division

• most similar to cloning in nature (identical twins)
• with the help of a microscope and a micromanipulator, an early embryo can be divided into two parts, which are allowed to develop in surrogate mothers, and identical twins are born
• used in macaque and human embryos that were condemned to abortions in the early stages of pregnancy due to developmental defects

Nuclear transfer (nuclear transplantation)

Dolly the sheep

• the nucleus of a long-term cultured somatic cell is introduced into the enucleated oocyte
• the transmitted nucleus must be in the G0 phase, so it does not risk a rapid entry into the S phase
• the cytoplasm is in the M phase and after accepting the nucleus it goes into the S phase
• the fusion of the nucleus and the oocyte was done by electrical pulses, these destabilize the cell membrane and allow the cells to fuse together and activate the oocyte to start developing -> roslin technique
• this is how Dolly the sheep was created, she had three mothers (a somatic cell nucleus donor from a mammary gland, an oocyte donor for cytoplast preparation, a surrogate mother)
• transfer of the "naked" core extracted from the donor by using a very fine glass capillary and a micromanipulation device -> Honolulu technique
• advantages: no admixture of cytoplasm enters the cytoplasm and microinjection does not trigger the immediate development of the embryo (possibility of an extended resting phase when reprogramming is completed)
• embryo development later started by strontium ions and the embryo develops better than with the Roslin technique

Chimera formation (sandwich method)

• has good prospects, is the negation of the embryo division method
• perfect copies of cloned individuals are created in almost unlimited quantities
• the essence is the aggregation of several early embryos into a single embryo that is able to complete its development
• bodies of chimeras are composed of cells of different origin - 2 types:
  1. ESCs (embryonic stem cells) – from them a fetus arises
  2. Tetraploid stem cells (impenetrable) - fetal membranes and placenta
• the ratio of the individual cells of the embryos is random
• the fusion of embryos is possible due to the ambiguously defined identity of the embryonic cells
• only successful in mice

Links

related articles

• Cloning

References

• NOVOTNÁ, Božena – MAREŠ, Jaroslav. Vývojová biologie pro mediky. 1. edition. Praha : Karolinum, 2005. 99 pp. ISBN 80-246-1023-X.