Nuclear transfer
Encyclopedia
Nuclear Transfer is a form of cloning
. The steps involve removing the DNA
from an oocyte
(unfertilized egg), and injecting the nucleus
which contains the DNA to be cloned. In rare instances, the newly constructed cell will divide normally, replicating the new DNA while remaining in a pluripotent state. If the cloned cells are placed in the uterus of a female mammal, a cloned organism develops to term in rare instances. This is how Dolly the Sheep
and many other species were cloned. Cows are commonly cloned to select those that have the best milk production.
Despite this, the low efficiency of the technique has prompted some researchers, notably Ian Wilmut
, creator of Dolly the cloned sheep, to abandon it. http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/11/16/scidolly116.xml
(small vacuum) to keep the oocyte in place, and a micropipette
(hair-thin needle) capable of extracting the nucleus of a cell using a vacuum. For some species, such as mouse, a drill is used to pierce the outer layers of the oocyte.
Various chemical reagents are used to increase cloning efficiency. Microtubule
inhibitors, such as nocodazole
, are used to arrest the oocyte in M phase, during which its nuclear membrane is dissolved. Chemicals are also used to stimulate oocyte activation. When applied the membrane is completely dissolved
(SCNT) or therapeutic cloning involves the nucleus of an unfertilized egg cell, replacing it with the material from the nucleus of a "somatic cell" (a skin, heart, or nerve cell, for example), and stimulating this cell to begin dividing. Once the cell begins dividing, stem cells can be extracted 5-6 days later and used for research. The AAMC supports on-going research into SCNT and has endorsed legislation that would allow such research to flourish.
is the key biological process behind nuclear transfer. Currently unidentified reprogramming factors present in oocytes are capable of initiating a cascade of events that can reset the mature, specialized cell back to an undifferentiated, embryonic state. These factors are thought to be mainly proteins of the nucleus.
Cloning
Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...
. The steps involve removing the DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
from an oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
(unfertilized egg), and injecting the nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
which contains the DNA to be cloned. In rare instances, the newly constructed cell will divide normally, replicating the new DNA while remaining in a pluripotent state. If the cloned cells are placed in the uterus of a female mammal, a cloned organism develops to term in rare instances. This is how Dolly the Sheep
Dolly the Sheep
Dolly was a female domestic sheep, and the first mammal to be cloned from an adult somatic cell, using the process of nuclear transfer. She was cloned by Ian Wilmut, Keith Campbell and colleagues at the Roslin Institute near Edinburgh in Scotland...
and many other species were cloned. Cows are commonly cloned to select those that have the best milk production.
Despite this, the low efficiency of the technique has prompted some researchers, notably Ian Wilmut
Ian Wilmut
Sir Ian Wilmut, OBE FRS FMedSci FRSE is an English embryologist and is currently Director of the Medical Research Council Centre for Regenerative Medicine at the University of Edinburgh. He is best known as the leader of the research group that in 1996 first cloned a mammal from an adult somatic...
, creator of Dolly the cloned sheep, to abandon it. http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/11/16/scidolly116.xml
Tools and reagents
Nuclear transfer is a delicate process that is a major hurdle in the development of cloning technology. http://www.pnas.org/misc/classics4.shtml Materials used in this procedure are a microscope, a holding pipettePipette
A pipette is a laboratory tool used to transport a measured volume of liquid.-Use and variations:Pipettes are commonly used in molecular biology, analytical chemistry as well as medical tests...
(small vacuum) to keep the oocyte in place, and a micropipette
Micropipette
A micropipette is one of two different instruments used in science laboratories.-History:The first micropipette was patented in 1960 by Dr Hanns Schmitz . The founder of the company Eppendorf, Dr...
(hair-thin needle) capable of extracting the nucleus of a cell using a vacuum. For some species, such as mouse, a drill is used to pierce the outer layers of the oocyte.
Various chemical reagents are used to increase cloning efficiency. Microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
inhibitors, such as nocodazole
Nocodazole
Nocodazole is an anti-neoplastic agent which exerts its effect in cells by interfering with the polymerization of microtubules. Microtubules are one type of fibre which constitutes the cytoskeleton, and the dynamic microtubule network has several important roles in the cell, including vesicular...
, are used to arrest the oocyte in M phase, during which its nuclear membrane is dissolved. Chemicals are also used to stimulate oocyte activation. When applied the membrane is completely dissolved
Somatic Cell Nuclear Transfer
Somatic Cell Nuclear TransferSomatic cell nuclear transfer
In genetics and developmental biology, somatic-cell nuclear transfer is a laboratory technique for creating a clonal embryo, using an ovum with a donor nucleus . It can be used in embryonic stem cell research, or, potentially, in regenerative medicine where it is sometimes referred to as...
(SCNT) or therapeutic cloning involves the nucleus of an unfertilized egg cell, replacing it with the material from the nucleus of a "somatic cell" (a skin, heart, or nerve cell, for example), and stimulating this cell to begin dividing. Once the cell begins dividing, stem cells can be extracted 5-6 days later and used for research. The AAMC supports on-going research into SCNT and has endorsed legislation that would allow such research to flourish.
Reprogramming
Genomic reprogrammingReprogramming
Reprogramming refers to erasure and remodeling of epigenetic marks, such as DNA methylation, during mammalian development. After fertilization some cells of the newly formed embryo migrate to the germinal ridge and will eventually become the germ cells...
is the key biological process behind nuclear transfer. Currently unidentified reprogramming factors present in oocytes are capable of initiating a cascade of events that can reset the mature, specialized cell back to an undifferentiated, embryonic state. These factors are thought to be mainly proteins of the nucleus.