Tuesday, 19 July 2011

What Lay People Should Know about Cloning – Other Types of Cloning

by Zad Datu

Preceeding linked article (Read first!):
What Lay People Should Know about Cloning – Animal Reproductive Cloning

Creating Embryos but Not Babies
October 13th 2001 – the Advanced Cell Technology in Worcester, Massachusetts made history in cloning the first human embryo. This represented the dawn of the new age in – no, not in human cloning, but rather – in medicine. The term “cloning” is so often thought of only as reproductive cloning, or mostly animal reproductive cloning, and often even specifically human cloning. But there is a form of cloning which involves embryos without the aim to produce a fully develop individual – Therapeutic cloning.

The aim of therapeutic cloning is not to produce live organisms, but instead to extract stem cells of an individual for therapeutic and research purposes. But simply because the word cloning is included, many confused opposition of creating lab baby duplicates extend their objections into this life saving field as well.

Therapeutic cloning starts off with the same procedure as SCNT for reproductive cloning, but the embryo is not to be transferred into the womb. Instead, it is allowed to develop until a stage where the cells have divided and multiplied into about 100 cells usually 4 to 5 days after fertilisation (a stage called blastocysts for mammals, homogonous to blastula for non mammals). Found in the inner cell mass (embryoblast) of the blacstocysts, the stems cells are extracted at this stage, and then cultured to large numbers. The stem cells can be directed to specialising into any type of cell to develop into a piece of human tissue or a complete human organ for transplant. The embryo is later killed. That’s the therapeutic side of therapeutic cloning. The research side of therapeutic cloning is part of stem cell research, which eventually is for therapeutic purposes

Adult stem cells have always been available from any individual in their adulthood, but it is very rare hence difficult to cultivate. The Dolly Success opened new doors to stem cell research, as for the first time scientists are able to grow embryonic stem cells, rather than just adult stem cells, from an individual in their adulthood. This was a breakthrough for the healing potentials from stem cell research because unlike adult stem cells, embryonic stem cells can be easily cultured into large amounts, and can differentiate to develop into all types of body cells. The types of cells which adult stem cells can differentiate into are generally limited to their tissue of origin. The idea is to culture embryonic stem cells from the patients themselves into large amounts to later be reintroduced into them as a transplant. Prior to therapeutic cloning, embryonic stem cells only of a donor can be transplanted which may result in rejection by the patient’s immune system.

If research leads to the possibility of deriving nerve cells from cloned embryos, light upon finding a cure to damage cords and brain disorders such as Parkinson’s disease, Alzheimer’s disease, stroke and epilepsy may shine. In fact in 2008, a research lead by Lorenz Studer, Head of the Stem Cell and Tumor Biology Laboratory at Memorial Sloan-Kettering Cancer Center, proved successful in using therapeutic cloning to treat a mice model of Parkinson’s disease.

Other possibilities include differentiating embryonic stem cells into blood and bone marrow cells to heal autoimmune disorders such as multiple sclerosis and arthritis; into pancreatic cells to treat diabetes; nerve cells to treat spinal cord injury; and into heart muscle cells as therapies for congestive heart failure, arrhythmias and cardiac tissue scarred by heart attacks. The possibilities seem endless.

But the technology is highly controversial resulting in bans, condemnations as well as legalisations, and also difficulty in advancing the technology to produce results. [More on these issues are discussed in depth succeeding articles.]

Cloning Since the Ancient Times
As mentioned in the previous article, Dolly was the first animal to be cloned from an adult somatic cell – not the first organism. The first cloned organism from somatic cells was a carrot plant in 1958, where F. E. Steward of Cornell University succeeded in growing a complete carrot plant from a fully differentiated carrot root cell – No, this isn’t the ancient time which the heading refers to just yet.

Also, as mentioned in the previous article, the usage of the term “clone” on animals was coined only in 1963 – not on plants. Before the 1963 coining, the term clone was mostly used for plants to a colony of organisms derived asexually from a single progenitor – but used mostly in the context of plants, as the person who coined this term was a plant physiologist of the US Department of Agriculture, Herbert John Webber in 1903. The word is derived from κλῶνος, the Greek word for “trunk, branch”.

Reproductive cloning in other words is asexual reproduction, which does occurs naturally through apomixis where embryos develops directly from the ova alone without fertilisation common in plants, insects and arthropods, and vegetative propagation (also known as vegetative reproduction, vegetative multiplication and vegetative cloning) where new individuals of plants arise without production of seeds or spore.

Flowering plants, the dominant form of plants, reproduce sexually through flowers, which consist of both male and female reproductive organ where once fertilised, the flowers form into fruits with seeds inside them. When the seed is placed in a suitable soil condition, a new individual plant will grow. But some flowering plants such dandelion, hawkweed and citrus trees can also produce seeds without fertilisation – a still poorly understood process called apomixis – hence producing offspring asexually, while other flowering plants such as strawberry plants, apple plants, potato plants, banana plants and onion plants are also capable of asexually reproduction through vegetative propagation.

Some non-flowering plants such as pine trees, ferns, mosses and algae, on the other hand, undergo a reproduction cycle called alternation generation. One generation is the gamete (sperms and ova) producing generation – the gametophyte generation. They start of their first stage of life as male or female spores in which they become individual male and female plants. The male plant produces sperms and the female plant will produces ova. As a sperm fertilises an uvum, just like sexual reproducing animals and humans, a zygote (seed) is produced growing into a new individual sporophytes – into the alternate spore producing generation – the sporophyte generation. Sporophyte asexually produces male and female spores which restart the cycle to the alternate generation. This asexual production of spores is another example of apomixis.

Other non-flowering plants such as grass and bamboo (a type of grass) reproduces only through vegetative propagation.

In technical terms the offspring reproduced asexually are clones of their parents just as twins are said to be clones of each other because of their genetics. But in general terms, when we speak of cloning, this definition is not generally accepted as nobody would, nor would any scientist credit the parents of the first born human twins as the first people to successfully clone a human or split an embryo. In fact, neither would scientist credit the first artificial embryonic splitting (also called artificial embryo twinning where an embryo is split in the maturation before it is placed into the uterus of the female to conceive to producing identical twins) as the first cloning.

Hence, the accepted term for cloning plants would be that of artificial vegetative propagation practiced in horticultures, plant tissue propagation performed in the laboratory conditions, and just recently possible artificial apomixis of plants (the cloning of plants as seeds).

The ancient times cloning spoken of here is artificial vegetative propagation practiced by the ancient Chinese which was then adapted by the Greeks and Roman which then later spread all over Europe. It includes methods such as cutting, layering, division, grafting and budding. Cutting is to cut off a part of the plant which contains at least one stem cell, either the root, stem, leaves or other parts depending on the type of plant, then placing it in a suitable soil condition which would then start rooting hence an independent new plant. In layering a part of the stem of the parent plant is placed into a suitable soil condition resulting rooting hence a new individual plant still attached to the parent plant, which is later cut off to be separated. Division is simply breaking apart the new plants which naturally grow from to the parent plant and placing it back into the soil environment. Grafting is where the upper part (scion) of one plant grows on the root system (rootstock) of another plant allowing them to grow as a single plant and budding is where a bud is taken from one plant and grown on another, both resulting in new individuals genetically identical to their parent plant which they were taken from. Vegetative propagation is exactly what the word “clone” was referred to in the first cloning and why Greek word for “trunk, branch” was used referred to.

Samples of vegetative propagated plants

Although these are generally accepted as reproductive cloning of plants, unlike the animal cloning, artificial vegetative propagation is simply the induction of natural forms of asexual reproduction – very comparable to in vitro fertilisation and artificial insemination, except that this natural form of reproduction is not asexual. But nonetheless, to artificially propagate vegetations is to produce clones.

Plant tissue culture is basically the culturing of plant tissues grown in isolation, in sterile condition and filtered air. The cultures can be initiated from almost any part of a plant, which would then slowly divide and grow into cells mostly resembling callus cells, which are undifferentiated cells that appear on damage surfaces which would gradually heal, and kept in special conditions. The original plant tissue (called explants) are usually placed on the surface of a solid or liquid medium composed of inorganic salts, organic nutrients, vitamins and plant hormones. Tissue cultured cells can also be induced to re-differentiate into whole plants by altering the growth media. Applications of plant tissue culture includes rapidly multiplying stock plants material to massively produce more plants (micropropogation), conserve rare or endangered plant species, crossing of distantly related species of plants, as well as other possibilities.

Formation of plants via plant tissue culture.

February 18th 2011 edition of the journal Science published the result of the first cloning of plants as seeds authored by scientists from UC Davis, US, Centre for Cellular and Molecular Biology, India, and L'Institut National de la Recherche Agronomique, France. They experimented with Arabidopsis (a flowering plant related to cabbage and mustard) which had genetic mutations that allows it to produce ova with equal number of genes as their parents (diploid) without sexual recombination. Normally sperms and ova are haploid (having only half the genes of their parents) so that they fuse to form a diploid individual. It has just been possible just a year ago to breed haploid Arabidopsis plant carrying genes only from one parent by introducing a genetic change so that the chromosomes from one parent were eliminated after fertilisation. By crossing these two Arabidopsis plants, about one third of the seeds produced were diploid seeds from a single parent. This form of cloning is very comparable to animal cloning through nuclear transfer as these plants do not reproduce naturally in this manner. The team hopes to produce crop plants that can fertilize themselves and produce clonal seeds.

The Last Few Types of Cloning
Other than reproductive and therapeutic cloning, the term “cloning” can also referrers to the duplication of biological material, as conventionally used by biologists, for example, cellular cloning and DNA cloning (also called molecular cloning, recombinant DNA technology, or gene cloning). Cellular cloning the process of growing a colony of cells from just one cell resulting in cells of identical DNA, whereas DNA cloning is the production of multiple copies of DNA from an isolated fragment of DNA.

Aside from biology related fields, cloning is often used as a term somewhat synonymous to creating a duplicate, common in computer programmes such as image and video editing software.

Succeeding linked article – coming soon:
What Lay People Should Know about Cloning – Fear Fuelled Objections (opinion) [Part 1] [Part 2]
What Lay People Should Know about Cloning – Ethical and Legal Issues (technical) [Part 1] [Part 2] [Part 3]
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