In metaphase, the chromosomes lie up along the equator and are attached to the spindle fibres by the centromere.
Anaphase consists of the centromeres dividing at the chromatids. The spindle fibres contract and pull the chromatids to opposite poles. This is done pulling the centromere first.
Telophase is where the chromatids uncoil. The nuclear membrane forms around each group of chromosomes. The last part of mitosis is called cytokinesis, here the cytoplasm divides making two new daughter cells.
How Embryonic Stem Cells are developed and used
Early Embryo
After the sperm has fused with the egg, fertilisation starts. Fertilisation is then followed by a rapid set of cell divisions. The first few divisions, divides the cell without growing in size. After the cell cycle has undergone three whole cell cycles, it consists of eight similar cells. Each of these cells can expand into a complete, healthy human. A hollow ball of cells forms about five days after conception known as blastocyst. The outer blastocyst cell layer goes on to form the placenta. The inner cell goes on to form the tissue of the early embryo. Each cell, made in the inner blastocyst, is known as pluripotent embryonic stem cell. These cells can become like most cell types, though they cannot give rise to all 216 diverse cell types that make up an adult human body. As the embryo develops, it has the potential of becoming a specialised function for the body and there becomes differentiated. Most of these cells could lose the ability to develop into a wide range of cells but do not.
The use of stem cells in medicine
Stem cells can one day create human donor cells that may provide new cells, tissues or organs for treatment and repair by transplantation. The probability of embryonic stem cells is quite high as it can develop into any cell type that offers the greatest flexibility for development. It is very unlike older adult’s cells that can only commit to doing one thing for the body.
In a laboratory, it would be accepted to grow embryos to form blastocysts. At this point, the embryo can be refined for a further certain amount of time to see if stem cells can be formed. The stem cell is then kept in remote place away from each and the rest of the embryo (which would later be thrown away). Hopefully the stem cells would be cultured and develop into tissues that can be used for transplantation.
Problems with using stem cells in medicine
Even though scientists may be able to get the stem cells into the body and into the right tissue, it may be rejected by the immune system of the person the cells are needed for. This is known as transplant rejection and there are many ways to get around it. One of the ways would be to use tissue typing. This type of practice has been used for decades when finding a suitable donor for blood transfusion.
Ethical concerns about the use of stem cells
There are no ethical objections to using multipotent stem cells copied from adults and this is agreed by just about everyone. The worry is that most scientists may think that the use of stem cells are likely to become less important, for research and initial new treatments than the pluripotent stem cells, which can only be taken from human embryos.
Different people see the status of the human embryo in another way. As stated in the SNAB Biology book, the official UK government committee set up to report on human stem cell research, which stated;
‘A significant body of opinion holds that, as a moral principle, the use of any embryo for research purposes is unethical an unacceptable on the grounds that an embryo should be accorded full human status from the moment of its creation. At the other end of the spectrum, some argue that the embryo requires and deserves no particular moral attention whatsoever. Others accept the special status of an embryo as a potential human being, yet argue that the respect due to the embryo increases as it develops and that this respect, in the early stages in particular, may properly be weighed against the potential benefits arising from the proposed research.’
On January 22, 2001, the UK House of Lords voted 212 to 92 votes to extend the purposes for which research on human embryos is allowed. This affected the 1990 Human Fertilisation and Embryology Act.
Other Ethical Issues
Through surveys done by science magazines, it has been proven that there is concerns about the use of Embryonic Stem Cells. In these surveys they have asked questions like;
- Do you believe that it is acceptable to use embryonic stem cells in tissue engineering? and
- Does it make any difference whether they are used for highly debilitating or life threatening purposes or for less serious conditions?
Some of these questions have been answered but with the answer, there were other concerns of religions and social interactions.
Future Developments
The stem cells can be used for many things; one of the most successful approaches is to use it in Orthopaedics. Among many exciting developments, medical technology company Medtronic Sofamor Danek has marketed a device for spinal application that delivers bone morphogenetic protein-2 (BMP-2), a naturally occurring protein that induce bone and cartilage growth. A metal cage is filled with a collagen sponge soaked in recombinant BMP-2. As the bone grows to fuse the vertebrae together, the collagen sponge dissolves.
Articular Cartilage
Articular Cartilage is an engineered tissue done by tissue engineering. This particular tissue is part of the knee join that allows humans to move about on their feet. As people get older, this tissue weakens and becomes very soft, at this stage it is usually said that the person should have surgery.
Structure
The heterogenous structure of the articular cartilage has an extracellular matrix network. This contains collagens, proteglycans and other proteins.
How to repair the cartilage using tissue engineering
To repair the cartilage, the patient could undergo total knee replacement (which they would eventually have to go back and do this surgery again) or they could implant cells to help build the lost cartilage. The first thing to do would be to take a healthy piece of cartilage from the knee so that scientists are able to collect the necessary amount of cells.
The cells would then be sent away to a laboratory where they are isolated and expanded. It is done the same way as embryonic stem cells are used.
The extracted cartilage (now known as chondrocyte) is expanded in a monolayer culture, here it would undergo mechanical, biochemical stimuli. The cells are then seeded in a scaffold where its mixed with a gel or placed in a fibroscaffold. Biochemical factors (also known as the processing of in-vitro fertilisation of neo-tissue. This could take weeks to do and the patient may need to stay in the hospital and wait for this to happen. The cells have to undergo the cell cycle and the longest time taken is usually in the interphase, where the cells are producing enough protein and replicating DNA.
After this has happen, the cells are then injected into the patient’s knee under periosteal graft.
This is usually successful but the patient would have to come back to redo later, maybe in the next 8-10 years, which is costly and sometimes depressing to the patient.
Issues and Concerns with this process
Every human being has moral views about what they thing is right or wrong, but there is no one universal way or acceptance to decide whether something is ethically acceptable or not. Instead there are a number of frameworks which allows you to work out whether a particular action would be right or wrong. Normally, if you accept the principles the framework is based you would get the same answer, but that is not always the case, and therefore that’s why there are intelligent and kind people to help us with this.
There are four main frameworks; rights and duties, maximising the amount of good in the world, making a decision for yourself, and leading a virtuous life.
In this case most people feel that there is a certain right you have to follow or it they may find the answer within their religious faith. Secondly, people may feel that if it maximises the amount of good in the world, then it must be acceptable. Although, making a decision for yourself, (which is the third point), as every human can make their own decision.
Bibliography
SNAB AS Biology Book-Heinemann Enterprises
PowerPoint Presentation by Dr. Tina Chowdhury from the Cell and Tissue Engineering department at the Queen Mary University of London in Mile End
The WellnessScience Magazine, published in March 2006
