Like a Virgin, Prasad, Aarathi [free children's ebooks pdf .TXT] 📗

egg is big – the biggest cell in the body. When an egg is frozen, the large cell’s greater fluid content often sustains ice-crystal damage. Even with an improved technique, known as vitrification, which flash-freezes the egg to avoid crystallization, there is only a ten percent success rate. If a young woman has her own eggs removed, chances are that when she is older and decides to use them, the process may very well have failed. And seeing that for women, removing eggs is quite invasive and uncomfortable, being able to make eggs in a lab from a woman’s DNA is very attractive: it would mean that most of the process takes place outside of her body with far less risk.

So, how close are we? Bone marrow stem cells have proved extremely promising in the early experiments to create in vitro-derived germ cells: given the right signals, bone marrow stem cells are capable of becoming sperm. Further, three types of stem cells exist in bone marrow and it contains the cell-level blueprints for much of the body, including the heart, lungs, liver, kidney, bone, cartilage, fat, muscle, tendon, skin, and even the brain.

Regardless of the provenance of human embryonic stem cells, the proteins that act as signposts for developing male (sperm) and female (egg) cells can be detected in them. In fact, eggs have been made in the lab from both female and male embryonic stem cell lines. This is because the male embryonic stem cells have not yet expressed the SRY gene, which triggers the development of the testes and eventually the generation of sperm. Female embryonic stem cells, on the other hand, can only give rise to eggs. So without an artificial Y chromosome, women could only ever make artificial eggs, while men could make either artificial eggs or sperm. However, by keeping eggs fashioned from embryonic stem cells in a culture (that is, in a nutrient/chemical soup incubated with a prescribed mixture of gases at an appropriate temperature), scientists have been able to create parthenogenic embryos – embryos that begin to develop despite never having been fertilized by sperm. (Of course, this isn’t all that peculiar when you consider that parthenogenesis is a relatively normal phenomenon; whenever eggs are kept in culture, they tend to start dividing on their own.)

In early 2006, two laboratories, one based in Germany and the other in the UK, reported some remarkable results using embryonic stem cell lines. Earlier, scientists had successfully developed immature sperm, or spermatogonial stem cells (SSCs), from embryonic stem cells that, when they were injected into mouse eggs, developed into early embryos. The new research went one better. The teams transplanted SSC artificial sperm into the testes of mice that had no sperm of their own. After four months, the scientists observed sperm in some of these mice, generated from the transplanted cells. Unfortunately, the sperm did not move, or move very far, unaided; they weren’t ever going make it to an egg. So to help the process along, the sperm were removed from the mice testes and injected into unfertilized eggs. Out of 210 eggs, 65 embryos were produced and transferred into surrogate mice mothers. Seven of these became baby mice, fathered by artificial sperm. But the baby mice sired this way were not very healthy, and they died at ages well below the average life expectancy of mice conceived naturally. Much remains to be worked out before artificial sperm are ready for humans.

Then in 2010, the first artificial human ovary was made, signalling a significant step towards the creation of eggs outside of a woman’s body. The artificial ovary, built by researchers based at Brown University and the Women & Infants Hospital of Rhode Island, could move oocytes along the path to becoming mature eggs.

An ovary is a complex organ, composed of three major cell types, all of which need to be developed in a tissue structure for an artificial organ to function fully. According to Sandra Carson, the obstetrician and gynaecologist at Brown who led the team, the ovary provides not only a living laboratory for investigating how healthy ovaries work but a way to test for exposure to toxins and other chemicals that can disrupt egg maturation and health. In the future, Carson believes an artificial ovary might play a role in preserving the fertility of women facing cancer treatment – immature eggs could be salvaged and frozen before the onset of chemotherapy or radiation, and then matured outside the patient in an artificial ovary.

Carson’s group has already used a lab-grown ovary to mature human eggs. To do so, they used a ‘3D Petri dish’ made of mouldable gel, on to which two types of ovarian support cell could attach, forming a honeycomb structure. Seventy-two hours later, the third cell type was introduced, enveloping the immature egg cells in exactly the manner that would happen inside a real ovary. They managed to keep the structure healthy for up to a week. It is unclear whether the eggs developed in the artificial ovary contained all of the important genetic imprinting information, but Carson and her colleagues are performing further studies that they expect will make this possible. And even though it has not yet been dealt with in their investigations, the artificial ovary might equally well be used to mature artificial eggs too. In a university press release, Carson emphasized that the techniques are ‘really very, very new’ and that, setting aside her hopes for the future, it would be sensible to be cautious about where the experiments may lead.

The obstacles to creating artificial sperm indistinguishable from healthy sperm created in a man are not so different, in some respects, to those faced in manufacturing mature eggs. Some of the labs that claim to have made sperm from bone marrow stem cells have made