Thursday March 24 2011
The fertility of the offspring is not a precise measurement of health
“Scientists have grown sperm in the laboratory in a landmark study that could help preserve the fertility of cancer patients and shed fresh light on male reproductive problems,” reported The Guardian.
It and many other newspapers reported on this pioneering laboratory study in mice. Small slices of testes from mice were cultured, then the sperm cells were used to fertilise eggs in a mouse IVF procedure. The apparently healthy young mice born after this went on to have babies themselves. Researchers claim that no one has managed to artificially mimic the whole cycle of sperm production in mammals before. They also successfully performed the same procedure after the testicular cells had been frozen. This indicates that the clinical need to freeze human sperm cells might be possible.
Having shown that it is possible in one species, the researchers hope that they can extend the results to other species and eventually humans. Experts have commented that the treatment, if successful and safe in humans, would be most useful for young boys who are receiving cancer treatment. Anyone after puberty can already freeze sperm rather than testicular cells for later use.
Where did the story come from?
The study was carried out by researchers from Yokohama City University Graduate School of Medicine, in Japan. The research was supported by the University, the Japanese Ministry of Education, Culture, Sports, Science and Technology, and the Yokohama Foundation for the Advancement of Medical Science.
The study was published in the peer-reviewed science journal Nature.
The newspapers all report the preliminary laboratory nature of this research. Some use quotes from experts to emphasise that this is a small but important step in understanding how sperm are formed, and that developing treatments based on the new technique will take time and more research.
What kind of research was this?
This letter summarises a research programme that has been undertaken by this laboratory and other research centres over several decades. The researchers say that they were interested in re-evaluating how cell and organ culture methods could be applied to growing sperm in the laboratory. Research began almost a century ago, focusing on meiosis, which is the type of cell division needed for sexual reproduction.
By the 1960s, culture of testis had progressed to a state where the production of sperm could reach a very early stage of meiosis (called the pachytene stage) before chromosomes divide. But the research had gone no further. After this, researchers looked at cell culture methods to see if the cell division could progress further, using special techniques. By the year 2000, it was possible to observe the whole cell division process needed to form sperm in rat cells.
This new research takes what has been learnt from all these previous efforts and, using the best techniques from these, has gone on to develop some new types of growth media, mixtures in which the fragile sperm cells can grow. The researchers give a detailed report of what they have done so that others can repeat and test the procedures further. As is the nature of this type of important research, each small step will help towards the goal of growing sperm successfully in the laboratory.
What did the research involve?
The research programme was comprised of several parts. The researchers used transgenic mice that were specially bred to carry the GFP gene. This gene makes sperm cells carry fluorescent marker proteins. This allowed the researchers to track the progress of sperm growth. The young mice used for the culture experiments were 12 hours to 11 days old.
Small pieces of testicular tissue (about 1-3mm in diameter) were taken from the mice and grown on special nutrients. Every 3–7 days these were examined under a microscope that illuminated the fluorescent markers, showing the extent of GFP expression in each tissue. Researchers could then measure the extent of any sperm production going on.
Some tissue was also taken for other histological and immunohistological examinations under the microscope. Different growth media, liquid mixtures designed to support the growth of cells, were used at different stages. When the sperm were ready, after about 42 days, the researchers carefully retrieved the delicate early sperm from the testicular tissue. They then injected a single sperm into an egg cell, using a technique called intracytoplasmic sperm injection (ICSI), which is similar to an IVF procedure used in humans. They also used another IVF technique called round spermatid injection (ROSI) in which less developed sperm that had been cultured for 23 days were injected.
The researchers also tested the ability of the testicular tissue to withstand being frozen, as this would improve the clinical usefulness of the procedure for treating some types of infertility in humans. Fragments of testis tissues were immersed in protective chemicals for several hours or overnight, then stored in liquid nitrogen. Later, the tissue was thawed to room temperature, cultured further and the sperm used for the ICSI procedure again.
The researchers then observed the resulting mice offspring until they bred naturally again.
What were the basic results?
The researchers say that sperm production, growth of sperm and meiosis are parts of one of the “most complex and longest processes … in the body”. They say that the whole process has never been reproduced in the laboratory before, except in fish.
In their experiments they showed that it was possible to maintain growth and development of sperm in mouse testicular tissue, and that the obtained sperm resulted in healthy offspring using an IVF technique. These offspring were themselves fertile.
Among the 35 egg cells inseminated by ICSI, 17 developed to the two-cell embryo stage, 10 implanted correctly into the uterus, and five (two male and three female) mice were born.
The researchers also succeeded in using the sperm for IVF following freezing and thawing of the tissue. The freezing is similar to what might occur if the technique were used to maintain fertility in humans treated with a chemotherapy that destroyed sperm production.
How did the researchers interpret the results?
The researchers claim to have demonstrated that in organ culture conditions in the laboratory they can show the complete process of artificial sperm development in mice.
They say that if the present results can be extended to other species, using refinements that they believe are possible, then the molecular mechanisms of sperm production can be clarified. They say this will lead to the development of new diagnostic and therapeutic techniques for male infertility.
This is groundbreaking laboratory research, which highlights both the time taken to develop new techniques and the complexity of these innovations in infertility treatment.
The researchers have carefully described the methods they used, thus allowing other researchers to follow them. There are a few cautions if this technique is to be applied to humans:
- The success of the technique depends on signalling molecules released by sperm cells and the surrounding tissue too. It is not known exactly how these molecules work.
- Fertility of the offspring is not a precise measurement of general health. More tests on the mice born after this procedure will be needed to ensure that they are entirely healthy.
- Adverse effects known as ‘epigenetic effects’ can occur when cells are maintained in culture. These non-genetic factors can cause the organism's genes to behave (or "express themselves") differently. Subtle genetic or epigenetic changes could still have occurred here and adversely affected the wellbeing of subsequent generations.
Clearly more research will be required to resolve any safety concerns and to test the technique in other mammals before it could be used for humans.