A Third Parent contributes her Mighty Mites (Mitochondria)

Two biological parents are enough for any baby, aren’t they? Maybe not: sometimes it’s better to have two mamas.

The media have hyped a story that broke in September about a boy who was conceived by “mitochondrial replacement therapy.” His parents had lost two previous children to Leigh syndrome, a rare but severe condition affecting the brain, nerves and muscles caused by mutations in mitochondria, the mites that energize every cell inherited from our mothers’ egg (never from our fathers’ sperm). Less than 2% of the boy’s mitochondria were damaged, which was well below the 18% threshold for disease. An anonymous egg donor has given him the prospect of a full and healthy life.

Mitochondrial transfer
Thousands of tiny mitochondria fluorescing brightly in a human egg and its moon-like polar body

John Zhang, whom I knew when I worked in NYC, led the clinical team and is director of a fertility service that is popular there among Asian Americans. But he carried out the procedure in Mexico where, according to reports of his words, there are “no rules (for assisted reproduction).” That statement was as responsible for the media furor as the procedure itself, and he may regret playing into the polemics of conservatives at a time when Mexico is considering legislation for assisted reproduction. Ahem!

His “breakthough” probably put noses out of joint in a Newcastle team in my mother country because they have done the painstaking research work. The UK has often been at the forefront of reproductive technology (clinical IVF, Dolly the cloned sheep, etc.), and has a well-respected system for ethical review (HFEA) which, admittedly, delays the launch of new treatments such as this projected to help 10-20 British families annually. The Geordies should have been first, but were scooped.

Two methods exist for switching mitochondria when a prospective mother carries a harmful load of mutations in her mitochondria. Zhang chose the spindle method in which maternal DNA is transferred to replace the nuclear DNA removed from a healthy donor egg before it is fertilized with her husband’s sperm. Only one of the five embryos thrived in vitro, but after placing in the uterus it conceived a healthy pregnancy.

In the 1990s, a New Jersey clinic transferred small fractions of cytoplasm from donor eggs to improve the quality of eggs for patients who repeatedly failed with IVF treatment. None of the women were carrying mitochondrial mutations, but the clinical team had a hunch that eggs often fail to develop if they are under-energized, but can be boosted with an infusion of fresh mitochondria. After treatment resulting in 17 viable pregnancies with two of the girls missing an X chromosome (Turner’s syndrome), the FDA set a bar too high for the program to continue.

There are now reports from other countries of imminent births after mitochondrial transfer, and these too are said to aim at improving embryo quality instead of correcting a genetic fault. And in Boston a company is offering an expensive treatment (‘Augment’) for improving fertility by transferring mitochondria from a type of ovarian stem cell that some of us doubt exists (my recent critique is available on request).

These therapies have been called ‘eugenic,’ which is a word that makes us shiver, but if they are safe and effective and purely aim to restore a healthy population of mitochondria, need we worry? Some commentators have called the boy in Mexico a GMO baby, but that’s strictly inaccurate, because the mitochondrial genome containing a mere 37 genes and 0.0005% of the nuclear DNA was switched, not chemically altered. Moreover, there is no basis for concern about transmitting his new mixture of mitochondria to future children, although a girl treated likewise could and that possibility requires deeper study. We can’t be sure how her mitochondria would segregate in the bottleneck when eggs inherit tiny numbers of them, possibly creating a very different mix compared to her grandmother and donor, even the remote possibility of bringing back the former disease to her descendants.

Robert Hughes coined the expression Shock of the New for a TV documentary about modern art, but it is an apt expression for public responses to the ongoing revolution in fertility treatment. I imagine hands lifted in horror after every new development is announced, but it would be a hard person who condemns joyful parents by saying their healthy children “should never have been born!” The arrival of healthy babies quenched most opposition to IVF in the 1980s, and I predict the same for the next generation of therapies provided they meet the same standard of ethics and safety.

Human fertility has been said to be the prerogative of God or the gods. The Ancient Greeks had a hoard of myths, and woe betide gods or mortals who broke the reproductive code! Hera was the patron of marriage and childbirth, yet she covered the shame of being raped by Zeus by marrying him. She ate lettuce to improve her fertility, probably because its white sap resembles semen, which is something to think about next time you are served a salad.

One of her sons was Hephaestus. The virgin goddess Athena fled when he lusted after her (he was ugly), but spilled his seed on the ground, which caused Gaia, the Mother of the Earth, to conceive Erichthonius (“Eric” for shorthand). Athena made no biological contribution to Eric, but she was the object of desire and necessary for his conception, and afterwards she helped to bring him up. She was the third parent, and no less for that.

Eric looked so monstrous that he alarmed people and they tried to conceal him (depicted by Peter Paul Rubens). The Greeks were pondering extraordinary conceptions long before we added a third parent by  surrogate pregnancies with IVF or mitochondrial transfer. They posed the question whether a parent is defined by nature or nurture, but the answer is, of course, nature and nurture, and three parents can be better than two.

Next Post: Rock Carving for the Ages

 

Who’s Afraid of Artificial Gametes (Eggs and Sperm)?

In the dystopic Brave New World of Aldous Huxley, he did not add artificial gametes to the bevy of reproductive technologies for replacing natural fertility in his future World State. Nevertheless, they might find a place one day for helping people build their families. I get stares when I ask what others think about artificial eggs and sperm. Perhaps they darkly imagine “Frankensperm” as DNA packages propelled by miniature motors, or “Frankeneggs” with DNA coiled around a silicon chip with a door to admit sperm. But biologists are not that creative!

The technology I have in mind, and which I addressed this week at a meeting in Israel, will only be judged successful if engineered gametes are biologically indistinguishable from “wild types” in normal ovaries and testes. This prospect may seem an odd subject to post from here (pictured), but it will never be a lasting controversy compared to the likes of theology and politics.

City of Jerusalem
Jerusalem by Berthold Werner (Own work) [Public domain], via Wikimedia Commons
Artificial gametes are a huge step towards the total conquest of infertility. They will bypass the deficiency of eggs and sperm in people unlucky to be born sterile, or rendered sterile by surgery and cancer drugs, and many others who are sterilized by age and an early menopause. The first revolutionary treatment for infertility (IVF) was received with a mixture of joy by childless couples and horror by people believing it would harm children and be an affront to “human dignity.” The record has been very positive for millions of IVF babies, and the harshest critics of IVF have mellowed. For who can be so hard to say a child should never have been born?

I suspect after a bumpy ride through sensationalist headlines, artificial gametes will follow a similar course, and possibly help to damp down the demographic anxiety now sweeping the globe. Back in the 1960s, there was a panic about spiraling population growth (The Population Bomb by Paul Ehrlich), but, although our numbers are still climbing from the momentum of high fertility in recent past, fertility rates are declining almost everywhere. Women have fewer babies and start their families later or not at all. Conception is more a matter of choice than chance, and smaller family sizes are desirable because raising children is expensive.

Such private decisions have public consequences, and nervous governments are encouraging parenthood again. Some countries offer free childcare and longer maternity leave. China has relaxed its one-child policy. Japan is in the vanguard of the demographic implosion, but not alone in having a birth rate below replacement levels. And in all but one Western country polled by The Economist (August 27, 2016), the expected average family size was lower than people aspired to as ideal. This reversal of attitudes to family building encourages services almost everywhere for folk who are involuntarily childless. There are now over 1,000 fertility clinics in India, a country long depicted as the epitome of overpopulation. If depopulation of young, working age people continues, surely we will see even more sympathy for these folks, and a greater welcome for the next revolution in fertility treatment than for the first.

Creation of gametes for those who have none would be such a revolution, and would surely bring joy to those who have no rosy options. At present, they may adopt a child or opt for gamete or embryo donation, but neither is an automatic entitlement and comes with financial and social obstacles. Moreover, the desire to have a genetically-related child is compelling because it is biologically grounded. But creating gametes de novo from patients’ own somatic cells is not a light undertaking as it is a turning back to a competence that was lost hundreds of millions of years ago in our evolutionary history.

The chief difficulty is that eggs and sperm are the end-products of slow, complicated processes that first started in our days as embryonic balls of cells. The germ cell lineage that leads to a mature gamete starts with a special type of cell which is “pluripotential,” meaning it is the stem of every cell in the body—brain, bone, blood and so on. It is like a joker in a card game, because it is not a member of a suit but can join any of them. But once a germ cell sets off on its journey of development it doesn’t look back—it loses the pluripotency of its parent cell and can’t switch to another “suit.” Neither can a nerve cell or red blood cell become a germ cell after they have differentiated. At least, they couldn’t until discovery of the trick of injecting nuclei into egg cells, which have “juices” for turning DNA back into thinking it is pluripotent again. That was the amazing lesson Dolly taught us.

When we engineer somatic cells (say, skin cells) to make clones or artificial gametes, both have reversed developmental time to the pluripotent state, but the goals are entirely different. The purpose of reproductive cloning is to duplicate individuals with genomes that are identical to the parent cell. On the other hand, making artificial gametes requires the parent cell to undergo a reduction division for halving its DNA so that it has a genome complementary to a gamete of the opposite sex with which the full chromosome complement is restored at fertilization. And before that division occurs the cell must go through a process of genetic recombination to generate daughter cells with different combinations of genes. Generating diversity is the game of normal reproduction, while uniformity is the hallmark of cloning. Artificial gametes are welcome in theory, but clones are scary.

Although it is very difficult to reverse a somatic cell into pluripotency and then drive it forward make a gamete (among the most specialized cells), two routes are open, although one is guarded by a traffic stop light.

The first involves injecting a nucleus from one of the patient’s somatic cells (e.g., skin) into an egg, which divides to create a ball of cloned cells looking very much like an embryo. It has to be killed, however, if the pluripotent stem cells are to be extracted for making germ cells and, hence, gametes. The moral uncertainty of these embryonic entities and debate about their rights to protection as “human” may never be resolved, thus I believe embryo stem cells are a route to nowhere.

The more attractive candidates by far are the famous iPS cells (induced pluripotent stem cells). They earned the head of a Kyoto University lab the 2012 Nobel Prize for Physiology and Medicine because iPS cells can be made from almost every type of cell in our body, and they are equally pluripotent as embryo stem cells.

In a nutshell, their story is that when a somatic cell is infused with special bunch of molecular transcription factors that are involved in the ground state of pluripotency, its nucleus will “think” it’s inside an embryo stem cell. Once an iPS cell is created it multiplies over and over to make millions of copies, and these daughter cells can be induced to differentiate outside the body along the developmental pathways of all other cell types in the body, including germ cells. The original molecular cocktail was only four factors, but two of them have oncogenic capacity. Oops! Shakespeare would mutter, The course of true science never did run smooth! Researchers are busy replacing them with less threatening ones, and the prospects are good. But there is another challenge for safeguarding health.

When differentiated cells are turned back to become pluripotent they express a different set of genes, which are said to be “epigenetically” controlled. The switches for gene activity lie in the cloud of proteins and methyl groups surrounding the DNA molecule, but what happens if this reprogramming process is incomplete? Is this why iPS cell development is inefficient and can go awry? Almost certainly it is. More to the point of this post, some iPS cells can’t make germ cells, although there is proof of principle.

Another lab at Kyoto University generated gametes from iPS cells made from fibroblast cells. When they were fertilized in vitro with gametes from healthy animals the embryos were transferred to surrogate mother mice which delivered healthy pups. This gold standard for proof is, however, a very long way from a technology for helping patients to conceive with their own gametes, but it does signal the path of progress, just as pioneering IVF studies with mice in the 1960s laid the groundwork for the first revolution in fertility treatment two decades later. It may take that long to bring iPS cells to clinical practice, as the Japanese scientists warn. There are not only technical hurdles to cross, but potential hazards to negotiate, the known and the known unknown.

And yet, there is already some progress towards making sperm from human iPS cells. Once a male germ cell has reached the stage of halving its chromosome number (to haploid), it is potentially ready for fertilization, which can be accomplished by the sperm injection technique (ICSI) before it becomes a motile cell. It is easier to make a sperm than an egg possessing a complex and voluminous cytoplasm, so the problem of equity between the sexes even exists at the cellular level.

A sensational technology that can revolutionize reproductive care is bound to attract huge publicity and suffer from the temptation of a few to push it ahead of biological understanding. The rewards in science go to the first at the finish line. A few years after Dolly was born, the Raëlian cult claimed to have cloned a human baby called Eve which, of course, was never confirmed. No doubt we will hear more stories of reproductive technology gone feral that were first inspired by Huxley. Such stories create anxieties that can arrest progress, and without the resolute pioneers of IVF technology the fertility treatments we now take for granted would have been delayed. Perhaps there are more justifiable concerns about artificial gametes than I have mentioned. Perhaps they will open the door to germline therapy, which is widely feared. And perhaps Huxley was prescient in anticipating human cloning and growing babies in bottles by the “Bokanovsky process!” To put those alarming thoughts to rest and sleep peacefully at night, I put my faith in future generations to make good decisions that we have no need of making as yet.