Life lines 17

BONES, FAT, AGING, AND VIBRATION

Dr. Clinton Rubin is the Chair of the Biomedical Engineering Department at Stony Brook University. His research is on the relation of stem cells to the formation of fat cells and bone cells and how these two types of cells respond to mechanical stimulation. For most people mechanical stimulation means exercise. And for most people exercise, unless they like it, means running, bending, squatting, pushing, or engaging in games that require such effort. For those who live a sedentary life and exercise is at best walking from a parking lot to a store, a consequence of the lack of mechanical stimulation is an increase in the size and number of fat cells and a decrease in the number and size of bone cells. That means as we age we get fatter and as we age we get more brittle bones that break when we fall. In fact, Rubin claims after age 35 we lose about 2 percent of our bone cells per decade (in my case an 8 percent loss of bone cells). About 35 percent of adults in the United States are obese. I guess I would belong to that category because when my wife looks at my buttoned shirt as I sit, she calls me Wimpy, Popeye’s friend (for those whose memories go back to Smilin’ Jack, think, too, of his sidekick, Fat Stuff).

A few years ago, a thought occurred to Dr. Rubin. If both fat cells and bone cells have a common cell origin from mesenchymal stem cells, would there be a similar response in these two cells to mechanical stimulation? Instead of exercise he tried something different. He used a very mild vibration (the sort of pleasant thrumming in a vibrator chair) and found that it isn’t how hard you exercise but how much total vibration you get that gives you a maximum effect of mechanical stimulation. This is a couch potato’s dream – press the vibrator, munch the chips, and watch football or other diversions and slim down. Before you fellow fatties get too carried away, Rubin suggests some common sense. It isn’t so much what you eat; it is how much you eat that counts for making the fat that goes into your fat cells. Few people stop at one pretzel or one fistful of potato chips. Few people push away the plate after a sliver of pie. Few people allow one glass of beer as the day’s limit.

The surprise to Dr. Rubin was the beneficial effect vibration had on bone. In mice he studied, it prevented loss of bone cells and that means it could reduce the risk of osteoporosis. The story, as usual in science, is more complex than our desire to make it simple. In a high fat (or high calorie) diet, mice suppress mesenchymal stem cell formation. This not only leads to obesity and bone loss, it also diminishes the immune system and it diminishes muscle cells. While “buzz your bones,” as Rubin calls it, in moderation is a good idea, excess buzzing is damaging. In moderation Rubin finds his buzzed mice (90 cycles per second) cannot feel the buzz but their fat diminished 25-30 percent compared to non-buzzed mice. Dr. Rubin’s work is on going and he intends to use human volunteers to test out his buzzing therapy as an approach to regulating fat, bone and muscle growth. Lots of problems remain. A tennis player’s racket arm has 30 percent more muscle than his or her throwing arm. This implies that vibration in one part of the body may not do the job for the rest of the body.

Life Lines 16

BDELLOID ROTIFERS: SIXTY MILLION YEARS WITHOUT SEX

Most living things reproduce by sex. It may not be the coupled intimacy we relate to when we read romance novels, because we do not usually imagine sex in bacteria, fungi or similar microscopic organisms. But sex is the rule and two strains of a species of bacteria can couple and swap genes or two fungal cells can fuse and form a new cell. What is rare among living plants and animals are species that have no known sexual activity

How does one show that sexual activity is absent in a species? It’s easy if there is one sex that lays eggs and no males are known to exist. We describe such species as reproducing by parthenogenesis (virgin birth). Even in such species there may be special occasions when males are produced and sex takes place or where a species is self-fertilizing.

There is one group of animals that have never given birth to males and show no evidence of self-fertilizing. They are called Bdelloid rotifers. They are multicellular microscopic animals. What makes them unusual is that they lost their sexuality about 60 million years ago. They were at the time unusual in having four of each chromosome instead of two. We and most animals and plants have only two of each chromosome represented in our body cells.

Matthew Meselson, whose laboratory studies rotifers at Harvard, told me that the story is by no means complete and he and his students are still following many leads to work out the past history of these sexless creatures. One unusual feature is that they gave up a process called meiosis which reduces the chromosome number in half for the production of eggs or sperm (in our own eggs or sperm there are 23 chromosomes instead of the 46 found in our body cells). Another lead they are following is their use of chunks of DNA from the food they eat which become incorporated in some of their cells.

The absence of meiosis means the eggs produced in rotifers have the same chromosome number as their body cells. Their chromosomes do not pair while eggs are formed and while some of their genes show 4 copies, considerable numbers of other genes have 1, 2, or 3 copies. Whatever the number present, no genes have identical sequences unlike our own genes where, with few exceptions, there are two of each kind of gene having identical sequences. This demonstrates that since the dinosaurs died out the rotifers have slowly been battered by newly arising gene mutations and what were once four sets of chromosomes is becoming one single set with approximately four times the DNA of its original set of genes in its sexual past.

Rotifers compensate for sex by their immense numbers. They are found on every continent and they are carried on the feet of birds and tag along in the scales of fish. They remind me of patchwork quilts, reshaping their genes as a quilter deftly converts pieces of old dresses into a repetitive design, both pleasing and functional.

Life Lines 15

AGING IS A MATTER OF HOW MANY MITOCHONDRIA YOU HAVE LEFT

Way back in high school you learned that the mitochondrion was “the powerhouse of the cell.” If you took a college biology course as an undergraduate you probably learned that the mitochondria in your cells are bacteria-like in size and have their own DNA and that their major function was to take small carbon-bearing molecules from your digested foods and burn them with the oxygen you breathe to produce chemically stored molecules, chiefly ATP. The mitochondria power the metabolic activities of the cell, tearing molecules apart and synthesizing more complex molecules from simpler ones. Each of your cells has about 1000 mitochondria and each mitochondrion has several dozen copies of its small circular DNA. There are about 60 genes in a mitochondrial chromosome. Most of those genes are involved in production of chemical energy and thus the “powerhouse” reputation that you may remember. If you multiply the number of your cells by the number of mitochondria per cell you get a staggering 100 quadrillion of them in your body (that’s a one followed by 17 zeroes). When they act collectively making ATP they produce heat. The warmth of your body reflects the activity of your mitochondria. That’s why you get hotter in the summer when you exercise and why you shiver and jump around in the cold to warm your body.

Unlike the genes in the nuclei of your cells that produce 99.99 percent of your body, the mitochondrial genes only function is this one essential function of producing the bulk of the energy you need to stay alive. They do so at a price. They lack repair enzymes so mutations accumulate faster in mitochondria than in your nuclear chromosomes. When you are young this is less of a problem because your cells are still dividing but when you are an adult most of your cells slow down and rarely divide. So the mutations accumulate and your cells do not replace worn out mitochondria. The business of making energy by burning small carbon-bearing molecules with oxygen also produces a lot of chemicals that damage DNA. Your mitochondria make hydrogen peroxide. Have you ever seen it bubble when you daub it on a sore? These reactive oxygens readily damage DNA. So here’s the problem. You begin to lose mitochondria as your cells age. That means less energy per cell. When the energy is too low the cell dies. So if I look at the 76 year old skin on the back of my hands I see wrinkles, as you do if you are also old like me, but because I am a biologist, I also see in my mind’s eye, the cells that have winked out on me like so many dead light bulbs over the years and those cells have not been replaced (because I am no longer a child or teenager). The dead cells in the lower layers of my skin reduce the mass of my hands and the covering skin wrinkles as it collapses into those numerous cavities. So now you know why you wrinkle when you get old. Dead mitochondria lead to dead cells that lead to wrinkles. But, alas, there is more. Because we get old eventually, our mitochondria are fewer in number per cell and thus we produce less heat for our body. So now you know why your grandparents need a warmer temperature in their apartments or homes and why they heap blankets on themselves or wear clothes around the house that younger people would take off or feel stifled. I think of my interview with Sir Julian Huxley in his home in London, and he sat with gloves on (the fingers cut off) and a shawl around his shoulders and a small blanket over his lap. His mitochondria were fading in his memory too and his wife had to keep correcting him. Those who long for extending their lives have a tough job when they begin to shift their attention from our nuclear genes and chromosomal telomeres and start looking at our disappearing

Life Lines 14

AFTER ONE MILLION YEARS BLIND CAVE FISH REGAIN THEIR EYES AND SIGHT.

An experiment by a NYU biologist, Richard Borowsky, confirmed a prediction made by evolutionary biologists on the origin of these cave dwellers in Mexico. There are 29 independent locations or unconnected caves where these fish reside, most of them assigned to the species Astynax mexicanus. They are usually albinos and they lack eyes (or at most show a small pinhead where the eye should be). A century ago Fernandus Payne studied fruit flies raised in the dark for 69 generations to see if disuse would lead to loss of eye color or loss of vision. He found that the flies had perfectly normal vision and the identical red eye color of those who were raised under ordinary day and night conditions. Geneticists speculated that random mutations leading to loss of pigment in the skin and loss of eyes in the cave environment were actually beneficial because these conserved energy and reduced infections. In the 1980s other geneticists identified some of the mutant genes involved with loss of the eyes and skin pigment.

Borowsky came up with an interesting idea. If the mutations are independent, those farther away from each other are less likely to have had a common mutant origin, which got dispersed by floods into nearby caves. By crossing these 29 varieties, he confirmed that those farthest away were the ones that produced the restored vision they had lost sometime over the past one million years when they became trapped in caves. Why should that be?

About the same time Payne was working in 1906-1908 on fruit flies, George Shull at Cold Spring Harbor was crossing different strains of inbred corn to one another. He found that the hybrid offspring were larger, had more grains, and did much better in the soil. He had discovered hybrid vigor which revolutionized American agriculture. The same principle is at work in the blind cavefish. If the blindness is due to inbred mutations in cave 1 a different inbred strain with a different mutation may lead to blindness in cave 25. When the two are crossed to one another their offspring show hybrid vigor and their normal functions are stored. An organ like an eye is put together by many genes, but anyone of them, if its father’s and mother’s genes are both mutant for that particular gene, may cause blindness or loss of the eye. What is remarkable is the difference in time. It took less than 10,000 years to make corn from teosinte by farmers selecting for the best plants and using their seeds for the next season. It took nature almost one million years for mutants arising hundreds of thousands of years ago to have a biologist breed them together and restore their sight. Borowsky devised a flashing light pattern that shows eye movement when the flash is on for a sighted fish but a blind fish will not respond to the flash. The results of Borowsky’s work show that unless gene functions are sifted by a natural environment (like the hazards encountered in day and night daily rhythms), the genes for blindness will accumulate in the cave. In the cave, no such advantage exists for eyes whether they function or not and they will disappear (especially if eyed flies require more food or are more likely to get scratched and infected). In some of the cave areas the original species from which the blind cave fish arose no longer exists. By crossing these varieties, the lost ancestor species can be approximated if not restored.

Life Lines 13

A VIRAL HYPOTHESIS OF LIFE BECOMES A THEORY

In 1926 geneticist H. J. Muller proposed “ the gene as the basis of life “ by which he meant that all other parts of a cell or organism are products of these genes. About five years earlier he proposed that scientists should study viruses by chemical and physical means because, at that time, one could not distinguish genes from viruses. Bacterial viruses were first discovered in 1919 and several diseases in humans like polio, yellow fever, flu, mumps, measles, and the common cold turned out to be caused by viruses. It took another 25 years for viruses to be studied as organisms and having a life cycle. Viruses are too small to be seen with optical microscopes. They are studied for their structure by using electron microscopes, which didn’t exit until the late 1930s. Experiments with viruses in the 1950s helped establish the field of molecular biology, demonstrating DNA as the genetic material.

When I was a student of Muller’s in the 1950s, I imagined an origin of life that included the formation of nucleotides by natural processes and the formation of nucleic acid strands that replicated themselves and their occasional errors (mutations). I imagined a viral origin of cells and that many of our own genes had an ancestry going back to these viral-like first forms of life.

It is exciting to know that this hypothesis is turning into a well-supported theory. Consider these discoveries about viruses, mostly published in the last twenty years. Viruses are more numerous in number and kind than all other forms of life. One of my colleagues, Martha Baylor, years ago at Stony Brook, used to go to the south shore beaches and hold up Petri dishes with agar on them. She harvested hundreds of new viruses that were blown in by the ocean winds. About 100 million varieties of viruses are estimated to exist, most of them in the oceans that occupy most of earth’s surface. About 1000 viruses have had their sequences worked out; most are small with ten or fewer genes. A few are large with several hundred genes. By contrast bacteria have about 1000 genes and animals like us have about 25,000 genes. Not all viruses are parasites that destroy the cells they infect. Some attach their viral chromosome to one of the host chromosomes and in some cases the spliced inserted viral chromosome contributes to the benefit of the cell it infects. About eight percent of our human DNA is composed of known viral DNA sequences and an additional forty percent of human DNA suggests it had a viral past. Some bacteria require inserted viruses to produce their toxins, including diphtheria, cholera, and bubonic plague. One such inserted virus sequence in human chromosomes produces an essential protein for placenta formation.

The idea that all of life might have a viral origin is thrilling enough, but equally exciting is the view that viruses continue to play in the evolution of life by carrying genes from one form of life into another. At a level we cannot see, these viruses move in and out of plants, animals, and bacteria and make all of life an integrated community at the molecular level.

Life Lines 12

A ROSE IS A ROSE IS A PRODUCT OF FIVE GENES NECESSARY FOR FLOWER DEVELOPMENT

Few things irritate those in the humanities more than the efforts of science to reduce the metaphorical, complex, and beloved through the reductionism of experimental analysis. The image of scientists plucking sepals, petals, stamens, carpels, and ovules from a flower is debasing to the aesthetic sense of a rose. One thinks of Charles Dickens’ horror in Hard Times, when a student defines a horse as a “gramniferous quadruped” to the teacher’s (appropriately named Gradgrind) delighted but sterile soul. But such studies lead to medical cures, commercial applications in horticulture, new varieties to delight the eye, new scents to bring ecstatic responses, and many an amorous kiss when flowers are delivered from one lover to another. For scientists it is the understanding that trumps all of these otherwise desirable uses of new knowledge. Why new knowledge is so threatening is difficult to understand because every scientist I know who has made a discovery will describe the thrill as akin to writing a novel, composing a poem, working out a dance routine, composing music, or painting a landscape. Think of the pleasure it must be to wrestle one more unknown from nature.

In the 1970s two laboratories independently isolated three (now there are five) genes associated with floral development. They gave them the generic letters A, B, and C (now D and E have been added) and they called their theory the ABC theory of floral development. That’s easier to remember than to call it the Coen-Meyerowitz theory. If you look at a flower and (shudder) strip it of its components, the outermost will be the sepals, which are usually leaf-like. Then come the gorgeous colored petals. Next come the male organs or stamens; then innermost is the female organ or carpel with its inner treasure, the ovules. All have gene E. Sepals add an A. Petals have A and B as well as the E. Stamens dump the A and replace its function by turning on gene C. The carpel turns off the B and that leaves C and E. The ovules add the D function and that makes them CDE. Scientists can mutate any of these five genes and make abnormal flowers lacking one or more of these structures or putting the wrong component in the ring of structures we call a flower. It’s possible to convert hermaphroditic plants into two sex plants, one bearing stamens and the other bearing the carpels.

Molecular botany is having a great time identifying genes for flower scent formation, flower color, and making plants to order for different climates. The horticulture business generates 50 billion dollars a year so they are quite happy to hire molecular biologists to develop new varieties. They are also identifying and synthesizing the thousands of plant scents and floral pigments. There are genes for petal number, petal shape, and petal texture. For many of these botanists, it is like selecting fabrics to make quilts or dresses. It is like an artist’s palate of colors squeezed from tubes. We love seeing the gorgeous carmine used to paint a rose, but we would be aghast when told that is produced by scraping off thousands of scale insects from a cactus and crushing them to a powder to make the carmine dye. Sometimes we prefer not be in the kitchen to see how gourmet food is made. We prefer the mouth-watering fantasy of a gorgeous cut of T-bone steak and not the sight of a gutted carcass from which it comes.

Life Lines 11

A PUBLIC APOLOGY FOR A PUBLIC MISDEED

On April 13, 2007 I was in Indianapolis for an unusual event. The State of Indiana was making an apology for an event that occurred one hundred years earlier. That event was the passage into law of the first compulsory sterilization law in the world. Actually

At the ceremony was a historical marker that was unveiled by a woman who was sterilized by that act. She said she was 15 when she was sterilized against her will and she was deceived and told she was having an appendectomy. When she later married and attempted to have children she learned the truth about her surgery. When she confronted the physician who did the surgery, he lied also, and denied she was sterilized. I thought about this situation. If you were not middle class and pretty helpless and ignorant, you could have been deceived and harmed by people who believed that they were wiser than you and could manipulate your body as they wished with the power of the state behind them. Would those who are still sympathetic to sterilizing “unfit” people be willing to sterilize the physician for lying to the patient and blame his lying habit on his genes?

I was attending the ceremony and symposium because I have written articles and books on the history of genetics and eugenics. Most people are unaware that some thirty states passed such laws in the first third of the twentieth century (including New York) and some 40,000 people (mostly white, the eugenics movement was motivated more by class than race) were sterilized against their will. Most of the sterilizations were carried out in California, where the support for sterilizations was strong among health groups and the middle class. The Supreme Court in 1927 even upheld the right of states to pass such laws by an 8-1 vote. They used Virginia’s law as consistent with the Bill of Rights and justified the sterilizations by citing the Constitutional right of the state to draft its youth during wartime against the will of the drafted. Fortunately most state courts have found their sterilization laws unconstitutional for their own state constitutions or the states have repealed them long ago. I have not read any news accounts of such sterilizations since the mid 1990s. Few of us appreciate the role of the Civil Rights movement in the 1960s in giving all of us autonomy of decision-making and freedom from state discrimination that did not exist for humanity before then. The history of eugenic laws around the world teaches us that they are more often used to harm the innocent than to benefit the health of humanity as a whole. That was certainly true for the Nazi Nuremberg laws and for the American eugenics movement of the first half of the twentieth century.