My Mother's Cells Within Me

Nearly all of us harbor cells that come from a close relative. The phenomenon, called microchimerism, occurs because the placenta is not a perfect barrier to formed cells - sometimes maternal cells make their way into the fetus, and vice versa. Apparently some of these cells live indefinitely in their new host, which is surprising since foreign cells are usually attacked and killed.

Scientists are still working out what the foreign cells may be doing in their host. In some cases they may differentiate into fully functional tissue cells in the host. For example, genetically female heart cells (presumably from the mother) have been found in males. In other cases these foreign cells may trigger immune disorders later in life, when the immune system of the host finally recognizes and attacks the foreign cells. Diseases that may have a microchimerism link include several autoimmune inflammatory diseases of connective tissue (scleroderma, lupus erythematosus, and rheumatoid arthritis), and perhaps even Type 1 diabetes, a disease characterized by poor regulation of blood sugar.

Reference: Nelson, J.Lee. Your Cells are My Cells. Scientific American Feb. 2008, pp. 72-79.

The Dangers of Antibacterial Soaps

If you're discussing antibiotic resistance of bacteria (p. 18 of Human Biology 5th ed.) or the benefits/risks of breast milk (p. 206) and are looking for an easy-to-read article for your students, take a look at "Fact or Fiction: Do Antibacterial Soaps Do More Harm than Good?" in the February issue of Scientific American (p. 96).

The brief one-page article concludes that for normal healthy people, antibacterial soaps have no apparent health advantage over frequent hand-washing with ordinary soap and water. On the risk side of the risk/benefit continuum, antibacterial additives such as triclosan are showing up in rivers and streams, in agricultural soil, and even in human breast milk. The article certainly would give students something to think about and discuss.

Creating Synthetic Life

Scientists at the J. Craig Venter Institute in Rockville, Md. have succeeded in synthesizing the entire genome of the bacterium Mycoplasma genitalium, using only the four nucleotides of which all DNA is comprised. It’s an astonishing feat, considering that the M. genitalium genome is nearly 600,000 base pairs long. The next step, say the researchers, is to insert the synthetic DNA into a cell. If all goes well, the DNA will replicate itself and the cell will divide, becoming the first living, self-reproducing organism ever created synthetically in a laboratory.

The synthesis of the entire genome of an organism paves the way for experiments to determine the minimum number of genes required for life – the minimum operating system, so to speak. Looking further to the future, someday it may even be possible to create synthetic organisms for specific purposes, such as manufacturing medicines or cleaning up the environment. We’d better start thinking about how we want to regulate or control this new technology.

A Beating Heart is Created in the Laboratory

University of Minnesota researchers have succeeded in producing a beating rat heart in the laboratory. In their experiments, the researchers first removed all the heart cells from a dead rat heart by dissolving them away with a strong detergent, leaving just a scaffold of connective tissue and heart valves. Then they infused cells harvested from the heart of a newborn rat. Within two weeks a new beating heart developed.

The research marks a significant advance in our understanding of what it would take to grow human hearts. However, scientists caution that the ability to produce human hearts for implantation still may be decades away. First, it will have to be shown that the technique can be adapted to larger animals. And second, methods will have to be developed to create the hearts from stem cells rather than cells from a newborn. Obviously, no one would sacrifice a human newborn just to produce a new heart for an adult!

Nevertheless, this is an encouraging first step.

AIDS proteins

The AIDS virus can only make about 15 proteins on its own. In order to reproduce, it must rely on its ability to force its human host cell to make all of the other proteins it needs.  And with the use of a new genetic screen, researchers at Harvard University have identified at least 273 of these human proteins.  Knowing precisely which human proteins the virus needs may lead to techniques for growing the virus in the laboratory for research purposes, or ways to block one or more of these key proteins in humans without disrupting the human body very much.

Instructors who are especially interested in how viruses reproduce may wish to read the full research article (Science online January 10; "Identification of Host Proteins Required for HIV Infection Through a Functional Genomic Screen") and comment on its findings in class.   The article itself is too difficult for entry-level students. 

Thimerosal and Autism

The results of a study by researchers at the Department of Public Health in California do not support the hypothesis that autism is caused by thimerosal, a preservative containing ethylmercury that was once used in childhood vaccines. The researchers found that the incidence of autism rose steadily in California from 1995 to 2007, even though thimerosal was removed from most childhood vaccines in 2001. If thimerosal were responsible for causing autism there should have been a sharp decline in new cases of autism after 2004. The new findings and a commentary about them are published in The Archives of General Psychiatry.

It is doubtful that the study will do much to reassure parents, however, some of whom continue to believe passionately that their child's autism was a direct consequence of childhood vaccinations despite research findings to the contrary.

The Limits of Science

The free online version of the New York Times has a recent article that could be used to start a discussion in your Human Biology classroom about the limits of science. (“Both Sides Cite Science to Address Altered Corn”, Dec. 26, 2007, nytimes.com). In this case, Europeans are arguing over whether or not to ban the planting of a pest-resistant strain of genetically modified (GM) corn.

Interestingly, both sides are trying to justify their position on the basis of science. Those opposing the planting of the GM corn argue that one can never be absolutely certain that the new corn is completely safe. They are right, of course; science cannot absolutely prove GM corn’s safety under all known (and as yet unknown!) conditions. On the other hand, those in favor of planting the GM corn argue that according to the currently available scientific evidence, GM corn is “unlikely” to pose a significant risk. They are right, too.

Ultimately, the decision of whether or not to ban GM corn will be a public policy decision based not only on the available scientific data, but also on political, economic, and social pressures. Nevertheless, science certainly does have an important role in issues such as this. Points of concern raised during public debate can perhaps be tested by science, improving our confidence in public policy decisions both now and in the future.