Nature Biotechnology pp 1129 - 1133 and pp 1117 - 1118

Two independent teams of researchers have taken a crucial step toward using human embryonic stem cells to treat nervous system disorders such as Huntington's disease or spinal cord injury. They have succeeded in coaxing human embryonic stem cells to differentiate into brain cell precursors that, when transplanted into mice brains, differentiate further into neurons and other types of brain cells.

Although all cells in the body contain the same set of genes, most cells are "differentiated"—that is, specialized for a particular function. For instance, a cell in the lens of the eye uses a different subset of genes than a bone cell or a brain cell. But a few cells, so-called stem cells, can differentiate into virtually any kind of cell, under the right conditions. However, the specific conditions needed to make a stem cell differentiate into a particular kind of cell are poorly understood.

Now, two papers published in December's Nature Biotechnology describe two slightly different approaches for inducing human embryonic stem cells to differentiate into precursors of brain cells. In both approaches, cells are grown on special surfaces and exposed to different types of signaling molecules, known as growth factors. After the stem cells had changed into brain cell precursors, the researchers transplanted them into the brains of newborn mice and showed that they further differentiated into various kinds of brain cells seen in normal brains. The ability to specifically control the development of embryonic stem cells into brain cells is an important step forward; however, further studies are needed to determine whether these brain cells are functional.

Nature Biotechnology pp 1168 - 1172 and pp 1120 - 1121

Combining tobacco and explosives might not seem like a good idea. But a research group in the UK has created tobacco plants that produce a bacterial enzyme (nitroreductase, or NR) that degrades the explosive trinitrotoluene--better known as TNT. Such plants might one day be used to decontaminate tracts of lands around munitions factories contaminated with the explosive.

Over the past century, widespread environmental contamination by explosives residues has caused increasing concern because of their extreme toxicity to both plant and animal life—with TNT one of the worst offenders. However, Neil Bruce and his team have built on the naturally evolved potential of many plants to tolerate low concentrations of deadly organic pollutants like TNT by degrading them into harmless organic molecules. They have transformed tobacco plants with a bacterial gene, nfsI, that encodes a TNT-degrading enzyme NR. When seeds from the engineered tobacco plants were placed in liquid medium containing concentrations of TNT toxic to normal plants, they germinated and grew, removing all of the TNT from solution.

Bruce hopes next to engineer trees that produce enzymes capable of degrading or sequestering all the major classes of explosives, noting that trees, as perennials, "are well suited for sustained remediation of heavily contaminated sites."

Nature Biotechnology pp 1141 - 1147

Stem cells have great therapeutic potential to replace diseased cells, because stem cells can now be isolated and differentiated into many different cell types. Tracking transplanted cells in vivo may provide information for the optimization of stem-cell therapies. To monitor their fate after transplantation, Jeff Bulte and colleagues have designed tiny magnetic tags that can be used for tracking labeled cells' movement in the body using a medical technique called magnetic resonance imaging (MRI).

MRI is a noninvasive technique that uses a strong magnet and radiofrequency waves to produce "images" of tissues or structures deep inside the body. For stem cells to be visualized and tracked by MRI, they need to be tagged magnetically so that they stand out from other tissues. Bulte and colleagues have developed a new class of highly magnetic probes called magnetodendrimers or MD-100. These were developed by enveloping magnetic iron particles within established polymers, termed dendrimers, that can ferry drugs and DNA into a wide variety of cell types. As a result, labeling can be achieved simply by adding MD-100 to cells in the culture dish—an advantage over other approaches that require tags to be attached to proteins or peptides that then interact with cell-surface receptors in order to enter cells.

The researchers showed that human neural stem cells labeled with MD-100 were viable and able to differentiate normally into neurons, which retained the tags. Labeled cells transplanted into rat brain could be tracked using MRI for at least six weeks after transplantation. This technique could be used to trace a variety of other cells, such as those from a tumor, to evaluate cell migration events.