The Importance of Tau Protein

• How many genes in a human cell? The three main gene-sequencing projects that analyzed human DNA do not agree. One study (RefSeq) reported 22,333 genes, another government database said there are 38,621, and a project called Gencode recognized 21,671 genes. Scientists are sifting through human DNA to identify previously unrecognized genes, and over time more are likely to be added to the present gene library. In the meantime, with 31,760 genes, tomatoes appear to have more genes than we do. The poplar tree, for that matter, has 45,000 genes, which challenges interpretation by the reader. (Science News, Oct. 20, 2010, and Nov. 6, 2010)

• A continuing mystery: a number of years ago, molecular geneticists discovered that most of the DNA in a cell is not made up of active genes and appears not to code for anything specific. This DNA is referred to as “junk” or “nonsense” DNA, but now these stretches of nucleic acid are called “introns” (meaning between the active genes). Introns obviously serve as long spacers between genes, but beyond this their function is uncertain. (ncbi.nlm.nih.gov /pubmed/22518112; other sources)

• The water flea, Daphnia pulex, a tiny freshwater crustacean, appears to have more genes than other animals. Its genome was recently sequenced and found to have 31,000 genes. Many of these are also found in humans. (Science, Feb. 4, 2011; newsinfo.iu.edu – Feb. 3, 2011)

• To understand the importance of a new drug that may be effective in treating Alzheimer’s Disease (AD), it is necessary to understand something about the inside of a neuron (nerve cell). A neuron has a long extension called an axon, along which signals are carried. Inside an axon there is a system of very small tubules that run its length. These structures are called microtubules, and they serve as railroad tracks along which material is transported back and forth, from one end of the axon to the other. In this way, the axon and its terminations are maintained. When microtubules fail to carry molecules back and forth, the neuron dies. In order for microtubules to remain intact and do their job, an important molecule called tau protein stabilizes them and allows them to grow normally.

In Alzheimer’s Disease, something happens to tau protein and it no longer attaches to and stabilizes microtubules, and they fall apart. At the same time, the tau forms tangled masses that accumulate inside the dying axon. Some neuroscientists theorize that if tau protein functioned normally in stabilizing microtubules, changes associated with AD would not occur in the brain.

Recently, it was discovered that a drug called epithilone D prevents tau protein from malfunctioning, and microtubules continue to do their job. In mice genetically modified to develop AD, the drug prevents formation of tau tangles and slows the progression of the disease. Treated mice also show improved brain function based on standard “thinking” tests for mice. Human patients with mild AD are now being enrolled in a phase I clinical trial. (uphs.upenn.edu/news; J. Neuroscience, 2010, vol. 30)