Summer 1995

Anti-Androgens and Dwarfed 'Gator Gonads

   The male alligators of Florida's Lake Apopka have a small problem; they have unusually high levels of the female hormone estrogen, low levels of the male hormone testosterone, and, as a result, unusually puny penises. These unfortunate reptiles' malformations are attributed to a pesticide spill in the lake that occurred in 1980, an accident that Environmental Protection Agency toxicologist L. Earl Gray believes released anti-androgens.
   Anti-androgens are chemicals which disrupt the normal functioning of male hormones (androgens) such as testosterone. Gray and his colleagues believe a compound called p,p'-DDE is the anti-androgen afflicting the alligators. Although researchers previously linked p,p'-DDE to the feminized 'gators, no one knew how the chemical functioned. Gray's research resolved this mystery by showing p,p'-DDE binds to androgen receptors in rats and humans, blocking the effects of natural androgens and preventing androgens from activating the gene sequences they are supposed to activate.
   Scientists previously believed the spill released environmental estrogens, compounds which, though they are not hormones, behave like estrogen. Since no one has ever isolated any environmental estrogens in Lake Apopka, Gray's research challenges the conventional environmental estrogen hypothesis. All of the known "estrogenic" compounds that Gray and his associates have investigated also exhibit anti-androgen behavior, which leads Gray to suspect that studies linking the sexual effects of these compounds to purely estrogen-like activity might not be telling the whole story. Compounds thought to be environmental estrogens are responsible for feminized fish in British rivers and feminized birds in the Great Lakes, and some scientists fear these chemicals may also pose a threat to humans.
—D.L.

Holographic Storage Advance
   Holographic materials promise a whole new dimension in data storage. Conventional magnetic and magneto-optical storage devices are limited to storing data on two dimensional surfaces, while holographic devices have the potential to achieve much greater storage-densities and data transfer rates by encoding data in photosensitive materials as three-dimensional interference patterns.
   In a photorefractive holographic device, data is written using the combination of a modulated laser beam and a reference laser beam. The beams combine to produce an interference pattern on a photorefractive material, and charges inside the material redistribute themselves to mimic the interference pattern, thus changing the material's refractive index. The pattern can be read off using a weaker laser beam shone along the path of the reference beam. The problem previously encountered with this encoding scheme was that the read-out beam was destructive. Not only does this prevent one from reading the data out more than once, it also prevents the storage of overlapping holograms, a necessity for ultra-high storage densities.
   Researchers at IBM's Almaden Research center in California have apparently found a solution to this problem. They developed fullerine-doped polymer films which, through a process that is not fully understood, store data when the recording laser beam is above a certain threshold illumination value, and can repeatedly read out the data using a beam with an illumination below the threshold value. The new polymers also appear to be resistant to the thermally generated conductivity that limits the period of time you can store data in conventional polymers.
   Holographic storage systems are currently under development in Tamarack Storage Devices in Austin, Texas, and at Stanford University in a joint venture that includes IBM and several other companies.
—D. L.

Defying the Central Dogma
   Almost a decade ago, specific RNA sequences were discovered to act as enzymes, serving in various functions ranging from the splicing of non-coding regions of messenger RNA to the joining of amino acids into proteins. However, its sister molecule, DNA, continued to be seen as the docile sibling, acting only as a rigid ladder of information to be bound to by proteins.
   Now, a discovery at the Scripps Research Institute has shown that DNA may not be as placid as many believed, and may in fact catalyze reactions. To show this, Ronald Breaker and Gerald Joyce synthesized a huge number of random, fifty nucleotide sequences of single-stranded DNA, enough for every possible sequence to be represented. They attached each of these to a single nucleotide of RNA bound to a column in a solution containing lead ions to serve as a core for the DNA to wrap itself. Molecules were able to break this bond were then observed to leave the attachment of the column. Isolated and sequenced, more than a dozen sequences of DNA were found to adopt a stable structure with a RNA-DNA bond cleaving activity. The methods by which these reactions are catalyzed are still unknown, but it is clear that this discover, DNA is able to finally join proteins and RNA in the class of enzymatic biomolecules.
—N.D.

Have Fire Ants Met Their Match?
   The Solenopis invicta species fire ant, a major headache to the population of the southern United States, may soon be getting a headache of its own from flies of the family Phoridae. These fearsome flies lay their eggs inside the heads of their adult fire ant victims.
    Since their invasion sometime before World War II, fire ants have occupied more than 250 million acres of the southern United States, and they still continue to spread. These pests damage crops, create 12-18 inch tall nesting mounds which bend and break agricultural equipment, and cause much irritation in their human sting victims. Furthermore, since these ants compete against and feed on native species, they contribute to a decline in biodiversity. A 20-year chemical war against S. invicta failed to stop the ants' spread. In fact, since these ants are better at re-populating poisoned sites than native species are, the use of pesticides probably contributed to the ants' proliferation.
   Scientists know that fire ant densities are 10-15 times higher in the United States than in the Brazil, where the fire ants originally came from. No one knew what factor limited Brazil's fire ant population, though.
   Recent research by the University of Texas in conjunction with the Universidade Estadual de Campinas in Brazil, however, suggests that the parasitic phorid flies, by diminishing the fire ants' competitive dominance at food sites, may be responsible for keeping Brazil's fire ant population in check. The presence of a phorid fly causes a feeding fire ant to forget its food, assume a defensive posture, and flee. Other types of ants, types the phorids do not attack, then have free access to the food.
   The experiments, observing the response of seven fire ant colonies to phorid attacks, demonstrated that the abundance of fire ants at food baits was always smaller when the phorids were present than when they were absent. The researchers suggest that the phorids may be a good candidate for biologically controlling fire ant populations in the United States, though they concede more research is needed to assess the flies' affinity for North American ants.
—D.L.