ARMING mosquitoes with the venom of a scorpion sounds like a terrible idea.
But researchers in Mexico say malaria could be stopped in its tracks by
genetically engineered mosquitoes that produce a scorpion toxin in their
gut.
For years, scientists have dreamed of displacing wild mosquitoes with
genetically modified insects that cannot carry the malaria parasite
Plasmodium (快猫短视频, 5 August 1995, p 36). Two weeks ago,
researchers in Europe announced the first successful attempt at genetically
modifying the malaria-carrying Anopheles mosquito. Now, in experiments
on a different insect, Lourival Possani and his colleagues at the National
Autonomous University of Mexico in Cuernavaca have shown that a little scorpion
venom can block the malaria parasite鈥檚 development.
Possani, who studies compounds derived from scorpions, recently discovered
that the venom of Pandinus imperator (below) contains a peptide, which
he calls scorpine, that blocks the development of malaria parasites growing in
culture. To see whether scorpine has the same effect in living insects, he and
his colleagues created transgenic fruit flies that express the gene for the
peptide in their gut.
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The researchers then injected young Plasmodium parasites directly
into the abdomens of the transgenic flies and their wild counterparts, and
compared how many of these parasites matured. Over 40 per cent of the normal
flies had mature malaria parasites. But only 12 per cent of the flies that made
scorpine had parasites that continued to grow, Possani told researchers at a
recent meeting at the Howard Hughes Medical Institute in Chevy Chase, Maryland.
鈥淚 think it鈥檚 a very promising result,鈥� he says.
Possani did his experiments in fruit flies because at the time no one had
managed to genetically modify Anopheles mosquitoes. He knew, however,
that David Schneider of the Whitehead Institute for Biomedical Research in
Cambridge, Massachusetts, had shown that Plasmodium parasites injected
into the guts of fruit flies develop in much the same way as they do in
mosquitoes. Details of Schneider鈥檚 technique were published in Science
last week (vol 288, p 2376).
鈥淚t鈥檚 wonderful to know that someone else can do it,鈥� Schneider says. 鈥淢y
guess is that the way we should do things is to model them in the fly first and
then hop into the mosquito.鈥�
While other types of mosquitoes have been genetically altered before, it鈥檚
only now that Fotis Kafatos of the European Molecular Biology Laboratory in
Heidelberg and his colleagues have succeeded in modifying the malaria-carrying
Anopeles (Nature, vol 405, p 959). In addition to introducing
the scorpine gene, researchers would like to try a whole slew of other
modifications to the mosquito.
Because Plasmodium affects mosquitoes鈥� lifespan and ability to
reproduce, researchers suspect that altered mosquitoes would outcompete the wild
ones. But many questions remain. 鈥淥nce you make this thing, how do you drive it
into the environment?鈥� wonders Schneider. 鈥淚鈥檓 not sure we understand the
ecology of it enough.鈥�