MED/BIO: Transgenic anti-malarial mosquitos

Date: Sat Jul 15 2000 - 15:08:44 MDT

Monday July 10, 7:40 PM

Pincer movement
By Nell Boyce

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 engineering mosquitoes to 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 (New Scientist, Two weeks ago,
researchers in Europe announced the first successful attempt to genetically
modify 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 scorpion venom
can block the malaria parasite's development.

Possani, who studies toxins derived from scorpions, recently discovered that
the venom of Pandinus imperator 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.

The researchers then injected young Plasmodium parasites directly into the
abdomens of the transgenic flies and their normal counterparts, and compared
how many of the parasites matured. More than 40 per cent of the normal flies
harboured 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. "I think it's a very promising result," 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's technique were published in Science last
week (vol 288, p 2376).

"It's wonderful to know that someone else can do it," Schneider says. "My
guess is that the way we should do things is to model them in the fruit fly
first and then hop into the mosquito."

While other types of mosquitoes have been genetically altered before, it's
only now that Fotis Kafatos of the European Molecular Biology Laboratory in
Heidelberg and his colleagues have succeeded in modifying the
malaria-carrying Anopheles (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 adversely affects mosquitoes' lifespan and ability to
reproduce, the researchers suspect that altered mosquitoes would outcompete
the wild ones. But many questions remain. "Once you make this thing, how do
you drive it into the environment?" wonders Schneider. "I'm not sure we
understand the ecology of it enough."

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