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Complete tadpole eyeballs grown in lab.
14:30 25 April 2002
Two
Japanese researchers have revealed the first details of their claim to
have grown tadpole eyeballs from scratch in the lab. They say the eyes
are functional when they are transplanted into
tadpoles, and even work
when the tadpoles metamorphose into frogs.
"None
of the eyes were rejected and none dropped out," said Makoto Asashima,
of the University of Tokyo. "All of the frogs can see."
Asashima
and colleague Ayako Sedohara say it is the first successful
transplantation of an eyeball grown in a test tube into a living
animal. They spoke of their achievement on Thursday at the XXIXth
International Congress of Ophthalmology in Sydney, Australia.
The
experimental results have not yet been published, making it
difficult for experts to judge their authenticity. But, says embryologist Patrick
Tam of the Children''s Medical Research Institute in Sydney, growing a
complete tadpole eyeball in a flask, rather than a simple cluster of
photosensitive cells, would be a "technical feat".
According
to Asashima, the cultured tadpole eyeballs have all the necessary
components, including a cornea, retina, lens, and optic nerve, before
they are transplanted.
Seeing the light
Asashima
and Sedohara grew their tadpole eyes from stem-cell-like cells taken
from a part of the early tadpole embryo called the animal cap. They
treated the cells for three days with different concentrations of
chemicals such as retinoic acid and activin that stimulate cells to
grow and to specialise into different types.
Once
the researchers had grown the eyes, they transplanted them into 60
tadpoles. Microscopic examinations conducted a week later revealed that
nerves from the eyes had connected to the tadpole brains.
The
scientists also say that the lab-grown tadpole eyes exhibited the same
electrical activity as normal eyes, and that they responded to light. A
proportion of tadpoles usually die during metamorphosis and in the
Japanese experiment 20 of the tadpoles with implanted eyes made it
through.
Jumbled image
However,
eye experts warn that using similar tissue engineering techniques to
treat human blindness is decades away. Human eyes are larger and more
complicated than the tadpole''s, making them far more difficult to grow
in a flask.
What
is more, previous attempts to transplant donated human eyes have always
ended in failure, because surgeons have found it impossible to connect
up the nerve and blood supplies.
Even
if surgeons overcame those problems, success would not be guaranteed.
"It would be very difficult to get the nerve fibres to grow the right
way, so that when you looked at something you got a meaningful image
rather than a jumble," warns Frank Martin, head of ophthalmology at The
Children''s Hospital in SydneyAsashima also claims to have successfully grown kidneys, hearts and other frog organs in lab flasks.