| Irreducibly complex my eye |
[Sep. 26th, 2005|08:36 am] |
Turns out that the
lens of our eye is
just a baby step from the invertebrate version:
Fish, frogs, birds and mammals all experience
image-forming vision, thanks to the fact that their eyes all
express crystallins and form a lens; however, the vertebrates'
nearest invertebrate relatives, such as sea squirts, have only
simple eyes that detect light but are incapable of forming an
image. This has lead to the view that the lens evolved within the
vertebrates early in vertebrate evolution, and it raises a
long-standing question in evolutionary biology: How could a
complex organ with such special physical properties have evolved?
In their new work, Shimeld and colleagues approached this
question by examining the evolutionary origin of one crystallin
protein family, known as the ß-crystallins. Focusing on sea
squirts, invertebrate cousins of the vertebrate lineage, the
researchers found that these creatures possess a single crystallin
gene, which is expressed in its primitive light-sensing system.
The identification of the sea squirt's crystallin strongly
suggests that it is the single gene from which the vertebrate
ß-crystallins evolved.
The researchers also found that,
remarkably, expression of the sea squirt crystallin gene is
controlled by genetic elements that also respond to the factors
that control lens development in vertebrates: The researchers
showed that when regulatory regions of the sea squirt gene are
transferred to frog embryos, these regulatory elements drive gene
expression in the tadpoles' own visual system, including the
lens. Sweet. |
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