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Genome
Biology
Volume 1

Issue
4

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Liu
K

Paper report

Fish
eye development

The importance of the lens in eye development has been
demonstrated using reciprocal transplantations between an eyed
surface-dwelling fish and an eyeless cave fish of the same species.

Central role for the lens in cave fish
eye degeneration.
Y Yamamoto and WR
Jeffrey Science 2000,
289:631-633 [Read the abstract on
PubMed]

Subject areas: Development,
Evolution, Model organisms

Reported by: Karen Liu

The electronic version of this article is the complete one and
can be found online at: http://genomebiology.com/2000/1/4/reports/0070

Report date

13 September 2000

Published

25 October 2000

Genome Biology 2000,
1:reports0070

© 2000
BioMed Central Ltd

Outline

Significance and context

Abstract

Significance
and context

Key
results

Links

Reporter's
comments

Table
of links

In Mexico, there are over 30 varieties of the fish
Astyanax mexicanus. Some populations of these fish live in surface
waters while others live in unlit caves. The cave-dwelling varieties are
eyeless, providing a unique opportunity to study the evolution of a
developmental process in a single species, rather than in distantly
related species. Using an eyed surface-dweller and an eyeless
cave-dweller, Yamamoto and Jeffrey are able to show that an inductive
signal from the lens influences eye formation.

In the surface-dwelling fish, eyes form by a process quite
similar to that in other vertebrates. First, the optic vesicle buds out
from the brain and contacts the overlying ectoderm, which forms the lens
precursor. The optic vesicle folds to become the optic cup, while the lens
develops and becomes internalized. The optic cup then differentiates into
the retina and the ectoderm overlying the lens becomes the cornea. In the
cave fish, the lens and optic cup develop normally for the first 24 hours;
after this, however, the lens cells undergo programmed cell death or
apoptosis. The cornea and iris do not form and the retina is extremely
disorganized. Growth of the eye stops and photoreceptor cells never
develop. The rudimentary eye eventually sinks back and is covered by
skin.

The authors proposed two hypotheses for eye degeneration in
the cave fish. In one, lens apoptosis is responsible for eye degeneration.
In the other, the optic cup, which is diminished in the cave fish,
produces insufficient amounts of some necessary signal, leading to the
deterioration of the eye and lens.

Outline

Key results

Abstract

Significance
and context

Key
results

Links

Reporter's
comments

Table
of links

Yamamoto and Jeffrey transplanted embryonic lenses from
eyed fish into the optic cups of eyeless fish and vice versa. They found
that a lens from a surface fish could induce normal-looking eyes in the
blind cave fish, whereas the reciprocal transplantation caused a
degeneration in the eye of the surface fish. In each case, the
unmanipulated eye on the other side served as a control. To determine
whether programmed cell death was responsible for this deterioration, the
authors looked for apoptosis in the donor lenses. They found that the cave
fish lens still underwent apoptosis when implanted in a surface fish
embryo and the resulting eye was small and disorganized. In the opposite
experiment, the surface fish lens did not undergo apoptosis and was able
to stimulate normal eye development in the blind cave fish host, including
differentiation of a lens, retina, iris and cornea. The restored cave fish
eye also expressed the transcription factor Pax6, which is ordinarily
present in the lens and corneal epithelia but is not detected in
unmanipulated cave fish eye precursors. Yamamoto and Jeffrey then labeled
the eyed fish donor tissue with a fluorescent dye prior to implantation to
determine whether the rescued eye parts were from host or donor tissues.
When they sectioned the embryos, only the lens was fluorescently labeled,
revealing that the rescued eye parts were from the cave fish tissues. This
showed that the implanted lens from the surface fish was capable of
inducing the development of eye parts that were normally lost in the cave
fish.

The authors also used molecular markers of retinal
development to investigate the organization of the restored eye. Pax6,
Prox1, proliferating cell nuclear antigen (PCNA) and rhodopsin mark
different cell types within the retina. Pax6, Prox1 and PCNA were all
expressed in the cave fish eye; however, the retinal layers were
disorganized and very few cells expressed rhodopsin, which marks the rod
cells. In the restored eye, the retina developed into distinct, organized
layers, indicating that normal patterning, growth and differentiation of
the eye can be induced in the cave fish.

Links

A comment on this paper appeared in the same issue of
Science and is available to subscribers (Pennisi E, Science289:552b). A Supplementary figure to Science289:631-633
can be accessed freely from the Science website.

Reporter's comments

This study shows quite clearly that the lens can play an
important role in patterning the eye. When the surface fish lens is
implanted into the blind cave fish, normal eye development is restored,
though it is unclear whether the restored eye is actually functional. The
authors note that there are at least 30 Astyanax cave fish
populations in north-east Mexico. Their results apply only to the Pachón
cave fish used in their study. The other varieties of blind cave fish may
have evolved by different mechanisms and further comparisons of these fish
may provide insight into the evolution of developmental
processes.

Table of links

Science

Pennisi E, Science289:552b

Supplementary figure to
Science289:631-633

Assumptions that are made
about each paper that is the subject of a report, unless otherwise
specified:

The full text and figures are available only to
subscribers of the journal, but are available over the internet from
the journal's website. The paper itself is abstracted by PubMed.
There is no supplementary material.

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