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A potential benefit of albinism in Astyanax cavefish: downregulation of the oca2 gene increases tyrosine and catecholamine levels as an alternative to melanin synthesis.
[oculocutaneous albinism]
Albinism
,
the
loss
of
melanin
pigmentation
,
has
evolved
in
a
diverse
variety
of
cave
animals
but
the
responsible
evolutionary
mechanisms
are
unknown
.
In
Astyanax
mexicanus
,
which
has
a
pigmented
surface
dwelling
form
(
surface
fish
)
and
several
albino
cave-dwelling
forms
(
cavefish
)
,
albinism
is
caused
by
loss
of
function
mutations
in
the
oca
2
gene
,
which
operates
during
the
first
step
of
the
melanin
synthesis
pathway
.
In
addition
to
albinism
,
cavefish
have
evolved
differences
in
behavior
,
including
feeding
and
sleep
,
which
are
under
the
control
of
the
catecholamine
system
.
The
catecholamine
and
melanin
synthesis
pathways
diverge
after
beginning
with
the
same
substrate
,
L-
tyrosine
.
Here
we
describe
a
novel
relationship
between
the
catecholamine
and
melanin
synthesis
pathways
in
Astyanax
.
Our
results
show
significant
increases
in
L-
tyrosine
,
dopamine
,
and
norepinephrine
in
pre-feeding
larvae
and
adult
brains
of
Pachón
cavefish
relative
to
surface
fish
.
In
addition
,
norepinephrine
is
elevated
in
cavefish
adult
kidneys
,
which
contain
the
teleost
homologs
of
catecholamine
synthesizing
adrenal
cells
.
We
further
show
that
the
oca
2
gene
is
expressed
during
surface
fish
development
but
is
downregulated
in
cavefish
embryos
.
A
key
finding
is
that
knockdown
of
oca
2
expression
in
surface
fish
embryos
delays
the
development
of
pigmented
melanophores
and
simultaneously
increases
L-
tyrosine
and
dopamine
.
We
conclude
that
a
potential
evolutionary
benefit
of
albinism
in
Astyanax
cavefish
may
be
to
provide
surplus
L-
tyrosine
as
a
precursor
for
the
elevated
catecholamine
synthesis
pathway
,
which
could
be
important
for
adaptation
to
the
challenging
cave
environment
.
Diseases
Validation
Diseases presenting
"loss of function mutations in the oca2"
symptom
oculocutaneous albinism
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