Page 116 - 80_02

C.
Hernández-­-Sánchez,
P.
Vázquez,
Flora
de
Pablo

INS1
chimeric
mRNA
also
generates
a
small
amount
of
insulin
(8).
Besides
this

unusual
post-­-transcriptional
regulation,
the
th
gene
displays
an
unexpected

expression
pattern.

We
found
that
the
expression
of
th
mRNA
in
the
chick
embryo
antecedes

development
of
the
nervous
system.
th
transcripts
were
detected
from
gastrulation

onwards,
and
they
were
enriched
in
the
cardiogenic
region.
Before
focusing
this

overview
in
the
heart
TH
during
cardiogenesis,
it
is
worth
however
to
emphasize

the
remarkably
similar
features
of
a
human
embryo
and
a
chick
embryo
during

that
period
(Figure
3).
In
vertebrates,
the
heart
is
initially
formed
by
the
fusion
of

the
two
bilateral
endocardial
tubes
arising
from
the
splanchnic
lateral
plate

mesoderm.
The
resultant
primitive
heart
tube,
located
at
the
ventral
midline
of
the

organism,
undergoes
a
complex
series
of
movements
and
tissue
remodeling
events

that
leads
to
the
formation
of
the
mature
chambered
organ
(12).

3.
USE
OF
THE
CHICK
EMBRYO
AS
A
MODEL
FOR
STUDYING
THE
ROLE
OF
TH
IN

CARDIOGENESIS

As
very
clearly
stated
by
Brand
(in
a
kind
editorial
comment
of
our
work,

13),
“despite
its
evolutionary
distance
to
mammals,
the
chick
embryo
is
a
valuable

model
to
work
out
the
mechanism
of
cardiac
specification.
The
embryo
is
large
and

accessible
and,
therefore,
manipulations
at
the
time
of
cardiac
specification
and

early
heart
formation
are
easily
performed”.
Research
in
the
last
two
decades

utilizing
this
model
organism
has
identified
several
signaling
molecules
that
are

important
for
cardiac
induction
(14).

The
fact
that
the
chick
embryo
can
be
accessed
and
manipulated
without

disrupting
early
development,
allows
to
perform
experiments
of
gain
of
function

and
loss
of
function
starting
during
gastrulation,
and
to
analyze
the
effects
on

embryonic
organogenesis
(Figure
4).
Factors
or
antibodies
may
be
added
and,
if

the
aim
is
to
look
for
effects
over
the
next
several
days,
the
embryo
can
be
reached

through
a
window
in
the
shell
and
incubation
can
continue.
To
look
for
short-­-term

effects,
as
in
the
series
of
studies
reviewed
here,
the
addition
of
molecules
or

plasmid
DNA
was
carried
out
maintaining
the
embryo
in
culture
under
specific

tension
conditions
(15).

The
chick
embryos
were
treated
at
stages
3-­-5
(12-­-22

hours
of
development,
according
to
Hamburger
and
Hamilton
(16)
and
were

studied
at
stages
11-­-12
(less
than
50
hours
of
development).
The
addition
of

dopamine
or
enzymatic
inhibitors
of
TH
activity
could
be
carried
out
using
heparin

or
resin
microbeads,
implanted
in
the
embryo
underneath
the
epiblast
(Figure
4B).

The
uptake
by
the
embryo
tissues
of
plasmid
DNA
containing
TH,
GFP
(Green

Fluorescence
Protein)
or
TH
antisense-­-morpholino
DNA
was
facilitated
by

electroporation
(Figure
4C).

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