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0:00
It's a pleasure for me to talk about the
"Development and Physiology of the Heart"
as part of the "Legacy of
Drosophila Genetics", Henry Stewart Talks.
My name is Rolf Bodmer.
0:13
The Drosophila heart during
embryogenesis starts out as
a simple tube as indicated here.
In the top panel you see the inner
blue myocardial cells and
the outer brown pericardial cells.
And the diagram below illustrates that
there's really only two layers of cells,
two rows of cells that come together and
form a lumen as indicated in
the bottom portion of that diagram.
0:42
Now over 15 years ago,
we started embarking in a search for
genes that are required for
heart formation in Drosophila,
because we thought we could learn
a lot from this organism in terms of
genetic determinants that are necessary
for the development of the heart,
sort of as a prototype for
any organism that had a heart.
The first mutant that we had identified,
we called tinman,
because in tinman mutants,
the heart does not form.
So in wild-type, you have a normal
heart being formed, in tinman mutants,
the heart does not form.
In addition, tinman is expressed
at these late stages of
embryogenesis exclusively in the heart.
1:25
To understand how
the Drosophila heart forms,
I would like to review some aspects
of gastrulation that will be
illustrative of how the heart
formation comes about embryologically.
So in the Drosophila blastoderm stage,
you can see that helix-loop-helix
transcription factor twist marks
the mesoderm which then invaginates and
migrates along the ectoderm
to the dorsal edge.
So it forms a sort of a monolayer.
And you can see the illustration of this
in a diagram that you have this
model here of mesodermal cells, and
the most dorsal cells marked in red
are then the cardiac progenitor cells.
And it's these cells that are in
the bottom right in situ panel of
RNA expression in stage 12 embryo marks
exclusively the heart progenitor cells.
Tinman is actually expressed all
through the mesoderm early on and
then becomes restricted to dorsal
mesoderm and only towards the middle and
end of embryogenesis is it marking
exclusively the cardiac progenitor cells.
