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Development and physiology of the heart
A selection of talks on Physiology & Anatomy
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.
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.
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.
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.