When a fertilized ovum is to grow into a viable organism during its embryonic development, one of the things the cells need to know is where left and right are, so that the organs eventually wind up in the right spot in the right shape.
Thus the heart of all vertebrates, for instance, develops from an initially tubular shape that already shows a flexion towards the right side of the body shortly after its formation. This initial asymmetry is the reason why the tip of the heart - after a number of further rotations - in the end points towards the left side of the body.
How the body distinguishes right from left
How does the organism manage distinguish right from left? And which processes are responsible, for example, for the fact that heart usually beats on the left? The Würzburg-based developmental biologist Professor Thomas Brand and his colleague Dr. Jan Schlüter pursued this question. The current online issue of Proceedings of the National Academy of Sciences PNAS reports their result. In chicken embryos, the two researchers were able to characterize a signal pathway that plays a role in the asymmetrical development of the heart.
"So far the leading opinion was that a certain signal pathway is responsible for the left-sided development of organs that needs to be inhibited on the right side so that an asymmetry can develop", says Thomas Brand. As the two developmental biologists have shown now, this concept is not accurate: "With the chicken embryo, we could prove that an autonomous signal pathway also exists on the right side", states Brand.
Asymmetry is the rule, not the exception
Asymmetry in the body: Is it not the exception from the rule that applies to no more than the heart, liver, and spleen, while the majority is virtually built as a mirror-image? "Not at all", says Brand. In principle, the entire body is built asymmetrically; to make it appear symmetrical nevertheless, numerous signal cascades have to become active during the embryonic development.
In their work, Brand and Schlüter intensively examined mechanisms that play a role in the right-left characteristics. One of them is the asymmetrical production of ionic pumps. "This leads to an uneven distribution of electrical charge on the right and left side of the body that seem to show the cells the way", explains Brand. In the developmental biologists' experiments, blocking these ionic pumps led to a random distribution of the cells in the heart that are the preliminary stage of coronary blood vessels: At times they were located, as is usual, on the right side; at times they ended up on the left. In other cases they settled on both sides; occasionally they were missing completely.
Dead cells show the way
"Thus this effect also plays an important role for the lateral orientation of the organs", says Thomas Brand. But to him, this is not sufficient as the sole explanation for the 'left-sided heart'. The same applies to another mechanism: the programmed cell death. "In this case, the organism ensures that cells die along the midline of the embryo to mark the border between the left and the right side of the body", explains Brand. If the scientists prevented this cell death, the cells would settle in the heart, also according to the random principle.
FGF8: This is the name of the signal factor that is responsible for the right-sided development of the chicken heart according to the findings of Brand and Schlüter. Thus, their conclusion is: "The models for the right-left development have to be expanded." The fact that other vertebrates, such as the South African clawed frog or the river lamprey, build hearts in a similar manner speaks for the concept that this aspect of the right-left asymmetry is evolutionarily ancient.
Further research necessary
If this is also relevant for mammals, and thus for humans, is not clear. After all: "FGF8 mutations cause heart deformities in mice. This signal pathway might be significant for the right-directed heart flexion in the very early stage of the development, says Thomas Brand. The focus of his further research will thus be to identify the target genes of this signal pathway to better understand this aspect of the heart development on a molecular level.
Jan Schlueter and Thomas Brand (2009). A right-sided pathway involving FGF8/Snai1 controls asymmetric development of the proepicardium in the chick embryo. Proc Natl Acad Sci U. S. A. Early Edition (EE) the week of April 6, 2009. www.pnas.org/cgi/doi/10.1073/pnas.0811944106
Contact: Prof. Dr. Thomas Brand, phone (0931) 31-84259, e-mail: email@example.com
Gunnar Bartsch | idw
Symbiotic bacteria: from hitchhiker to beetle bodyguard
28.04.2017 | Johannes Gutenberg-Universität Mainz
Nose2Brain – Better Therapy for Multiple Sclerosis
28.04.2017 | Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences