There is a fair amount of literature on the topic, especially on gastropods, most of it aimed at identifying genes or loci responsible for chirality. But what I’m interested in is not the genes responsible (assuming inheritance is genetic), but in how those genes (or some other entity) actually carry a chiral signal. The properties of “left-ness” and “right-ness” are irreducible. Neither can be defined without tautology, and it is impossible to devise a set of instructions that will, say, place the human heart on the left side of the body if those instructions do not assume you already know what “left-ness,” and “right-ness” are. It seems that inheritance of chirality requires the inheritance of a chiral structure or structures that define handedness during development. What are these structure or structures? Molecular biology is highly chiral so it is not hard to think of possibilities, but have any mechanisms for inheriting and expressing chirality actually been identified? If so, can you give me citations?
By chirality, do you mean right-left
asymmetry of the body? It is caused
by cilia that sense the flow of fluids
outside the cells. On the other hand,
cilia propel the outside fluid by
a molecular motor "clockwise as
viewed from above".
https://www.researchgate.net/publication/8587371_Fluid-dynamical_basis_of_the_embryonic_development_of_left-right_asymmetry_in_vertebrates
More:
http://www.eurekalert.org/pub_releases/2006-10/si-iee101906.php
http://www.eurekalert.org/pub_releases/2006-04/fi-fsg040506.php
http://www.ncbi.nlm.nih.gov/pubmed/9707115
http://www.sciencedaily.com/releases/2007/10/071003130813.htm
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2222619/
http://www.cell.com/current-biology/abstract/S0960-9822%2806%2902498-5
Regards,
Joachim
Article Fluid-dynamical basis of the embryonic development of left-r...
Mechanisms for breaking symmetry are different for different situations.
Although it has yet to be defined, there’s an interesting situation in which logarithmic spirals appear on mouse corneas, which will stimulate your imagination on potential mechanisms.
For example, which way would you expect the spirals to turn in the left eye…the right eye of the same individual? What if pitch angle distributions are conserved?
Best, Jerry
Promoting convergence: the phi spiral in abduction of mouse corneal behaviors
Our paper contributed to the story on vertebrates, in particular on mice. Since then there has been research showing that similar fluid flow determines left-right in zebrafish, for example. I'm not sure whether anyone knows yet whether we humans also use the same flow mechanism, which depends on the direction the cilia rotate, which in turn -as the question suggested- ultimately depends on the chirality of the proteins that make up the molecular motor that powers a cilium. But the original question also asked about molluscs, and there things are different: symmetry breaking in gastropods depends on the direction of the third cleavage - see doi:10.1038/nature07603 .
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