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Asymmetry switched in snail

Scientists have found a new way to manipulate the direction of snail shell coiling, altering the animal's left-right asymmetry. The research, published linkurl:online;http://www.nature.com/nature/journal/vaop/ncurrent/index.html today (November 25) in Nature, may offer clues as to how "handedness" develops in invertebrates, which could improve scientists' understanding of the mechanics that drive cell regeneration and embryonic development. 'Left-handed' and 'right-handed' shells of L. stagnali

By | November 25, 2009

Scientists have found a new way to manipulate the direction of snail shell coiling, altering the animal's left-right asymmetry. The research, published linkurl:online;http://www.nature.com/nature/journal/vaop/ncurrent/index.html today (November 25) in Nature, may offer clues as to how "handedness" develops in invertebrates, which could improve scientists' understanding of the mechanics that drive cell regeneration and embryonic development.
'Left-handed' and 'right-handed'
shells of L. stagnalis

Image: Kuroda laboratory
"This paper illustrates how chirality" -- the inability of a structure to be superimposed on its mirror image -- "arises," said linkurl:Michael Levin,;http://ase.tufts.edu/faculty-guide/fac/mlevin11.biology.htm a developmental biologist at Tufts University, who was not involved in the study. This new research, he said, shows that snails are a useful way to track early embryonic-stage signaling for handedness. The left-right asymmetry of an animal's internal organs and physical appearance are important evolutionary traits that often make tasks easier, such as an owl's unbalanced ears for better hearing, but researchers have only recently begun to decipher the mechanisms underlying it. Most studies have focused on what dictates asymmetry in late-stage development, suggesting, for example, that the structural patterning happens when an embryo shifts from a spherical ball of cells into a multi-layered organism. But linkurl:Reiko Kuroda,;http://www.pwri.go.jp/icharm/activities/act_e/act20090402prof_kuroda.html a biochemist at the University of Tokyo, and colleagues demonstrate that a snail shell's coil orientation is determined much earlier -- at the eight-cell embryonic development stage. Using two glass rods, Kuroda's team inverted the layout of the early stage cells in Lymnaea stagnalis, essentially creating a mirror image of their original grouping pattern. As the snails developed into adulthood, their shells coiled in the opposite direction than expected based on their genetic code. Simply put, genetically "right-handed" snails developed "left-handed" shells, and vice versa, said Kuroda. Kuroda's team also found that altering the layout of the eight-cell stage completely reversed the expression patterns of the nodal gene -- the gene that dictates the direction in which the shell will spiral under normal conditions. The gene is the regulating factor of the Nodal signaling pathway, which scientists have previously identified as the system that dictates organ laterality and handedness as an embryo develops into a multi-layered organism. The pathway is also responsible for determining the direction of embryonic axes and stimulating the creation of the germ cell layers. In previous studies, scientists were able to determine an animal's handedness by looking at how the nodal gene was expressed. But Kuroda and her colleagues' results indicate that the decision of which way the shell will coil originates upstream of the Nodal signaling pathway and not in the pathway itself. This altered handedness, however, did not pass from generation to generation; offspring of reversed-coiled snails reclaimed the pre-manipulated orientations of their ancestors, suggesting the physical manipulations by researchers did not affect the genetically programmed structural pattern. "Putting a finger on the actual onset of handedness in invertebrates may shed light on how it is determined in other, more complex organisms," said Kuroda, which will allow scientists to determine the mechanics driving asymmetric evolutionary traits.
**__Related stories:__***linkurl:Chasing the cilium;http://www.the-scientist.com/article/display/14976/
[11th October 2004]*linkurl:Humor and handedness;http://www.the-scientist.com/article/display/14731/
[7th June 2004]*linkurl:Investigators isolate 'handedness' gene;http://www.the-scientist.com/article/display/18184/
[31st August 1998]
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Comments

Avatar of: Dov Henis

Dov Henis

Posts: 97

November 29, 2009

Upgrade Evolution Comprehension Beyond Darwin\n\n\nA. From "Asymmetry switched in snail (by manipulation)"\nhttp://www.the-scientist.com/blog/display/56187/\n\nThis altered handedness, however, did not pass from generation to generation; offspring of (manipulated) reversed-coiled snails reclaimed the pre-manipulated orientations of their ancestors, suggesting the physical manipulations by researchers did not affect the genetically programmed structural pattern.\n\nB. Again and again: Upgrade Evolution Comprehension Beyond Darwin\n\nPhysical manipulations that do not result in augmented energy constrainment by the organism do not affect the expression of its primal organism, the gene. (PS: why refer to an organism as "genetically programmed structural pattern"?. Are we genetically programmed structural patterns?)\n\nPlease consider the following concept of the origin and nature of life and organisms, of the origin and nature of cosmic and life evolution: \n\n- Genes, Earth's primal organisms, and all their take-off organisms - Life in general - are but one of the cosmic forms of mass, of constrained energy formats. \n\n- The on-going cosmic mass-to-energy reversion since the Big-Bang inflation is resisted by mass, this resistance being the archtype of selection for survival by all forms of mass, including life.\n\n- The mode of genes', Earth's primal organisms, response to the cultural feed-back signals reaching them from their upper stratum take-off organism is "replicate without change" or "replicate with change". "Replicate with change" is selected in case of proven augmented energy constrainment by the the new generation, this being "better survival". This mode of Life's normal evolution is the mode of energy-mass evolution universally. \n\n\nDov Henis\n(Comments From The 22nd Century)\nUpdated Life's Manifest May 2009 \nhttp://www.the-scientist.com/community/posts/list/140/122.page#2321\nImplications Of E=Total[m(1 + D)] \nhttp://www.the-scientist.com/community/posts/list/180/122.page#3108
Avatar of: Val Fitzgerald

Val Fitzgerald

Posts: 11

December 1, 2009

explains 'handedness'--then why am I ambidextrous???\nPlease explain...\n\nI don't understand why I was "gifted" with the equal use of both hands in handwriting (an ability that came in real handy when I had to have my right shoulder replaced last year)--so my surgery didn't cramp my style, not a bit.\n\nLeaving religion out of this discussion, I must nonetheless remind all on these boards, that GOD GAVE US TWO HANDS--and I don't think that He only meant us to use just ONE OF THEM!!!!
Avatar of: JOHN COLLINS

JOHN COLLINS

Posts: 37

December 8, 2009

I find this phenomenon amazing. Also it seems that the novel experimental design sheds enlightenment on approaches for other workers. Pasteur detected chemical asymmetry as a signature of life, when looking at the (handedness) asymmetry of tartaric acid crystals in wine. Only one form of the acid had accumulated due to an asymmetric substrate-binding pocket in an enzyme and lack of rapid conversion (through chemical equilibrium reactions) to the other form. Here, however, we see that a macroscopic asymmetry is already determined with a (less than two) hand(s) full of cells, implying that it involves an intracellular handedness asymmetry already in the fertilized egg or even in the oocyte, which was genetically predetermined and not influenced by the existing tissue 'handedness' of the parent.

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