RIKEN Center for Developmental Biology
(CDB) 2-2-3 Minatojima minamimachi, Chuo-ku, Kobe 650-0047,
Japan |
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Skin pattern formation in a hermaphrodite angelfish |
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March 13, 2003 - The angelfish genus Genicanthus is noted for the ability of females in populations
lacking a dominant male to switch genders in a process known as protogynous hermaphroditism.
This is a highly visible process, as Genicanthus females are relatively plain-patterned, while
males (including transsexual males) are vividly striped. Since the proposal of the reaction-diffusion
mechanism model of pattern formation by Alan Turing in 1952, it has been suggested that the
generation of regularly spaced patterns, such as spots, stripes and networks, can be achieved
through interactions between a local activator and a long-range inhibitor.
In 1995, Shigeru
Kondo provided the first convincing case for the reaction-diffusion mechanism in skin
patterning when he demonstrated that the Turing model sufficiently describes the stripe formation
process in Pomacanthus, a different genus of angelfish, spurring a new wave of interest in
the mathematical modeling of skin and body patterning. However, the Turing model cannot account
for the directionality of stripes, which is significant in the case of Genicanthus. To investigate
the principles underlying stripe direction, Kondo studied two closely related species, Genicanthus
watanabei and Genicanthus melanospilos, which are similar in nearly all regards save the direction
of the males’ striping. (G. watanabei stripes are vertical while those of G. melanospilos
are horizontal.) The results of this work are published in the April issue of Developmental
Dynamics.
Kondo approached the problem from the mathematical side, searching for an adjunct to the Turing
mechanism capable of explaining the difference in stripe direction. The results of extensive
theoretical modeling show that unequal diffusion (anisotropy) can provide that missing factor.
By factoring different anisotropic states into simulations of Turing’s reaction-diffusion
equation, Kondo found it is possible to generate stripe patterns arrayed in specific directions
in stages that closely mirror the gradual development of stripes in both species of Genicanthus.
In these simulations, even slight variations in anisotropy can account for marked changes
in directionality. Kondo speculates that in the case of Genicanthus, the source of the anistropic
diffusion lies in subtle differences in scale structure between the two species. These results
provide new insight into a previously unexplained phenomenon in pattern formation, and may
shed light on similar directional striping in the skin of other species.
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[ Contact ]
Douglas Sipp : sipp@cdb.riken.jp
TEL : +81-78-306-3043
RIKEN CDB, Office for Science Communications and International Affairs |
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