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Laboratory of Molecular Genetics |
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Evolutionary Genetics Group
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Hiroshi Hori, medaka and mimetic butterflies |
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Hiroshi Hori (Professor)
Molecular evolution of animal body color
Akihiko Koga (Associate Professor)
Evolutionary mechanism of vertebrate transposable
elements
Akira Kanamori (Assistant Professor)
Molecular mechanisms of sex differentiation
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We are interested in the molecular genetic mechanisms underlying
vertebrate evolution and speciation using the medaka fish (Oryzias
latipes, a small, freshwater teleost) as a vertebrate model organism.
Our current research includes: (1) molecular evolution of animal body
color, (2) evolutionary mechanism and population dynamics of vertebrate
transposable elements, and (3) molecular mechanisms of sex differentiation.
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Molecular evolution of animal body color
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Nearly all animals are colored. The colors may be subdued and cryptic
when serving protective functions, or vivid and dramatic when serving
as important recognition marks and mimics. Organic evolution explains
the diversity of animal body color. While mammals have only one type
of chromatophore, the melanocyte, fish have three, the melanophore
(black, equivalent to the melanocyte), the xanthophore (yellow), and
the iridophore (silver).
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| Wild medaka |
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| albino mutant |
| Fig. 1. Wild medaka and albino mutant. Medaka
is a useful model for pigmentation studies because many boby
color mutants have been isolated. |
Thus, fish pigmentation is a tractable model
for understanding the mechanisms of molecular evolution of animal
body color.The medaka fish is a suitable model for pigmentation studies
because it has all three types of chromatophores, and approximately
70 spontaneous pigmentation mutants have been isolated. We are now
cloning the genes responsible for several mutants using techniques
such as molecular genetics and genome analysis.
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Evolutionary mechanism of vertebrate transposable elements
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The medaka fish is also an excellent model animal for population
and evolutionary studies because it is distributed in a wide area,
including Japan, Korea, and China, and about twenty closely related
species inhabit Asia from Japan to India. Taking advantage of this
natural infrastructure, we have been, and will continue, researching
the evolution of transposable elements. Recent significant results
from our lab include evidence for invasion of the fish genome by a
transposable element, several factors that control the transposition
frequency, and a sudden resumption of transposition leading to mutator
activity.
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Molecular mechanisms of sex differentiation
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We are interested in the sexually dimorphic development of vertebrate
gonads. Medaka is particularly suitable for this research because
it has an XX-XY sex determination system and is easy to be used in
genetic studies. In fact, the medaka male-determination gene, dmy,
was identified by positional cloning and was the second sex-determination
gene identified in vertebrates (after mammalian sry). Dmy expression
starts on 2 days before hatch in the male somatic cells in the gonads.
In females, sex is first apparent at hatch when the germ cells enter
meiosis. Using cDNA subtraction, we cloned female-specific genes and
analyzed their expression. Many of these genes, including the bHLH
transcription factor, fig-alpha, are expressed in the oocytes
at the earliest stages of differentiation. Expression of these genes
starts around hatch together with some of the meiosis-specific genes.
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| Laboratory Members |
At present, we are examining cascades of events during these two days
by 1) analyzing the promoter of fig-alpha and 2) looking for
medaka sex differentiation mutants.
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References
- Matsuda M et al. Nature. 417: 559-563 (2002).
- Koga A et al. Mar. Biotech. 4: 6-11 (2002).
- Koga A et al. Heredity 89: 446-452 (2002).
- Kanamori A et al. Gene 305: 35-45 (2003).
- Koga A et al. J. Hum. Genet. 48: 231-235 (2003).
- Tsutsumi M et al. Genet. Res. 82: 33-40 (2003).
- Sasaki T et al. Marine Biotech. 6: S445-S448 (2004).
- Naruse K et al. Mech. Dev.121: 619-628 (2004).
- Khorasania MZ et al. Mech. Dev.121: 903-913 (2004).
- Iida A et al. Genes Genet. Syst. 79: 119-124 (2004).
- Iida A et al. Pigment Cell Res. 17:158-164 (2004).
- Iio K et al. Comp Biochem Physiol B Biochem Mol Biol.140:
569-78 (2005).
- Kurauchi K et al. Environ. Sci. Tech. 39: 2762-68
(2005).
- Inoue K et al. Mol. Biol. Evol. 22: 2428-34 (2005).
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i n d e x |
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 Evolutionary
Genetics Group
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Molecular
Neurobiology Group