The scientists on Thursday described experiments involving a small fish
called the medaka, or Japanese rice fish, that revealed the role of a
gene called foxl3 in controlling the fate of germ cells.
Providing insight into the sometimes mysterious biology of reproduction, researchers in Japan have
identified a gene that controls whether the reproductive precursor
cells known as germ cells eventually become sperm or eggs.
The
scientists on Thursday described experiments involving a small fish
called the medaka, or Japanese rice fish, that revealed the role of a
gene called foxl3 in controlling the fate of germ cells.
Germ
cells are present in the bodies of vertebrates of both sexes, but the
molecular mechanism that drives them to develop into either sperm, the
male reproductive cell, or an egg, the female reproductive cell, has
been elusive.
In determining that foxl3 serves as a
genetic switch for deciding the sperm-or-egg question, the researchers
found that the gene is primarily active in a female's germ cells to
prevent them from becoming sperm cells instead of egg cells in the
ovaries.
The gene is not active in the surrounding cells of the fish's reproductive organs.
When
the scientists inactivated the gene in female fish, the germ cells
turned into sperm in the medaka's ovaries rather than eggs cells, as
might be expected in a female. Those sperm cells functioned normally,
successfully fertilized egg cells and produced healthy offspring.
Humans
do not possess the exact same gene, but the researchers suspect a
similar genetic switch mechanism may be at play in people, too.
Reproductive biologist Minoru Tanaka
of Japan's National Institute for Basic Biology said nobody knew that
in vertebrates germ cells have a switch mechanism to decide their own
sperm-or-egg fate.
"The germ cells were regarded as passive cells that are regulated by other cells," added Tanaka, whose research was published in the journal Science.
Fellow National Institute for Basic Biology reproductive biologist Toshiya Nishimura added: "In
spite of the environment surrounding the germ cells being female, the
fact that functional sperm has been made surprised me greatly. That this
sexual switch present in the germ cells is independent of the body's
sex is an entirely new finding."
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