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.
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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." - Reuters
