http://www.nature.com/news/2005/050228/full/050228-4.html

Study gives clue to how genes and environment create sex cells

To say that eggs grow only in females and sperm grow only in males seems a
pretty uncontroversial statement. But Japanese researchers have shown that
it's not as simple as that, by nurturing female eggs in the testes of male
mice.

In a growing mouse embryo, the cells that will become the testes or ovaries,
known as germ cells, start out the same in both sexes. In males, a gene on
the Y chromosome called Sry switches on about halfway through gestation and
prompts these undecided cells to develop into testes containing sperm.
Females lack Sry and, by default, develop ovaries and eggs.

But what happens if you have a female germ cell surrounded by male cells?
Will it be influenced by the male signals around it and become a sperm, or
will it follow its own genetic path and become an egg?

Masaru Okabe at Osaka University and his colleagues expected the former, but
to find out for sure they sandwiched together cells from male and female
embryos and allowed the 'chimeric' embryos to grow into mice.

As suggested by previous studies, most of the female cells growing in the
testes of the male mice abandoned their genetic legacy and went through the
early stages of sperm development. Okabe found that signals from surrounding
cells with an active Sry gene triggered these female cells to start up a
pattern of gene activity that is normally only found in male cells.

But some of the female cells that lodged in the testes developed partly into
eggs, the researchers report in the Proceedings of the National Academy of
Sciences1. The eggs were able to fuse with sperm, but did not develop into
embryos. "It was a big surprise," says Okabe, who dubbed the cells
'testicular eggs'.

Cell pockets

Testicular eggs are not entirely new. A study 25 years ago reported eggs
that seemed to grow in male mice2. But that was simply based on the shape
and size of the cells. Okabe's study is the first to use modern genetic
techniques to confirm that such cells are genetically female.

The idea of eggs growing in the testes is "a nice concept", says Wolf Reik,
who studies egg and sperm development at The Babraham Institute in
Cambridge, UK. He suspects that the eggs are able to develop because they
grow in a little of pocket of female cells within the testis.

The researchers hope their studies will help scientists to understand what
goes wrong when the testes develop in patients with chromosomal sex
disorders. In Klinefelter syndrome, for example, males carry an additional X
chromosome and budding sex cells disappear. Okabe says that the chimeric
mice could help explain exactly what happens to these cells and why

Helen Pearson

--
Men are everywhere that matters!





--- UseNet To RIME Gateway {at} 3/18/05 4:59:39 PM ---