MCP wrote:

> 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
>

I think this is just a load of gonads. ;-)

D.


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