Female eggs grown in male testes

[Guest guest]

Thanks to intruththatwetrust for this

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

Female eggs grown in male testes

Helen Pearson

Study gives clue to how genes and environment create sex cells.

 

 

 

 

 

What makes an egg an egg?

 

© SPL

 

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.

 

 

 

 

 

Ovaries may lay new eggs

11 March 2004

 

Brain development: The most important sexual organ

29 January 2004

 

Human genetics: Dual identities

02 May 2002

 

Cells reprogram in 24 hours

19 April 2002

 

 

Nature Fertility outlook