WASHINGTON, Feb. 5 (Xinhua) -- American researchers have identified a protein in mice eggs that is proved crucial to fertility, lending a new clue to unexplained causes of female infertility since humans also have the same protein.
In a study published on Monday in the journal Developmental Cell, scientists at University of California San Diego found that mice eggs without the protein called L2, appear ordinary, but cannot be fertilized by sperm.
Heidi Cook-Andersen, the paper's senior author, who worked with couples struggling with infertility, said, "it's frustrating that for many of them, we have no idea why it's difficult for them to conceive. All of their tests come back normal."
"That's why this study is so exciting to us. It's another clue," Cook-Andersen said.
The study shows that L2 plays a role in cells by turning off gene expression when the proteins encoded by the mRNAs are no longer needed.
The mRNA is the messenger that carries DNA's recipe to the cell's protein-making machinery.
To determine what effect the L2 lacking had on fertility, Cook-Andersen's team set up an equal number of fertile male mice with 10 females lacking L2 in their eggs and 10 normal females.
Then they tracked the groups for six months. In that time, the normal mice produced regularly but the female mice lacking the L2 protein in their eggs didn't have a single pup.
The team found that L2-deficient eggs were unable to shut off the global transcription, a process that normally happens in the final stages of egg growth. It means that eggs lacking L2 continued transcribing genes into mRNA and producing proteins.
"Many research groups are looking at how genes are regulated from the perspective of which genes need to be turned 'on' for a cell to advance to the next stage of development, but now we see that it's just as important to know which genes need to be turned 'off,'" Cook-Andersen said.
In the future, the team plans to determine if L2 plays a role in human infertility. Currently, the underlying causes for approximately 15 percent of human infertility cases is not known.