Two egg cells make fatherless mouse.

Is it time to start buying Mother's Day cards in bulk? Japanese researchers have created a mouse that has two mothers but no father. Don't expect to see the option offered at fertility clinics anytime soon, however. The experiment had a very low success rate.

In many animals, including some lizards and insects, a female's egg can develop into a normal embryo without being fertilized by sperm, a process called parthenogenesis. In mammals, such embryos typically die a week or two into gestation, indicating that it takes the union of sperm and egg to produce a healthy offspring.

A phenomenon called imprinting may offer an explanation for this usual requirement. While a mammalian embryo inherits similar sets of genes from its mom and dad, certain genes are imprinted. That is, only the mother's or the father's version of the gene becomes operative (SN: 5/15/99, p. 312). As a result, it appears that mammalian embryos need genes from both a male and female parent.

Tomohiro Kono of Tokyo University and his colleagues devised a way to overcome the imprinting barrier and used the technique to produce a fatherless rodent. The investigators fused one mouse egg to another one whose DNA was altered to change the activity of two imprinted genes. In essence, the gene activity in the modified egg resembled that of a sperm, according to the researchers.

Out of 457 such procedures, 371 embryos developed to the stage at which Kono's team could implant them into surrogate mothers. But only 10 of the embryos survived long enough to be born. In the end, only one mouse pup lived until adulthood, the investigators report in the April 22 Nature.

Drawing upon the Japanese legend of a princess found as a girl in a bamboo forest, the scientists named the fatherless mouse Kayuga. They now plan a similar experiment with pigs next.--J.T.