Friday April 9 4:30 AM ET
Second 'Good Mother' Gene Found
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - Researchers said Thursday they had found a second gene for good motherhood and that males appear to have the upper hand when sexes battle over how much time to spend with the babies.
They said both genes, which come from the father, may ensure that their daughters are good mothers -- thus making sure that male interests are paramount when it comes to reproduction.
Female mice that lack the genes failed to take care of their babies, letting most of them die.
The genes are controlled by a special process called imprinting, which ensures that only the father's version of the gene actually works.
Animals, and people, inherit two copies of a gene -- one from the father and one from the mother. In imprinted genes, poorly understood controls ensure that only the father's version ``expresses'', or works.
Azim Surani and colleagues at Britain's Cambridge University reported last September that female mice lacking their father's version of a gene called ``Mest'' made poor mothers, failing to feed their babies or carry out other maternal duties.
Now they have discovered a second such gene, this one known as ``Peg3''.
Mice bred to lack a working version of the gene were not only small, but also strikingly bad mothers, Surani's team reported in the journal Science.
``Because the newborn rodents are deaf, blind and immobile, the mother normally builds a nest, gathers her pups together and keeps them warm by crouching over them,'' they wrote in their report. But the mutant mothers did not do any of these things, or took a long time in doing so.
Only eight percent of the first litters of mutant mothers survived to weaning, compared to 83 percent of the babies of normal mice.
``Their failure to thrive showed the existence of a maternal nurturing defect,'' they wrote. Babies from mutant males and normal females did survive, which meant the babies did not inherit some genetic weakness, but rather died from poor mothering, the researchers said.
Dr. Sam Aparicio of the Wellcome Trust at Cambridge, who worked on the study, said humans have the same gene and it would be interesting to see if variations in the gene affect human mothering.
``Mice do exhibit rearing behavior in ways that humans exhibit rearing behavior,'' Aparicio said in a telephone interview. ``But it could be some other aspect of maternal response to a child (that ``Peg3'' controls). We just don't know.''
Surani's team thinks the ``Peg3'' gene may affect brain cells that produce oxytocin, a compound that brings on the contractions of labor and that also helps start milk production for nursing mothers.
In rodents, oxytocin stimulates maternal behavior. Mutant female mice had fewer of these brain cells, they said.
They noted that most scientists think that imprinting occurs because of a genetic war between the sexes.
Males have the best chance of passing their genes on through many offspring if their mates spend a lot of time caring for babies. If a male wants more young, he can always impregnate more females.
But it is tough on a female to both feed babies and carry a pregnancy. Thus the conflict.
This could explain why males might evolve genes that help them control maternal behavior, the researchers concluded.
Aparicio said such theories were still controversial.
``The point is, it is in the interest of the male who has already produced offspring, to ensure that those offspring are then cared for, whereas it may be in the female's interest to have more litters,'' he said.
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