Dad's genes affect dominance

Which parent an allele comes from may influence how dominant mice are with their peers, according to a study in the January 27th issue of Nature, providing the first evidence that an imprinted gene may regulate a social behavior.

Grb10 knockout embryos (mom-left; dad-right)
showing opposite imprinting of the parental alleles
in different tissues (expression in blue)
Photo courtesy Alastair Garfield et al and Nature

"I think this paper greatly increases the plausibility of imprinted expression underpinning adult social behavior," linkurl:Tom Moore,;http://www.ucc.ie/ucc/depts/biochemistry/staff/tmoore.html a developmental geneticist at the University College Cork in Ireland who was not involved in the research, said in an email to The Scientist. Normally, offspring inherit two copies of each gene, one from each parent, both of which are expressed at similar levels in the same locations of the body. Imprinted genes, however, come with additional information from the parent of origin. The allele from mom may be turned off, for example, while the copy from dad is expressed, or vice versa. Genes are imprinted through DNA methylation or histone modification during the development of the egg and sperm.To explore the effects of gene imprinting in mice, geneticist linkurl:Andrew Ward;http://www.bath.ac.uk/bio-sci/research/profiles/ward-a.html of the University of Bath in the UK and his colleagues examined Grb10, an imprinted gene known to have maternal-specific expression that regulates cell growth. "At the outset, we had no prior expectation that we would be looking for social dominance," said Ward.But after performing a forced encounter test, where two mice are placed at each end of a narrow tube that prevents them from turning around, Ward and his group found that mice that lacked a copy of Grb10 from their father tended to "win" the encounter -- thus stood its ground as the other mouse backed away and became submissive. The researchers also found that these same mice were more likely to over-groom their peers, a sign of dominance in mice and other mammals. In addition, mice that lacked the paternal Grb10 alleles were more likely to rip out the whiskers of their genetically similar cage-mates than mice that expressed the allele, all suggesting that the Grb10 paternal allele influences social dominance, said Ward.The maternal allele of Grb10, on the other hand, was confirmed to regulate fetal growth, metabolism and fat storage. When the maternal gene was silenced, mice were often larger and heavier. Interestingly, the alleles were expressed in completely different areas of the body: The paternal copy was found in the brain, and the maternal copy in the rest of the body. It's unusual that "one imprinted gene is doing two strikingly different tasks in the body," said Ward. Normally, he explained, if a gene is imprinted, one parent's alleles are silenced while the other's are expressed. But it's not that "black and white" in this case, he added. "This is the most exciting thing I've seen in the lab in my career," said Ward, who plans to investigate the evolutionary causes of this strange phenomenon in Grb10. The results support the idea of kinship theory, for example, added Moore, which states that natural selection may favor alleles with effects that vary based on the parental origin. A.S. Garfield et al., "Distinct physiological and behavioural functions for parental alleles of imprinted Grb10," Nature, 469:534-538, 2011.Correction: This article has been updated from a previous version to correctly indicate that "winning" an encounter involves a mouse standing its ground as another mouse backs away and becomes submissive. The Scientist regrets the error.
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[8th July 2010]