Researchers have made a discovery that may in future help to explain many aspects of human social behavior and disorders such as autism.
The researchers, Drs. Larry Young and Elizabeth Hammock, of Emory University, using the native vole, traced social behavior traits, such as monogamy, to seeming glitches in DNA that determines when and where a gene turns on.
The length of these repeating sequences , at one time dismissed as mere junk DNA, in the gene that codes for a key hormone receptor determined male-female relations and parenting behaviors in a species of voles.
This is the latest discovery in a two decades-old scientific quest for the neural basis of familial behavior begun at the National Institute of Mental Health (NIMH) Intramural Research Program in the mid l980s by NIMH director Thomas Insel, M.D. By l993. His team had discovered that the distribution of brain receptors that bind to the hormone vasopressin differed dramatically between monogamous and polygamous vole species and accounted for their divergent lifestyles. How such behavioral differences could have evolved in animals that otherwise appear almost identical remained a mystery.
Insel says that the research appears to have found one of those hotspots in the genome where small differences can have a large functional impact, and individual differences are not in a protein-coding region, but in an area that determines a gene’s expression in the brain. He says this is an extraordinary example of research linking gene variation to brain receptors to behavior.
Hammock and Young were particularly intrigued with microsatellites, repeating sequences of letters in the genetic code peppered throughout these regulatory areas of the vasopressin receptor gene.
Apparently each animal species has its own signature microsatellites; for example, the repeating letter sequences are much longer in monogamous than in polygamous vole species, and even within a species, there are differences in the number of letters in the sequence among individuals.
The researchers first demonstrated in cell cultures that the vole vasopressin receptor microsatellites could modify gene expression.
Then they bred two strains of a monogamous species, the prairie vole, one with a long version of the microsatellites and the other with a short version.
Adult male offspring with the long version had more vasopressin receptors in brain areas involved in social behavior and parenting and they also checked out female odors and greeted strangers more readily and were more apt to form pair bonds and nurture their young.
Hammock says it helps if brain circuits are thought of as as locked rooms, and the vasopressin receptor as a lock on the door, and vasopressin as the key that fits it, so only those circuits that have the receptors can be 'opened' or influenced by the hormone.