14 DAY TRIAL // What's the connection between black hair, body weight and stress? Just one gene encoding for proteins previously believed to be involved in the immune system. This is the conclusion of a research carried on dogs at Stanford University and published in the journal Science. Defensins appear to be rather involved in regulating pigmentation, metabolism and synthesis of glucocorticoid hormones (involved in stress).
"This study could have implications for understanding genetic factors involved in obesity, diabetes, and related diseases," said co-author Glenn Millhauser, professor of chemistry and biochemistry at the University of California, Santa Cruz.
Most mammals have a common genetic pattern causing the coat color, but dogs are different. The new research detected a new dog gene adding to the two main coat-color genes common with other mammals. But the new gene encodes a beta-defensin protein, from a type named defensin, previously believed to be involved in immunity.
This protein appeared to be involved in the melanocortin circuit, determining the type of melanin and cortisol quantities synthesized by the body. This causes not just the skin/hair color, but also stress reaction and weight control.
"We suspect that defensins will turn out to have a role in all aspects of melanocortin signaling, not just coat color," Millhauser said.
"The discovery of a new participant in this pathway opens up additional areas for drug research," said co-first author, Sophie Candille, a Stanford geneticist.
The DNA analysis was made on 38 dog breeds, from Large Munsterlanders to minute schnauzers.
"Looking within one breed rapidly identifies the general region, but looking at different breeds allows you to home in on the gene that's responsible," said lead researcher Greg Barsh, Stanford geneticist.
One type of beta-defensin gene turns dogs yellow, while another mutation causes black dogs. When the last dog gene was inserted in transgenic mice, their fur turned black.
Humans have 40 to 50 various defensin genes; dogs a maximum of 46.
"We really have very little evidence that defensins do much in terms of defending. The genetic approach is more agnostic, and suggests that defensins have additional or alternative functions outside the immune system." said Barsh.