Monday, September 8, 2014

Your Sperm Talk To Your Children

"In a recent paper in the Proceedings of the National Academy of Sciences USA, Qing-Yuan Sun of the Chinese Academy of Sciences and colleagues used a drug to make male mice prediabetic. And unexpectedly, their offspring also became prediabetic as adults.

Was this due to the fathers' behavior around their offspring? No—the males were there solely for mating. Instead, becoming prediabetic caused epigenetic silencing of some genes in the pancreas of these males (an organ centrally involved in diabetes). And the same epigenetic changes occurred in their sperm as well, also affecting their offspring's pancreases.

This applies to behavior too, as reported in a recent paper in Nature Neuroscience by Isabelle Mansuy of the University of Zurich and colleagues. Prior work showed that if you stressed young male mice, as adults, they differed from control mice in how readily they explored a new environment and how quickly they gave up trying to cope with a challenging task (findings pertinent to understanding anxiety and depression).

Critically, the offspring of those males showed the same behaviors. Again, Dad wasn't doing any parenting. Instead, the stressful upbringing caused epigenetic changes (due to those micro-RNAs) in sperm. In a tour de force, the authors injected micro-RNAs from sperm of stressed males into fertilized eggs—passing on the behavioral trait. Thus, early life stress changed adult behavior of male mice, who passed it on to their offspring via epigenetic changes in their sperm."

Summing up the prior state of knowledge about sperm and epigenetics, the author states: "Naturally, this is turning out to be wrong."

Naturally. The most remarkable thing about Science, I think, is how it lays bare the arrogance of man.

Weston Price observed, in the 1930s:

"While it has been known that certain injuries were directly related to an inadequate nutrition of the mother during the formative period of the child, my investigations are revealing evidence that the problem goes back still further to defects in the germ plasms as contributed by the two parents. These injuries, therefore, are related directly to the physical condition of one or of both of these individuals prior to the time that conception took place.

"A very important phase of my investigations has been the obtaining of information from these various primitive racial groups indicating that they were conscious that such injuries would occur if the parents were not in excellent physical condition and nourishment.

"...In the light of these data important new emphasis is placed on the quality of the germ cells of the two parents as well as on the environment provided by the mother. The new evidence indicates that the paternal contribution may be an injured product and that the responsibility for defective germ cells may have to be about equally divided between the father and mother.

"...We are apparently dealing here with a factor which, while it may be related to the germ plasm and to the prenatal growth period, clearly involves other forces than those that are at work in the case of hereditary defectives. Since these changes have to do directly with disturbances in growth of the head, particularly of the face and of the dental arches, we are concerned with such evidence as may be available as to the nature of the forces that readily affect the anatomy of the skull.

"The general architecture of the body is apparently determined primarily by the health of the two germ cells at the time of their union. This architectural design may not be completely fulfilled due to interference with nutritive processes both before and after birth."

Nice to see Price confirmed.

And if there's a way to turn these triggers on, there's a way to turn them off.

In other news:

[Paragraph breaks added for readability.]

"Because germline mutations are the source of all evolutionary adaptations and heritable diseases, characterizing their properties and the rate at which they arise across individuals is of fundamental importance for human genetics.

After decades during which estimates were based on indirect approaches, notably on inferences from evolutionary patterns, it is now feasible to count de novo mutations in transmissions from parents to offspring.

Surprisingly, this direct approach yields a mutation rate that is twofold lower than previous estimates, calling into question our understanding of the chronology of human evolution and raising the possibility that mutation rates have evolved relatively rapidly...."

Surprisingly? Direct measurement is best for a reason, any carpenter can tell you that!

But at any rate, I suspect that the epigenetic effect will prove to be much more important that currently thought, and will explain how a low rate of mutation can produce high rates of change: if you can turn genes on and off in response to the environment, you can adapt without needing to change genes, and in a more predictable fashion.

That trait would be evolutionarily useful...