Sokolowski – generational epigenetic transmission

So one of the exciting possibilities for epigenetic modification is that it may be inherited from one generation to the other, I don’t mean inherited in the DNA sequence but the patterns in the way that the chromosomes were wrapped up or marked are inherited. And this would have to be somehow in the germ line, it would have to be in the egg or sperm or both of the parents, because that’s what’s continued into the next generation and Art Petronis who’s a professor at the Centre of CAM-H, Centre for Addiction and Mental Health in Toronto, has recently taken sperm from humans and shown even from one man that the sperm have different epigenetic markings on it so there is some evidence that sperm can be differentially modified. So there is some evidence coming along that it could be that some of the patterning, if you’ve had a stress as a child and then you have your children, children could pass on the problem that your genes have with being able to cope with stress, so that’s one idea. 

The other way that it can be translated from generation to generation has to do with a kind of cultural transmission if you like where, and Michael Meany at Mc Gill has shown this with his high and low-licking mother rats, and so in this situation you have a distribution of behavior for a mother rat, so mothers look after their babies by licking and grooming them, and people have said this is synonymous to how humans look after their babies; we don’t lick and groom our babies but we cuddle them, talk to them, touch them, and so the touching from the licking and grooming is similar, and certain mother rats tend to exhibit high-licking and grooming, so they would be at the high end licking and grooming continuum, and others exhibit low levels of licking and grooming, and when Michael takes those mothers and then looks at the babies, if the babies when they become mothers have had experience of high-licking and grooming, they tend to be high lickers and groomers, and similarly if the low-licking and grooming mothers have babies that have been low-licking and groomed, and they have babies, they tend to be low-licking and grooming and so that information alone doesn’t tell you whether this is due to genetic polymorphism, or a kind of epigenetic process, but he did a cross-fostering study where he took two pups from a high licking and grooming mother, and put those pups in with a litter that was with a low-licking and grooming mother, and then he did the opposite, he took two pups from the low-licking and grooming mother and cross-fostered them with the high licking and grooming litter. So you have a pup that is from a high-licking and grooming mother that was “genetically” from high-licking and grooming, and then you ask “what does that pup do when she’s a mom?” and you find that the main thing that matters is what your foster mom did, so if you were high-licked and groomed, whether it was your biological mother or your foster mom, you will be a high-licking and grooming mother, suggesting that it’s like a kind of, it’s due to the environment, it’s a cultural kind of inheritance, it’s not, there’s not a genetic explanation for it, and he has shown that this is epigenetics. 

So you can have grandmothers that were very high stressed, and had low-licking and grooming compared to high, and then you can give mothers, mothers who were all high-licking and grooming right, or all in the middle, and you can still see some carryover from the grandmother in some cases so, in other words, how much is going to be transmitted in this cultural way, and how much can be modified depending on experience- we don’t know. 

And so there is evidence that it’s translated from generation to generation. We don’t know the biological mechanism, if you look at epigenetic marks, which are methylation patterns we all have them, twins differ in them, we all have them, and it isn’t that they’re totally stable through your life either, they come and they go so it’s very new. And in humans it’s very difficult to study because unlike mice and flies we can’t take a part of the brain and say “well, what’s happening in that part of the brain?” We have to use blood, and when we talk about gene expression it changes depending on what tissue you look at so the blood, information from the blood may not be at all representative of the brain. So, there’s suggestion that these things can be translated but the biological analysis of it is still, I would say more work needs to be done. And the thing to keep in mind with epigenetics again is it’s not fixed, so epigenetics is not deterministic, just like DNA variation is not deterministic, and you can enrich and change the epigenetic marking.