So the second example we're going to think about in terms of a change in human diet, potentially having an outcome in the offspring is the Överkalix data. So, Överkalix is a relatively small region in Northern Sweden, and it's a quite an isolated region where they've been frequently over the, over the years, over the generations subject to to famine. But they also have extremely good records of harvest and food process, so they know when there were periods of famine, and they know when there were periods of feast. And so, this is the sort of thing, if we think back to the Dutch famine, where we would like to know in another separate study, that something similar could happen. In this case the diet, the information's not quite the same as in the Dutch famine. So, I'll explain how it differs. In this case is a correlation between increased grandparental food supply and the grand children's longevity. So, if you have too much food, if the grandparent had too much food or a surplus of food, this has a negative impact on the grandchildren. So, this is not exactly the same at all as for what we're seeing for the Dutch famine. In this case I also found sensitive periods, but the sensitive periods weren't necessarily the periconceptional period, but rather where the periods that are termed the slow growth periods. So, in grandfathers, this happens from 9 to 12 years of age, and in grandmothers, it happens in two periods. First of all, from eight to ten years of age, and then also in their fetal or infant life for the grandmothers. So, these aren't quite the same sorts of periods as we thought about for the Dutch famine. However, these are a period when you still are having germ cell maturation occurring, at least for these, eight and 9 to 12 years and eight to ten years in grandfathers or grandmothers. So, they found two grandparental effects that we'll think about in turn, using these pedigrees that we've got here. These grandparental effects were sex specific. So, in other words it depended on the gender of the grandchildren. So, if you can imagine yourself being in this generation down in the bottom here the third generation. If you are the grandsons, here they're shown as the squares, then your paternal grandfather, in other words your father's father. So, if we track back his food supply during these slow growth periods seems to alter your longevity. So, if your paternal grandfather, if you're a son and your paternal grandfather had too much food then you're more likely to get diabetes or have chronic vascular disease and have a shortened lifespan. By contrast, if you're now a granddaughter down here, if you thought, again think about your paternal grandmother this time. So, your dad's mother. Then, if your dad's mother had, an increased food supply, then we could again link these sort of sex specific effects grandparentally. So, these effects are obviously quite complicated. First of all, they're happening through the grandparents and second of all they're sex specific, but they are further complicated by the fact that there also sex specific parental effects. So, in other words, just from this generation here. So, this data, while it's absolutely tantalising that it might be that our grandparents' food supply, our grandmother in my case or a grandfather if it was, in the case of a male, might alter our own epigenetic makeup. Clearly this is a very interesting concept and something we'd like to know about. But it's quite difficult to understand because of these sex-specific parental effects. And also because although in the Överkalix data they have several cohorts, because as I said this population was exposed to feast or famine many times throughout the years and they have very good records for all of these times. They don't necessarily see these effects in every cohort. This is something that comes out of a lot of a human epidemiological studies that we need to consider. So, normally what happens with human epidemiological studies is that you would like to have whatever effect that you see in your cohort replicated in a different cohort somewhere else. This really gives people some confidence that what you're seeing might be a more generalisable effect. At the moment for this Överkalix studies, while they are extremely interesting, they haven't been replicated anywhere else yet. Although, there are ongoing studies in Britain and other countries to see if they can find these similar effects. And in contrast to the Dutch famine, at the moment there's no molecular data that goes with these Överkalix studies. So, while there's a tantalising example, this is a tantalising example, we really don't have any evidence to say that this is certainly an epigenetic event, rather than perhaps say, being a genetic difference. So, I guess what we want to think about then in terms of how these general sorts of findings is, do grandparental effects when you have an effect through two generations. So, you've got the grandparents, the parents and the children. Do these actually mean transgenerational epigenetic inheritance through the gametes. Is one synonymous with the other? Well, what we know with these human studies in particular is that we don't have any molecular data to say that the effects being passed are only through epigenotype, rather than perhaps being due to genetic changes. So, in lower organisms, in mice or in rats where can control the environment we can control the experiments we are performing. We can control for genetics, because we have inbred strains of mice that are all genetically identical. We can also control for maternal behaviours because we can take pups from one set of parents and foster them over to a different mother. And we can also control for the timing of effect. So we can control when the particular experience of famine or feast was experienced for in an animal model. But in these cases in this human data we don't have very much control for any of these things. We also need to consider, whenever we think about grandparental effect in general, the exposure of the germ cells to that particular altered environment. In this case the altered diet. So, this is just a simple picture if we consider a pregnant mother and she's pregnant with a baby and when that baby is in utero at mid gestation it's already developing the primordial germ cells for the next generation. So, if this pregnant mother experiences a change in diet, which could influence epigenetic control, then she of course, is being exposed as the mom. Her baby, which is the second generation is being exposed. But importantly, we need to remember that there are also the primordial germ cells in that baby that are already developing and that will create that next generation. And so grandmaternal effects could be explained through an alter diet in the grandmother, exposing all of these generations at once. So, actually for the Överkalix data, you remember I said there, the sensitive period was the slow growth period of about eight to ten years in the grandmother's or around the time they were born. This is, it wasn't a period when the grandmother was already pregnant with the next generation. So, probably this is not case for the Överkalix data but is something we need to think about in general for environmental grandmaternal effects. Other than grandmaternal effects in Överkalix data, there were also grandpaternal effects. So, we had an effect where the grandfather's food supply then through his son only not through daughters had an effect on the grandsons. So, this passage down the male line only is also something that we need to consider what the appropriate controls would be or how this effect might be mediated. Now if you think about it, we know that the Y chromosome has to come from the grandfather, to the father and to these grandsons. This is the only place where these Y chromosomes can come from. And it's possible that there some epigenetic change to the Y chromosome that's being transgenerationally inherited. But it's also possible that there's been some genetic change on the Y chromosome that could be being passed through in the very normal inheritance type of fashion in this case. When we think about the exposure of this grandfather, if he's being exposed and this was in his slow growth period from 9 to 12 years of age. At this stage when he's being exposed he's clearly not pregnant, he's a male, but he is developing germ cells. So, that will effect this next generation but does not explain how the subsequent generation could be effected in this case. So, grandpaternal effects have different considerations to grandmaternal effects. There's been one other study, actually by the same group as the people who have the Överkalix data that I'll mention. There have been some, some others that are coming out now that looked at paternal effects of the environment. In this case, it's to do with prepubertal smoking. So, this is where the onset of paternal smoking begins in that same slow growth period. So 9 to 12 years in boys, as opposed to if they started smoking later, in adolescence or later in adulthood. And what they found was that if these males started smoking in this prepubertal period, then they had an increased body mass index in their sons. So, as compared with if they smoked, started smoking later. So, in other words, their sons were more likely to be overweight or obese or morbidly obese if their father started smoking in this period. So again, there's no molecular data yet to go with this finding. Again it's a very interesting finding and something that we'd really like to know about. But because it's only from a father to a son again it's possible that yes, that it's the Y chromosome, which is epigenetically changed or it's the Y chromosome which is genetically changed. Because we know smoking is actually also mutagenic. So, we know, its very well known that smoking has a carcinogenic effect because of this mutagenic effect. It's really likely in this case, or it's certainly possible that there may be some sort of genetic mediator here rather than an epigenetic mediator. And until we have molecular data it's hard to work out which of these two might be the case. So, if you want to summarise what I've spoken about for this lecture and the last lecture, can we really think about transgenerational epigenetic inheritance through the gametes in humans? Does this really happen? Well, I think the point what I want to make is that, it may well happen and if it does it's extremely important first to know and very interesting to study. But at the moment it's extremely difficult to study in humans. So, it's very difficult to really have the right controls and feel that we know we are studying transgenerational epigenetic inheritance through gametes rather than some genetic alterations that we haven't yet found. So, as I said they’re can be genetic differences that could account for different epigenetic state and we'll talk about an example of this later in the week. We know that in humans it's very difficult or next to impossible to have formal proof of epigenetic inheritance via the gametes. Because the sorts of controls we need to do here are simply not possible. So, we can't transfer gametes from one parent into another to control for you know, that particular parent's environment, if you like, and even if we could do those sorts of studies, so, usually we can't access gametes, so while we probably could access sperm, we're certainly not going to be able to access very many eggs. Even if we could do those we often can't study the cell type that's relevant. So, if for example we have a phenotype that's associated with the brain, we can't go and take a little piece of brain just to be able to work out whether this is transgenerational epigenetic inheritance. And so, while this concept is very interesting at the moment, most of the studies that have looked at the potential of transgenerational epigenetic inheritance through the gametes in humans have been epidemiological in nature because this is what's feasible to do in humans. So, this is why, over the next several lectures, what we're going to do is, we're going to turn to thinking about mouse and rat model systems where we can actually answer these questions because if we can understand mechanisms that are occurring in these organisms then we might be better placed to understand how it's happening in humans. But of course if transgenerational epigenetic inheritance through the gametes is true, if in other words we inherit more than just our genetics from our parents. But also some epigenetic marks that they potentially acquire during their lifetime, then this has a huge influence on how we interpret our inheritance of phenotypic traits. And so, we're really interested to see how this happens.
