Writing your behaviour, your skills and your fears on top of your genes and passing it on to your kids - Epigenetic inheritence

Do we pass on our habits, our behaviour, our talents or our fears to our young ones? Or you can ask in a less colloquial manner – can the learnt behaviour be passed on to the young ones via molecules that causes other genetic traits to be passed on? Just like you pass on genes for skin colour, eye colour, height, etc to your kids, do you pass on the ability to play piano as well. In a way yes, but it might not be as straight forward and simple.

Well for beginners, you don't pass on learnt behaviour by passing on the genes to next generation. This is for a simple reason that learnt behaviour does not reside in the DNA sequence. When you learn something new during your lifetime, let’s say playing a piano, you don't have to mutate your genes to remember how to learn piano. All you need to do is modify how cells in the brain, specifically neurons that process music and motor neurons that make your fingers play the piano are connected. The more you learn, more optimised those connections become. You get better and better at coordinating the musical notes in your head and strokes your fingers make. At best what you change at level of genes is how much of the gene required in making and maintaining these connections, in these cells is expressed. So while one way of passing on your talent to your kids would be to invest time and teach them, but what is the probability that if you learnt piano your kid will too, without you teaching it to him or her? Or at least your kid will have higher relative probability to play any other musical instrument, vaguely? Well in this case without you teaching your kid the piano , him/her learning the piano is quite unlikely, but it appears that there might be something yet more elegant going on.

First of all, memory , as we know it , in form of synapses is not passed on. However what does get passed on is likelihood of response to a given stimulus in environment. That is giving training child of a piano player might learn playing piano faster. Or if a parent develop a fear to certain odour in environment, the child is might be more likely to be sensitive to that and related orders in his/her lifetime. Like mentioned before, this kind of behaviour inheritance doesn't require genes to mutate and pass on. Nonetheless, what happens in this case if that the way amount of gene is expressed in cells gets regulated. Think of it this way, genes are not binary switches which make protein when they are on and stop making protein when they are off. They are quantitative, That is there is a tight regulation on how much certain gene is expressed. The cells can pump up expression of protein produced by single genes or it can pump it down, The final amount of end-product or protein product of the gene in the cells is what will eventually display the behaviour. Just like you control the fan speed based on how hot you are feeling. To achieve this kind of regulation cells tend to methylate the genes or they chemically modify the proteins that pack the DNA. So if cell methylates a gene or add an acetyl group to the hi stone (the surrounding protein), you get a tightly packed region of DNA, where the mRNA --> protein machinery does not get recruited. Leading yo down regulation of genes. Similarly they can also modify the proteins surrounding the gene in such a way that it becomes loosely packed giving easy access to RNA making enzyme called RNA polymerase.
This regulation of quantitative gene expression by modifying either the DNA by methylation or by modfying the surrounding protein hi stones is the crux of new knowledge – genetics. Genetics or extra genetic information help regulates the genes in lifetime of a person became apparent quite sometime ago. In fact one of the best example of effect of epigenetic in person’s life is the dutch famine winter. Where people who were in there mother’s womb during her second/third trimester turned out to be obese later in life. This was a clear example on how what mother faces in pregnancy is written into how the offspring will express his/her genes. In this case since mothers programmed the kids to to store more fat, they had high expression of fat storing genes.Probably because fat cells of fetus were thinking – hey looks like there aint much food in the outside world, lets store whatever we can in our lifetime to avoid such starvation again.

Nonetheless, what about there epigenetic tags on DNA and hostones getting tranffered to next generation. The thing is that from the few studies of transgenetational epigenetic it does look like that these imprinted epigenetic marks are transffered to the offsprings. At least some them do make it not all. So let’s say the mice parent is given a smell , folled by a fear stimulus such as foot shock. It has been shown that under all contorlled conditions these mice seem to become sensitive towards this ordor.
In fact, here is summary of some research that I posted earlier in my fb group discussion of the topic -
In fact, in April 2017 Lehner's and Vevouri's labs in Spain showed that exposing C elegans to high temperature caused it to express the endogenously repressed copies of genes. This was linked with altered methylation of Histones. They found that the expression pattern was inherited over 19 generations.
Now one may ask , alright but does changed expression of genes even happen in mammals , if so does it do anything. In fact earlier in 2014 Dias and Ressler , published in Nature neuroscience. These guys saw that if you fear conditioned the mouse to certain odor, the expression of genes that make receptor for that odor changed. The fear response to that odor persists in F1 and F2 generation, which have never been exposed to this odor. The credit for this response goes to reduced methylation of receptor gene and change in neuroanatomy in F1 and F2. To rule out learnt behavior they even made F2 generation using IVF. The F2 still displayed similar characteristics.
Now comes the important question. Does it happen in humans? Well decesendants of Holocaust victims show decreased cortisol levels. Making them less resistant to stress.
I can describe more research but that will just make this post longer. I think these stiudies covers the crux of what I want to say. In a nutshell think of it this way - if you learnt playing piano, it might not make you child a piano player. However to learn piano , the gene expression changes , that enhanced your motor coordination skills can be inherited. So child will be better at picking up other activity that also required motor coordination skills. (Also, this is just an example to give an idea, the piano related research has not been conducted, but wont it be cool if it is done).
What remains elusive is how the epigentic changes that are supposed to be limited to the brain cells of parent who learnt a certain behaviour tranffered to germ cells. (Well if you didint know the germ cells compartment is kept seprate in most organism in kingdom animilia. So while rest of the body cells, aka somatic cells , which include brain cells – help you survive; the germ cells dedicate their life in isolation to make sure you repoproduce well). Lets cross the fingers and watch what future research will reveal.

PS -
Food for thought: If we get hints on expressing which genes in what quantity will make you more skilled for learning music or playing football, the good news is you may be able to control epigenetic changes by mere modifaction via drugs. This means you might not have to do all the fancy genetic engineering to to make those designer babies.

Sources:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2579375/
2. https://www.ncbi.nlm.nih.gov/pubmed/28428426
3. https://www.ncbi.nlm.nih.gov/pubmed/24292232
4. https://www.scientificamerican.com/article/descendants-of-holocaust-survivors-have-altered-stress-hormones/