My name is Aya Sato. I’m a staff scientist in the Carlton Lab at iCeMS. Today I will tell you about the biological
process by which you can pass your DNA, genetic information to your children. and how understanding this biological
process is important to our health. As you know, you resemble your father and mother
because you have a mixture of genetic information from both of your parents. This is what our genetic information, DNA,
looks like. DNA is actually composed of four letters, ATGC. And the sequence of these 4 different letters specify what kind of proteins are made and functional in our body. In our cells, DNA is organized by being wrapped around proteins and exist as multiple strings called chromosomes. And this is how chromosomes look like in real life. We have typically 46 chromosomes in every single cell. We inherit 23 from your mother through her egg, and the other 23 are coming from your father through his sperm. And having exactly 46
chromosomes is critical to our health. If you had even one too many or too few chromosomes, you would not be able to survive and this leads to miscarriage or infertility issues. and even if you survived, you will be born with developmental abnormalities. So the question is how are these problems of infertility and chromosomal abnormalities are coming from. Our lives start from a single cell when your mother’s egg cell came together with your father’s sperm cell. As I told you, an egg cell provides 23 chromosomes, and a sperm cell provides 23 chromosomes, and this restores 46 chromosomes in the fertilized embryo. But sometimes, our body makes mistakes, so that one too many or one too few chromosomes could be packaged in our eggs and sperm and this
leads to an embryo carrying too many or too few chromosomes, leading to infertility problems. The biological process that creates eggs and sperm is called meiosis. It’s a special type of cell division. In typical cell divisions, one cell
replicates its DNA and divides into two cells. In contrast, meiosis requires two rounds of cell divisions to generate sperms and eggs. These extra steps in the cell division make meiosis a little more complicated, little more challenging for DNA. It’s been known that humans are not very
good at doing this meiosis. Here, I’m showing the rate of eggs or sperm, or spores that carry the correct number of chromosomes. Compared to other organisms, humans have much higher error rates in meiosis. Becuase having healthy offsprings is quite essential for the maintenance of species, everyone tries to do meiosis as accurately as possible. But compared to other organisms that can produce in 99.99% success rates, we human only have 70-90% of good eggs, that carry the correct number of chromosomes meaning that 10-30% of fertilized human eggs are carrying the wrong number of chromosomes. In addition, the rate of eggs and sperm carrying the wrong number of chromosomes increase as we age. Here is the rate of babies born with Down syndrome, who have 47 chromosomes, one extra chromosome. As the mother’s age goes up, especially from late 30’s to 40’s, the rate of having babies with extra chromosomes increases quite rapidly. This means that when you are young, your meiosis is fine and generates good eggs and sperm Whereas as you get older, you make more errors in meiosis. and this leads to fertility issues. This kind of infertility problem affects about 10-15% of couples and therefore is a common issue in society. So understanding the molecular mechanisms of meiosis is very important to understand infertility issues. However, doing meiosis experiments, doing some research on human beings is not that easy. So , in our Lab, we use this model organism called C. elegans. It’s a tiny worm, but they’re one of the most widely used model organisms in the biology field. Worms are great
to study meiosis because they produce lots and lots of sperm and eggs. Another advantage of using worms is that the majority of genes in worms work in the same way as they do in humans. What we learn from these tiny worms could be directly applicable to human health. One approach we take using worms is that we can modify or remove whichever genes in worms as we want. So, for example, I could remove gene A in worms and see if this leads to a fertile worm or infertile worm. If I get infertile worms at the end, I know
that, ok, this gene A is important for meiosis and fertility. with this approach, currently we are trying
to expand the list of important genes for meiosis and fertility. The question is how we can use this information in our society. One prospect is you can specifically look at the DNA sequence of important genes that’s known to be involved in fertility. If you had an alteration in part of the DNA sequence, then this would make you realize you have certain risks which may influence how you plan your family. You can do this kind of genetic forecasting, with current technology, relatively easily. You can simply take out a little bit of your cells from your mouth with cotton swabs, and send your sample to a company
to analyze your DNA sequence. and this would make you forecast your future reproductive health. One example of this type of genetic forecasting
is breast cancer. Since the molecular mechanisms of breast cancer has already been well studied so far, we know which genes are associated with it. If you had an alteration in your DNA, then you know that you have pretty good chance of getting breast cancer in the future. As you have probably heard, the actress Angelina Jolie has this alteration in her DNAf and that made her decide to have a breast removal surgery even before she gets cancer to avoid this risk. you may think this is type of medical practice is rather futuristic or very expensive. But actually we are in the era of personal
DNA sequencing and precision medicine This year, the U.S. have decided to spend 200 million dollars to analyze 1 million people’s DNA sequences. The idea of this project is that they analyze
sequences of lots of people, and compare this information with the already existing
knowledge about certain diseases or how certain medicine and treatment would work in human bodies. And try to forecast risk of certain health
conditions or how effectively certain medicines would work for certain type of people. As of today, you can analyze your DNA sequence
starting from 100 USD So it’s not expensive any more and the cost is going down and down. This will predict the risks
of diseases like diabetes, Parkinson’s disease or certain types of cancer. Our hope is that
by learning more about meiosis and fertility, we can discover new genes that will let us forecast our reproductive health. and this will give us more power to predict and prepare for our future health. With that, I’d like to thank you for your attention and I will take your questions. [applause]