Tag Archives: Science Saturdays

Science Saturdays: Differences in DNA – what makes you, you?

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In May, Birkbeck’s School of Science held ‘Science Saturdays’, a programme of free online talks every Saturday, open to a global audience. In this blog, Maria Pitharouli, Birkbeck and UCL PhD student, gives her account of the talk she attended by Dr Emma Meaburn, Reader in Human Genetics, about DNA and its role in shaping each person’s development, behaviours, and health.

‘What makes us who we are?’, is a question that has occupied Dr Emma Meaburn since she was a teenager and it is what led her towards becoming a Behavioural Geneticist, as she explained in her recent talk.

Behavioural genetics is focused on the influence of nature (our genes) and nurture (the environment we are exposed to during our lives) on the differences we can observe or measure amongst people. But to understand the effect of nature and nurture we need to understand first what DNA is and how big a role it plays in our day-to-day lives.

The human genome is contained in the nucleus of every cell in our bodies, and it is the complete set of genetic instructions: a sequence of approximately 3 billion of the DNA bases adenine (A), cytosine (C), guanine (G) and thymine (T). Each cell has two copies of these genetic instructions, one inherited from the mother and one from the father. Most of the genetic code is identical amongst humans and follows a specific order. Dr Meaburn talked about why this similarity in the genetic code between people is so important; the sequence of A’s, C’s, G’s and T’s acts as a guide for our cells so they can function properly and create all the components needed to sustain life.

Image 1. The letter “V” indicates the genetic variants scattered throughout the human genome. Source: Polygenic Risk Scores (genome.gov)

However, despite this similarity there are parts of the DNA code that differ between people, called genetic variants (image 1), and they are scattered throughout the human genome. These DNA differences are what really interests Dr Meaburn as they might explain some of the variation in how we think, feel, and act, or why some of us develop health conditions. In the talk, Dr Meaburn described how behavioural genetic research has shown that there isn’t a single gene (or DNA difference) that can explain differences in human intelligence, personality, or susceptibly to mental health conditions such as depression. These complex (or multifactorial) traits and disorders are the result of lots (and lots!) of common genetic variants in combination with our different life experiences.

The talk then described a method called genome-wide association studies (or ‘GWAS’) that have been hugely successful in identifying the specific DNA differences that relate to complex human behaviours and traits.  The GWAS approach requires very large numbers of research participants – typically tens of thousands of people – who donate both DNA and information about their health and behaviours. Interestingly, while GWAS have identified many of the genetic variants that contribute to differences in human health and behaviour, Dr Meaburn emphasised that each of the variants found explains just a tiny amount of the differences we see amongst people. As a result, we now know that complex mental health conditions such as depression are polygenic; any single genetic variant does not cause the disorder, rather many of them together can increase or decrease one’s predisposition to depression.

Dr Meaburn went on to describe how polygenic scores – the sum of the effect of all genetic variants that can either increase or decrease risk to develop a disorder – could potentially be useful for identifying individuals more (or less) susceptible to a wide range of human behaviours or health outcomes (image 2).  However, it is important to keep in mind that polygenic scores will never be a ‘crystal ball’, as while DNA differences are important, we know that our environment and life experiences matter too.

Image 2. Polygenic scores can help us identify someone’s genetic likelihood to develop a specific disorder or trait. Source: Polygenic Risk Scores (genome.gov)

The take home message from the talk is that the DNA sequence you have inherited from your parents is an important piece of the puzzle in explaining what makes you, you. Your own unique DNA code plays a role in shaping your development and nudging your health in certain directions.  In the last ten years GWAS research has shown us which DNA variants are important, and the real challenge for the next ten years is understanding how they lead to differences between us in how our brains work, and how we interact with others and the wider world around us.

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Science Saturdays: Coughing up a lung, pollutants in our air

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In May, Birkbeck’s School of Science held ‘Science Saturdays’, a programme of free online talks every Saturday, open to a global audience. In this blog, Tina Wright, Birkbeck PhD student, gives an overview of the talk she attended about pollutants in the air and how they affect the physical wellbeing of humans.

The Science Saturdays talk, ‘Coughing up a lung: pollutants in our air’ delivered by Dr Katherine Thompson, Reader in Biophysical Chemistry, observed how the environment influences physical wellbeing, more specifically, how the atmosphere and its composition of gases and particulate matter, which includes pollutants, interacts with a monolayer of molecules (surfactant) at the air-water interface of the lung to cause respiratory problems.

The content of the talk was a boon to the global cause of tackling climate change and its subsequent effects on worldwide mortality and morbidity rates. It provided information on how to investigate exactly what is happening on a molecular level and systemically in our bodies.

Our atmosphere, pollution and photochemical smog

Our atmosphere predominantly consists of nitrogen (N) and oxygen (O2) along with trace amounts of unnatural and naturally sourced gases, the former being sourced from human processes, for example, car exhaust fumes. These may be from petrol or diesel motors. Petrol motors release some water combined with lots of carbon monoxide (CO), hydrocarbons from incomplete combustion of fuel and nitrogen oxides (NOx) which includes nitric oxide (NO) and nitrogen dioxide (NO2). Diesel motors burn fuel differently, therefore generate a different composition of exhaust gases, such as CO and hydrocarbons, but also release tiny particles that may be dangerous for human health, dependent on particle size.

As I’ve already mentioned, there are some natural sources of trace gases that add to our atmosphere and these include green plants that emit organic pollutants, called volatile organic compounds (VOCs).

Photochemical smog is pollution present on sunny days and has a distinct character. Nitrogen dioxide (NO2) features as a brown/orange gas, visible on the horizon on a clear day. A combination of this with volatile organic compounds (VOCs) and sunlight produces ozone (O3). It is vital for life to have O3 in the stratosphere as it absorbs short wavelengths of light that may damage our DNA, however, when present in the troposphere as a secondary pollutant, the VOC-NOx-O3 relationship keeps its concentration high during warmer months, therefore, adverse effects may occur, notably at the air-water interface of the lung.

Lung physiology, function and properties on a molecular level

The lung is composed of the trachea, bronchi, bronchioles and finally, millions of alveoli, which are tiny sacs that increase the surface area of the lung for gas-exchange of oxygen (O2) and carbon dioxide (CO2).

Our bodies are wet systems but if the alveoli were lined with pure water, the surface tension (cohesive forces between water molecules), would be too high for expansion of the lung after compression. This issue is resolved by the action of surfactants present as a film on the lung interface that are composed of lipids, proteins, and cholesterol. Its importance is reflected by premature, newborn babies that lack lung surfactant and consequentially, experience difficulties breathing.

Diagram of the human lung. Credit: Frontiersin.org.

What happens when pollutants reach the lung interface?

Dr Katherine Thompson’s research focuses on the interaction of pollutants with the lung. A single layer of molecules (monolayer) of lung surfactant, similar to when it is found on the surface of the lung, may be analysed by the reflection of light. For example, a technique known as Brewster Angle Microscopy, allows the observation of the organization of molecules at the surface or interface, a simile of the lung.

A monolayer is very thin, therefore, the wavelength of light chosen for the reflection experiments should be shorter than the thickness of the monolayer. The wavelength of x-rays (photons) are very short, therefore, it can be used to look at these reflections. Photons may hit a surface and ‘bounce off’ to a detector, comparable to a gymnast jumping and landing on a mat, then coming away. This will give information, in the case of the gymnast, on the thickness of the mat or in the experiment, the single layer of molecules.  These experiments may be undertaken whilst the lung surfactant is simultaneously exposed to ozone and a thinning of the monolayer can be observed from rearrangement, breaking and bending of molecules at the surface. Physiologically, this may lead to inflammation of the lung.

This research is of paramount importance in the modern world, where the extent of the damage to our environment, and the subsequent effect on human health, needs further investigation and awareness raised to all.

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