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What is Gene Expression?



In these resources, we will explore how environment during early life impacts on gene expression throughout life, and the work that scientists in New Zealand are undertaking to try to understand more about this important phenomenon.

Scientists from the Developmental Origins of Health and Disease (DOHaD) research group at the Liggins Institute are investigating how epigenetic mechanisms underpin the relationship between early life environment and phenotype. 

Gene expression is the term used to describe the process of taking the information that is contained on the genes (the genotype) and building proteins, which create the phenotype of the individual.  

A copy of the entire genome of an individual is contained in the nucleus of every cell, yet only those genes required by a particular cell are turned on, or expressed in that cell. There is a system of control designed to ensure that genes are only expressed when they are needed. However, the phenotype is not simply determined by the genotype. Interactions between genes and the environment impact on gene expression, and therefore on phenotype.  

Watch this video to learn more about epigenetics.


The Effect of Environment on Gene Expression


The photograph on the right is a typical group of year nine girls starting secondary school in New Zealand. They are between 12 and 14 years of age, and most of them will have already begun the journey of puberty, changing physically from a child to an adult. However, if we went back 100 years and looked at a group of equivalent New Zealand girls, we would discover that it would be extremely unusual for any of them to have started puberty. Why has this change happened?   


In 1900, the average age for girls in most western societies to get their first period was between 15 and 16 years. Boys would have been approximately two years older when they began puberty. In 2010, the average age for girls in western societies to get their first period was around 12 years. For boys, puberty now begins at around 13 ‐ 14 years.


Puberty, like all physiological processes, is controlled by genes. So what has caused the genes that initiate puberty to turn on (express) earlier?


For many years scientists believed that the earlier onset of puberty that we have observed over the last 100 years was caused by better living conditions for children. Better nutrition combined with improved sanitation, hygiene and infection control meant that children were healthier and were entering puberty earlier.   


Scientists are now sure that improved childhood conditions, while contributing to the change in timing of puberty, are not the only cause. A number of prominent scientists, including New Zealand’s Professor Sir Peter Gluckman, believe that the change in timing of puberty is linked to environmental factors in early life that are contributing to changes in life history. 


Scientists from the Liggins Institute and the National Research Centre for Growth and Development have shown that the nutritional environment that a fetus experiences in the womb has a strong influence on the age at which puberty starts. If the mother eats a high-fat diet or is undernourished, when the fetus grows up it is more likely to start puberty early. They have also found that as these offspring grow up they are more likely to have learning difficulties, eat more, exercise less, become obese and suffer from type two diabetes and/or high blood pressure.


Evidence in Human Populations


Evidence from the Raine Study 

Dr Deborah Sloboda, a Senior Research Fellow at the Liggins Institute, with Australian colleagues investigated adolescent girls that are part of the Raine Study at the University of Western Australia. This longitudinal study started in 1989 and followed 3000 pregnant women and their children. The study recorded fetal growth, birth weight and body mass index (BMI) at age eight years and age at menarche (first period).    


Information from the Raine Study showed that girls who were youngest when they had their first period were smaller at birth and fatter at eight years of age.


Professor David Barker’s Studies 

Professor David Barker and his colleagues presented extensive data in the 1990s demonstrating that there is a relationship between low birth weight and increased likelihood of heart disease and type two diabetes in adult humans (Fig 3). 

Using meticulous data about pregnancy, birth and early life kept by Ethel Margaret Burnside, the UK’s first Inspector of Midwives, they could compare the early life records of 16,000 men and women born in Hertfordshire between 1911 and 1930, with their health as adults. They showed that those born smaller were more likely to suffer from heart disease and type two diabetes as adults.