What makes some parts of our bodies pudgy - but others free of fat?
An important breakthrough, unveiled today, will help scientists get to grips with one of the most complex and intriguing systems - our own.
Massey University scientist Dr Sebastian Schmeier has been working with an international team that has identified the central control regions for all human genes.
Their work, published today in the leading journal Nature, will boost our understanding of how cell types differ - something that could address issues from disease treatment to so-called "fat genes".
Different types of cells turn different genes on and off, giving the cells their unique properties.
But understanding why different genes are on or off in a particular type of cell is a mystery that Dr Schmeier, a lecturer in bioinformatics and genomics at the university's Albany campus, and his colleagues have long been trying to solve.
All genes have central control regions, called promoters, which decide whether they are turned on or off.
The collaboration Dr Schmeier has been involved with, known as the FANTOM5 project, has offered what he described as the most comprehensive atlas on the regulatory regions of human cells so far.
"To understand why, for example, fat cells behave differently to brain cells, we need to know how different genes are turned on and off in different cells."
The problem, he said, had been that the locations of the regions that control gene behaviour hadn't been known.
Technology developed by the Riken science institute in Japan had finally allowed scientists to track all these regions down.
"Many human diseases result from genes being inappropriately turned on or turned off," he said.
"Identifying the regions that control these decisions will allow us to understand why this happens."
The project's scientific coordinator, Dr Alistair Forrest, described humans as "complex multicellular organisms" composed of at least 400 distinct cell types.
"This beautiful diversity of cell types allows us to see, think, hear, move and fight infection yet all of this is encoded in the same genome," he said.
The difference between all these cells was what parts of the genome they use - brain cells, for example, used different genes than liver cells, and therefore worked very differently.
"In FANTOM5, we have for the first time systematically investigated exactly what genes are used in virtually all cell types across the human body, and the regions which determine where the genes are read from the genome."
The results were expected to be an essential resource for developing a wide range of technologies for the life sciences, leading to the development of regenerative and personalised medicine in the near future.
Solving the puzzle
*The human body is a complex organism composed of at least 400 distinct cell types.
*The diversity of cell types allows us to see, think, hear, move and fight infection - but it's all encoded in the same genome.
*Scientists have now mapped out the central control regions for all human genes, allowing them to see how and why these regions turn different genes on and others off, giving cells their own unique properties.
*The breakthrough is expected to boost the development of regenerative and personalised medicine in the near future