How we are built
The genes that control how specific tissues and organs develop in human embryos have been identified.
Individual organs and tissues form in human embryos during the first two months of pregnancy. Any errors during this crucial stage of human development can result in miscarriage or serious birth defects. Yet remarkably little is known about how this process works. What is known has been inferred from studies of how other animals develop, human stem cells grown in a laboratory, and babies born with genetic conditions that cause developmental problems.
Genes control the way that organs and tissues form, and are switched on or off in complex patterns during development to ensure that particular cells develop into one type of organ and not another. When genes are switched on, their DNA is copied into molecules called RNA. Many RNA molecules are used as templates to make proteins, which then perform critical roles in cell processes. One way to find out which genes are activated during development is to identify which RNAs are made by cells in the embryo.
Dave Gerrard. Andrew Berry and colleagues used a technique called RNA-sequencing to identify the RNAs that human embryos make while their organs and tissues form. The RNA came from many different tissues including the heart, limbs and the roof of the mouth — which had been collected according to the Codes of Practice of the UK Human Tissue Authority. Gerrard, Berry and colleagues developed a new computational model that used the identity of the RNAs to decode the precise patterns of gene activity in the tissues. The model correctly identified many genes that were already known to cause developmental problems when faulty, and identified numerous others that are now predicted to cause developmental defects in humans.
Gerrard, Berry and colleagues also discovered over 6,000 RNAs in the human embryos that are unlikely to code for proteins. These “non-coding” RNAs may have other roles in cells, such as switching off genes, and many of them appear to be specific to human embryos. Together, these findings have uncovered new patterns of gene activity that drive development in human embryos and provide a resource for studying how organs and tissues form. Future challenges are to understand what controls these patterns of gene activity, and how the patterns change over time.
To find out more
Read the eLife research paper on which this eLife digest is based: “An integrative transcriptomic atlas of organogenesis in human embryos” (August 24, 2016).
Read a commentary on this research paper: “Transcriptomics: How to build a human”.
