Embryonic cells count to control their development
28 November 2007
Scientists have uncovered embryonic cells’ ability to measure and respond to the strength of the molecular signals that guide nerve development in the growing spinal cord. The discovery may help scientists learn how to direct stem cells to turn into any cell type including nerve cells. The team from the MRC National Institute for Medical Research (NIMR) and led by Dr James Briscoe publish their research in Nature.
It has long been understood that cells respond to chemical signals and that different strengths of a signal generate varied responses. Now, Dr Briscoe’s research has shown how cells translate signal strength into developmental instructions by converting the strength of a molecular signal into time. The length of time is then interpreted as a command to produce a specific cell type.
‘‘The cells appear to translate the strength of a chemical signal into time. The stronger the signal, the longer it is received and the less sensitive to the signalling molecule the cell becomes. It’s a bit like measuring how loud a stereo is by timing how long it takes to turn the volume down. The cell counts down the signal and then translates the time taken into instructions to direct growth of the many different kinds of nerve cells that build the spinal cord.’’ Dr Briscoe explains.
Variation in the strength of a signal is crucial in controlling embryo cell development. The team used cells from chicken embryos to study how nervous system tissue develops. They monitored the effect of different concentrations of a signalling molecule called SHH; different levels of SHH create diverse types of nerve cell in the spinal cord.
By focusing on SHH the team discovered that nerve cells actually convert the concentration of the SHH signal into time.
A microscopic image of the developing nervous system in a chicken embryo, the different colours represent the activity of genes in nervous system stem cells. The pattern of gene activity is established in response to different concentrations of SHH.
Dr Briscoe is confident that the study results could be used to help understand how to guide stem cells to a chosen cell type, he said:
“Understanding how cells respond to different amounts of a signal raises the possibility that we can direct stem cells to become specific types of nerve cells, which could be really useful in developing new therapies. Moreover, it’s possible that the same mechanism is used elsewhere in the embryo to organize the development of other tissues.”
Original research paper: Interpretation of the sonic hedgehog morphogen gradient by a temporal adaptation mechanism is published in Nature.
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