Scientists have discovered how the production of different types of nerve cell and the growth of the spinal cord are coordinated during the development of embryos.
The research was led by scientists at the Medical Research Council's National Institute for Medical Research (NIMR; now part of the Francis Crick Institute).
Embryonic development requires the production of new cells with specific identities and functions. But until now, scientists didn't know how a growing tissue establishes and maintains the right proportions of different cell types.
Dr James Briscoe's team at NIMR addressed this question by studying the development of nerve cells, or neurons, in mouse and chicken embryos.
Progenitor cells are cells that can generate one or more cell types but cannot divide and reproduce indefinitely. In this work, the scientists showed that the proportions of progenitor cells that give rise to different types of spinal cord neurons change during embryonic development.
These changes in proportions were similar in both mouse and chick embryos, and in a mutant strain of mouse that is smaller than normal.
The changes in progenitor cell proportions couldn't be explained by differences in the rate of cell division. Instead, the researchers revealed that different mechanisms are employed during two distinct phases of spinal cord development. Initially, morphogen gradients - long range signals that partition the tissue into domains of distinct cell types - establish the pattern and proportion of different cell types.
During the second phase, the growth of these domains is controlled by the speed at which progenitor cells differentiate to become neurons. It is this regulation of differentiation rate that appears to account for the proportions of different domains and accommodate variations in size.
Anna Kicheva of NIMR said: "The use of quantitative methods has allowed us to measure, for the first time, how the number of each type of neural progenitor cell in the spinal cord changes during embryonic development. Our data reveal that the proportions of different cell types are controlled using different mechanisms at different developmental times and that the rate of differentiation is key to explaining the final pattern."
Dr Briscoe added: "Our study provides new insight into the long-standing question of how growth is coordinated with the production of different types of cells in developing tissues. It's likely that similar strategies are used in other developing tissues.
"Our findings might help to inform tissue engineering research - which aims to artificially grow tissues to repair or replace diseased or damaged tissues in patients."
The paper, Coordination of progenitor specification and growth in mouse and chick spinal cord, is published inScience.
