How is embryonic development timed and scaled?

How do cells know how long they need to divide to allow structures such as limbs to grow to their correct sizes?

We will work on the developing chick wing bud to test if two molecules – one that tells the cells to divide and one that tells them to stop dividing – form the mechanism of a growth/size clock. In this hourglass timer model, the level of the molecule that tells cells to stop dividing increases until it passes a threshold that stops cell division and growth. We will also test if these growth clocks can be reset to an earlier time in the embryo. We will also investigate why different species have differently sized limbs. We will ask if limb growth clocks run at species-specific rates in a range of birds of different sizes, including quails, chickens and ducks. Understanding how these clocks function can give insights into human disorders in which the timing of embryonic growth is disrupted.

If we can use this information to reset limb clocks later in adults and reset development, we might be able to devise clinical strategies to aid limb regeneration.