New work out @Cell!

Our new work on developmental timing is out in Cell!

Why do different parts of the body develop at different times, and how have these differences evolved? One striking example comes from our limbs: while birds initiate their forelimbs and hindlimbs at approximately the same time, mammals show a pronounced delay in hindlimb development. This difference in developmental timing, known as heterochrony, has long been recognised, but what causes it and why it evolved has remained unclear. In our new study, we found an unexpected connection between limb developmental timing and the environment experienced by the early embryo. Before the placenta becomes fully functional, mammalian embryos develop under relatively low oxygen conditions. We discovered that hypoxia selectively delays the developmental programme that initiates the hindlimb, while forelimb development is comparatively protected. Our findings reveal how an environmental factor can reshape developmental timing in a tissue-specific manner, and suggest that the evolution of mammalian limb heterochrony may be intimately linked to the unique physiological environment of mammalian pregnancy.