Cellular mechanisms of facial primordium growth

Cleft palate and cleft lip are not only disfiguring birth defects, they also cause serious problems for children affected, ranging from speech difficulties to shortened lifespan. Management and treament are stressful and costly. Facial clefting happens when bulges in the sides of the developing embryo s face fail to meet or fuse. These bulges normally make the upper lip and the roof of the mouth. This project will look at how cells making the mouse face (which develops in the same way) multiply, rearrange themselves and change shape normally and in mouse strains in which clefting happens. Individual cells will be tracked and monitored to build up a three-dimensional picture of what the cells do. This will provide a map of what should happen, and therefore help pinpoint what goes wrong when clefting happens. Understanding how the face develops normally and what goes wrong with the cells in facial tissue when clefting occurs will help future diagnosis (for example, finding mothers at risk) and treatments (potentially re-growing what is missing).

Normal development of the early face and palate depends upon controlled elongation and spatial co-ordination of the early embryonic processes that build these structures. Disruption of these mechanisms can lead to clefting of the oro-facial region, which is the commonest form of craniofacial anomaly. The directional orientation of embryonic tissue can take place through a number of cellular mechanisms, which include terminally localised and orientated cell division, changes in cell shape and cell rearrangement. Whilst an increasing number of mutant mouse models have demonstrated the importance of normal cell proliferation, particularly during palatogenesis, there is currently little known about the relative contributions of these different processes during development of the early face and palate; in particular, the relationship between cell proliferation and tissue elongation. We aim to identify and quantify in detail the cellular events underlying tissue elongation in the developing mouse embryo. Proliferation and programmed cell death will be mapped in three-dimensions using wild type embryos to provide a hitherto unavailable baseline of these cell activities during facial development. In addition, detailed lineage-tracing studies will be carried out to provide a picture of cellular lineage growth and extension using diI-labelling of murine facial explants in vitro and in vivo clonal-labelling using Tamoxifen-inducible conditional reporter mice. Finally, directional cellular rearrangement and shape change will be analysed in developing murine facial processes using time-lapse live imaging of diI-labelled explants and immunofluoresent labelling. The proposed detailed and systematic analysis of tissue growth and elongation in the facial processes will allow progress in understanding how genetic mutation can lead to cellular disruption during the complex process of facial morphogenesis.