Tanigami, James and colleagues then went on to create a comparative map between genomes of the rat, human and another rodent popular with geneticists, the mouse. They found that large regions of the rat genome have a similar structure and arrangement of genes as that of human and mouse. Comparative maps are useful because they enable information about genomic organization from one species to be transferred to another and provide insight into genomic evolution. These genome and comparative maps of the rat will greatly facilitate the identification of genes controlling traits and disease, as well as arming the research community with the resources needed to undertake the genome sequencing of the rat. The defect is often inherited, but the large number of genes involved in facial development has confounded geneticists.
Palate fusion is orchestrated by a series of events.
The edges of the two developing palatal shelves are coated with a layer of epithelial cells, and are separated from each other by a basal membrane. Molecular signals from the basal membrane keep the epithelial cells growing and dividing. In the absence of signals from the basal membrane, the epithelial cells die, migrate or change their identity - this allows the palatal shelves to fuse. Egfr-deficient mice have decreased levels of MMPs, indicating that impaired Egfr signalling reduces MMP activity, leaving the basal membrane intact and inhibiting palate fusion. These findings reveal how defects in Egfr signalling inhibit palate closure and raise the possibility that mutations of genes encoding additional binding partners of the Egfr receptor, as well as the downstream targets of the Egfr signalling pathway, may cause human cleft palate.