Mesodermal phenotype of loss of heartless function

On the left, transverse sections of wild type embryos stained with an antibody to Twist protein (which stains the entire mesoderm at these stages) show the normal process of mesodermal migration. The invaginated mesoderm loses its epithelial character and spreads dorsolaterally, until by stage 10 it forms a monolayer underlying the ectoderm. The mesodermal cells then divide during stage 10.

On the right, age-matched embryos lacking functional Heartless protein (one of the two Drosophila fibroblast growth factor receptors) are shown. Note the failure of orderly migration, and the random segment-to-segment variation at the end of the migration period. (The four small images represent four sections from a single htl embryo.