9317299 O'Farrell Cells develop in accord with their position within an embryo. To do so, they either read position by communicating with neighbors (regulative control), or inherit information about position through lineage (determination). Typically, embryonic cells go through a transition from regulative control to determination. In Drosophila, we know many of the genes that direct the fates of cells. The transition from regulative control to determination should be associated with a change in the regulation of these genes. One of these genes, engrailed, directs cells to form the posterior parts of segments. There is a multistepped transition in the control of engrailed expression that appears to represent a transition from regulative control to determination. Dr. O'Farrell has defined four tiers of engrailed control: initial patterning by localized transcription factors, maintenance by the wingless signal, autoregulation and control by Polycomb group genes. Dr. O'Farrell will precisely define the relationship between the type of control of engrailed and developmental determination. This will involve the use of new lineage tracing methods and the development of a method to follow gene expression in real time. Additionally, he will begin biochemical analysis of the involvement of Polycomb regulators in stable control of engrailed expression. ***
