NYU, Biology Department
April 19, 2011
Experimental tests of the Bicoid morphogen hypothesis
The fly body plan is established early in embryogenesis by a series of transcription factors, several of which are expressed in gradients. One transcription factor, Bicoid (Bcd), is distributed as a long-range gradient that extends along much of the anterior posterior axis. Bicoid has been proposed to provide "morphogen-like" patterning activities, and intense efforts are underway in numerous labs to quantify the gradient and mathematically model the responses of Bcd-dependent target genes. I will discuss two experimental approaches designed to directly test the most critical assumptions of the model. Briefly, our results suggest that Bcd concentration in the wildtype gradient is in excess at every position along the AP axis, and that most target genes are not positioned primarily by Bcd concentrations. We present data that support the idea that target gene registration is achieved by a network of genes that include the Bcd gradient, the terminal patterning system, and several repressor gradients that antagonize Bcd-dependent activation.