Several morphogenetic gradients have been shown to pattern the early Drosophila embryo. Bicoid patterns head, thorax and abdomen through the specific activation of zygotic genes that direct proper development along the antero-posterior axis. However at least two other systems hunchback (hb) and caudal (cad), appear to also play important roles in the embryo. These two genes may represent the ancestral patterning system of insects whose function has been partially taken over by Bicoid in Drosophila.
One of the problems in uncovering the role of these genes is the high level of redundancy and of cross-interactions among the different maternal systems. We propose to analyze the morphogenetic properties of each system in an embryo that is fully responsive to patterning by these molecules, but where all potential interactions/redundancy with the other maternal systems have been eliminated. Construction of this 'embryonic test tube' requires that we genetically remove all maternal patterning systems (by generating flies whose germline is mutant for bicoid, hunchback, caudal, nanos, the terminal and dorso-ventral pathways). In this background, we will provide artificial gradients for each morphogen to be tested. We will first focus our attention on the role of Bicoid, Hunchback and Caudal. Because of the cross-interactions among these systems, it is still unclear whether Bcd has any role on his own, and what the morphogenetic roles of Hb and Cad are. We will also test the ability of Nanos and the terminal system to pattern the embryo. As an extension of this work, we will test the role other molecules that have been proposed to act as morphogens, in particular the gap genes products as well as secreted molecules such as Dpp, Wg and Hh. The function of these molecules has so far been analyzed in situations where an extensive pre-pattern already exists.
This work will provide insights into the direct role of critical patterning molecules on cellular events that lead to the determination of positional values in the embryo or, more generally, in other tissues.
