Evolution of Axis Formation

University Of California-Irvine, Irvine CA

Investigators

Abstract

0130375 Hans Bode During the last 20 years a great deal has been learned about the genes and the molecular mechanisms that regulate the processes underlying the development of an embryo into a functioning animal. One of the most interesting aspects of the accumulating knowledge is that similar sets of genes and mechanisms underlie similar developmental processes in many of the diverse animals studied so far. These common features raise a number of important questions. When during animal evolution did these genes arise? Were they already present in the earliest metazoan? To what extent has the function of a particular gene, or pathway of genes been conserved throughout metazoan evolution? One approach to these issues is to study these genes and their functions in organisms that belong to groups of animals that arose very early during metazoan evolution. One of the earliest groups is the Cnidaria, whose members include jellyfish, sea anemones, and the freshwater hydra. Of these, hydra, is particularly useful since the developmental processes are well-understood. The overall aim of the proposed work is to determine the extent that the genes and mechanisms underlying axis formation in hydra are similar to those found vertebrates and arthropods. Though hydra, and all cnidarians, have a single axis compared to the two axes [anterior-posterior and dorsal-ventral] in bilaterians, a number of genes known to be involved in axis formation in vertebrates and arthropods play similar roles in hydra. A specific problem that needs to be addressed concerns the genes and mechanisms involved in the initiation of axis formation. In vertebrates, a region termed the organizer plays a central role. Recently, a region of the hydra head, the hypostome, has been shown to have clear similarities with this vertebrate structure. Thus, the focus of this proposal is to isolate genes from the hydra organizer, determine their roles, and determine to what extent the same or similar genes are involved in hydra and vertebrate organizers as well as arthropod organizing regions. The common approach is to look for homologues of genes that function in the organizer activity of a vertebtate or the fruit fly, Drosophila. This approach has been very successful but is slow and tedious. DNA array analysis provides a means for identifying a subset of genes among several thousand that are candidates for roles in organizer activity in hydra. Sequence analysis will reveal which are homologues of known genes, which belong to a specific class of gene and which are novel genes. Thereafter, the role of each of these genes will be analyzed by examining their expression patterns during the development and functioning of the organizer region as well as with the use of a functional assay. The information gained will provide (a) a more detailed understanding of the organizer in hydra, (b) a more detailed understanding of the molecular evolution of this structure, (c) and possibly the identification of novel genes that may generally be involved in organizer development and activity.