Drs. de Couet and Callaerts are trying to understand the molecular and developmental mechanisms underlying the invention of morphological novelty. Much of the progress in this area of evolutionary biology has been derived from comparing the developmental modes and the causative genes of model organisms such as Drosophila with those of representatives from other phyla. The identification of genes involved in pattern formation and their conserved structure highlight the importance of developmental events for the evolution of new form and function, and provides new directions for evolutionary biology. Whilst arthropod and vertebrate development have been studied in great detail, the development of Mollusks is poorly understood at the molecular and cellular levels. The phylum Mollusca comprises several classes of highly diverse invertebrates without overt segmentation and metameric organization. Mollusks are characterized by an external shell, a muscular foot and a rasping organ, and are commonly elongated along the dorsoventral axis. Among the Mollusks, the cephalopods have achieved the highest morphological and physiological complexity. It is proposed to investigate developmental processes and molecular parameters that give rise to the adult characteristics of the cephalopod Euprymna scolopes, a small sepiolid squid endemic to Hawaiian waters. Cephalopods are highly specialized Mollusks with a complex nervous system and powerful sensory organs. A subset of homeobox-containing genes, the Hox-genes, are commonly considered pivotal determinants in anteroposterior patterning. The expression patterns of these genes have been extensively used as molecular markers for judging evolutionary relationships, such as homologies of structures along the anteroposterior axis. In preliminary studies they isolated sequences of a family of Hox genes and of other homeobox-containing regulatory genes from Euprymna. Extensive phylogenetic analyses led to the conclusion that cephalopods have a set of at least nine Hox-like genes most closely resembling those isolated from polychaetes and ribbonworms. Specifically, this study aims to (1) To establish techniques for experimental and molecular-genetic manipulation of Euprymna scolopes arm development, and (2) To isolate and characterize Euprymna genes homologous to Dll/Dlx, apterous/Lhx2/Lmx1, Tbx genes, BMP2, hh, and Wnt, and to initiate the study of their expression patterns. The detailed molecular analysis of cephalopod axial patterning genes and their developmental expression patterns may hold important cues to explaining the diversification of appendage number and appearance.
