Meeting Abstract

S5.3  Jan. 5  Origins of Sensory and Neural Organization in Basal Metazoa JACOBS, David K.*; NICHOLS , Scott; HARTENSTEIN, Volker; NAKANISHI, Nagayasu; YUAN, David; UCLA; UC, Berkeley; UCLA; UCLA; UCLA djacobs@ucla.edu

The roots of the word animal imply muliticellular motility with inherent requirements for sensation and locomotory response. Cnidarians are traditionally viewed as the most basal animals with formal sense organs, yet sponges have an array of neural specific structural and regulatory genes. In summary: 1) Cnidarians employ a suite of canonical bilaterian sense-organ regulatory genes e.g. sine oculus, Brain 3, and eyes absent which are expressed in the statocyst and eye of the rhopalia in Aurelia medusae supporting a common evolutionary origin of cnidarian and bilaterian sense organs. 2) In the planula larvae sensory cells develop laterally and extend axons that integrate in the “locomotory” anterior. These larval structures are lost folowing settlement as the nerve nets, that constitute the neural organization of the polyp and medusa, develop. Thus, only the planula appears to integrate the output of multiple sensory cells in a single brain-like anterior plexus, a condition supportive of the acoel-planuloid theory of bilaterian origin. 3) Sponges, despite limited "animal-like" motility, possess a number of genes closely associated with sensory and neural organization. These include canonical sensory genes such as sine oculus and Brain 3. In addition, recent EST work documents the presence of genes such as slit and spondin that function in bilaterian axon guidance, as well as genes know to function in synaptic vessical formation and fusion. These genes may have distinctive functions in sponges, and the sensory and motor repertoire of sponges is likely more sophisticated than has been assumed in some zoological traditions. Understanding the range of roles of "sensory" genes in basal metazoans will help clarify the evolution of the multiple sensory modalities across the Metazoa as well as the functional evolution of these gene families.