Developmentally‐regulated expression of caspases during cyclic blastogenesis in a colonial urochordate

Abstract

Botryllus schlosseri is a clonally modular ascidian that reproduces asexually by blastogenesis, and utilizes a unique lifecycle whereby every new asexual generation in a colony resorbs the old adult generation on a weekly basis. During this process, cells from adult tissues and organs synchronously undergo programmed cell death by apoptosis, and cell corpses are engulfed by circulating phagocytes. Resorption of the entire adult generation is completed within 24‐36 hours and occurs simultaneously within the functional emergence of a new asexual generation of individuals. We have previously shown that developing buds and phagocytic cells are critical effectors in this process and as such engineer the reconstitution of a new asexual generation. Based on it unique lifecycle, Botryllus provides an excellent model system to investigate the developmental regulation of organismal apoptosis. Caspases are cysteinyl aspartases that are functionally involved in both the initiation and execution phase of apoptosis in multicellular animals. An expressed sequence tag (EST) sequencing project is currently underway in Botryllus, and has yielded several candidate caspases orthologs. In this study we have investigated their expression patterns during cyclic blastogenesis using semi‐quantitative PCR. Work is currently underway to determine whether caspase expression is up regulated during organismal apoptosis.