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Developmental regulation of caspases during death and regeneration events in an invertebrate chordate

Programmed cell death (PCD) by apoptosis is an essential process in the development and maintenance of multicellular animals. We study the colonial marine urochordate Botryllus schlosseri which undergoes synchronized apoptosis throughout its entire adult generation every week. During a colony's death phase, the old adult cells are engulfed and recycled by circulating phagocytes simultaneously as asexually‐derived buds reach functional maturity. Thus, Botryllus is a unique model organism to study the cyclical regulation and function of cysteinyl aspartases called “caspases” during organismal apoptosis. It is well documented that caspases ‐8 and ‐9 play a role in apoptosis initiation, while caspases ‐3 and ‐7 are used in its execution. We have investigated whether caspase expression is developmentally regulated during asexual development in Botryllus. An expressed sequence tag (EST) sequencing project has uncovered several candidate sequences of the apoptotic death program, including several caspase orthologs. Using standard, semi‐quantitative PCR, we have previously demonstrated that initiator and executioner caspases are developmentally regulated in Botryllus, and exhibit maximal expression at the onset of a colony's death phase. However, as these experiments made use of genotypically distinct colonies for comparison, the effects of genetic background on caspase expression could not be excluded. In the current study, we sought to investigate the regulation of caspase expression using clonal replicates and quantitative polymerase chain reaction (Q‐PCR). Experiments are currently underway to determine whether caspase expression is associated with specific death and regeneration events in the lifecycle of Botryllus.