Pharmacological and molecular investigations of mechanisms of metamorphosis in the marine gastropod Phestilla sibogae

Metamorphosis is the critical link between the larval and adult forms in the biphasic life cycle of many diverse metazoans. Metamorphosis in the marine gastropod Phestilla sibogae is rapid (taking less than 24 hours) and results in a change in habitat and feeding mode from larval facultative planktotrophs to benthic, carnivorous adults feeding on the coral P. compressa. During metamorphosis larvae of P. sibogae lose several structures such as the larval shell and operculum, the velum, larval kidney cells, larval retractor muscles, nephrocysts, and foot glands. In addition, morphogenic changes such as synthesis of the buccal mass and epidermal cell movement also occur during metamorphosis. The goal of this dissertation was to elucidate mechanisms that regulate metamorphosis in P. sibogae. A survey of agents with putative affects on transcription, translation, and phosphorylation indicated that further investigation into the possible role of transcription and translation in the progression of metamorphosis, and of phosphorylation in both the induction and subsequent metamorphic response is warranted. Pharmacological assays using transcription inhibitors to determine the importance of gene expression before, during, and after metamorphosis in the marine gastropod Phestilla sibogae indicated that no increase in the net rate of transcription occurs during metamorphosis. However, changes that occur within the first 12 hours, such as epidermal cells movement, degradation of larval musculature, and synthesis of the buccal mass, plus completion of metamorphosis, and early juvenile development may depend on de novo transcription. Additional approaches were necessary to measure quantitative changes in specific transcripts during metamorphosis, and therefore cDNA libraries were constructed and then a subtractive screen was performed to narrow the pool of possibly interesting candidate genes with a role in metamorphosis. Measurements by Real Time RT-PCR indicated that the relative abundance of a putative laminin receptor in cDNAs isolated from a single metamorphosing larva was 8-fold greater than in an individual competent larva. Together these studies add to the knowledge of what role transcription plays during metamorphosis in P. sibogae.