Molecular biological analyses of nutrient transporters and growth physiology in marine invertebrate larvae

Despite the impact of recruitment success on the population biology of animals in the ocean, the physiological rates influencing this process remain poorly understood. The series of investigations reported here provide a description of these traits from the perspective of molecular physiology. The overall approach consisted of isolating genes involved in these physiological rate processes from cDNA libraries and evaluating their expression patterns in the context of development. Genes encoding amino acid transporters in embryos of the purple sea urchin Strongylocentrotus purpuratus were expressed in oocytes of the frog Xenopus laevis, providing experimental proof of their amino acid transport functions. Comparison of expression patterns revealed that while multiple transporter genes are simultaneously expressed during sea urchin development, the expression patterns differ between genes, suggesting a complex model of regulation of expression and amino acid transport physiology. Genes showing differential expression in fast-growing genotypes of the Pacific oyster Crassostrea gigas were identified through comparison of transcriptomes, resulting in the selection of ca. 200 candidate growth genes. These genes were tentatively identified by sequence similarities with previously characterized genes, revealing the involvement of multiple physiological processes in growth heterosis (e.g. protein synthesis, regulation of feeding, and energy metabolism). Differential expression of a subset of these candidate genes (ribosomal protein genes) was verified in fast-growing genotypes through independent methods and in independent genetic crosses, suggesting that non-additive expression of ribosomal protein genes is a common feature among fast-growing hybrid genotypes. These genotype-specific differences in expression were shown to occur early in development. The data presented here represent the first functional characterization of dissolved nutrient uptake genes in echinoderm larvae, and the first description of global gene expression profiles characteristic of rapid growth in bivalve larvae. These findings thus provide new insights into decades-old questions in marine biology, and molecular tools that will allow more thorough characterization of the mechanisms involved in ecologically important physiological rate processes in marine invertebrate larvae.