MEYER, E.*; HAAG, A.L.; MANAHAN, D.T.: Ontogenetic changes in expression of putative amino acid transporter genes in sea urchins measured by immunoblotting

Changes in the kinetics of amino acid transport occur during sea urchin development, but little is known about the mechanisms of these physiological changes. Clones with strong sequence similarity to previously characterized amino acid transporter genes have recently been isolated from cDNA libraries of the purple sea urchin Strongylocentrotus purpuratus (see abstract by D.T. Manahan, this volume). To address questions of mechanisms behind developmental changes in nutrient uptake, the expression of two of these genes was examined through development. Synthetic peptides were constructed based on membrane topology models of the two proteins and were used to generate polyclonal antibodies to extracellular domains of the putative transporters. Immunoblots using these antibodies showed the transporter proteins to be present in unfertilized eggs and that both proteins increased in abundance during embryogenesis. In early larval stages, in situ staining revealed the expression of both proteins to be localized in ectoderm, consistent with the known site(s) of amino acid uptake from seawater by echinoderm larvae. In 4- to 5-d-old larvae, expression of one of the proteins (533) ceased while the other transporter protein (442) continued to be expressed. This shift in expression pattern coincided with the developmental stage at which an ontogenetic change in amino acid transport kinetics is known to occur. The patterns of gene expression described here demonstrate the potential for developmental regulation to control physiological changes in nutrient uptake.