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Control of Larval Metamorphosis, Recruitment and Gene Expression: (Figures)
Flypapers” for coral larvae. Based on techniques used in the nanofabrication of semiconductors, these artificial surfaces for larval recruitment include the purified signal molecules we discovered that induce settlement and metamorphosis of coral larvae - linked to self-assembled monolayers on inexpensive surfaces. (Biological Bulletin 186:172-181, 1994;BioScience 64:254-262, 1996.)
Scanning electron micrographs of a swimming, planktonic coral larva (above, left) and a newly metamorphosed coral (right). Metamorphosis was induced by contact with the morphogenetic signal molecule attached to an artificial plastic surface; tissue of the coral has been removed to show the newly formed skeleton.(J. Exper. Mar. Biol. Ecol. 116:193-217, 1988;Biol. Bull. 181:104-122, 1991,BioScience 64:254-262, 1996)
In earlier work, we discovered the chemical signals that induce spawning in abalones (above, left) and a number of other marine invertebrates(Science196: 298-300, 1997), and the chemical signal on the surface of crustose coralline algae that induces abalone larvae to settle from the plankton and metamorphose on the surfaces of the recruiting algae (above, right)(Science204: 407-410, 1979;J. Exp. Mar. Biol. Ecol.75:191-215, 1984;Bull. Mar. Sci. 46:465-483, 1990).
We and our students and colleagues characterized the signal molecules, the larval chemosensory receptors and the signal transducers controlling settlement, metamorphosis and the induction of gene expression controlling early post-metamorphic cellular differentiation in abalones and several other invertebrates. Based on these findings, we developed simple methods for the reliable control of larval settlement and plantigrade attachment (left); metamorphosis (center: the abalone sibling on the left was induced to metamorphose and begin growth of the post-larval shell 40 hours previously; the sibling larva on the left received no inducer); and the analysis of gene regulation controlling post-metamorphic development (right: induction of tropomyosin gene expression and myogenesis). (Please see references in topical list above.)
Molecular schematic of the convergent morphogenetic and regulatory pathways that provide fine-tuning and control of settlement and metamorphosis of planktonic abalone larvae in response to chemical signals from the environment. R-1, R-2 = chemosensory receptors; GABA, DAPA = amino acid analogs of the signal molecules normally encountered by the larvae at the surfaces of crustose coralline red algae and in the water column, respectively. CC = chloride ion channel; other abbreviations = signal transducers.(Proc. Natl. Acad. Sci. USA 84:1867-1870, 1987;Proc. Natl. Acad. Sci. USA 83:7658-7662, 1986;Bull. Mar. Sci. 46:465-483, 1990;Biological Bulletin 180:318-327, 1991;Biological Bulletin 183:147-154;Nature363: 406, 1993.)
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