Aileen N. C. Morse

Recruitment and metamorphosis of Haliotis larvae induced by molecules uniquely available at the surfaces of crustose red algae

Crustose red algae induce substratum-specific settlement, attachment and metamorphosis of the planktonic larvae of Haliotis rufescens Swainson (gastropod mollusc), upon direct contact by the larvae with any of a number of algal species tested. Larvae are not induced by contact with intact foliose red, brown or green macroalgae. Geniculate red algae are only slightly active. Larval settlement and metamorphosis are shown to be triggered by a class of chemical inducers associated with macromolecules and found in extracts of all species of crustose, geniculate, and foliose red algae tested; these inducers are not found in extracts of brown or green macroalgae. The substratum specificity of larval settlement and metamorphosis is shown to result from the unique availability of these inducers at the surfaces of the crustose red algae. Using a newly-developed improved method of purification based upon size-separation by gel-filtration, followed by ion-exchange chromatography over a diethylaminoethyl (DEAE)-acrylamide matrix, the principal inducer of Haliotis larval settlement and metamorphosis has been resolved from the red algal phycobiliproteins. Sensitivity of this inducer to reduction in molecular weight by digestion with trypsin demonstrates that this inducer is associated with protein.

Control of larval metamorphosis and recruitment in sympatric agariciid corals

Abstract The larvae of three sympatric shallow-water agariciid corals, Agaricia tenuifolia Dana, A. agaricites humilis Verrill, and A. agaricites dana Milne Edwards et Haime, are shown to be induced to metamorphose by crustose coralline red algae (CCA). These corals display different degrees of stringency and specificity in their requirements for CCA to induce metamorphosis, and different responses to light in the control of the distribution of newly metamorphosed individuals. The morphogenetic inducer from CCA has been fractionated by ultrafiltration, and shown to be a water-insoluble, ether-insoluble, and acetone-insoluble unstable biochemical. This inducer of agariciid metamorphosis is different from the water-soluble peptide inducer of gastropod metamorphosis previously isolated from CCA. Transduction of the morphogenetic signal in the agariciid larvae also is apparently controlled by an internal pathway that is different from the signal-transduction pathway found to control metamorphosis in several other species. Analysis of the distribution of recruits of two of the agariciid species indicates that larval requirements and specificities for metamorphosis may contribute significantly to determine the distribution of recruits in the natural environment. Our evidence suggests that differences in larval requirements for metamorphosis thus may contribute to the maintenance of niche diversification among the sympatric shallow-water agariciids. The competence and CCA requirement of the larvae of these species persist for at least 1–2 wk in the plankton, thereby promoting dispersal and site-specific metamorphosis. For these sympatric shallow-water agariciid corals, then, larval metamorphosis and recruitment are not wholly stochastic lottery-like processes, but instead appear to be determined, in part, by larval recognition of, and responses to, environmental and biochemical factors that can be experimentally resolved and identified.

An Ancient Chemosensory Mechanism Brings New Life to Coral Reefs

The first scleractinians, progenitors of modern corals, began to appear 240 million years ago; by the late Jurassic (150 Ma) most families of modern corals had evolved and begun forming reefs (1, 2). Mechanisms controlling the recruitment of new corals to sustain these structures are, however, poorly understood (3). Corals, like many marine invertebrates, begin life as soft-bodied larvae that are dispersed in the plankton (3, 4). As the first step in developing a calcified coral colony, the larva must settle out of the plankton onto a suitable substratum and metamorphose to the single calcified polyp stage cemented to the reef (3, 5). Our analyses of the metamorphic requirements of larvae in divergent coral families surprised us by revealing the existence of a common chemosensory mechanism that is required to bring larvae out of the plankton and onto the reef. This mechanism appears to be quite old, predating both the phylogenetic divergence of these coral families and the development of different modes of coral reproduction.

THE CONSEQUENCES OF COMPLEX LARVAL BEHAVIOR IN A CORAL

The leaf coral Agaricia humilis occurs mainly on the undersides of surfaces in shallow water, a distribution different from the vast majority of corals at our study site in Bonaire, Netherlands Antilles. A series of hypotheses were tested for specific mechanisms that could cause the observed distributions of Agaricia humilis. We found that a suite of larval swimming and settling behaviors, in large part, drives the adult distribution of the species. These behaviors include: (1) swimming behavior that cause larvae to position themselves in shallow water, (2) orientation behavior during settlement that causes larvae to preferentially settle on the undersides of surfaces, and (3) settlement behavior where chemosensory recognition of morphogenic molecules associated with the cell walls of specific crustose red algae is required for induction of settlement and metamorphosis. The consequences of atypical larval behavior are severe and include decreased survivorship, growth, and ability to reproduce sexually.

Interaction of vinblastine with steady-state microtubules in vitro

Abstract At low concentrations, vinblastine binds rapidly and reversibly to a very limited number of high affinity sites on steady-state bovine brain microtubules (mean Kd, 1.9 × 10−6 m ; 16.8 ± 4.3 vinblastine binding sites per microtubule) which appear to be located at one or both ends of the microtubules. At high concentrations, vinblastine binds to a high binding capacity class of sites of undetermined affinity, located on helical strands of protofilaments which form at the ends of depolymerizing microtubules, and/or along the surface of the microtubules. Substoichiometric inhibition of microtubule assembly, which occurs at low vinblastine concentrations, appears to be due to the binding of vinblastine to the high affinity class of sites. Fifty per cent inhibition of tubulin addition to the net assembly ends of steady-state microtubules occurred at 1.38 × 10−7 m -drug, and at this concentration, 1.16 ± 0.27 molecules of vinblastine were bound to the high affinity class of sites. Vinblastine appeared to bind directly to the microtubule ends, and our results indicate that vinblastine inhibits the assembly of steady-state bovine brain microtubules by binding rapidly and with high affinity to one or two molecules of tubulin at the net assembly ends. Splaying and peeling of protofilaments at microtubule ends and the active depolymerization of microtubules occurred only at vinblastine concentrations greater than 1 × 10−6 to 2 × 10−6 m . This action of vinblastine is associated with and may be due to the binding of vinblastine to the high capacity class of sites. Both actions of vinblastine may be due to the binding of vinblastine to the same binding sites on the tubulin molecule, with the sites exhibiting either a high or low affinity depending upon the location in the microtubule.

Enzymatic Characterization of the Morphogen Recognized by Agaricia humilis (Scleractinian Coral) Larvae

Larvae of the common Caribbean scleractinian coral, Agaricia humilis, are induced to settle and metamorphose by contact with specific crustose (nongeniculate) coralline red algae. This requirement for an exogenous trigger of settlement and metamorphosis has been shown to control the distribution of recruits of this coral in the natural environment. Results reported here demonstrate that the stringency and specificity of this larval requirement persist for at least 30 days following the planktonic release of the brooded larvae, thus enhancing both the capacity for dispersal of the larvae and the substratum specificity of their metamorphosis and recruitment. The inducer of metamorphosis is shown to be associated with an insoluble macromolecular carbohydrate. This molecule is found with the partially purified cell walls obtained from a morphogenetic crustose red alga, Hydrolithon boergesenii, or its associated microflora. Because two non-inductive crustose red algal species also lack the cell wall-associated inducer, the substratum specificity of metamorphosis is probably the result of larval recognition of this molecule. In procedures that should prove widely applicable to other systems, purified and highly specific enzymes were used to cleave the inductive cell wall-associated polysaccharides and to solubilize the active morphogen. Enzymes were also used as probes with which to identify essential structural features required for the morphogenetic activity. These enzymatic and related biochemical studies show that the morphogen is associated with, and may itself contain, a sulfated glycosaminoglycan that includes multiple N-acetylglucosamine and galactose residues. The larval receptors that recognize this complex carbohydrate cue may thus be related to lectins. The solubilized morphogen induces normal settlement, attachment, and the metamorphosis of A. humilis and A. tenuifolia larvae on clean polystyrene surfaces, and the larvae seem to have no other requirement. This effect is apparently specific for larvae of species induced to settle by the intact alga; larvae of the sympatric coral Tubastraea aurea are not induced by this chemical, or by the intact algal surface. A wide variety of other natural and synthetic sulfated polysaccharides and related polymers have little or no inductive effect on the A. humilis larvae, suggesting that the larval receptors involved in substratum recognition are highly specific. A similar high specificity of lectin- and sulfated polysaccharide-mediated recognition, and the resulting control of differentiation, has been observed in a wide variety of biological systems.

Induction of metamorphosis in larvae of the brooding corals Acropora palifera and Stylophora pistillata

Many coral larvae require surface contact with crustose red algae (CRA) to induce metamorphosis; however, many features of the ecology of pocilloporid corals, such as their ability to colonize primary substrata, suggest that their larvae respond to different cues. We compared the metamorphosis of larvae of the brooding corals Stylophora pistillata (family Pocilloporidae) and Acropora palifera (family Acroporidae) in response to a variety of environmental cues. Acropora palifera metamorphosed only in the presence of three species of CRA. In contrast, S. pistillata metamorphosed in all assays, except those containing the brown alga Lobophora sp. Metamorphosis was highest (80 ± 20%) in unfiltered sea water; however, metamorphosis also occurred in 0.2-μm filtered sea water. These results suggest that S. pistillata larvae respond to both large and small water-borne molecular cues. The lack of a stringent requirement for surface contact with CRA will allow S. pistillata larvae to pre-empt species that require a more developed fouling community to induce metamorphosis and this feature of larval ecology may be the key to understanding the success of many opportunistic benthic species.

Dual-control of the tryptophan operon is mediated by both tryptophanyl-tRNA synthetase and the repressor☆

Abstract Tryptophanyl-tRNA synthetase, functioning in tandem with the repressor-operator system, mediates homeostatic regulation of tryptophan biosynthetic operon expression. Whereas the repressor, activated directly by tryptophan, binds to the operator and blocks the initiation of transcription at the trp promoter, tryptophanyl-tRNA synthetase apparently regulates the termination of transcription at the attenuator site between the operator and the structural genes of the operon. There is an inverse correlation between aminocylation of tRNA Trp and expression of the operon; a relA + ribosomal product (ppGpp?) may be required for maximal expression. None of the recognized structural genes or their products are required for regulation of trp expression.

Flypapers for Coral and Other Planktonic Larvae New materials incorporate morphogens for applications in research, restoration, aquaculture, and medicine

any animals in the sea reproduce to yield vast numbers of minute, weakly swimming larvae that remain arrested in development while they are dispersed in the plankton. In many species, the larvae settle randomly and then continue to develop, but in other species the larvae emerge from developmental arrest only after settling in a particular microhabitat that is suitable for their postmetamorphic growth and survival to reproduction. What cues might indicate to such larvae that they have reached the appropriate environment? We and other investi-

Characterization of acetyl-3H-labeled vinblastine binding to vinblastine-tubulin crystals.

Purified vinblastine-tubulin crystals, induced in vivo by incubation of unfertilized sea urchin eggs with [acetyl-3H]vinblastine sulfate, contained 0·7 to 1·0 mole of bound vinblastine per mole of tubulin in a form which dissociated only when crystals were suspended in stabilizing buffer containing free vinblastine. Vinblastine was found to bind to crystals with a stoichiometry of two mole per mole of tubulin in vitro. Vinblastine bound to both sites with similar affinities of 2·4 × 105 liters per mole (18°C). The binding of vinblastine to crystals was not affected appreciably by temperature between 0°C and 35°C, and was not at all influenced by the presence of high concentrations of GTP, colchicine, griseofulvin, or calcium ions. Vinblastine binding to crystals of tubulin was competitively inhibited by other active vinca alkaloid derivatives, and the abilities of the derivatives to bind crystal tubulin paralleled the abilities of the derivatives to inhibit polymerization of brain microtubules in vitro.