Availability of chemosensory receptors is down-regulated by habituation of larvae to a morphogenetic signal

Microalgal biofilm induces larval settlement in the model marine worm Platynereis dumerilii

A free-swimming larval stage features in many marine invertebrate life cycles. To transition to a seafloor-dwelling juvenile stage, larvae need to settle out of the plankton, guided by specific environmental cues that lead them to an ideal habitat for their future life on the seafloor. Although the marine annelid Platynereis dumerilii has been cultured in research laboratories since the 1950s and has a free-swimming larval stage, specific environmental cues that induce settlement in this nereid worm are yet to be identified. Here, we demonstrate that microalgal biofilm is a key settlement cue for P. dumerilii larvae, inducing earlier onset of settlement and enhancing subsequent juvenile growth as a primary food source. We tested the settlement response of P. dumerilii to 40 different strains of microalgae, predominantly diatom species, finding that P. dumerilii have species-specific preferences in their choice of settlement substrate. The most effective diatom species for inducing P. dumerilii larval settlement were benthic pennate species including Grammatophora marina, Achnanthes brevipes and Nitzschia ovalis. The identification of specific environmental cues for P. dumerilii settlement enables a link between its ecology and the sensory and nervous system signalling that regulates larval behaviour and development. Incorporation of diatoms into P. dumerilii culture practices will improve the husbandry of this marine invertebrate model.

Opsin expression varies across larval development and taxa in pteriomorphian bivalves

Introduction

Many marine organisms have a biphasic life cycle that transitions between a swimming larva with a more sedentary adult form. At the end of the first phase, larvae must identify suitable sites to settle and undergo a dramatic morphological change. Environmental factors, including photic and chemical cues, appear to influence settlement, but the sensory receptors involved are largely unknown. We targeted the protein receptor, opsin, which belongs to large superfamily of transmembrane receptors that detects environmental stimuli, hormones, and neurotransmitters. While opsins are well-known for light-sensing, including vision, a growing number of studies have demonstrated light-independent functions. We therefore examined opsin expression in the Pteriomorphia, a large, diverse clade of marine bivalves, that includes commercially important species, such as oysters, mussels, and scallops.

Methods

Genomic annotations combined with phylogenetic analysis show great variation of opsin abundance among pteriomorphian bivalves, including surprisingly high genomic abundance in many species that are eyeless as adults, such as mussels. Therefore, we investigated the diversity of opsin expression from the perspective of larval development. We collected opsin gene expression in four families of Pteriomorphia, across three distinct larval stages, i.e., trochophore, veliger, and pediveliger, and compared those to adult tissues.

Results

We found larvae express all opsin types in these bivalves, but opsin expression patterns are largely species-specific across development. Few opsins are expressed in the adult mantle, but many are highly expressed in adult eyes. Intriguingly, opsin genes such as retinochrome, xenopsins, and Go-opsins have higher levels of expression in the later larval stages when substrates for settlement are being tested, such as the pediveliger.

Conclusion

Investigating opsin gene expression during larval development provides crucial insights into their intricate interactions with the surroundings, which may shed light on how opsin receptors of these organisms respond to various environmental cues that play a pivotal role in their settlement process.

Molecular and behavioural evidence that interdependent photo - and chemosensory systems regulate larval settlement in a marine sponge

Marine pelagic larvae use a hierarchy of environmental cues to identify a suitable benthic habitat on which to settle and metamorphose into the adult phase of the life cycle. Most larvae are induced to settle by biochemical cues and many species have long been known to preferentially settle in the dark. Combined, these data suggest that larval responses to light and biochemical cues may be linked, but this has yet to be explored at the molecular level. Here, we track the vertical position of larvae of the sponge Amphimedon queenslandica to show that they descend to the benthos at twilight, by which time they are competent to respond to biochemical cues, consistent with them naturally settling in the dark. We use larval settlement assays under three different light regimes, combined with transcriptomics on individual larvae, to identify candidate molecular pathways underlying larval settlement. We find that larvae do not settle in response to biochemical cues if maintained in constant light. Our transcriptome data suggest that constant light actively represses settlement via the sustained up-regulation of two putative inactivators of chemotransduction in constant light only. Our data suggest that photo- and chemosensory systems interact to regulate larval settlement via nitric oxide and cyclic guanosine monophosphate signalling in this sponge, which belongs to one of the earliest-branching animal phyla.

Chemically induced metamorphosis of polychaete larvae in both the laboratory and ocean environment

Planktonic larvae of the marine polychaetePhragmatopoma californica preferentially attach to substrata and metamorphose to the adult form upon contact with cement in tubes built by conspecifics. This gregarious settlement and metamorphosis contributes to the formation of large aggregations or reefs. Larvae also metamorphose upon contact with 2,6-di-tert-butyl-4-methylphenol (DBMP), a possible aromatic analog of cross-linked dihydrox-yphenylalanine (DOPA) residues (present in the polyphenolic protein cement as 2.6% of the amino acid residues). Morphogenesis occurs in the laboratory when larvae are exposed to DBMP either adsorbed to solid surfaces or when dissolved in dimethyl sulfoxide (DMSO) to render it soluble in seawater. Larvae in the ocean were induced to settle and metamorphose on plates coated with DBMP prior to their deployment in the ocean. This is the first report in which a defined organic molecule, identified as an inducer (or precursor to an inducer) of larval settlement and metamorphosis in the laboratory, has been shown to induce these processes in the ocean. Both forskolin and isobutylmethylxanlhine (IBMX) induce metamorphosis ofP. californica larvae, presumably by causing increases in intracellular cyclic AMP (cAMP). A discussion of the pathway controlling chemically mediated metamorphosis and evidence suggesting the possible role of cAMP in the process are presented. Other compounds known to increase intracellular cAMP levels, including arachidonic, linoleic, and palmitoleic acids, found by other workers to induce settlement and metamorphosis ofP. californica, may exert this activity by direct modification of internal cAMP levels in the larvae.

Variation in rates of early development in Haliotis asinina generate competent larvae of different ages

INTRODUCTION

Inter-specific comparisons of metazoan developmental mechanisms have provided a wealth of data concerning the evolution of body form and the generation of morphological novelty. Conversely, studies of intra-specific variation in developmental programs are far fewer. Variation in the rate of development may be an advantage to the many marine invertebrates that posses a biphasic life cycle, where fitness commonly requires the recruitment of planktonically dispersing larvae to patchily distributed benthic environments.

RESULTS

We have characterised differences in the rate of development between individuals originating from a synchronised fertilisation event in the tropical abalone Haliotis asinina, a broadcast spawning lecithotrophic vetigastropod. We observed significant differences in the time taken to complete early developmental events (time taken to complete third cleavage and to hatch from the vitelline envelope), mid-larval events (variation in larval shell development) and late larval events (the acquisition of competence to respond to a metamorphosis inducing cue). We also provide estimates of the variation in maternally provided energy reserves that suggest maternal provisioning is unlikely to explain the majority of the variation in developmental rate we report here.

CONCLUSIONS

Significant differences in the rates of development exist both within and between cohorts of synchronously fertilised H. asinina gametes. These differences can be detected shortly after fertilisation and generate larvae of increasingly divergent development states. We discuss the significance of our results within an ecological context, the adaptive significance of mechanisms that might maintain this variation, and potential sources of this variation.

Involvement of a novel p38 mitogen-activated protein kinase in larval metamorphosis of the polychaete Hydroides elegans (Haswell)

Hydroides elegans is a common marine fouling organism in most tropical and subtropical waters. The life cycle of H. elegans includes a planktonic larval stage in which swimming larvae normally take 5 days to attain competency to settle. Larval metamorphosis marks the beginning of its benthic life; however, the endogenous molecular mechanisms that regulate metamorphosis remain largely unknown. In this study, a PCR-based suppressive subtractive hybridization (SSH) library was constructed to screen the genes expressed in competent larvae but not in precompetent larvae. Among the transcripts isolated from the library, 21 significantly matched sequences in the GenBank. Many of these isolated transcripts have putative roles in the reactive oxygen species (ROS) signal transduction pathway or in response to ROS stress. A putative novel p38 mitogen-activated protein kinase (MAPK), which was also isolated with SSH screen, was then cloned and characterized. The MAPK inhibitors assay showed that both p38 MAPK inhibitors SB202190 and SB203580 effectively inhibited the biofilm-induced metamorphosis of H. elegans. A cell stressors assay showed that H(2)O(2) effectively induced larval metamorphosis of H. elegans, but the inductivity of H(2)O(2) was also inhibited by both SB inhibitors. The catalase assay showed that the catalase could effetely inhibit H. elegans larvae from responding to inductive biofilm. These results showed that the p38 MAPK-dependent pathway plays critical role in controlling larval metamorphosis of the marine polychaete H. elegans, and the reactive oxygen radicals produced by biofilm could be the cue inducing larval metamorphosis.

G protein and diacylglycerol regulate metamorphosis of planktonic molluscan larvae

The regulatory guanine nucleotide binding protein (G protein) activators cholera toxin and the GTP analog 5-guanylyl imidophosphate, the second messenger diacylglycerol, and certain diamino acids all facilitate (amplify) the settlement and metamorphic responses of planktonic larvae of Haliotis rufescens (marine mollusc) to morphogenetic chemical stimuli. In contrast, the G protein-inhibiting analog guanosine 5'-O-[beta-thio]diphosphate inhibits facilitation by L-alpha,beta-diaminopropionic acid but does not block facilitation by diacylglycerol. Diacylglycerol, cholera toxin, and the guanine nucleotide analogs alone neither induce the settlement and metamorphosis of the larvae nor do they inhibit induction of metamorphosis by gamma-aminobutyric acid. These results thus establish the existence of separate regulatory and inductive pathways controlling larval metamorphosis in response to two classes of exogenous chemical signals from the environment. The regulatory pathway, operating independently through a G protein-diacylglycerol cascade apparently controlled by facilitating diamino acids in the water column, can amplify the larval responsiveness to inducers of metamorphosis. This mechanism may have adaptive significance in the recognition and selection of favorable habitats for metamorphosis of the larvae. Similar regulatory pathways, based on exogenous control of a G protein-diacylglycerol cascade, may govern responsiveness to stimuli in other sensory and developmental systems.

The initiation of metamorphosis as an ancient polyphenic trait and its role in metazoan life-cycle evolution

Comparative genomics of representative basal metazoans leaves little doubt that the most recent common ancestor to all modern metazoans was morphogenetically complex. Here, we support this interpretation by demonstrating that the demosponge Amphimedon queenslandica has a biphasic pelagobenthic life cycle resembling that present in a wide range of bilaterians and anthozoan cnidarians. The A. queenslandica life cycle includes a compulsory planktonic larval phase that can end only once the larva develops competence to respond to benthic signals that induce settlement and metamorphosis. The temporal onset of competence varies between individuals as revealed by idiosyncratic responses to inductive cues. Thus, the biphasic life cycle with a dispersing larval phase of variable length appears to be a metazoan synapomorphy and may be viewed as an ancestral polyphenic trait. Larvae of a particular age that are subjected to an inductive cue either maintain the larval form or metamorphose into the post-larval/juvenile form. Variance in the development of competence dictates that only a subset of a larval cohort will settle and undergo metamorphosis at a given time, which in turn leads to variation in dispersal distance and in location of settlement. Population divergence and allopatric speciation are likely outcomes of this conserved developmental polyphenic trait.

Marine biofilms as mediators of colonization by marine macroorganisms: implications for antifouling and aquaculture

In the marine environment, biofilms on submerged surfaces can promote or discourage the settlement of invertebrate larvae and macroalgal spores. The settlement-mediating effects of biofilms are believed to involve a variety of biofilm attributes including surface chemistry, micro-topography, and a wide range of microbial products from small-molecule metabolites to high-molecular weight extracellular polymers. The settled organisms in turn can modify microbial species composition of biofilms and thus change the biofilm properties and dynamics. A better understanding of biofilm dynamics and chemical signals released and/or stored by biofilms will facilitate the development of antifouling and mariculture technologies. This review provides a brief account of 1) existing knowledge of marine biofilms that are relevant to settlement mediation, 2) biotechnological application of biofilms with respect to developing non-toxic antifouling technologies and improving the operation of aquaculture facilities, and 3) challenges and future directions for advancing our understanding of settlement-mediating functions of biofilms and for applying this knowledge to real-life situations.

Transcription and translation inhibitors permit metamorphosis up to radiole formation in the serpulid polychaete Hydroides elegans haswell

Settlement and metamorphosis in most well-studied marine invertebrates are rapid processes, triggered by external cues. How this initial environmentally mediated response is transduced into morphogenetic events that culminate in the formation of a functional juvenile is still not well understood for any marine invertebrate. The response of larvae of the serpulid polychaete Hydroides elegans to inhibitors of mRNA and protein synthesis was examined to determine if metamorphosis requires these molecular processes. Competent larvae of H. elegans were induced to metamorphose by exposing them to a bacterial film or a 3-h pulse of 10 mM CsCl in the presence of the gene-transcription inhibitor DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole) or the translation inhibitor emetine. When induced to metamorphose in the presence of either inhibitor, larvae of H. elegans progressed through metamorphosis to the point at which branchial radioles start to develop. DRB and emetine inhibited the incorporation of radiolabeled uridine into RNA and radiolabeled methionine into peptides, respectively, indicating that they were effective in blocking the appropriate syntheses. Taken together, these results indicate that the induction of metamorphosis in H. elegans does not require de novo transcription or translation, and that the form of the juvenile worm is achieved in two phases. During the first phase, larvae respond to the inducer by attaching to the substratum, secreting a primary tube, resorbing the prototroch cilia, undergoing caudal elongation, and differentiating the collar; once the collar is formed, they begin secreting the secondary, calcified tube. During the second phase, the small worm develops branchial radioles and begins to grow, requiring new mRNA and protein syntheses.

Foundations of gregariousness: a dispersal polymorphism among the planktonic larvae of a marine invertebrate

Theory predicts that selection should favor genotypes that can vary their tendency to disperse in habitats that are spatially or temporally variable or those that remain near their carrying capacity. Although many marine habitats appear to fit these criteria, confirmed examples of dispersal polymorphism among marine invertebrates are exceedingly rare. Competent larvae of the gregarious tubeworm, Hydroides dianthus, settle specifically in response to living conspecific worms, but a small proportion of each spawn settle nonspecifically on uninhabited substrata concurrently with their gregarious siblings. Here, using a parental half-sib analysis, we show that the proportion of a spawn settling in response to uninhabited biofilm is highly heritable. When estimated as a continuous trait based on a one-way ANOVA, heritability is estimated to be 0.83 +/- 0.31. When founder production was analyzed as a threshold trait, heritability was estimated to be 0.68 +/- 0.10 based on the breeding design experiment and 0.65 +/- 0.09 based on the artificial selection experiments. Realized heritability based on the selection experiments was considerably lower, however (0.17 per generation and 0.02 cumulative). Artificial selection was ineffectual at sequentially increasing the proportion of founder larvae among inbred family lines, but after three generations of selection, the proportion of larvae settling in response to biofilm was significantly higher among inbred lines than among the field-collected parents. The obligate planktonic larval stage common among so many marine invertebrates is thought to preclude the evolution of dispersal polymorphisms in these animals. Theoretical expectations of variable dispersal may instead be realized through individual behavioral differences resulting in differential transport or settlement preference, but this possibility remains largely unexplored among marine invertebrates.

Hemps, a novel EGF-like protein, plays a central role in ascidian metamorphosis

All chordates share several characteristic features including a dorsal hollow neural tube, a notochord, a pharynx and an endostyle. Unlike other chordate taxa, ascidians have a biphasic life-history with two distinct body plans. During metamorphosis, the larval nerve cord and notochord degenerate and the pharyngeal gill slits and endostyle form. While ascidians, like other marine invertebrates, metamorphose in response to specific environmental cues, it remains unclear how these cues trigger metamorphosis. We have identified a novel gene (Hemps) which encodes a protein with a putative secretion signal sequence and four epidermal growth factor (EGF)-like repeats which is a key regulator of metamorphosis in the ascidian Herdmania curvata. Expression of Hemps increases markedly when the swimming tadpole larva becomes competent to undergo metamorphosis and then during the first 24 hours of metamorphosis. The Hemps protein is localised to the larval papillae and anterior epidermis of the larva in the region known to be required for metamorphosis. When the larva contacts an inductive cue the protein is released, spreading posteriorly and into the tunic as metamorphosis progresses. Metamorphosis is blocked by incubating larvae in anti-Hemps antibodies prior to the addition of the cue. Addition of recombinant Hemps protein to competent larvae induces metamorphosis in a concentration-dependent manner. A subgroup of genes are specifically induced during this process. These results demonstrate that the Hemps protein is a key regulator of ascidian metamorphosis and is distinct from previously described inducers of this process in terrestrial arthropods and aquatic vertebrates.

Changing properties of GABA(A) receptor-mediated signaling during early neocortical development

Evidence from several brain regions suggests gamma-aminobutyric acid (GABA) can exert a trophic influence during development, expanding the role of this amino acid beyond its function as an inhibitory neurotransmitter. Proliferating precursor cells in the neocortical ventricular zone (VZ) express functional GABA(A) receptors as do immature postmigratory neurons in the developing cortical plate (CP); however, GABA(A) receptor properties in these distinct cell populations have not been compared. Using electrophysiological techniques in embryonic and early postnatal neocortex, we find that GABA(A) receptors expressed by VZ cells have a higher apparent affinity for GABA and are relatively insensitive to receptor desensitization compared with neurons in the CP. GABA-induced current magnitude increases with maturation with the smallest responses found in recordings from precursor cells in the VZ. No evidence was found that GABA(A) receptors on VZ cells are activated synaptically, consistent with previous data suggesting that these receptors are activated in a paracrine fashion by nonsynaptically released ligand. After neurons are born and migrate to the CP, they begin to demonstrate spontaneous synaptic activity, the majority of which is GABA(A) mediated. These spontaneous GABA(A) postsynaptic currents (sPSCs) first were detected at embryonic day 18 (E18). At birth, approximately 50% of recordings from cortical neurons demonstrated GABA(A)-mediated sPSCs, and this value increased with age. GABA(A)-mediated sPSCs were action potential dependent and arose from local GABAergic interneurons. GABA application could evoke action potential-dependent PSCs in neonatal cortical neurons, suggesting that during the first few postnatal days, GABA can act as an excitatory neurotransmitter. Finally, N-methyl-D-aspartate (NMDA)- but not non-NMDA-mediated sPSCs were also present in early postnatal neurons. These events were not observed in cells voltage clamped at negative holding potentials (-60 to -70 mV) but were evident when the holding potential was set at positive values (+30 to +60 mV). Together these results provide evidence for the early maturation of GABAergic communication in the neocortex and a functional change in GABA(A)-receptor properties between precursor cells and early postmitotic neurons. The change in GABA(A)-receptor properties may reflect the shift from paracrine to synaptic receptor activation.

A Mox homeobox gene in the gastropod mollusc Haliotis rufescens is differentially expressed during larval morphogenesis and metamorphosis

We have isolated a homeobox-containing cDNA from the gastropod mollusc Haliotis rufescens that is most similar to members of the Mox homeobox gene class. The derived Haliotis homeodomain sequence is 85% identical to mouse and frog Mox-2 homeodomains and 88.9% identical to the partial cnidarian cnox5-Hm homeodomain. Quantitative reverse transcription-polymerase chain reaction analysis of mRNA accumulation reveals that this gene, called HruMox, is expressed in the larva, but not in the early embryo. Transcripts are most prevalent during larval morphogenesis from trochophore to veliger. There are also transient increases in transcript prevalence 1 and 3 days after the intitiation of metamorphosis from veliger to juvenile. The identification of a molluscan Mox homeobox gene that is more closely related to vertebrate genes than other protostome (e.g. Drosophila) genes suggests the Mox class of homeobox genes may consist of several different families that have been conserved through evolution.

Inhibition of taurine and 5'AMP olfactory receptor sites of the spiny lobster Panulirus argus by odorant compounds and mixtures

1. The effects of the odorant compounds adenosine-5'-monophosphate (5'AMP), ammonium, betaine, L-cysteine, L-glutamate, DL-succinate, and taurine and of mixtures of these compounds on binding of taurine and 5'AMP to dendritic membrane from the olfactory organ of spiny lobsters (Panulirus argus) were quantified to evaluate the contribution of inhibition of odorant-receptor binding to the generation of physiological responses to mixtures. 2. Taurine binding sites belong to two affinity classes, while 5'AMP binding sites belong to a single affinity class. Binding of either taurine or 5'AMP was partially inhibited in an apparently noncompetitive, concentration dependent fashion by most odorant compounds, with 25-40% inhibition by 1 mM of odorant. Mixtures of two or more odorant compounds also inhibited binding of taurine or 5'AMP to its sites. However, the inhibition by mixtures was often significantly less than expected from the inhibition produced by a mixture's components assuming either a noncompetitive or competitive mechanism. 3. By including this binding inhibition between compounds into models for predicting physiological responses to mixtures from the responses to the components, the predictive power of the models is significantly improved. This result strongly suggests that binding inhibition can influence the physiological responsiveness of chemoreceptor cells to mixtures.

Stereoselective detection of amino acids by lobster olfactory receptor neurons

1. Biochemical and electrophysiological assays were used to test the hypothesis that the olfactory system of the Caribbean spiny lobster, Panulirus argus, contains populations of chemosensory receptors that are differentially sensitive to the L- and D-stereoisomers of the amino acid alanine. 2. Independent binding sites for L-alanine (dissociation constant (KD) of 6.6 microM and maximum binding (Bmax) of 16.8 fmole/microgram protein) and for D-alanine (KD of 21.6 microM and Bmax of 17.8 fmole/microgram protein) were characterized biochemically. The interaction of ligand with each binding site is rapid, reversible and saturable with respect to both time and concentration. 3. Based on a difference of at least 20% in the relative sensitivity of an olfactory receptor cell to alanine enantiomers, 44% and 34% of the 77 neurons tested were classified as L-alanine and D-alanine sensitive, respectively. The relative sensitivity to alanine enantiomers was independent of the concentration tested. Stereoselective receptors are likely for 17 of 20 other amino acids tested. 4. The congruence of biochemical and electrophysiological results leads to the conclusion that the lobster's responses to D- and L-alanine are mediated by receptors specific for each stereoisomer and that the receptors are differentially distributed among receptor cells.

Effects of pyrantel pamoate on adult and preadult Toxocara canis worms: an electron microscope and autoradiography study

Adult as well as preadult Toxocara canis isolated from the intestine of a beagle were incubated for 2, 4, and 14 h in medium containing either different concentrations of pyrantel pamoate (23.6, 236, and 2360 micrograms/ml medium) or tritiated pyrantel pamoate (2.36 micrograms/ml medium). These incubations were performed to study the effects of pyrantel pamoate on the morphology of the parasitic nematodes and to obtain information concerning the mode of uptake, the distribution, and the total amount of pyrantel pamoate ingested by T. canis. The results of the ultrastructure studies indicate that the intestine, hypodermis, and muscle cells are the organs that are predominantly affected by the drug. Additionally, it turned out that the duration of the treatment, i.e., the incubation time, was more important in determining the efficacy of pyrantel pamoate against T. canis than was the concentration itself. Autoradiography studies revealed that the adult worms ingest the drug orally, whereas preadults absorb pyrantel pamoate mainly through the whole body surface. Finally, measurements of the total amount of pyrantel pamoate taken up by T. canis indicated that adult worms can limit or even reduce the ingestion of pyrantel for more than 4 h, but then ingest large amounts of the drug. Preadult worms, however, absorb the drug more or less continuously during the first 14 h through the cuticula, albeit in lower concentrations than the adults. The different experiments elucidate differences in the uptake of pyrantel pamoate as well as in the total amount of drug ingested or absorbed by adult or preadult worms, leading to the assumption that repeated treatment with lower concentrations will be more effective than high concentrations given only once.

Biochemical characterization of independent olfactory receptor sites for 5'-AMP and taurine in the spiny lobster

To understand the initial events in chemosensory transduction (i.e. binding of odorants to olfactory receptor sites), we have utilized a radioligand-receptor binding assay on a tissue preparation that is enriched in dendritic membrane from olfactory receptor cells in the spiny lobster Panulirus argus. Radioligands used were tritiated adenosine 5'-monophosphate (AMP) and taurine, which are two of the most excitatory compounds for spiny lobsters. Our results indicate the existence of two independent types of binding sites--a taurine binding site and an AMP binding site. For both the taurine and AMP binding sites, odorant binding is rapid, reversible, and saturable. KD values for the taurine and AMP binding sites are 2.3 and 2.0 microM, respectively, and Bmax values are 159 and 3.2 fmol/micrograms protein, respectively. The fact that the specificity, affinity, and independence of these two binding sites as defined in these biochemical studies are in agreement with those from electrophysiological studies suggests that these binding sites are olfactory receptor sites involved in sensory transduction.

Purification and characterization of sulfatases from Haliotis rufescens: evidence for changes in synthesis and heterogeneity during development

The digestive glands of many marine molluscs are rich sources of arylsulfatase enzymes which may function in the catabolism of sulfated polysaccharides in the diets of herbivorous species. Arylsulfatases, partially purified from the hepatopancreas of the red abalone, Haliotis rufescens, were investigated with respect to heterogeneity, catalytic requirements, and timing of induction during development. Four hepatopancreatic enzymes were purified from adult animals using a combination of hydrophobic interaction and anion-exchange chromatography. Zymograms of the four partially-purified enzymes produced by electrophoresis under nondenaturing conditions revealed a fifth, relatively more basic isozyme. All four partially-purified enzymes appear to be monomeric, with molecular weights of approximately 43,000 Da each, as measured by gel filtration. The affinities for p-nitrocatechol sulfate, pH optima, and strengths of inhibition by anions displayed by these enzymes are similar to the values reported for other molluscan arylsulfatases. Three of the four enzymes have Km values between 0.8 and 2.0 mM for p-nitrocatechol sulfate; the remaining enzyme (A2) has a Km of 6.7 mM. All four enzymes have pH and temperature optima of 5.5 and 45 degrees C, respectively. Three of the four enzymes have-t 1/2 (50 degrees C) values of 3.5 min; the enzyme A4 has a t 1/2 (50 degrees C) of 8.5 min. A monoclonal antibody directed against form A1b does not cross react with any of the other hepatopancreatic arylsulfatases when assayed by Western blot, confirming the structural heterogeneity of the adult enzymes. Total arylsulfatase activity increases in a biphasic manner during early abalone development, with the first increase occurring early in larval maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

The gastropod nervous system in metamorphosis

Many gastropods, including the sea hare Aplysia californica, undergo metamorphosis in passing from the larval to the juvenile phases of their life cycle. During metamorphosis, the gastropod nervous system is affected by both progressive and regressive neuronal events. In addition to this metamorphic reorganization, the nervous system appears to be centrally involved in initiating metamorphosis. We propose that gastropods not only possess temporally distinct neuronal adaptations for the specific needs of the larval and juvenile phases, but also another transient neuronal adaptation specialized to subserve the metamorphic episode.