Events Of Metamorphosis Research Articles

The larval midgut of Anopheles, Aedes, and Toxorhynchites mosquitoes (Diptera, Culicidae): a comparative approach in morphophysiology and evolution.

The mosquito larval midgut is responsible for acquiring and storing most of the nutrients that will sustain the events of metamorphosis and the insect's adult life. Despite its importance, the basic biology of this larval organ is poorly understood. To help fill this gap, we carried out a comparative morphophysiological investigation of three larval midgut regions (gastric caeca, anterior midgut, and posterior midgut) of phylogenetically distant mosquitoes: Anopheles gambiae (Anopheles albimanus was occasionally used as an alternate), Aedes aegypti, and Toxorhynchites theobaldi. Larvae of Toxorhynchites mosquitoes are predacious, in contrast to the other two species, that are detritivorous. In this work, we show that the larval gut of the three species shares basic histological characteristics, but differ in other aspects. The lipid and carbohydrate metabolism of the An. gambiae larval midgut is different compared with that of Ae. aegypti and Tx. theobaldi. The gastric caecum is the most variable region, with differences probably related to the chemical composition of the diet. The peritrophic matrix is morphologically similar in the three species, and processes involved in the post-embryonic development of the organ, such as cell differentiation and proliferation, were also similar. FMRF-positive enteroendocrine cells are grouped in the posterior midgut of Tx. theobaldi, but individualized in An. gambiae and Ae. aegypti. We hypothesize that Tx. theobaldi larval predation is an ancestral condition in mosquito evolution.

Topical Semisolid Products-Understanding the Impact of Metamorphosis on Skin Penetration and Physicochemical Properties.

Recently, the United States Food and Drug Administration published a series of product-specific guidance for the development of topical drugs, with in vitro options consisting of qualitative sameness (Q1) and quantitative sameness (Q2) assessment of formulations, physiochemical and structural characterization of formulations (Q3), and, potentially, in vitro drug release and permeation tests. In these tests, the topical semisolid product's critical quality attributes (CQAs), such as rheological properties, thermodynamic activity, particle size, globule size, and rate/extent of drug release/permeation, are evaluated to ensure the desired product quality. However, alterations in these CQAs of the drug products may occur under 'in use' conditions because of various metamorphosis events, such as evaporation that leads to supersaturation and crystallization, which may eventually result in specific failure modes of semisolid products. Under 'in use' conditions, a limited amount of formulation is applied to the skin, where physicochemical characteristics of the formulation are substantially altered from primary state to secondary and, eventually, tertiary state on the skin. There is an urgent need to understand the behavior of topical semisolid products under 'in use' conditions. In this review, we attempt to cover a series of metamorphosis events and their impact on CQAs (Q3 attributes), such as viscosity, drug activity, particle size, globule size, and drug release/permeation of topical semisolid products.

Conceptual framework for the insect metamorphosis from larvae to pupae by transcriptomic profiling, a case study of Helicoverpa armigera (Lepidoptera: Noctuidae)

BackgroundInsect metamorphosis from larvae to pupae is one of the most important stages of insect life history. Relatively comprehensive information related to gene transcription profiles during lepidopteran metamorphosis is required to understand the molecular mechanism underlying this important stage. We conducted transcriptional profiling of the brain and fat body of the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) during its transition from last instar larva into pupa to explore the physiological processes associated with different phases of metamorphosis.ResultsDuring metamorphosis, the differences in gene expression patterns and the number of differentially expressed genes in the fat body were found to be greater than those in the brain. Each stage had a specific gene expression pattern, which contributed to different physiological changes. A decrease in juvenile hormone levels at the feeding stage is associated with increased expression levels of two genes (juvenile hormone esterase, juvenile hormone epoxide hydrolase). The expression levels of neuropeptides were highly expressed at the feeding stage and the initiation of the wandering stage and less expressed at the prepupal stage and the initiation of the pupal stage. The transcription levels of many hormone (or neuropeptide) receptors were specifically increased at the initiation of the wandering stage in comparison with other stages. The expression levels of many autophagy-related genes in the fat body were found to be gradually upregulated during metamorphosis. The activation of apoptosis was probably related to enhanced expression of many key genes (Apaf1, IAP-binding motif 1 like, cathepsins, caspases). Active proliferation might be associated with enhanced expression levels in several factors (JNK pathway: jun-D; TGF-β pathway: decapentaplegic, glass bottom boat; insulin pathway: insulin-like peptides from the fat body; Wnt pathway: wntless, TCF/Pangolin).ConclusionsThis study revealed several vital physiological processes and molecular events of metamorphosis and provided valuable information for illustrating the process of insect metamorphosis from larvae to pupae.

Functional analysis of thyroid hormone receptor beta in Xenopus tropicalis founders using CRISPR-Cas.

ABSTRACTAmphibians provide an ideal model to study the actions of thyroid hormone (TH) in animal development because TH signaling via two TH receptors, TRα and TRβ, is indispensable for amphibian metamorphosis. However, specific roles for the TRβ isoform in metamorphosis are poorly understood. To address this issue, we generated trβ-disrupted Xenopus tropicalis tadpoles using the CRISPR-Cas system. We first established a highly efficient and rapid workflow for gene disruption in the founder generation (F0) by injecting sgRNA and Cas9 ribonucleoprotein. Most embryos showed severe mutant phenotypes carrying high somatic mutation rates. Utilizing this founder analysis system, we examined the role of trβ in metamorphosis. trβ-disrupted pre-metamorphic tadpoles exhibited mixed responsiveness to exogenous TH. Specifically, gill resorption and activation of several TH-response genes, including trβ itself and two protease genes, were impaired. However, hind limb outgrowth and induction of the TH-response genes, klf9 and fra-2, were not affected by loss of trβ. Surprisingly, trβ-disrupted tadpoles were able to undergo spontaneous metamorphosis normally, except for a slight delay in tail resorption. These results indicate TRβ is not required but contributes to the timing of resorptive events of metamorphosis.

Escherichia coli expressing a green fluorescent protein (GFP) in Anopheles stephensi: a preliminary model for paratransgenesis

Issues, like emerging insecticide resistance in Anopheles mosquitoes, have led to a breakdown in many vector control programs. In this study, a recombinant Escherichia coli with plasmid expressing a green fluorescent protein (E.coli-GFP) was used as a paratransgenesis model to determine: the possibility of E. coli-GFP trans-stadial transmission. The effect of the water microflora, of bacteria-impregnated sugar solutions, and of blood-feeding on E. coli-GFP colonization and localization within An. stephensi tissues, were studied. The results demonstrated the persistence of E. coli-GFP during molting and metamorphosis events and its trans-stadial transmission. Also the efficacy of bacteria-impregnated sugar solutions for transferring the bacteria to the adult mosquito’s midgut was shown. A blood meal dramatically increased the number of bacteria within 24–48 h post feeding. In addition to fluorescence microscope evaluation, GFP gene PCR amplification showed the presence of the bacteria in the midgut of larvae, pupae, and adults up to 13 days after eclosion. Massive colonization of bacteria was observed in the larvae and in the adult mosquito’s malpighian tubules which may play a role in retaining bacteria in adult mosquitos. The results of this study showed that E. coli could be used as a laboratory model in paratransgenesis studies for the evaluation of various effector molecules as anti-parasite agents for malaria and filariasis.

Sponges as substrata and early life history of the tubulariid Zyzzyzus warreni (Cnidaria: Hydrozoa) in the São Sebastião Channel, Brazil

The hydroid Zyzzyzus warreni is usually found in shallow coastal waters forming aggregations of solitary polyps embedded in demosponges. Early life history transformations and settlement responses by the actinulae of this hydroid were studied in the laboratory using 13 species of sponges and 2 species of algae collected in the São Sebastião Channel (Brazil) as substrata. The absence of oral tentacles and mouth in the actinulae and early events of metamorphosis suggest that these larvae are unable to spend long periods in the plankton and attach quickly near conspecifics when a preferred substratum is encountered. The time required for settlement and the number of elicited settlings indicated four settlement responses: (a) frequent and short-time settlement, in actinulae exposed to Halichondria cebimarensis, Mycale angulosa, M. aff. americana, M. laxissima (skeleton) and Tedania ignis; (b) moderate and delayed settlement, in actinulae exposed to Aplysina caissara, A. fulva, Haliclona melana and M. microsigmatosa; (c) no settlement, in actinulae exposed to Suberites aurantiacus and to the algae Hypnea musciformis and Sargassum cymosum; and (d) lethal response, in actinulae exposed to Amphimedon viridis, Aplysilla rosea, Dragmacidon reticulatum and M. laxissima. These responses indicate a considerable degree of species discrimination by the actinulae and are consistent with substrata used by the hydroid in the natural environment.

Characterization of a GABA A receptor β subunit in the abalone Haliotis asinina that is upregulated during larval development

In the tropical abalone Haliotis asinina, the neurotransmitter γ-aminobutyric acid (GABA) is a potent inducer of larval settlement, a process beginning with the onset of a behavioral search for a suitable substratum and ending with metamorphosis. In the natural environment, larvae can encounter GABA or GABA-like molecules through association with conspecific foot mucus and crustose coralline algae. To understand the role of GABA in the molecular process leading to settlement required identification and analysis of GABA's cognate receptor. We now have isolated the first abalone full-length GABA A receptor ( Has-GABA AR) β subunit gene, which encodes a protein of 485 amino acids, from juvenile H. asinina neural tissue. Similar to other metazoan GABA ARs, the abalone GABA AR contains four transmembrane domains, a conserved cysteine loop in the N-terminal extra-cellular domain, and highly conserved sequence motifs. The Has- GABA A R gene is expressed at extremely low levels in unfertilized eggs, but increases significantly just prior to settlement, peaking at 120 h post fertilization (hpf). We further demonstrate that during the period of larval competence (96–144 hpf), gene transcripts and the encoded Has-GABA AR were localized in a cluster of cells along the dorsal and lateral edges of the foot, as well as the posterior epithelium. In functional settlement assays using GABA and 5-AVA, we found that there was significantly lower settlement of veligers pre-treated with antibodies to an external domain of the Has-GABA AR than those treated with preimmune serum, or untreated veligers. We postulate that this receptor may act as a highly sensitive chemical sensor, whose activation is necessary to trigger chloride-mediated sensory neuron activation or inhibition, leading to the initiation of settlement and metamorphosis events.

A Switch in the Control of Growth of the Wing Imaginal Disks of Manduca sexta

BackgroundInsulin and ecdysone are the key extrinsic regulators of growth for the wing imaginal disks of insects. In vitro tissue culture studies have shown that these two growth regulators act synergistically: either factor alone stimulates only limited growth, but together they stimulate disks to grow at a rate identical to that observed in situ. It is generally thought that insulin signaling links growth to nutrition, and that starvation stops growth because it inhibits insulin secretion. At the end of larval life feeding stops but the disks continue to grow, so at that time disk growth has become uncoupled from nutrition. We sought to determine at exactly what point in development this uncoupling occurs.MethodologyGrowth and cell proliferation in the wing imaginal disks and hemolymph carbohydrate concentrations were measured at various stages in the last larval instar under experimental conditions of starvation, ligation, rescue, and hormone treatment.Principal FindingsHere we show that in the last larval instar of M. sexta, the uncoupling of nutrition and growth occurs as the larva passes the critical weight. Before this time, starvation causes a decline in hemolymph glucose and trehalose and a cessation of wing imaginal disks growth, which can be rescued by injections of trehalose. After the critical weight the trehalose response to starvation disappears, and the expression of insulin becomes decoupled from nutrition. After the critical weight the wing disks loose their sensitivity to repression by juvenile hormone, and factors from the abdomen, but not the brain, are required to drive continued growth.ConclusionsDuring the last larval instar imaginal disk growth becomes decoupled from somatic growth at the time that the endocrine events of metamorphosis are initiated. These regulatory changes ensure that disk growth continues uninterrupted when the nutritive and endocrine signals undergo the drastic changes associated with metamorphosis.

The club‐shaped gland of amphioxus: export of secretion to the pharynx in pre‐metamorphic larvae and apoptosis during metamorphosis

AbstractIn amphioxus larvae, the club‐shaped gland is a tube connecting the pharyngeal lumen with the external environment. The functions of the gland and its fate during the larva‐to‐juvenile metamorphosis have long been controversial. Here we use a fixative including ruthenium red to preserve extracellular secretions (presumably glycoproteins) in late pre‐metamorphic larvae. This procedure reveals reddish, fibrogranular material in the lumen of the club‐shaped gland and in the pharynx adjacent to the gland's inner opening. This finding strengthens the idea that secretions of the club‐shaped gland are exported to the pharyngeal lumen to help form a mucous trap for capturing food particles entering the mouth. We also use the terminal desoxynucleotidyl transferase‐mediated dUTP nick end labelling (TUNEL) assay to study apoptosis in the tissues of metamorphosing larvae. One of the earliest events of metamorphosis is the massive apoptotic destruction of the club‐shaped gland. Therefore, despite some previous opinions to the contrary, the cells of the gland do not survive to participate in the genesis of the definitive endostyle or any other post‐larval structures.

Paedomorphosis in Ambystoma talpoideum: effects of initial body size variation and density

Facultative paedomorphosis is the ability of a salamander to either metamorphose into a terrestrial, metamorphic adult or retain a larval morphology to become a sexually mature paedomorphic adult. It has been hypothesized that density and initial body size variation within populations are instrumental in cueing metamorphosis or paedomorphosis in salamanders, yet few studies have adequately tested these hypotheses in long-term experiments. Beginning in the spring of 2004, 36 experimental ponds were used to manipulate three body size variation levels (low, medium, high) and two density levels (low, high) of Ambystoma talpoideum larvae. Larvae were individually marked using visible implant elastomers and collected every 2 weeks in order to measure snout-vent length and mass. Bi-nightly sampling was used to collect new metamorphs as they appeared. Analysis revealed significant effects of density, size variation and morph on body size of individuals during the summer. Individuals that metamorphosed during the fall and following spring were significantly larger as larvae than those becoming paedomorphic across all treatments. These results support the Best-of-a-Bad-Lot hypothesis, which proposes that the largest larvae metamorphose in order to escape unfavorable aquatic habitats. Large larvae may metamorphose to leave aquatic habitats, regardless of treatment, due to the colder climate and lower productivity found in Kentucky, which is in the northern-most part of A. talpoideum's range. By maintaining a long-term experiment, we have provided evidence for the transition of both larvae and paedomorphs into metamorphs during fall and spring metamorphosis events. Furthermore, the production of similar morphs under different environmental conditions observed in this research suggests that the ecological mechanisms maintaining polyphenisms may be more diverse that first suspected.

Effects of Endocrine Disrupting Chemicals on Amphibian Metamorphosis and Mitochondrial Membrane Permeability Transition

The estrogenic chemical bisphenol A (BPA) has multiple hormonal activities, but its effects on thyroid hormone (TH) action are not fully understood. TH is required for the metamorphosis of tadpoles into frogs, and thus tadpole tail regression, one of the most spectacular events in metamorphosis, can be used for studying the effect of BPA and related compounds (BPAs) on TH action. We found that 3,3 � ,5-triiodothyronine (T3)-induced tadpole tail regression in the wrinkled frog Rana rugosa (R. rugosa )i ss uppressed by BPA, tetrabromobisphenol A (TBBPA), tetrachlorobisphenol A (TCBPA), and tetramethylbisphenol A (TMBPA). BPAs also inhibited spontaneous metamorphosis in the tropical clawed frog Silurana tropicalis (S. tropicalis )c ontrolled by endogenous circulating TH. These results indicate that BPAs are TH antagonists. For the African clawed frog Xenopus laevis (X. laevis), transgenic tadpoles carrying plasmid DNA containing TH response element (TRE) and 5 � -upstream promoter region of the TH receptor (TR) β A1 gene linked to an enhanced green fluorescent protein (EGFP) gene, T3 induced a strong EGFP expression in the hind limbs. This expression was suppressed by BPA, TBBPA, TCBPA and TMBPA, suggesting BPAs all act as antagonists to prevent the binding of T3 to TR, resulting in inhibition of TR-mediated gene expression. Much work has been done in examining the apoptotic and other detrimental effects of polychlorinated biphenyls (PCBs), but the role of mitochondrial damage in such toxic action remains obscure. There is evidence however that mitochondrial membrane permeability transition (MPT) plays a crucial role in apoptosis. We investigated the effect of 4-hydroxy-3,3 � ,4 � ,5-tetrachlorobiphenyl (4-OH-TCB) on isolated rat liver mitochondria. In order to help clarify this, biochemical analysis revealed that 4-OH-TCB induced calcium release, reactive oxygen species (ROS) generation, depolarization, swelling and cytochromec (Cyt. c )r elease in a time- and concentration-dependent manner. These 4-OH-TCB-induced changes in mitochondrial function were found to be inhibited by the presence of cyclosporin A (CsA), a specific inhibitor of MPT, suggesting a classic type of MPT. It is concluded that 4-OH-TCB induces MPT together with ROS generation, causing apoptosis in certain cells.

Electrophoretic protein pattern and acid phosphatase activity in the midgut extracts of Apis mellifera L. (Hymenoptera: Apidae) during metamorphosis

The electrophoretic pattern of proteins and the activity of acid phosphatase were described in the midgut extracts during the post-embryonic stages of Apis mellifera L. in order to stablish a correlation with the metamorphosis events. The results show the greatest variation in proteic electrophoretical bands during prepupal stage and the smallest variation during the brown eyed pupae stage. The acid phosphatase activity was higher during the larval last instar and lower in white eyed pupae. The greatest variety of bands during the prepupal stage coincides with the histolysis of the larval midgut epithelium and the lowest variability in the brown eyed pupa coincides with the end of the midgut differentiation. In another hand, the greatest phosphatase activity in the last larval stage must reflect this enzyme actuation in the histolysis of the larval epithelium.

Synthesis and Mobilization of Glycogen during Metamorphosis of the Medfly Ceratitis capitata

There are no recent reports focusing on insect glycogen metabolism that take the advances made in mammalian and yeast systems into account. Moreover, little is known about glycogen synthesis and degradation during insect metamorphosis. The biosynthesis and mobilization of insect glycogen were measured during the larva to adult transition in the Medfly, Ceratitis capitata. The glycogen accumulated by larva decreased to reach almost undetectable levels at the beginning of the pupation process. Histological preparations of 40 h muscles and fat body confirmed a low glycogen content, in contrast with high glycogen images in third larva tissues. After 40 h, glycogen was synthesized de novo and accumulates up to adult ecdysis. We obtained the metamorphosis-dependent profiles of phosphorylase, glycogen synthase, and a glycogenin-like protein. This novel insect glycogen initiator protein (the first measured in an arthropod) appeared to be similar to the homologous enzymes from vertebrates and yeast. We have correlated these results with other biochemical events and anatomical landmarks to understand the use of storage carbohydrates during the sequence of metamorphosis events.

Isolation of genes involved in ascidian metamorphosis: epidermal growth factor signaling and metamorphic competence.

Although embryonic development in ascidians has been studied for over a century, the signals involved in coordinating post-larval development and metamorphosis are just beginning to be investigated. In this paper, we demonstrate that transcription is necessary for both the acquisition of metamorphic competence and the completion of the initial events of metamorphosis in Boltenia villosa. Transcripts expressed during metamorphic competence were isolated by a suppressive PCR subtraction of Boltenia villosa larval cDNAs. One of these transcripts is homologous to cornichon. Cornichon has a crucial but undefined role in epidermal growth factor (EGF) signaling during Drosophila embryogenesis. In situ hybridization demonstrates that Boltenia cornichon (Cnib) is expressed in the anterior papillary region of larvae as they gain competence. Our hypothesis is that Cnib acts to potentiate EGF signaling, thereby allowing Boltenia larvae to respond to cues for metamorphosis. Further research into the role of Cnib in urochordate metamorphosis may provide insight into the function of cornichon in other organisms. A better molecular understanding of urochordate metamorphosis will also provide a foundation for exploring the role of metamorphosis in chordate evolution.

Isolation and characterization of genes that are expressed during Ciona intestinalis metamorphosis.

In ascidians, the events of metamorphosis transform the non-feeding, mobile tadpole larva into a filter-feeding, fixed juvenile, and the process involves rearrangements of cells, two organs and physiological changes. Differential screening was used to isolate two genes that are not expressed in swimming larvae but are expressed immediately after the initiation of metamorphosis in Ciona intestinalis. One of the genes, Ci-meta1, encodes a polypeptide with a putative secretion signal sequence, 6 epidermal growth factor (EGF)-like repeats and 13 calcium-binding EGF-like repeats. The gene begins to be expressed immediately after the beginning of metamorphosis in the adhesive organ and is likely to be associated with the signal response for metamorphosis. Another gene named Ci-meta2 encodes a protein with a putative secretion signal and three thrombospondin type-1 repeats. Ci-meta2 gene expression begins at the larval stage and is upregulated in the metamorphosing juveniles. Ci-meta2 expression is found in three regions; the adhesive organ which is also associated with settlement, the neck region between the trunk and the tail of the larva which is associated with tail resorption, and dorsal regions of the trunk which correspond to the location of the siphon primordium. This gene may be involved in the dynamic arrangement of cells during ascidian metamorphosis.

Bonus, a Drosophila Homolog of TIF1 Proteins, Interacts with Nuclear Receptors and Can Inhibit βFTZ-F1-Dependent Transcription

The Drosophila bonus ( bon) gene encodes a homolog of the vertebrate TIF1 transcriptional cofactors. bon is required for male viability, molting, and numerous events in metamorphosis including leg elongation, bristle development, and pigmentation. Most of these processes are associated with genes that have been implicated in the ecdysone pathway, a nuclear hormone receptor pathway required throughout Drosophila development. Bon is associated with sites on the polytene chromosomes and can interact with numerous Drosophila nuclear receptor proteins. Bon binds via an LxxLL motif to the AF-2 activation domain present in the ligand binding domain of βFTZ-F1 and behaves as a transcriptional inhibitor in vivo.

Effects of low salinity on metamorphosis in estuarine colonial ascidians

Abstract. We studied the effects of brackish water on larval attachment, events of metamorphosis, and juvenile mortality in three colonial ascidian species that live in a Florida coastal lagoon. Eudistoma olivaceum and Eudistoma hepaticum are restricted in their adult distribution to areas of relatively high and constant salinity near inlets, whereas Ecteinascidia turbinata extends more than 20 km into the Indian River, where salinity can be much more variable. In all three species, metamorphosis proceeded more quickly at 33 ppt than at lower salinities. The thresholds for successful metamorphosis differed among species in a manner that corresponded to the adult distributions, with E. turbinata being capable of completing metamorphosis at salinities as low as 22 ppt, E. hepaticum as low as 24 ppt, and E. olivaceum as low as 26 ppt. Larvae of both Eudistoma species delayed settlement in very low salinity water, whereas those of E. turbinata settled very quickly, then failed to complete metamorphosis. Juvenile mortality at salinities lower than 22 ppt was 100% for all three species. Survival in salinities higher than 22 ppt was strongly correlated with salinity in E. olivaceum and E. hepaticum, but not E. turbinata.

JNK and decapentaplegic signaling control adhesiveness and cytoskeleton dynamics during thorax closure in Drosophila.

One of the fundamental events in metamorphosis in insects is the replacement of larval tissues by imaginal tissues. Shortly after pupariation the imaginal discs evaginate to assume their positions at the surface of the prepupal animal. This is a very precise process that is only beginning to be understood. In Drosophila, during embryonic dorsal closure, the epithelial cells push the amnioserosa cells, which contract and eventually invaginate in the body cavity. In contrast, we find that during pupariation the imaginal cells crawl over the passive larval tissue following a very accurate temporal and spatial pattern. Spreading is driven by filopodia and actin bridges that, protruding from the leading edge, mediate the stretching of the imaginal epithelia. Although interfering with JNK (Jun N-terminal kinase) and dpp (decapentaplegic) produces similar phenotypic effects suppressing closure, their effects at the cellular level are different. The loss of JNK activity alters the adhesion properties of larval cells and leads to the detachment of the imaginal and larval tissues. The absence of dpp signaling affects the actin cytoskeleton, blocks the emission of filopodia, and promotes the collapse of the leading edge of the imaginal tissues. Interestingly, these effects are very similar to those observed after interfering with JNK and dpp signaling during embryonic dorsal closure.

Role of Chemical Inducers in Larval Metamorphosis of Queen Conch, Strombus gigas Linnaeus: Relationship to Other Marine Invertebrate Systems.

Chemical cues are important in the exogenous and endogenous control of metamorphosis in many marine invertebrate larvae. In the queen conch, Strombus gigas Linnaeus, larval metamorphosis is induced by low molecular weight compounds associated with dominant species of red algae found in conch nursery grounds; these species include the foliose rhodophyte Laurencia poitei (Lamouroux). The responses of conch larvae to the algal-associated cues are dependent on concentration and length of exposure, with the initial events of metamorphosis occurring within 10 min of treatment with an aqueous extract of L. poitei. The free amino acids valine and isoleutine mimic the effects of the natural inducer, and they may bind to and be recognized by the same sites on the larvae as the algal cues. Hydrogen peroxide, vanadate, and {gamma}-aminobutyric acid (GABA), as well as elevated K+ concentrations (i.e., above ambient seawater levels), also induce larval metamorphosis. Acetylsalicylic acid decreases the responses of conch larvae to the algal-associated cues and to the free amino acids, but it has no effect on the induction triggered by hydrogen peroxide. The chemical induction of metamorphosis in conch larvae shares many general features with chemoreception in aquatic invertebrates. The natural inducers of metamorphosis, like the cues involved in olfactory responses in other marine organisms, are of low molecular weight and water soluble. In addition, the results of the experiments with hydrogen peroxide, vanadate, and GABA suggest that second messenger pathways are involved in conch metamorphosis.

Induction of metamorphosis of the marine Hydrozoan Hydractinia echinata fleming, 1828

The marine hydrozoan Hydractinia echinata Fleming, 1828 develops through a demersal planula larval stage. Recent work on the induction of metamorphosis of the planula has contributed greatly to understanding of the role of cell communication by signals, signal transmission, and signal transduction during metamorphosis of marine invertebrates. The purpose of this paper is to survey what is known about the natural induction of metamorphosis and to provide information on the biochemical and cellular mechanisms underlying the metamorphic events in H. echinata. A critical look at the effect of inhibitors is given, in conjunction with an hypothesis about the sequence of early events in metamorphosis.