Male-female larval interactions in Schistosoma mansoni-infected Biomphalaria glabrata

This paper investigates Schistosoma mansoni male-female larval interactions in simultaneous bi-miracidial Biomphalaria glabrata infections. Larval interactions were analysed at four levels of infection: (i), miracidial infectivity, estimated by the prevalence of mollusc infection; (ii), mollusc pathology, measured by the mollusc growth and survival; (iii), dynamics of the cercarial sex ratio; and (iv), cercarial infectivity, measured as the success of development into adulthood. Our results showed that larval interactions exist in S. mansoni-infected B. glabrata. These interactions do not occur in miracidial infectivity, but occur in mollusc pathology, cercarial sex ratio dynamics and cercarial infectivity. Regarding mollusc pathology, we showed that the bi-miracidially-infected molluscs were smaller than the mono-miracidially-infected ones. This could be the result of larval competition. Regarding the dynamics of the cercarial sex ratio, we showed larval female superiority as compared with male larvae inducing the shedding of female-biased cercarial sex ratios. These sex ratios were rhythmic and could be the reflection of an external expression of the intramolluscan development. Regarding cercarial infectivity, we showed that the simultaneous presence of both sexes in a mollusc increased the cercarial infectivity. This result could be due to male-female larval synergism.     

Developmental constraint on gene duplicability in fruit flies and nematodes

A previous study in nematodes suggested that developmental constraint reduces the duplicability of genes involved in early development. Recent large-scale gene expression studies of fly development enabled us to conduct a more detailed study of this issue. We found that the average duplicability of genes involved in embryonic development is indeed lower than that of genes involved in larval development but not significantly lower than that of genes involved in later stages of development. Moreover, in both flies and nematodes genes with multiple expression peaks do not seem to have a lower duplicability than do genes with a single expression peak. Thus, although developmental constraint does appear to reduce gene duplicability, the effect seems weak or at best moderate.     

Conserved and novel gene expression between regeneration and asexual fission in <Emphasis Type="Italic">Nematostella vectensis</Emphasis>

Due to work in model systems (e.g., flies and mice), the molecular mechanisms of embryogenesis are known in exquisite detail. However, these organisms are incapable of asexual reproduction and possess limited regenerative abilities. Thus, the mechanisms of alternate developmental trajectories and their relation to embryonic mechanisms remain understudied. Because these developmental trajectories are present in a diverse group of animal phyla spanning the metazoan phylogeny, including cnidarians, annelids, and echinoderms, they are likely to have played a major role in animal evolution. The starlet sea anemone Nematostella vectensis, an emerging model system, undergoes larval development, asexual fission, and complete bi-directional regeneration in the field and laboratory. In order to investigate to what extent embryonic patterning mechanisms are utilized during alternate developmental trajectories, we examined expression of developmental regulatory genes during regeneration and fission. When compared to previously reported embryonic expression patterns, we found that all genes displayed some level of expression consistent with embryogenesis. However, five of seven genes investigated also displayed striking differences in gene expression between one or more developmental trajectory. These results demonstrate that alternate developmental trajectories utilize distinct molecular mechanisms upstream of major developmental regulatory genes such as fox, otx, and Hox-like.     

Apical sensory neurones mediate developmental retardation induced by conspecific environmental stimuli in freshwater pulmonate snails

Freshwater pond snails Helisoma trivolvis and Lymnaea stagnalis undergo larval development and metamorphosis inside egg capsules. We report that their development is permanently under slight tonic inhibitory influence of the anterior sensory monoaminergic neurones, which are the remnants of the apical sensory organ. Conspecific juvenile snails, when reared under conditions of starvation and crowding, release chemical signals that are detected by these neurones in encapsulated larvae and reversibly suppress larval development, thus providing a link between environmental signals and developmental regulation. Induced retardation starts from the trochophore stage and results in up to twofold prolongation of the larval lifespan. Upon stimulation with the signal, the neurones increase synthesis and release of monoamines [serotonin (5-HT) in Helisoma and dopamine in Lymnaea] that inhibit larval development acting via ergometrine-sensitive internal receptors. Thus, the novel regulatory mechanism in larval development of molluscs is suggested and compared with the phenomenon of dauer larvae formation in the nematode Caenorhabditis elegans.     

Ecological regulation of development: induction of marine invertebrate metamorphosis

In the marine environment a wide range of invertebrates have a pelagobenthic lifecycle that includes planktonic larval and benthic adult phases. Transition between these morphologically and ecologically distinct phases typically occurs when the developmentally competent larva comes into contact with a species-specific environmental cue. This cue acts as a morphogenetic signal that induces the completion of the postlarval/juvenile/adult developmental program at metamorphosis. The development of competence often occurs hours to days after the larva is morphologically mature. In the non-feeding--lecithotrophic--larvae of the ascidian Herdmania curvata and the gastropod mollusc Haliotis asinina, gene expression patterns in pre-competent and competent stages are markedly different, reflecting the different developmental states of these larval stages. For example, the expression of Hemps, an EGF-like signalling peptide required for the induction of Herdmania metamorphosis, increases in competent larvae. Induction of settlement and metamorphosis results in further changes in developmental gene expression, which apparently is necessary for the complete transformation of the larval body plan into the adult form.     

Black Sea mollusc, Cerithium vulgatum (Gastropoda, Cerithiidae), a new intermediate trematode host

The mollusc Cerithium vulgatum was first recorded as a new intermediate host of trematodes from the Black Sea. Two species of cercariae (Cercaria I and Ceracaria II) parasitizing this mollusc were found and described. The general infestation of molluscs was 7.54 per cent. Eight species of larval trematodes parasitzing 7 other species of sea molluscs were found.     

A tolloid homologue from the Pacific oyster Crassostrea gigas

The genes governing mesoderm specification have been extensively studied in vertebrates, arthropods and nematodes. The latter two phyla belong to the Ecdysozoan clade but little is understood of the role that these genes might play in the development of the other major protostomal clade, the Lophotrochozoa. As part of a wider project to analyze the functions associated with transforming growth factor beta superfamily members in Lophotrochozoa, we have cloned a gene encoding a tolloid homologue from the bivalve mollusc Crassostrea gigas. Tolloid is a key developmental protein that regulates the activity of bone morphogenetic proteins (BMPs). We have determined the intron-exon structure of the gene encoding C. gigas tolloid and have compared it with those of homologous genes from both protostomes and deuterostomes. In order to analyze the functionality of oyster tolloid the zebrafish embryo has been employed as a reporter organism and we show that over-expression of this protein results in the ventralization of zebrafish embryos at 24h post fertilization. The expression of the C. gigas tolloid gene during embryonic and larval development as well as in adult tissues is also explored.     

Long-term sensitization training in Aplysia leads to an increase in calreticulin, a major presynaptic calcium-binding protein.

Long-term memory for sensitization in Aplysia requires new protein and RNA synthesis. Here, we identify a late protein as calreticulin, the major Ca(2+)-binding protein of the lumen of the endoplasmic reticulum. An antiserum against Aplysia calreticulin reveals an enrichment of calreticulin immunoreactivity in presynaptic varicosities. Quantitative S1 nuclease analysis indicates that the steady-state level of calreticulin mRNA in Aplysia sensory neurons increases during the maintenance phase of long-term sensitization. The finding that this mRNA increases in expression late, some time after training, is consistent with the idea that long-term neuromodulatory changes underlying sensitization may depend on a cascade of gene expression in which the induction of early regulatory genes leads to the expression of late effector genes.