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The Wnt family of secreted proteins has been proposed to play a conserved role in early specification of the bilaterian anteroposterior (A/P) axis. This hypothesis is based predominantly on data from vertebrate embryogenesis as well as planarian regeneration and homeostasis, indicating that canonical Wnt (cWnt) signaling endows cells with positional information along the A/P axis. Outside of these phyla, there is strong support for a conserved role of cWnt signaling in the repression of anterior fates, but little comparative support for a conserved role in promotion of posterior fates. We further test the hypothesis by investigating the role of cWnt signaling during early patterning along the A/P axis of the hemichordate Saccoglossus kowalevskii. We have cloned and investigated the expression of the complete Wnt ligand and Frizzled receptor complement of S. kowalevskii during early development along with many secreted Wnt modifiers. Eleven of the 13 Wnt ligands are ectodermally expressed in overlapping domains, predominantly in the posterior, and Wnt antagonists are localized predominantly to the anterior ectoderm in a pattern reminiscent of their distribution in vertebrate embryos. Overexpression and knockdown experiments, in combination with embryological manipulations, establish the importance of cWnt signaling for repression of anterior fates and activation of mid-axial ectodermal fates during the early development of S. kowalevskii. However, surprisingly, terminal posterior fates, defined by posterior Hox genes, are unresponsive to manipulation of cWnt levels during the early establishment of the A/P axis at late blastula and early gastrula. We establish experimental support for a conserved role of Wnt signaling in the early specification of the A/P axis during deuterostome body plan diversification, and further build support for an ancestral role of this pathway in early evolution of the bilaterian A/P axis. We find strong support for a role of cWnt in suppression of anterior fates and promotion of mid-axial fates, but we find no evidence that cWnt signaling plays a role in the early specification of the most posterior axial fates in S. kowalevskii. This posterior autonomy may be a conserved feature of early deuterostome axis specification.

The trunk is a key feature of the bilaterian body plan. Despite spectacular morphological diversity in bilaterian trunk anatomies, most insights into trunk development are from segmented taxa, namely arthropods and chordates. Mechanisms of posterior axis elongation (PAE) and segmentation are tightly coupled in arthropods and vertebrates, making it challenging to differentiate between the underlying developmental mechanisms specific to each process. Investigating trunk elongation in unsegmented animals facilitates examination of mechanisms specific to PAE and provides a different perspective for testing hypotheses of bilaterian trunk evolution. Here we investigate the developmental roles of canonical Wnt and Notch signaling in the hemichordate Saccoglossus kowalevskii and reveal that both pathways play key roles in PAE immediately following the completion of gastrulation. Furthermore, our functional analysis of the role of Brachyury is supportive of a Wnt-Brachyury feedback loop during PAE in S. kowalevskii, establishing this key regulatory interaction as an ancestral feature of deuterostomes. Together, our results provide valuable data for testing hypotheses of bilaterian trunk evolution.

We evaluated marine aggregates as environmental reservoirs for a thraustochytrid pathogen, Quahog Parasite Unknown (QPX), of the northern quahog or hard clam, Mercenaria mercenaria. Positive results from in situ hybridization and denaturing gradient gel electrophoresis confirm the presence of QPX in marine aggregates collected from coastal embayments in Cape Cod, Massachusetts, where QPX outbreaks have occurred. In laboratory experiments, aggregates were observed and recorded by entering a quahog's pallial cavity, thereby delivering embedded particles from the water column to its benthic bivalve host. The occurrence of pathogen-laden aggregates in coastal areas experiencing repeated disease outbreaks suggests a means for the spread and survival of pathogens between epidemics and provides a specific target for environmental monitoring of those pathogens.

The starlet sea anemone, Nematostella vectensis S tephenson 1935, is a burrowing, estuarine species that has become a model organism for fundamental studies of cnidarian and metazoan development. During early oogenesis, oocytes appear in the basal region of the gastrodermis in the reproductive mesenteries and gradually bulge into the adjacent connective tissue space (mesoglea) where the majority of oocyte growth and vitellogenesis occurs. However, oocytes do not physically contact the cellular and amorphous matrix of the mesogleal compartment due to a thin, intervening basal lamina. Oocytes retain limited contact with the basal gastrodermal epithelium via groups of ultrastructurally modified gastrodermal cells called trophocytes. Trophocytes are monociliated accessory cells of somatic origin that collectively form a structure called the trophonema, a unique accessory cell/oocyte association not observed outside the Cnidaria. The trophonema consists of 50-60 trophocytes that maintain contact with <1% of the oocyte surface and forms a circular, bowel-shaped depression on the luminal surface of the gastrodermis as they sink into the mesoglea with the oocyte. The oocyte remains highly polarized throughout oogenesis with the germinal vesicle positioned near the trophonema and presumably representing the future animal pole of the embryo. Contact between the trophonema and the oocyte is restricted to cell junctions connecting peripheral trophocytes and narrow extensions from the oocyte. Previous studies suggest that the trophonema plays a role in transport of extracellular digestive products from the gastrovascular cavity to the oocyte, and the ultrastructural features described in this study are consistent with that view. Vitellogenesis is described for the first time in a sea anemone. Yolk synthesis involves both autosynthetic and heterosynthetic processes including the biosynthetic activity of the Golgi complex and the uptake of extraoocytic yolk precursors via endocytosis, respectively.

Opanus tau, the oyster toadfish, is an important laboratory animal used in hearing and balance research at the Marine Biological Laboratory. Baird et al observes Edwardsiella tarda, a member of the Enterobacteriaceae as the major cause of disease in toadfish held at the Marine Research Center. The results as determined by electrophoresis, showed that the appropriate primers could distinctly amplify DNA of E. tarda and E. ictaluri.

Nematostella vectensis, a widely distributed, burrowing sea anemone, was raised through successive sexual generations at room temperature in non-circulating seawater. It has separate sexes and also reproduces asexually by transverse fission. Cultures of animals were fed Artemia sp. nauplii every second day. Every eight days the culture water was changed, and the anemones were fed pieces of Mytilus spp. tissue. This led to regular spawning by both sexes at eight-day intervals. The cultures remained reproductive throughout the year. Upon spawning, adults release either eggs embedded in a gelatinous mucoid mass, or free-swimming sperm. In one experiment, 12 female isolated clonemates and 12 male isolated clonemates were maintained on the 8-day spawning schedule for almost 8 months. Of the female spawnings, 75% occurred on the day following mussel feeding and water change, and 64% of the male spawnings were similarly synchronized under this regime. Fertilization and development occur when gametes from both sexes are combined in vitro. At 20°C, the embryos gastrulate within 12-15 hours. Spherical ciliated planulae emerge from egg masses 36-48 hours post-fertilization. The planulae elongate and form the first mesenteric couple, as well as four tentacle buds, by day five. By day seven, they metamorphose and settle as 250-500 μm long, four-tentacled juvenile anemones. More tentacles and all eight macrocnemes are present at 2-3 weeks. Individuals may become reproductively mature in as few as 69 days. Nematostella vectensis has the potential to become an important model for use in cnidarian developmental research.

Nematostella vectensis is one of only 5 sea anemones known to reproduce asexually by transverse fission. Sibling individuals of this species divide at highly variable rates with some individuals dividing rarely or not at all, while others may divide many times a year. Field populations are frequently unisexual, and such populations may be clones derived from a single founder. As individual anemones grow, the asexual fragments produced do not necessarily become larger, nor is the time taken to regenerate a functional oral crown on a fragment related to the size of the fragment. The inclusion of a bolus of undigested food in an aboral fragment may delay completion of regeneration as compared to fragments without a bolus. Increased food intake increases the frequency of fission and results in smaller fragments but does not significantly influence the time fragments take to regenerate. Starvation suppresses fission in individuals but does not totally eliminate it. Multi-crowned anomalies are common in natural and in laboratory populations. Subsequent fission of multi-crowned individuals produces normal, single-crowned anemones and meets the definition of budding, a truly rare phenomenon in sea anemones.

The use of ozone to clean and disinfect fresh and seawater life-support systems has become increasingly popular. Many analyses have been performed on their initial setup and design, but as they age and disinfection technology advances, they may require adjustments to function at optimum levels. Hsieh et al examine the efficacy of the ozone disinfection system that was installed at the Marine Resources Center of the Marine Biological Laboratory in 1992.

The small, burrowing, edwardsiid sea anemone Nematostella vectensis is widely distributed in estuaries and bays. Most typically it occurs in pools in marshes though it may occur subtidally as well. We have compiled records of its occurrence in North America from Nova Scotia to Georgia along the shores of the Atlantic Ocean, from Florida to Louisiana in the Gulf of Mexico and from California to Washington on the Pacific coast. To date we have found no records of its presence in Alabama or Texas, though it is present in all other of the contiguous coastal states of the United States. The species also occurs in England. We have obtained living specimens from many locations and have crossed females from England, Maryland, Georgia, California, Oregon, and Washington with males from Nova Scotia, Maryland, Georgia, and Oregon. These 24 crosses all yielded viable first-generation anemones that in turn produced second-generation animals. We accept this as proof that this widely distributed anemone is a single species. We have obtained living N. vectensis from 11 areas. Of these, only samples from Maine, Maryland, Georgia, and Oregon contained both sexes. The sample from Nova Scotia was all male and our samples from England, New Hampshire, California, and Washington were all female. We hypothesize that the unisexual samples were from clones resulting from asexual reproduction in this species.

An abstract of the study on the diagnosis of Edwardsiella tarda infection in oyster toadfish (Opsanus tau) by Horenstein et al is presented. The study adapted a PCR-based method into a diagnostic test, to be used with blood and mucus, for identifying E. tarda in toadfish.