Morphogenesis of the digestive tract of the pluteus larva of Strongylocentrotus purpuratus: sphincter formation

In the developing pluteus larva of S. purpuratus, the initial morphogenetic event in the formation of a functional gut is the appearance of two constrictions in the archenteron. These two constrictions become the cardiac and pyloric sphincters. During the 2 h in which the constrictions form, the sphincter cells change from cuboidal to wedge-shaped, and the apical ends of the sphincter cells develop an electron-dense region in which microfilaments can be resolved. Constriction of the archenteron was reversibly inhibited by cytochalasin B, although cytochalasin B had no effect once the constrictions had fully formed. Neither the electron-dense region nor the microfilaments were observed after cytochalasin B treatment. It is suggested that sphincter formation is initially accomplished by a microfilament-mediated contraction of the apical ends of the sphincter cells, which changes their shape and constricts the archenteron.     

The structure of the nervous system of the pluteus larva of Strongylocentrotus purpuratus

Summary Tissues that have the ultrastructural characteristics of nervous tissues are associated with ciliary and muscular elements of the pluteus larva of Strongylocentrotus purpuratus. The nerve cells are found along the margins of the ciliary bands, which are composed predominantly of spindle-shaped ciliated cells. The nerve cells contribute axonal processes to a tract of axons, which runs at the base of the ciliary band throughout its length. Axonal tracts, in the esophagus, lie beneath the circumesophageal muscles. Branched microvilli, which have been interpreted as sensory receptors, are located on the oral side of the main ciliary band and connect with the nerve cells in the ciliary band. The nervous structures described here, and other tissues of the pluteus that have been previously described as nervous, are compared on the basis of their association with receptor and effector organs, and their ultrastructural characteristics.     

Development of the nervous system of the pluteus larva of Strongylocentrotus droebachiensis

Summary Development of the nervous system of the pluteus larva of Strongylocentrotus droebachiensis was investigated using indirect immunofluorescence with antibodies against dopamine, GABA, and serotonin, and glyoxylic acid-induced fluorescence of catecholamines. Serotonergic cells first appear in full gastrulae; dopaminergic and GABAergic cells are present in early four-arm plutei. The number of neurons and the complexity of the nervous system increases through development of the pluteus. In the pluteus the dopaminergic component of the nervous system includes a ganglion in the lower lip of the mouth and a pair of ganglia at the base of the post-oral arms which extend axons along the base of the circumoral ciliary band. The distribution of cells visualized by glyoxylic acid-induced fluorescence is similar to that of dopaminergic cells. GABAergic neurons occur in the upper lip and in the wall of the esophagus. Serotonergic neurons are present in the lower lip; the pre-oral hood contains an apical ganglion which extends axons along the base of the epidermis overlying the blastocoel. The dopaminergic and GABAergic components of the nervous system are associated with effectors involved in feeding and swimming. The serotonergic component is not associated with any apparent effectors but may have a role in metamorphosis.     

Gastrulation in the Sea Urchin,Strongylocentrotus purpuratus,Is Disrupted by the Small Laminin Peptides YIGSR and IKVAV

Laminin is present on the apical and basolateral sides of epithelial cells of very early sea urchin blastulae. We investigated whether small laminin-peptides, known to have cell binding activities, alter the development of sea urchin embryos. The peptide YIGSR-NH₂ (850 μM) and the peptide PA22-2 (5 μM), which contains the peptide sequence IKVAV (Tashiro et al., J. Biol. Chem. 264, 16174, 1989), typically blocked archenteron formation when added to the sea water soon after fertilization. At lower doses, the YIGSR peptide allowed invagination of the archenteron but blocked archenteron extension and differentiation and evagination of the feeding arms. The effect of YIGSR and PA22-2 peptides declined when added to progressively older stages until no effect was seen when added at the mesenchyme blastula stage (24 hours after fertilization). Control peptides GRGDS, YIGSE, and SHA22, a dodeca-peptide with a scrambled IKVAV sequence, had no effect on development. The YIGSK peptide containing a conserved amino acid modification had only a small effect on gastrulation. The results suggest that YIGSR and IKVAV peptides specifically disrupt cell/extracellular matrix interactions required for normal development of the archenteron and feeding arms. Our recent finding that YTGIR is at the cell binding site of the B1 chain of S. purpuratus laminin supports this conclusion. Evidently, laminin or other laminin-like molecules are among the many extracellular matrix components needed for the invagination and extension of the archenteron during the gastrulation movements of these embryos.     

Structure of the digestive tract of the pluteus larva of Dendraster excentricus (Echinodermata: Echinoida)

Summary Histological and ultrastructural observations of the digestive tract of eight-armed plutei of Dendraster excentricus are reported. The esophagus is divided into two regions. The uppermost is a narrow tube comprised of ciliated cells that assist in transporting food to the more bulbous lower esophagus where food particles are formed into a bolus prior to entering the stomach. The esophagus is surrounded by a network of smooth muscle fibers that are predominantly oriented circumferentially in the upper esophagus, and longitudinally in the lower esophagus. The musculature of the upper esophagus produces peristaltic contractions, whereas contractions of the muscle of the lower esophagus open the cardiac sphincter and force food from the lower esophagus into the stomach. Axons are associated with the ciliated cells and the muscles of the upper esophagus. The cardiac sphincter consists of a ring of myoepithelium, with cross-striated myofibrils oriented around the bases of the cells. The gastric epithelium is comprised of two cell types. Type I cells, which predominate, absorb and store nutrients, and may be the source of secreted digestive enzymes. Type II cells apparently phagocytize and intracellularly digest whole algal cells. The intestine is comprised of relatively unspecialized cells and probably functions primarily as a conductive tube for the elimination of undigested materials.     

Effect of Fixed Daylengths on the Photoperiodic Regulation of Gametogenesis in the Sea Urchin Strongylocentrotus purpuratus

Summary

The gametogenic response of the sea urchin Strongylocentrotus purpuratus was compared under treatments of different photoperiod regimes of fixed and seasonal changing daylength. Quantification of gametogenic activity in en- zymatically dissagregated ovaries and in histological sections of testes have shown that the sea urchin is sensitive to both fixed and variable daylengths. After one year at fixed short day (8L:16D) or fixed neutral day (12L:12D) the gonads were ripe and in active gametogenesis, the same as were gonads of animals reared at changing photoperiod and sampled during the short-day phase of the cycle. Under fixed long day (16L:8D) the gonads lacked significant amount of gametes and had the cell constitution found in gonads of animals reared at changing photoperiod and sampled during the long-day phase of the cycle. Measurement of a critical daylength related to the autumnal equinox seems to be part of the mechanism in the photoperiodic regulation of vitellogenic oocyte growth and spermatogenesis in these animals.     

Development of the esophageal muscles in embryos of the sea urchin Strongylocentrotus purpuratus

Summary Development of the esophageal muscles in embryonic sea urchins is described using light- and electron microscopy. The muscles develop from processes of about 14 cells of the coelomic epithelium that become immunore-active to anti-actin at about 60 h (12–14° C). Initially, eachmyoblast extends a single process with numerous fine filopodia around the esophagus. By 72 h the processes have reached the midline and fused with those from cells of the contralateral coelomic sac. Myoblasts begin to migrate out of the coelomic epithelium between 72 and 84 h. By 72 h the processes stain with the F-actin specific probe NBD-phallacidin. The contractile apparatus is not evident in transmission electron-microscopic preparations of embryos at 70 h, but by 84 h the contractile apparatus is present and the muscle cells are capable of contraction. Because the myoblasts migrate free of the coelomic epithelium and are situated on the blastocoelar side of the basal lamina, it is suggested that that they should be considered as a class of mesenchymal cells.     

Complete Sequence of SpHox8 and Its Linkage in the Single Hox Gene Cluster of Strongylocentrotus purpuratus

SpHox8 is the paralog group 8 Hox gene of Strongylocentrotus purpuratus. This identification follows from an analysis of the sequence of the complete open reading frame of a late-gastrula-stage cDNA clone; from direct linkage to adjacent Hox genes in a fosmid contig; and from blot hybridizations carried out on pulse field gel electrophoretic separations. SpHox8 is a single-copy gene, and there is only one Hox gene cluster per genome in S. purpuratus. Received: 7 November 1996 / Accepted: 4 December 1996     

Identification and developmental expression of the ets gene family in the sea urchin (Strongylocentrotus purpuratus)

A systematic search in the available scaffolds of the Strongylocentrotus purpuratus genome has revealed that this sea urchin has 11 members of the ets gene family. A phylogenetic analysis of these genes showed that almost all vertebrate ets subfamilies, with the exception of one, so far found only in mammals, are each represented by one orthologous sea urchin gene. The temporal and spatial expression of the identified ETS factors was also analyzed during embryogenesis. Five ets genes (Sp-Ets1/2, Sp-Tel, Sp-Pea, Sp-Ets4, Sp-Erf) are also maternally expressed. Three genes (Sp-Elk, Sp-Elf, Sp-Erf) are ubiquitously expressed during embryogenesis, while two others (Sp-Gabp, Sp-Pu.1) are not transcribed until late larval stages. Remarkably, five of the nine sea urchin ets genes expressed during embryogenesis are exclusively (Sp-Ets1/2, Sp-Erg, Sp-Ese) or additionally (Sp-Tel, Sp-Pea) expressed in mesenchyme cells and/or their progenitors. Functional analysis of Sp-Ets1/2 has previously demonstrated an essential role of this gene in the specification of the skeletogenic mesenchyme lineage. The dynamic, and in some cases overlapping and/or unique, developmental expression pattern of the latter five genes suggests a complex, non-redundant function for ETS factors in sea urchin mesenchyme formation and differentiation.     

Novel procedures for collection of sea urchin egg cortical granule exudate: Partial characterization and evidence for postsecretion processing

We have developed two procedures to collect total cortical granule exudate in a soluble form from eggs of the sea urchin Strongylocentrotus purpuratus. Egg suspensions were either treated with dithiothreitol to disrupt the vitelline envelope or divalent cations were removed postinsemination to prevent the normal vitelline-to-fertilization envelope transition. Rapid acidification of the insemination mixture (dithiothreitol-treated eggs) to pH 6.0 prevented precipitation of the paracrystalline protein fraction described by Bryan [1970a]. Exudate was partitioned into three fractions. The pH 8.0-insoluble fraction appeared to be identical to the paracrystalline protein fraction. The pH 8.0-soluble fraction was separated into pH 4.0-soluble and-insoluble fractions. Analysis for peroxidase and protease activities showed that peroxidase activity was localized in all three fractions whereas protease activity was restricted to the pH 4.0 insoluble fraction as reported [Carroll and Epel, 1975]. A minimum of six major proteins were detected on native polyacrylamide gels of total exudate. Under reducing and denaturing conditions, 12 polypeptides ranging from 19,000 to 165,000 in molecular weight were detected in total exudate; six polypeptides were recovered in the pH 8.0-insoluble fraction. To test the hypothesis that protease and peroxidase activities process cortical granule proteins after secretion, we inseminated eggs in solutions containing peroxidase and protease inhibitors. The paracrystalline protein fraction crystallized slowly from insemination mixtures containing both inhibitors compared to controls and there were dramatic differences in exudate electrophoretic patterns. We suggest that cortical granule protease and peroxidase activities process the exudate so that the paracrystalline protein fraction rapidly crystallizes during normal fertilization.     

Development of the digestive tract in larval summer flounder

Histological changes of the digestive system and its associated glands, and structures of the jaw were studied in summer flounder Paralichthys dentatus from hatching (day 0) until day 44. Specimens for this study were hatched from artificially spawned broodstock and maintained in the laboratory (20 ± 1° C). During the first 3 days after hatching, the formation of the oral jaw apparatus, lengthening of the digestive tube, yolk resorption, and mucosae differentiation are the most conspicuous elements of development. The larval digestive system is morphologically ready to process external food at the time of mouth opening (3–4 days after hatching). Epithelial cells of the anteromedian and the posterior intestine show evidence of lipid and protein absorption, respectively, after first feeding. The most noticeable events occurring during the next month of independent life are an increase in mucosal folding, cellular differentiation in the luminal epithelia, gut segmentation and looping, and liver growth. Gastric glands and pyloric caeca appear by day 31 and complete the morphological digestive features characteristic of the juvenile stage.     

The coeloms in a late brachiolaria larva of the asterinid sea star Parvulastra exigua: deriving an asteroid coelomic model

Morris, V.B., Selvakumaraswamy, P., Whan, R., and Byrne, M. 2011. The coeloms in a late brachiolaria larva of the asterinid sea star Parvulastra exigua: deriving an asteroid coelomic model. —Acta Zoologica (Stockholm) 92 : 266–275. The coeloms and their interconnexions in a late pre‐metamorphic brachiolaria larva of a sea star are described from the series of images in the frontal, transverse and sagittal planes obtained by confocal laser scanning microscopy. A larval, brachial coelom connects with the coeloms of the adult rudiment that lie posteriorly. The connexion is through the anterior coelom, which lies over the head of the archenteron, to the right anterior coelom and then to the left posterior coelom through the ventral horn of the left posterior coelom. The right posterior coelom is a separate coelom. The hydrocoele is on the larval left side separated from other coeloms except for a connexion to the anterior coelom. On the larval right side, the anterior coelom and right anterior coelom connect with the pore canal that opens to the exterior at the hydropore. From these coeloms, we derived an asteroid coelomic model comprising the larval left and right coeloms linked over the head of the archenteron by a common anterior coelom. The asymmetry of the hydrocoele and the left posterior coelom on the left side linked through the common anterior coelom to the right side, with the external opening, translates into the oral and aboral coeloms of the adult stage. The coelomic model has application in the search for morphological homology between the echinoderm classes and the deuterostome phyla.     

Microbial Composition and Genes for Key Metabolic Attributes in the Gut Digesta of Sea Urchins Lytechinus variegatus and Strongylocentrotus purpuratus Using Shotgun Metagenomics

This paper describes the microbial community composition and genes for key metabolic genes, particularly the nitrogen fixation of the mucous-enveloped gut digesta of green (Lytechinus variegatus) and purple (Strongylocentrotus purpuratus) sea urchins by using the shotgun metagenomics approach. Both green and purple urchins showed high relative abundances of Gammaproteobacteria at 30% and 60%, respectively. However, Alphaproteobacteria in the green urchins had higher relative abundances (20%) than the purple urchins (2%). At the genus level, Vibrio was dominant in both green (~9%) and purple (~10%) urchins, whereas Psychromonas was prevalent only in purple urchins (~24%). An enrichment of Roseobacter and Ruegeria was found in the green urchins, whereas purple urchins revealed a higher abundance of Shewanella, Photobacterium, and Bacteroides (q-value < 0.01). Analysis of key metabolic genes at the KEGG-Level-2 categories revealed genes for amino acids (~20%), nucleotides (~5%), cofactors and vitamins (~6%), energy (~5%), carbohydrates (~13%) metabolisms, and an abundance of genes for assimilatory nitrogen reduction pathway in both urchins. Overall, the results from this study revealed the differences in the microbial community and genes designated for the metabolic processes in the nutrient-rich sea urchin gut digesta, suggesting their likely importance to the host and their environment.     

Purification and characterization of a digestive alkaline protease from the larvae of Spilosoma obliqua

A digestive protease from Spilosoma obliqua (Lepidoptera: Arctiidae) fifth instar larval guts was purified and characterized. The protease was purified using ammonium sulfate fractionation, ion-exchange chromatography, and hemoglobin-sepharose affinity chromatography. The purification procedure resulted in a 37-fold increase in the specific activity of the protease. Protease thus obtained was found to be electrophoretically pure under native and denaturing conditions. The purified protease had a molecular mass of 90 kDa as determined by gel filtration, and a pH optimum of 11.0. The purified protease optimally hydrolyzed casein at 50 degrees C. A Km of 2 x10(-6) M was obtained using BApNA as a substrate for the purified alkaline protease. The ability of S. obliqua protease and bovine trypsin to hydrolyze various synthetic substrates (BApNA, BAEE, and BAME), and the inhibition patterns of S. obliqua and bovine trypsin with "classical" trypsin inhibitors are also reported.     

Effects of location,exposure and physical structure on juvenile recruitment of the sea urchin Strongylocentrotus droebachiensis in the Gulf of Maine

Summary

Studies of juvenile recruitment of the green sea urchin Strongylocentrotus droebachiensis in the Gulf of Maine were conducted during the summer of 1995. These experiments confirmed 12 years of previous observations that settlement only occurs during the months of June and July. Settlement panels were placed at a series of sites along the Maine and New Hampshire coastline to compare recruitment in the northeastern and southwestern regions of the Gulf of Maine. The densities of urchins recruiting in Casco Bay and at the Isles of Shoals were two orders of magnitude higher than those from Eastport and Winter Harbor. There was a discontinuity in settlement densities at Penobscot Bay. Experiments conducted at the Isles of Shoals showed a positive relationship between water motion and larval supply, but neither parameter correlated with recruitment density over eight stations. Contrary to previous results, recuitment was greater within natural, as well as, artificial kelp beds compared to urchin barren areas and control panels outside the experimental kelp beds. The impact of changing community structure due to urchin harvesting was discussed as an factor influencing differences in juvenile urchin recruitment.     

PERMANENT GENETIC RESOURCES: Development of microsatellite markers for the ecosystem bioengineer mussel Perumytilus purpuratus and cross-priming testing in six Mytilinae genera

Eight microsatellite markers have been characterized from the Perumytilus purpuratus genome. Their gene diversity ranged from 0.057 to 0.873 and significant interpopulation genic heterogeneity was observed between two populations of southeastern Pacific (Chile) and southwestern Atlantic (Argentine). Distinct cross-priming amplification rates were recovered on nine additional species belonging to six Mytilinae genera. The microsatellites developed herein would likely be a powerful intraspecific genetic tool to undertake fine population studies in the intertidal ecosystem bioengineer P. purpuratus along the South American shoreline.     

Evaluation of hydrolytic enzyme activities from digestive fluids of Anthonomus grandis (Coleoptera: Curculionidae)

The cotton boll weevil, Anthonomus grandis, is a major pest of cotton crops in South America. In this work, partial biochemical characterizations of (hemi) cellulases and pectinases activities in the digestive system (head- and gut- extracts) of A. grandis were evaluated. Gut extract section from third instar larvae exhibited endoglucanase, xylanase, β-glucosidase, and pectinase activities. The endoglucanase and xylanase activities were localized in the foregut, whereas β-glucosidase activity was mainly detected in the hindgut. In addition, no difference in pectinase activity was observed across the gut sections. Thus, A. grandis digestive system is a potentially interesting reservoir for further lignocellulolytic enzymes research.     

Histological and morphological evaluations of the digestive tract and associated organs of haddock throughout post-hatching ontogeny

At hatching, the oesophagus of haddock Melanogrammus aeglefinus lacks goblet cells, the intestine is a simple undifferentiated tube, the liver is present as a rounded mass caudal to the heart, and numerous zymogen granules are present in the pancreas. The first intestinal convolution appears at day 2, at the posterior end of the digestive tract. The oesophagus displays alcian blue and PAS positive mucus secreting cells on day 12, which become numerous by day 15. By day 18, epithelial cells of the posterior intestine show evidence of protein absorption in the form of supranuclear vacuoles. The swimbladder inflates in 50% of the larvae by day 22, although inflation rate is highly variable. By day 35, or 10 mm, a pyloric caecal ridge appears which separates the presumptive stomach, which is now showing evidence of gastric gland formation, from the intestine. This marks the beginning of digestive features characteristic of the juvenile stage.