Fine-grained secretory cells in the intestine of the lancelet,Branchiostoma (Amphioxus) lanceolatum,studied by light microscopy

Summary In the posterior part of the mid-gut epithelium in the lancelet, Branchiostoma lanceolatum, fine-grained cells occur. The appearance of the these cells is conspicuous with a basal and an apical swelling with small secretory granules. At the end of the secretion cycle the granular content is released into the gut lumen. The secretion product seems to consist of proteins and probably has an enzyme function. The restricted localization, the fine granulation, and the characteristic shape are features, that make these cells distinguishable from other secretory cells in the lancelet intestinal epithelium. A possible endocrine capacity of the cells is discussed.This work was supported by grant 2124-23 from the Swedish Natural Science Research Council and by grants from the Faculty of Science, University of Stockholm, Sweden.     

Decay of Branchiostoma: implications for soft-tissue preservation in conodonts and other primitive chordates

Decay experiments on the cephalochordate Branchiostoma lanceolatum ('amphioxus') demonstrate that the most decay resistant structures are the notochord sheath and the cartilaginous rods which support the gill bars. However, even more labile soft parts, such as the muscles and skin may survive for at least 124 days under totally anoxic conditions. As the chevron-shaped muscles of the myomeres shrink and collapse, those on opposite sides of the trunk maybe displaced, resulting in pronounced offsetting. Only 1.42% of the initial dry weight of Branchiostoma is resistant to alkali and acid hydrolysis, compared to 46% in the polychaete Nereis virens. Branchiostoma is only likely to be fossilized as a result of decay inhibition and replication by early diagenetic minerals. The results of these experiments cast light on the interpretation of a number of primitive fossil chordates. There is no reason to infer extracellular decay-resistant cuticle in the Burgess Shale Pikaia. The axial lies preserved in the conodont animal specimens from the Carboniferous of Edinburgh, Scotland, represent the notochord. The displacement of the elements to one side of the head reflects the true position of the apparatus - the surrounding tissue has been lost through decay. The chevron-shaped structures in the Carboniferous chordate Conopiscius are the muscles of the myomeres, not external scales. The lines delineating the segments in the Silurian Jamoytius most likely represent the myosepta. There is some doubt about the nature of the only specimen interpreted as a fossil cephalochordate, Palaeobranchiostoma hamatotergum from the Permian of South Africa. □ Taphonomy, decay, softparts, Cephalochordata , Branchiostoma, lancelet, Chordata , Pikaia, conodont , Conopiscius, Jamoytius, Palaeobranchiostoma.     

Immunocytochemical localization of serotonin in embryos, larvae and adults of the lancelet, Branchiostoma floridae

Serotonin (5-hydroxytryptamine) is a biogenic amine distributed throughout the metazoans and has an old evolutionary history. It is involved as a developmental signal in the early morphogenesis of both invertebrates and vertebrates, whereas in adults it acts mainly as a neurotransmitter and gastrointestinal hormone. In vertebrates, serotonin regulates the morphogenesis of the central nervous system and the specification of serotonergic as well as dopaminergic neurons. The present study uses, as an experimental model, an invertebrate chordate, the lancelet Branchiostoma floridae, characterized by its remarkable homologies with vertebrates that allows the 'bauplan' of the probable ancestor of vertebrates to be outlined. In particular, the involvement of serotonin as a developmental signal in embryos and larvae, as well as a neurotransmitter and gastrointestinal hormone in adult specimens of Branchiostoma floridae, gives further support to a common origin of cephalocordates and vertebrates.     

Laboratory spawning and development of the Bahama lancelet, Asymmetron lucayanum (cephalochordata): fertilization through feeding larvae

Here we report on spawning and development of the Bahama lancelet, Asymmetron lucayanum. Ripe adults collected in Bimini spawned the same evening when placed in the dark for 90 minutes. The developmental morphology is described from whole mounts and histological sections. A comparison between development in Asymmetron and the better known cephalochordate genus Branchiostoma reveals similarities during the early embryonic stages but deviations by the late embryonic and early larval stages. Thus, the initial positions of the mouth, first gill slit, and anus differ between the two genera. Even more strikingly, Hatschek's right and left diverticula, which arise by enterocoely at the anterior end of the pharynx in Branchiostoma, never form during Asymmetron development. In Branchiostoma, these diverticula become the rostral coelom and preoral pit. In Asymmetron, by contrast, homologs of the rostral coelom and preoral pit form by schizocoely within an anterior cell cluster of unproven (but likely endodermal) origin. Proposing evolutionary scenarios to account for developmental differences between Asymmetron and Branchiostoma is currently hampered by uncertainty over which genus is basal in the cephalochordates. A better understanding of developmental diversity within the cephalochordates will require phylogenetic analyses based on nuclear genes and the genome sequence of an Asymmetron species.     

The distribution of Branchiostoma senegalense (Acrania,Branchiostomidae) in the off-shore shelf region off North West Africa

During investigations on the macrobenthos between 17° N and 26° N on the North West African continental shelf, abundant stocks of Branchiostoma were found off Spanish Sahara (23° N-25° N), on the d'Arguin Bank (21° N-20° N) and off Gambia (12° N-13° N). The lancelets were identified as Branchiostoma senegalense (WEBB, 1955) by means of statistical analyses. The lancelet populations occur at dephts down to about 40 m. Deeper regions are probably avoided because of the excessively high detritus content. Favourable environmental factors such as temperature, composition of the sediment and food supply permit high lancelet abundancies. Up to 9000 animals'm² were found in the population off Spanish Sahara. Rough calculations showed that the lancelet population comprises about 6 × 10¹² individuals with a biomass of 1.5 million tons. The potential natality amounts to about 45 × 10¹⁵ larvae a year.     

Darting behavior of a sandburrower fish,Limnichthys nitidus (Creediidae), in the Red Sea

Synopsis Creediid fishes usually live burrowed in sand. When disturbed they make quick movements out and back into the sand. The darting behavior of 35 individualLimnichthys nitidus was recorded on videotape with the aid of SCUBA in the shallow bay, Marsa Muqabelah, Egypt, on the NE coast of Sinai in the Gulf of Aqaba, Red Sea. Thirty-nine sequences show that these fish travel distances of 26.7 to 110 mm in a single dart (1.7 to 5.5 times their total length), can reach speeds of nearly 0.5 m per sec, and execute turns up to 185° to avoid objects in their path. The darting movements, size and cryptic coloration ofL. nitidus make them difficult to see yet they may be the most numerous fish in shallow sandy areas of the Red Sea reaching concentrations of over 50 m^-2, a density exceeded in chordates only by the lancelet,Branchiostoma caribaeum. Their population in Marsa Muqabelah was drastically reduced, along with that of other sand fishes, between 1987 and 1989 when the sand became mostly covered with an overgrowth of algal mats and sea grasses.     

Characterisation and tissue-specific expression of the two keratin subfamilies of intermediate filament proteins in the cephalochordate Branchiostoma

The cloning of three intermediate filament proteins expressed at the gastrula stage (kl, Y1, X1) extends the size of the IF multigene family of Branchiostoma to at least 13 members. This is one of the largest protein families established for the lancelet. Sequence comparisons indicate five keratin orthologs, three of type I (E1, k1, Y1) and two of type II (E2, D1). This assignment is confirmed by the obligatory heteropolymeric polymerisation behaviour of the recombinant proteins. In line with the hetero-coiled-coil principle IF are formed by any stoichiometric mixture of type I and II keratin orthologs. In spite of the strong sequence drift chimeric IF are formed between K8, a human keratin II, and two of the lancelet type I keratins. We discuss whether the remaining 8 IF proteins reflect three additional and potentially cephalochordate-specific subfamilies. The tissue-specific expression patterns of the 5 keratins and some other IF proteins were analysed by immunofluorescence in the adult. Keratins are primarily present in ectodermally derived tissues. Developmental control of the expression of some IF proteins is observed, but three keratins (k1, Y1, D1) and an additional IF protein (X1) detected at the gastrula stage are expressed throughout the life cycle.     

Preserved ascomatal and other fungal structures on the remains of a ninth century Longobard abbess exhumed from a Monastery in Pavia,Italy

Auxarthron californiense, Mixotrichum aeruginosum, Oncocladium flavum and Chaetomium elatum were recognized on the basis of ascomatal structures on the remains of a Longobard abbess who died in the IX century A.D. These fungi, which had remained isolated in a crypt of the S. Felice Monastery of Pavia for almost 1000 years, are phenotypically identical to the type specimens. The occurrence of these fungi and their ecological role are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

The globin gene family of the cephalochordate amphioxus: implications for chordate globin evolution

Background  

The lancelet amphioxus (Cephalochordata) is a close relative of vertebrates and thus may enhance our understanding of vertebrate gene and genome evolution. In this context, the globins are one of the best studied models for gene family evolution. Previous biochemical studies have demonstrated the presence of an intracellular globin in notochord tissue and myotome of amphioxus, but the corresponding gene has not yet been identified. Genomic resources of Branchiostoma floridae now facilitate the identification, experimental confirmation and molecular evolutionary analysis of its globin gene repertoire.     

Glycoconjugate profiles of the lancelet (Branchiostoma lanceolatum) ovary: a lectin histochemical study by laser confocal microscopy

The presence and the distribution of carbohydrate moieties in ripe lancelet (Branchiostoma lanceolatum) oocytes (mean diameter 130 microm) was studied by lectin histochemistry in combination with enzyme and chemical treatments. Binding sites for eight lectins with specificities towards different glycan moieties were studied on sections of the whole body of mature female lancelets. Only three of the lectins tested reacted positively. Concanavalin-A (ConA)-binding glycoconjugates were localized in the cytoplasm, namely in yolk granules, whereas Artocarpus integrifolia (AIA) and Ricinus communis (RCA) agglutinins bound strongly to extracellular coats of the oocyte identified as the jelly coat and vitelline layer. No other tissues of the lancelet body were found to be positive to any lectin tested, except gut enterocytes which reacted strongly with AIA. Reactivity to ConA was abolished by pretreatment of sections with N-glycosidase F but not by mild alkaline hydrolysis, confirming that the glycoconjugates were of the N-linked type. On the contrary, chemical removal of O-linked chains by mild alkaline hydrolysis abolished AIA and RCA reactivity but had no effect on ConA positivity.     

Continuous culture of two lancelets and production of the second filial generations in the laboratory

The lancelet is considered to be a promising laboratory model animal. To establish laboratory colonies of lancelet, we collected parental lancelets of Branchiostoma belcheri and B. japonicum (previously named as B. belcheri tsingtauense) with fully developed gonads from Xiamen Rare Marine Creature Conservation Areas (Fujian, China) on dates just before their spawning in the field in 2005. Those parental lancelets spawned spontaneously in the laboratory and produced thousands upon thousands of fertilized eggs. After carefully hatching and maintaining for almost 1 year, we successfully obtained about 500 first generation (F1) adults of B. belcheri and 3,300 of B. japonicum. Part of those F1 lancelets ripened and spontaneously spawned in 2006, and several thousands of second generation (F2) individuals of both species were produced. The young F2 lancelets are growing in good condition and some of B. japonicum initiated gonad development in December, 2006. Our experience emphasizes that cleanness of settlement substratum and sufficient food supply are important factors for long-term culture of lancelets in the laboratory.     

Renewal of genetic composition of a lancelet, Branchiostoma belcheri, in the Seto Inland Sea, Japan

We studied renewal of genetic composition of a lancelet, Branchiostoma belcheri, at a station in the Seto Inland Sea, Japan, using random amplified polymorphic DNA (RAPD) technique. We detected a total of 49 DNA bands from 27 individuals of 5 seasonal samples. Among these, some were specific to individual or seasonal sample. There were no bands common to all individuals. We calculated the Band Sharing Index (BSI) values for each combination of individuals. BSI was in a wide range of 0.00-0.97 and the average BSI between the individuals of a sample was remarkably different from sample to sample (0.37-0.83). In cluster analysis on the basis of BSI, largely 3 clusters were constructed, which finally connected to a single cluster at as low as about 0.2 of BSI. Besides, many clusters were constructed exclusively by a seasonal sample. These results suggest a large gene pool of lancelets in this area, the remarkable differences in gene pool size among the samples and a seasonal renewal of genetic composition at a habitat.     

The main features of the craniate mitochondrial DNA between the ND1 and the COI genes were established in the common ancestor with the lancelet

We have cloned the mitochondrial DNA fragment extending from tRNA-Leu to the cytochrome oxidase subunit 1 (COI) genes of Branchiostoma lanceolatum, Myxine glutinosa, Lampetra fluviatilis, and Scyliorhinus caniculus and have determined their respective gene sequences and organization. In all four species, this region contains the ND1 and ND2 genes and the genes coding eight tRNAs, namely, tRNA-Ile, -Gln, -Met, - Trp, -Ala, -Asn, -Cys, and -Tyr. The gene order is the same in the hagfish, lamprey and dogfish. In the lancelet, the location of the tRNA genes is slightly different. The mitochondrial code of Myxine, Lampetra, and Scyliorhinus is identical to that of vertebrates. The code used by the lancelet is the same with the exception of AGA (a stop codon in vertebrates), which codes for glycine in the lancelet. From the comparison of the four maps with already published ones for other species, we propose that the main features of the craniate mtDNA between the ND1 and COI genes were established in the common ancestor to cephalochordates and vertebrates more than 400 MYA. The origin of replication of the light-strand (Ori-L), usually located between the tRNA-Asn and tRNA-Cys genes in vertebrates, was not found in the lancelet, hagfish, or lamprey (Lampetra). In contrast, it was found in the dogfish. Thus the position of Ori-L was established for the first time in the common ancestor to the Chondrichthyes and Osteichthyes and remained present in all later-emerging vertebrates.      

文昌鱼AmphiRab23b基因的克隆、进化分析及表达模式

Hedgehog信号通路在胚胎发育过程中发挥着重要作用, 同时与多种肿瘤的发生密切相关。Rab23蛋白在Hedgehog信号通路中扮演着十分重要的角色。目前关于文昌鱼Rab23同源基因的研究仅局限于佛罗里达文昌鱼(Branchiostoma floridae)基因组中的注释。文章首次克隆了中国文昌鱼(Branchiostoma belcheri) Rab23b基因 (AmphiRab23b)cDNA全序列 , 对其演译的蛋白序列进行了序列比对、进化树分析以及基因时空表达分析。研究结果显示, 文昌鱼AmphiRab23b基因的 cDNA总长为2 062 bp (包括UTR区), 其中开放阅读框 (Open reading frame, ORF) 714 bp, 编码237个氨基酸; 虽然在进化树中不属于脊椎动物Rab23进化支, 但是AmphiRab23具有保守的Rab23_lke结构域, 暗示该基因在进化过程中可能在功能上是保守的。时空表达的研究结果进一步显示, AmphiRab23b基因在胚胎发育中的神经板和消化道中表达, 与其脊椎动物同源基因的表达模式相似, 这说明该基因可能对文昌鱼神经系统和消化道的发育有重要作用。     

The respiratory performance and survival of the bivalve Macoma balthica (L.) at the southern limit of its distribution area: a translocation experiment

The hypothesis was tested that animals near their extreme Southern limits, due to high temperatures, have a high respiration rate, whereby they reach an extreme low weight-index and ultimately disappear. At estuarine stations the respiration rate of Macoma balthica (L.) (Baltic clam) did not show interseasonal changes, indicating seasonal acclimation, but within the season the respiration increased with increasing temperature, indicating the absence of short-term acclimation. In clams translocated from the Netherlands towards the Bidasoa estuary, 200 km South of their Southern distribution limit, their respiration rate was higher and weight-index lower than in specimens living in Dutch estuaries. Irrespective of an effect of the temperature, clams exposed in experiments to water from Bidasoa showed a higher respiration than clams exposed to water from the other stations. Moreover, at non-estuarine stations with a low food content, the clams showed reversed acclimation, i.e., the respiration rates in winter were much lower than summer rates, most probably a strategy to conserve energy by means of a depressed metabolism. A weight index of 5 mg DW/cm(3) and glycogen content of 2% DW are suggested as the minimal values below which the metabolic energy balance of Baltic clams becomes more negative and the clam population disappears. It was concluded that factors other than temperature influenced the respiration and weight-index of clams, and hence their presence or absence, e.g., food concentration, innate seasonal cycles, and possible pollutants in the water.     

Larval development of the oriental lancelet, Branchiostoma belcheri, in laboratory mass culture

We are successfully maintaining a laboratory colony of the lancelet Branchiostoma belcheri bred in the laboratory. Based on living individuals in this mass culture, morphological characteristics from the seven-day larval to benthic juvenile stages have been studied. Most striking was that later larval development of B. belcheri showed great individual variation even in a rather stable culture environment. Metamorphosis first occurred on 60 days post fertilization (dpf) and was continuously observed throughout the present study up to 100 dpf. Morphological traits such as the number of primary gill slits and body size at the start of metamorphosis are apparently affected by culture condition. Body size measured in the largest individuals showed nearly linear growth at 0.087 mm/day. The variability found in larval development calls for caution when developmental stages and chronological ages are compared between populations. However, the developmental flexibility of this animal also raises the possibility that growth and sexual maturation could be controlled artificially in captivity.     

Appraisal of contaminants in sediments of the Inner Bristol Channel and Severn Estuary

In the inner Bristol Channel and Severn Estuary, most contaminated stations were in muddy, depositional areas of the estuary, particularly along the Welsh coast between the Rivers Taff and Usk, and also on the English coast between Avonmouth and Severn Beach. Some deeper areas, dominated by sand and mixed sediments, also showed contaminant concentrations in excess of those predicted from sediment texture, organic matter, and aluminium or iron concentrations.
Concentrations of lead, copper, chromium, nickel and zinc have decreased in the muddy sediments since the 1970s, but only lead has decreased in sand. With the exception of zinc, which is high in the Severn, trace element concentrations were comparable to those from other British estuaries.
Landward of the proposed barrage, contaminants are associated with the sub-estuaries and muddy areas at their confluence with the main estuary. Post-barrage effects on contaminants will be focused in these muddy areas. However, fine sediment deposition on what are now sandy areas would increase their contaminant burden unless calcium build-up from the resulting molluscan fauna has the antagonistic effect of contaminant dilution in the sediment.     

Variations in body size of the lancelet Branchiostoma belcheri at different depths in the Seto Inland Sea: effect of food supply on the growth rate

Variations in body size of the suspension-feeding lancelet Branchiostoma belcheri were examined from April 2001 to December 2001 at different water depths of 10-80 m. The lancelets were abundantly collected (220 indiv./dredge) at water depth of 10 m. The maximum size, ranging from 36.8 to 50.4 mm BL, decreased with increasing water depth. However, the minimum size of 7.4-7.8 mm BL, which corresponds to settling size, did not different with water depth. From seasonal changes in the length-frequency histograms, five cohorts were observed at every water depth. The lancelets grew to 44 mm BL at water depths of 10-20 m and to 34 mm BL at water depth of 80 m with four years of life span. Developmental stages of the gonads at an age of two years showed that no individuals had undeveloped gonads at water depth of 10 m, but 82% of them did at water depth of 80 m. The analysis of the stepwise multiple regressions of monthly growth rate on environmental variables showed that chlorophyll a was the best explanatory variable and showed a significant positive correlation with the growth of 1-2 years age groups. These results suggested that variations in the body length were mainly fluctuated by phytoplankton supply.     

Die Feinstruktur der Josephschen Zellen im Gehirn von Amphioxus

Zusammenfassung Die in der Dorsalwand des Gehirns von Amphioxus (Branchiostoma lanceolatum, Pall.) liegenden Josephschen Zellen wurden elektronenmikroskopisch untersucht. Diese Zellen sind durch folgende Strukturen als Lichtsinneszellen charakterisiert: ein aus Mikrovilli bestehendes, intrazelluläres Rhabdom, eine darunterliegende Schicht von Mitochondrien, ein dichtes Maschenwerk eines glatten, röhrenförmigen Membransystems und einen Fortsatz mit Neurofibrillen und Mikrotubuli. Begleitende Pigmentzellen fehlen. Die Josephschen Zellen zeigen weitgehende Übereinstimmungen mit Photorezeptorzellen von Anneliden u. Mollusken.

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Summary The fine structure of a group of large cells situated in the dorsal wall of the brain of the lancelet (Branchiostoma lanceolatum, Pall.), known as Joseph's cells, was investigated with the electron microscope. These cells proved to be photoreceptor cells by the following characteristic features: an intracellular photoreceptoral organelle consisting of an array of microvilli, a layer of mitochondria directly underneath the microvilli, a tightly packed system of smooth tubular membranes, and a cellular process with neurofilaments and microtubules. There are no pigment cells near the photoreceptors. Joseph's cells are remarkably similar to the photoreceptor cells of annelids and molluscs.