Evolution of gnathostome lateral line ontogenies

An outgroup analysis of multiple ontogenies provides the most robust approach to understanding phylogeny. Such an analysis of the lateral line system among extinct and extant gnathostomes reveals that lateral line placodes constitute the basic ontogenetic unit responsible for the development of this system. Six pairs of lateral line placodes appear to have existed in the earliest gnathostomes, and eight stages (stages A-H) can be recognized in their differentiation. Terminal truncation (heterochronic changes) in the primitive sequence of placodal development has occurred in one or more placodes in each gnathostome radiation, with the most extensive truncations occurring in arthrodire placoderms, lepidosirenid lungfishes and extant amphibians. The most extensive nonterminal changes in the primitive sequence of placodal development involve the failure of electroreceptors to form within the lateral zones of the elongatiang sensory ridges of the placodes. This nonterminal change appears to have occurred independently in ancestral neopterygian bony fishes, in many amphibians and, possibly, in the extinct acanthodians. At least two teleost radiations, osteoglossomorphs and ostariophysines, have re-evolved electroreceptors which may represent additional nonterminal changes in placodal patterning or, possibly, a change in the embryonic source of these receptors.

Establishment of the axis in chordates: facts and speculations

A master plan for the early development of all chordates is proposed. The radial symmetry of the chordate ovum is changed at or after fertilization into a bilateral symmetry by an external signal. Until now two alternative triggers, sperm entry and gravity, have been demonstrated. It is suggested that a correlation exists between the amount of yolk stored in the egg and the mechanism used for axialization. The speed at which axialization of the embryo proper takes place depends on the translocation speed of maternal determinants from the vegetal pole towards the future dorsoposterior side of the embryo. On arrival at their destination, the activated determinants form, in all chordates, an induction center homologous to the amphibian ‘Nieuwkoop center’, which induces the formation of ‘Spemann's organizer’. On the basis of the above general scenario, a revision is proposed of the staging of some embryonic types, as well as of the identification of germ layer and the spaces between them.

The development of the dentigerous bones and teeth in the hemiramphid fish Dermogenys pusillus (Atheriniformes, Teleostei)

The development of the dentition and dentigerous bones was studied in the hemiraphid Dermogenys pusillus using histological sections, scanning electron microscopy, and cleared and stained specimens. Five days after birth, the toothless tip of the lower jaw begins to grow longer than the tip of the upper jaw. The growth originates from small cartilaginous triangles connected with Meckel's cartilage. The peri- and enchondrial ossification of the growing cartilaginous bars advances rostrad. The pharyngeal tooth plates are formed by fusion of the slat-like dentigerous dermal bones with the bony fractions of the gill branches. Hence, the tooth plates are composite bones. The ventral tooth plate ist formed by the two ceratobranchials V and the basibranchial IV together with the respective dermal bones. The paired pharyngobranchials III and IV are fused with the dorsal tooth plate, and the pharyngobranchials II is fused with the two respective lateral tooth plates. Mineralization starts after birth in elements of the pharyngeal tooth plates and their teeth. There are no indications that the pedicel on which the tooth is established is formed by the enamel organ, which is covered by pulpal cells. The enamel organ originates from the stratum basale of the oropharyngeal epithelium and moves within the jaw from labial toward lingual, the site of the establishment of the tooth. The anlage of the tooth on the tooth plates of the pharynx lies at the level of the tooth base.

Biosynthesis in vivo and excretion of cortisol by fish larvae

There is a posthatching rise in levels of endogenous cortisol during the ontogeny of those teleosts studied to date. This is thought to be the result of de novo synthesis of cortisol by the larvae, although there is no direct evidence for this. The present study aimed to demonstrate this process in Asian seabass (Lates calcarifer). Larvae (4 days posthatching) were maintained for up to 12 hours in seawater containing [3H]17 alpha-hydroxyprogesterone. High performance liquid chromatography analysis of extracts of the medium, before and after treatment with glucuronidase, indicates conversion of the precursor to several metabolites. One of these was identified as cortisol on the basis of its isopolarity with authentic standard in thin-layer chromatography, and confirmed by recrystallisation to constant specific activity. Immunohistochemistry on siblings shows that the interrenals are immunoreactive for adrenodoxin (adrenal ferredoxin) and cytochrome P-450(21) (steroid 21-monooxygenase [steroid, hydrogen-donor:oxygen oxidoreductase, 21-hydroxylating]; EC 1.14.99.10), and the pituitary for adrenocorticotrophic hormone. These findings suggest that the pituitary-interrenal axis is functional even at this early stage, and are consistent with the hypothesis that the posthatching rise in endogenous cortisol levels is the result of de novo steroidogenesis.

Production of fish chimeras from embryonic cells

The efficiency of two cell-transplantation methods were compared for the production of embryonic cell derived fish chimeras. The classic microinjection technique (blastula stage donor cells are microinjected into blastula embryos) was compared to a novel aggregation method for fish developed by our group. This method utilises the ability of dechorionated fish embryos to aggregate. Morula cells dissociated in Ca2+, Mg2+ free medium were aggregated to recipient embryos of different developmental stage. Donor cells and recipient embryos of different developmental stages were used for most efficient incorporation in the chimeras. THe fate of donor cells derived from blastulae, was followed by labelling them with FITC-dextrane (FD). The most efficient transplantations were gained by using 16-32 cell stage recipients for aggregation (18% survival of chimeras at swim up stage). Labelled donor cells were contributing to the embryos in varying ratio. A comparison of the efficiency of aggregation was made between diploid-diploid, diploid-haploid and diploid-interspecfic (diploid) hybrid chimeras. In all three cases chimeras containing different proportion of donor cells were gained. After one day incubation the embryos were dissociated by trypsin digestion and number of labelled and non-labelled cells were counted under fluorescent microscope. Experiments were performed on Rosy barb (Barbus conchonius), Carp (Cyprinus carpio) and African catfish (Clarias gariepinus).

[Analysis of expression of foreign genetic material under the control of heterogeneous promoters in the process of early development of the loach (Misgurnus fossilis L.)]

Promoters normally active in the nuclei of evolutionarily distant from fishes taxa-bacteria, insects, and Protozoa-are shown to be able to regulate heterologous genes during early development of the loach. It is shown that particular DNA sequences can drastically influence the function of eukaryotic promoters, enhancing the expression level.

Responses of embryonic and larval inland silversides, Menidia beryllina, to a water-soluble fraction formed during biodegradation of artificially weathered Alaska North Slope crude oil

Weathered Alaska North Slope crude oil (ANS 521) was stirred for 2 and 14 days in 20 per thousand salinity sterile seawater or for 14 days in seawater with nutrients and a group of three (GO3) microorganisms from Prince William Sound, Alaska, that were capable of biodegrading hydrocarbons. A total of 0.65 and 0.69 mg/L water soluble fraction (WSF) of neutral fraction hydrocarbons was recovered from the 2- and 14-day stirred sterile systems, respectively. In comparison, a total of 7.5 mg/L WSF neutral fraction hydrocarbons was recovered from systems containing ANS 521 that were stirred and biodegraded by the GO3 microbes for 14 days. Toxicity/teratogenicity tests were conducted with neutral fraction hydrocarbons recovered from the sterile and biodegraded systems using embryonic inland silversides, Menidia beryllina. Hydrocarbons from the sterile systems did not cause statistically significant teratogenic responses at concentrations of 1%, 10%, and 100% (w/v) of recovered fractions (redissolved in 20 per thousand salinity sterile seawater). Counts of heart contraction rates were significantly lower (alpha</=0.05) at the 100% WSF concentration of hydrocarbons on days 5 and 6 of embryogenesis. In contrast, recovered and redissolved neutral fraction hydrocarbons from ANS 521, that were biodegraded for 14 days, caused statistically significant (alpha</=0.05) teratogenic responses at the 1, 10, and 100% WSF concentrations. Measurement of heart contraction rates showed statistically significant (alpha</=0.05) reductions at the 100% WSF concentration on days 2 through 6 of embryogenesis, compared to controls.

Toxicity of weathered coal tar for shortnose sturgeon (Acipenser brevirostrum) embryos and larvae

Weathered coal tar collected from the Connecticut River near Holyoke, Massachusetts, was toxic to shortnose sturgeon embryos and larvae in whole sediment flow-through and elutriate static-renewal laboratory exposures. Sterile laboratory sand and clean Connecticut River sand, collected upstream from the coal tar deposits, produced no significant difference in toxicity to sturgeon embryos-larvae, while coal tar-contaminated sediment produced over 95% embryo-larval mortality. Hydrocarbon transfer and subsequent toxicity appeared to be via direct contact of the embryos with contaminated sediment, rather than via exposure to soluble hydrocarbons. This conclusion was supported by exposure of embryos and larvae to elutriates (e.g., water soluble extract) of coal-tar sediments, that resulted in embryo and larval mortality at low molecular weight PAH concentrations-0.47 mg/L, higher than would occur naturally. No decrease in petroleum hydrocarbon concentration was observed in sediments exposed to flowing water for 14 d, supporting the contention that soluble hydrocarbons were not responsible for the observed toxicity in whole sediment exposures under the conditions employed in this study.

Structures in material transference and vitelline envelope formation in Betta splendens follicles

Structures were found by transmission electron microscopy, they were located within follicular cells and the oocyte, and in the interspace between them in follicles of the teleost fish Betta splendens. Some structures with features characteristic or lamellar bodies were found in small follicles. The possible role of these structures in the formation of the vitelline envelope as well as in the material transference is discussed. Vacuoles, vesticles and particles intensely stained were found in the microvilli and the cortical cytoplasm of the oocyte at the onset of vitellogenesis. These results suggest that different substances present in the cellular components of the follicle might be transferred from cell to cell through the extracellular space and through the prolongations that cross the extracellular space.

The Agnathan ark: the origin of craniate brains

An outgroup analysis of head organization of tunicates, lancelets and craniates indicates that the origin of craniates involved the development of a new muscular pharyngeal pump, which was a key innovation underlying the evolution of a more metabolically active group of chordates. This innovation involved the genesis of new embryonic tissues, neural crest and neurogenic placodes, whose derivatives formed skeletal elements of the new pump as well as new receptors advantageous to the more mobile craniates. These changes also involved the evolution of a more complex brain by elaboration and reorganization of a lancelet-like cephalic neural tube. All of these events appear to be linked to a number of homeobox genes that were duplicated in the ancestral chordates leading to craniates. An outgroup analysis of the life histories of lancelets, hagfishes and lampreys suggests that hagfishes and lampreys have life histories that are substantially derived in comparison to that of ancestral craniates and that the highly derived features of the brain of hagfishes evolved in conjunction with their invasion of a bathyal benthic environment.

Ontogeny of GABA-immunoreactive neurons in the central nervous system in a teleost, gasterosteus aculeatus L

The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is known to exert various neurotrophic actions in the developing nervous system, but little is known about its distribution in the central nervous system during early development. We have studied the development of GABA-immunoreactive (GABAir) neurons during embryogenesis of a teleost fish, the three-spined stickleback. As early as 51 h postfertilization (PF; hatching occurs 144-168 h PF, and the first monoaminergic neurons appear around 72 h PF) GABAir neurons appear in the ventral prosencephalon caudal to the optic recess, in the ventral mesencephalon, and in the spinal cord. Then, there is a gradual addition of GABAir cell groups in the rostral prosencephalon and ventral rhombencephalon (66 h PF), dorsal and caudal hypothalamus and pretectum (72 h PF), ventral hypothalamus (78 h PF), preoptic region, thalamus, and in the mesencephalon and rhombencephalon (96 h PF). GABAir axons appear in the spinal cord already at 51 h PF, and then gradually appear in the various tracts of the early axonal scaffold of pathfinding fibers, so that by 96 h PF the entire axonal scaffold contains GABAir fibers. It appears likely that GABAergic axons contribute a major population to the formation of the axonal scaffold. Moreover, in the prosencephalon GABAir neurons are arranged in clusters that may reflect a neuromeric organization with six prosencephalic neuromeres.

Effects of azinphos-methyl on the reproductive success of the bluegill sunfish, Lepomis macrochirus, in littoral enclosures

Adult bluegills were exposed to a single application of azinphosmethyl in 12 littoral enclosures in a northern Minnesota pond. Responses measured were adult behavior and spawning, embryo hatchability, larval survival until swim-up, young-of-year (Y-O-Y) growth, and total biomass. Four enclosures each were treated at 1.0 and 4.0 micrograms/liter and four remained untreated. The half-life of azinphos-methyl was 2.3 and 2.4 days at each of the two treatment levels, respectively. Quantifiable residues remained in the water for 8 days. Concentrations of 4.0 or 1.0 microgram/liter did not cause any significant long-term (63 day) effects on bluegill reproduction, embryo hatchability, larval survival, growth, or biomass. Although important bluegill prey such as copepod nauplii and cladocerans were significantly or greatly reduced by Day 7 following treatment, they recovered to levels equal to or greater than some of the control enclosures by Day 35. The apparent lack of significant long-term effects on reproductive success can be partially explained by the relatively short half-life of azinphos-methyl in littoral enclosures.

[The results of multiyear research on fish populations from reservoirs falling within the area of the Kyshtym accident (a review)]

The results of long-term studies of fish populations of various kinds from lakes polluted with radionuclides as a result of the Kyshtym accident are considered. The literary and own data on embryonic development studies with cytogenetic analysis, results of morphometric and morphological studies of fish populations, investigations of population structures by electrophoretic analysis of markers of structural genes were analysed. Critical comparison of the data obtained by the various authors in different years was conducted. The conclusion was made that none of the tests showed unequivocal effect of radionuclide contamination on ichthyofauna.

[Change in the activity of antioxidant enzymes in the process of early ontogenesis of various species of Black Sea fishes]

The dynamics of activities of lipoxygenase, superoxide dismutase, catalase, proxidase and glutathione reductase during the development of eggs and hatched larvae of five species of Black Sea fishes was studied. The increase of enzyme activities at the end of embryogenesis and in the larvae was established. High correlations between the activities of superoxide dismutase, catalase and glutathione peroxidase (r > 0.95) and the average coefficients for Neogobius melanostomus (0.4957) for Proterorhinus marmoratus (0.3933) and for Blennius sanguinolentus (0.5853), for Psetta maeotica (0.5579) were found. It proved the resemblance of processes of antioxidant system formation during the early development of fishes.

Developmental changes in the brain-stem serotonergic nuclei of teleost fish and neural plasticity

1. During early ontogeny, the serotonergic neurons in the brain stem of the three-spined stickleback shows a temporal and spatial developmental pattern that closely resembles that of amniotes. 2. However, in the adult fish, only the midline nuclei of the rostral group (dorsal and median raphe nuclei) and the dorsal lateral tegmental nucleus are consistently serotonin-immunoreactive (5-HTir), whereas the groups of the upper and lower rhombencephalon (raphe pontis, raphe magnus, and raphe pallidus/obscurus nuclei) are variable and, when present, contain relatively small numbers of 5-HTir neurons. 3. Using specific antisera against tryptophan 5-hydroxylase and aromatic L-amino acid decarboxylase, we have shown that the lateral B9 group and the groups of the upper and lower rhombencephalon are consistently present in adult sticklebacks. The results are discussed in relation to other known instances of neurotransmitter plasticity or transient neurotransmitter expression in teleost fish. 4. While there are several instances of transient expression of neurotransmitter markers by discrete neuronal populations, there is so far no evidence of changes from one neurotransmitter phenotype to another in the brain of teleost fish. However, there are indications of plasticity of expression of catecholamines and indoleamines, and their respective synthesizing enzymes, as reflected in age-dependent changes and variation between individuals of different physiological status. 5. As the brain grows continuously in teleost fish, and new neurons are added from proliferative regions, synaptic connections may be expected to undergo remodeling in all brain regions throughout life. Thus, the teleostean brain may be considered a suitable model for experimental studies of different aspects of neural plasticity.

Infectivity and teratogenicity of Beauveria bassiana in Menidia beryllina embryos

Developing embryos of the inland silverside fish, Menidia beryllina, were exposed to conidiospores of the insect pathogenic fungus, Beauveria bassiana, that possessed activity against the migratory grasshopper, Melanoplus sanguinipes. Various adverse effects were observed in Menidia beryllina embryos and larvae. They included rupture of the chorion, embryo death, developmental defects (vertebral abnormalities) in the embryo or hatched larvae, and fungal infections on the mandibles of larvae. Although there was little evidence of a definitive dose-response trend based on densities of viable conidiospores, statistically significant (p < or = 0.01) responses were observed in tests in which conidiospore densities were as low as 7.1 x 10(3)/ml and as high as 1.3 x 10(6)/ml. Viable spores were required for adverse effects to occur; heat-killed spores failed to cause significant adverse effects.

Disruption of mesoderm and axis formation in fish by ectopic expression of activin variants: the role of maternal activin

Formation of mesoderm in Xenopus embryos is the result of an induction event in which peptides such as FGF or activins have been implicated. It was recently demonstrated, by the ectopic expression of a truncated activin receptor, that activin receptor signaling pathways are involved in the processes of mesoderm and axis formation in vivo. However, this approach does not directly address the role of activin itself nor the involvement of activins in the formation of mesoderm in embryos from other vertebrates. In addition, activins are expressed maternally as a protein component of the egg as well as transcribed zygotically, and it is not clear which of the two forms is involved in mesoderm formation. To address those three issues, we analyzed the role of activins in the development of fish embryos by generating two activin dominant-negative variants. One of the variants behaves as an inhibitor of activin protein. The second variant was found to deplete the activin pool when cotranslated with wild-type activin. Injection of RNA encoding these variants into the two-cell embryo of the small teleost fish Oryzias latipes (Japanese medaka) demonstrates that only the maternally provided activin protein is required for mesoderm and axis formation in fish in vivo.

Cardiovascular development. Prospects for a genetic approach

Genetics is a powerful tool, especially when used in combination with embryology, in the seeking of genes necessary for assembly of the cardiovasculature. The first questions must address the types of cellular decisions that are made during development. As for simpler systems in C elegans and D melanogaster, the lineage and cell-fate decisions of the cardiovascular progenitors need to be assessed. In addition it is likely that new paradigms will emerge for multicellular assembly. The study of cardiovascular mutations will define individual genetic steps that define organotypic decisions. A genetic approach is a natural extension of embryology, physiology, and anatomy, fields of great sophistication with regard to the cardiovasculature, because, like them, it focuses on integrative biology and on the intact organism. The zebrafish is particularly well suited to a combination genetic-embryologic study of the fashioning of the cardiovasculature.

A dual embryonic origin for vertebrate mechanoreceptors

Neuromasts, the mechanoreceptors of the lateral line system of fishes and aquatic amphibians, have previously been thought to develop exclusively from embryonic epidermal placodes. Use of fate mapping techniques shows that neuromasts of the head and body of zebrafish, Siamese fighting fish, and Xenopus are also derived from neural crest. Neural crest migrates away from the neural tube in developing vertebrates to form much of the peripheral nervous system, pigment cells, and skeletal elements of the head. The data presented here demonstrate that neuromasts are derived from both neural crest and epidermal placodes.

Growth of fish cell lines in glutamine-free media

The glutamine requirement for the in vitro proliferation of fish cells was investigated with cell lines from four different species and three tissues: goldfish skin (GFSk-S1), Chinook salmon embryo (CHSE-214), and rainbow trout liver (RTL-W1) and spleen (RTSp-W1). With a supplement of fetal bovine serum, the basal medium, Leibovitz's L-15, without glutamine supported the proliferation of all four cell lines as well, or nearly as well, as L-15 with 2 mM glutamine. This was true over short term assays of two to four weeks and for continuous propagation. CHSE-214 also grew as well with or without 2 mM glutamine in Minimum Essential Medium with fetal bovine serum. However, when the supplement was dialyzed fetal bovine serum, CHSE-214 grew much better in L-15 without glutamine. Therefore, glutamine was not required for growth in L-15, and in fact, was inhibitory in the absence of the dialyzable fraction of serum. By contrast, glutamine appeared to be important for growth in Minimum Essential Medium. When the supplement was dialyzed fetal bovine serum, CHSE-214 grew much better in Minimum Essential Medium with 2 mM glutamine. These results suggest that the glutamine requirement for the in vitro proliferation of fish cells is conditional and depends on the basal medium and serum supplement.

Development of hatchability in halibut (Hippoglossus hippoglossus) embryos

Halibut (Hippoglossus hippoglossus) eggs raised in darkness hatched between days 14.5 and 16 after fertilization. Eggs incubated in white light (3.2 microE/sr1/m2) remained unhatched, so that time of intra ovo development could be doubled. Photo-arrest of hatching was non-diapausal since embryonic growth continued. Transfer of photo-arrested eggs to darkness induced rapid and synchronous hatching. This procedure allowed analysis of development of hatchability. Hatching was not observed prior to day 14. Nonsynchronous hatching over three days was seen when eggs were induced on day 14 + 1 h, or on day 14 + 9 h. However, darkness-induction on day 14 + 22 h produced synchronous hatching within 140 min. This high rate of inducibility persisted until day 18, before declining slowly. Hatching-induction was not observed beyond day 22. Low hatchability in long-term photo-arrested embryos apparently reflects a loss of the anatomical prerequisites for the rim-hatching mechanism. Altered hatchability and morphogenesis after prolonged intra ovo development indicate that hatching in halibut is possible only at an early, defined ontogenetic stage.

Gastrulation and mesoderm morphogenesis in the white sturgeon

This study presents a detailed description of gastrulation in the white sturgeon, Acipenser transmontanus, using scanning electron microscopy, histology, and time-lapse filming and video microscopy. This morphological analysis describes the similarity of gastrula structure in the sturgeon and the amphibian Xenopus laevis, and suggests that the species share many developmental mechanisms. It also identifies important differences, such as the equatorial dorsal lip in sturgeon, and provides a basis for interpreting experiments that test the effect of these differences on gastrulation. The onset of gastrulation in the sturgeon is marked by the appearance of a blastoporal equatorial pigment line that forms as the apices of bottle cells contract and concentrate surface pigment granules. Bottle cell formation at the blastopore lip and involution of surface material through the blastopore are strikingly similar to the equivalent processes in amphibian embryos. As gastrulation continues, a distinct cleft of Brachet forms between pre-involution and post-involution material. Following involution, the prospective axial mesoderm located on the dorsal surface of the late blastula (Ballard and Ginsburg: J. Exp. Zool., 213:69-103, 1980) ingresses from a central zone in the posterior archenteron roof surface in a process that is unlike any in Xenopus, but resembles events in other amphibians (Purcell, 1992; Smith: Dev. Biol., 98:250-254, 1983; King: Biol. Bull., 4:287-300, 1903). The detailed comparison of similarities and differences in gastrulation in different vertebrate lineages yields insights into the function and versatility of common developmental mechanisms.