Establishment of neuronal connectivity during development of the Drosophila larval visual system

We used confocal microscopy in conjunction with specific antibodies and enhancer trap strains to investigate the development of specific neuronal connections in a simple model system, the larval visual system of Drosophila. We find that the establishment of axonal projections from the larval photoreceptor neurons to their central nervous system targets involves a series of discrete steps. During embryogenesis, the larval optic nerve contacts several different cell types, including optic lobe pioneer (OLP) neurons and a number of glial cells. We demonstrate that OLP neurons are present and project normally in glass (gl) mutant embryos in which the larval optic nerve fails to develop, suggesting that they do not depend on interactions with the larval optic nerve for differentiation and proper axonal projection. The OLPs fail to differentiate properly in disconnected (disco) mutant embryos, where appropriate connections between the larval optic nerve and its targets in the brain are not formed. The disco gene is expressed in the OLPs and may therefore act autonomously to direct the differentiation of these cells. Taken together, our results suggest that the OLPs act as an intermediate target required for the establishment of normal optic nerve projection and connectivity. © 1995 John Wiley & Sons, Inc.     

The development of connections in the tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos

Light and electron microscopic studies have been made on degenerative changes in the nervous tissue induced by experimental destruction of the median brain bulb at the 5th day of incubation, in parts of the tecto-thalamo-telencephalic visual system in 13-day chick embryos (in the visual tectum, round nucleus of the thalamus and ectostriatum of the telencephalon). It was shown that to this period tecto-thalamic connections are already formed in the visual system, whereas thalamo-telencephalic connections are, presumably, indirect ones.     

Post-embryonic larval development and metamorphosis of the hydroidEudendrium racemosum (Cavolini) (Hydrozoa,Cnidaria)

The morphology and histology of the planula larva ofEudendrium racemosum (Cavolini) and its metamorphosis into the primary polyp are described from light microscopic observations. The planula hatches as a differentiated gastrula. During the lecithotrophic larval period, large ectodermal mucous cells, embedded between epitheliomuscular cells, secrete a sticky slime. Two granulated cell types occur in the ectoderm that are interpreted as secretory and sensorynervous cells, but might also be representatives of only one cell type with a multiple function. The entoderm consists of yolk-storing gastrodermal cells, digestive gland cells, interstitial cells, cnidoblasts, and premature cnidocytes. The larva starts metamorphosis by affixing its blunt aboral pole to a substratum. While the planula flattens down, the mucous cells penetrate the mesolamella and migrate through the entoderm into the gastral cavity where they are lysed. Subsequently, interstitial cells, cnidoblasts, and premature cnidocytes migrate in the opposite direction, i.e. from entoderm to ectoderm. Then, the polypoid body organization, comprising head (hydranth), stem and foot, all covered by peridermal secretion, becomes recognisable. An oral constriction divides the hypostomal portion of the gastral cavity from the stomachic portion. Within the hypostomal entoderm, cells containing secretory granules differentiate. Following growth and the multiplication of tentacles, the head periderm disappears. A ring of gland cells differentiates at the hydranth's base. The positioning of cnidae in the tentacle ectoderm, penetration of the mouth opening and the multiplication of digestive gland cells enable the polyp to change from lecithotrophic to planktotrophic nutrition.     

Structure and metamorphic remodeling of the larval nervous system and musculature of Phoronis pallida (Phoronida)

The structure of the larval nervous system and the musculature of Phoronis pallida were studied, as well as the remodeling of these systems at metamorphosis. The serotonergic portion of the apical ganglion is a U-shaped field of cell bodies that send projections into a central neuropil. The majority of the serotonergic cells are (at least) bipolar sensory cells, and a few are nonsensory cells. Catecholaminergic cell bodies border the apical ganglion. The second (hood) sense organ develops at competence and is composed of bipolar sensory cells that send projections into a secondary neuropil. Musculature of the competent larva includes circular and longitudinal muscle fibers of the body wall, as well as elevators and depressors of the tentacles and hood. The juvenile nervous system and musculature are developed prior to metamorphosis and are integrated with those of the larva. Components of the juvenile nervous system include a diffuse neural net of serotonergic cell bodies and fibers and longitudinal catecholaminergic fibers. The juvenile body wall musculature consists of longitudinal fibers that overlie circular muscle fibers, except in the cincture regions, where this pattern is reversed. Metamorphosis is initiated by the larval neuromuscular system but is completed by the juvenile neuromuscular system. During metamorphosis, the larval nervous system and the musculature undergo cell death, and the larval tentacles and gut are remodeled into the juvenile arrangement. Although the phoronid nervous system has often been described as deuterostome-like, these data show that several cytological aspects of the larval and juvenile neuromuscular systems also have protostome (lophotrochozoan) characteristics.     

Oogenesis and larval development of Ephydatia fluviatilis (Porifera,Spongillidae)

Summary In Ephydatia fluviatilis young oocytes already appear in autumn. They pass the winter in the highly reduced sponge, but vitellogenesis and further development do not take place before following spring. The fact that the young oocytes appear before the normal period of reproduction makes E. fluviatilis different from all other local freshwater sponges, which reduce totally in autumn. E. fluviatilis seems to be a gonochorist. The oocytes originate from archaeocytes and during the first growth phase they reach a diameter of approximately 40 m. In the second growth phase the oocyte is enclosed in a single-layered follicle epithelium and grows to 170–180 m by phagocytosis of trophocytes. The fully developed egg cell finally shows a distinct layering of the incorporated yolk material. Cleavage is totally equal to unequal so that macro- and micromeres appear in some cleavage stages. Cleavage leads to a solid embryo consisting of uniform cells. At this stage of development the first scleroblasts appear. As the cells develop they are surrounded by companion cells, managing the transport of the scleroblasts. The further development to the larva is marked by the appearance of the larval cavity, typical for larvae of Spongillids, which finally occupies about half the volume of the larva at emergence. The periphery of the larva consists of a single-layered ciliated epithelium. After emergence the larva forms flagellated chambers, which are integrated into the primordia of the excurrent canal system. This system connects with the larval cavity and ensures that it becomes part of the excurrent canal system of the young sponge. Particularly in the region of the larval cavity the ciliated epithelium of the free larva is reduced. Here a new larval surface epithelium is formed by pinacocytes.     

Oogenesis and larval development of Scypha ciliata (Porifera,Calcarea)

Summary Scypha ciliata is a syconoid sponge. Its oocytes differentiate from choanocytes located near the apopyle of a flagellated chamber, and initially they remain in that location, in a trophic complex with neighbouring choanocytes. When this first growth phase is completed, the oocyte migrates to the periphery of the sponge. There it undergoes a second growth phase, in which it phagocytizes choanocytes and mesenchyme cells.Fertilization of the mature egg is assisted by a converted choanocyte, the sperm carrier cell. This cell penetrates the oocyte and transfers to it the sperm contained in a carriercell vacuole. No meiotic events have yet been observed.Cleavage is asynchronous, with holoblastic, approximately equal divisions. After the first cleavage steps the blastomeres often contain multiple nuclei. The single-layered blastoderm of the stomoblastula consists of many micromeres with flagella that project into the blastocoel, a few macromeres and four cruciform cells. There is no development of a follicle epithelium.The stomoblastula develops into the amphiblastula by inversion; with the assistance of the maternal choanocyte epithelium, the hollow sphere turns inside out, simultaneously moving out of the mesoderm and into the lumen of the adjacent flagellated chamber. In this process, the blastocoel of the stomoblastula is lost. The flagellated cells that form the wall of the amphiblastula now have their flagella extending outward; the amphiblastula also comprises four cruciform cells, macrogranular and agranular cells. The larval cavity of the amphiblastula is a newly formed structure.Abbreviations AB amphiblastula - AP apopyle - BC blastocoel - aC agranular cell - maC macrogranular cell - miC microgranular cell - CB crystalline body - CC central cavity - Ch choanocyte - fCh flat choanocyte - gCh granulate choanocyte - CM cell membrane - Co collar of choanocyte - CrC cruciform cell - DM dense material - EM electron micrograph - F flagellum - FC flagellated cell - FCm flagellated chamber - FL free larva - FV food vacuole - IR interior region - LC larval cavity - M mesenchyme - Ma macromere - MC mesenchyme cell - Mi micromere - N nucleus - Nu nucleolus - O opening - OC oocyte - P psudopodium - PC pinacocyte - PhM phase-contrast micrograph - Po pore - PP prosopyle - S sperm - SB stomoblastula - SC segmentation cavity - SCC sperm-carrier cell - SV sperm vacuole - lT large trophocyte - sT small trophocyte - V vacuole - VC vesicular cytoplasm - VM vacuole membrane     

The larval and post-larval development of Percnon gibbesi (Crustacea, Brachyura, Grapsidae) and the identity of the larval genus Pluteocaris

The larval and post-larval development of Percnon gibbesi , from a combination of laboratory-reared and plankton-caught material, is described, and larval characters within the Plagusiinae are discussed. The synonymy of Percnon and Pluteocaris is established.     

The formation of the nervous system during larval development in Triops cancriformis (Bosc) (crustacea,Branchiopoda): An immunohistochemical survey

We provide data of the development of thenervous system during the first five larval stages of Triops cancriformis. We use immunohistochemical labeling (against acetylated α‐tubulin, serotonin, histamine, and FMRFamide), confocal laser scanning microscopy analysis, and 3D‐reconstruction. The development of the nervous system corresponds with the general anamorphic development in T. cancriformis. In larval stage I (L I), all brain parts (proto‐, deuto‐, and tritocerebrum), the circumoral connectives, and the mandibular neuromere are already present. Also, the frontal filaments and the developing nauplius eye are already present. However, until stage L III, the nauplius eye only consists of three cups. Throughout larval development, the protocerebral network differentiates into distinct subdivisions. In the postnaupliar region, additional neuromeres and their commissures emerge in an anteroposterior gradient. The larval nervous system in L V consists of a differentiated protocerebrum including a central body, a nauplius eye comprising four cups, a circumoral nerve ring, mandibular‐ and postnaupliar neuromeres up to the seventh thoracic segment, each featuring an anterior and a posterior commissure, and two parallel connectives. The presence of a protocerebral bridge is questionable. The distribution of neurotransmitters in L I is restricted to the naupliar nervous system. Over the course of the five stages of development, neurotransmitter distribution also follows an anteroposterior gradient. Each neuromere is equipped with two ganglia innervating the locomotional appendages and possesses a specific neurotransmitter distribution pattern. We suggest a correlation between neurotransmitter expression and locomotion. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Characterization of the esterase isozymes of Ips typographus (coleoptera,scolytidae)

Four esterase isozymes hydrolyzing α-naphthyl acetate (α-NA) were detected screening whole body homogenates of larvae and adults of Ips typographus by electrophoresis. Two of the four isozymes (isozymes 3 and 4) were not detected by α-NA staining in the pupal stage, but topical application of juvenile hormone III (JH III) on the pupa induced these isozymes. The JH esterase (JHE) activity on the gel was associated with the proteins of isozyme 2. The compounds OTFP, PTFP, and DFP inhibited this catalytic activity of isozyme 2 on the gel at low concentrations, whereas the proteins of isozyme 3 and 4 were affected only at higher concentrations. A quantitative developmental study was performed to characterize which of the esterases hydrolyzed JH III, using a putative surrogate substrate for JH (HEXTAT) and α-NA. The I₅₀ of several esterase inhibitors and the JH metabolites were also defined. All findings supported the results that a protein associated with isozyme 2 is catabolizing JH and that isozymes 3 and 4 are the main contributors to the general esterase activity on α-NA. The JHE from Tenebrio molitor was purified by affinity chromatography. Although the recovery was low, an analytical isoelectric focusing gel showed that the JHE activity of the purified enzyme. T. molitor cochromatographed at the same pl as the JHE activity of I. typographus. Arch. Insect Biochem. Physiol. 34:203–221, 1997. © 1997 Wiley-Liss, Inc.     

Structure of the stridulatory apparatus and analysis of the sound produced by Smicronyx fulvus and Smicronyx sordidus (coleoptera,curculionidae, erirrhininae,smicronychini)

Wing folding spicules, elytral binding patches, and elytral locking devices of adult male and female seed weevils, Smicronyx fulvus LeConte and S. sordidus LeConte, involved in stridulation are described. Sound is produced by both sexes of the two species when the plectrum, paired conical teeth located along the anterior margin of the dorsally elevated seventh sternite, is struck against an elongate file, the pars stridens, on the under surface of the apical portion of each elytron. A second plectrum, on the sixth tergite, is well-developed in males of both species and is used by males to produce sound before and during mating. Sex-specific and species-specific differences in the sound produced is attributed to structural variation in the pars stridens and the elytra. The pars stridens determines frequencies, while the elytra may further modify the sound. The frequency range for male S. fulvus is 1,000 cycles per second (cps) through 13,000 cps and for male S. sordidus is 2,500 cps through 13,000 cps. The frequency range for female S. fulvus is 2,000 cps through 11,500 cps and for female S. sordidus is 900 cps through 11,500 cps.     

Laboratory experiments on the larval development ofHyas araneus (Decapoda,Majidae)

Experiments have been carried out on the duration of larval development of the spider crabHyas araneus L., in relation to temperature, food quality, and individual variation. A graphical model is presented which predicts larval occurrence and settlement in the field (Helgoland waters, North Sea). Preliminary observations are reported on predator-prey interactions with larvae of the spionid polychaetePolydora ciliata. Cannibalism and necrophagy during starvation experiments with zooplankton are considered: In larvae which are not kept in individual confinement, maximum survival time doubles due to feeding on living or dead sibling larvae. Analyses are presented revealing elemental and biochemical composition of starved and fed larvae as well as energy equivalents calculated from these data. During starvation, early larvae lose carbon, nitrogen, and hydrogen. Their main metabolic substrate is protein; lipid is utilized to a much lesser extent. Exoskeleton formation is, apparently, independent of nutrition: Zoea-1 larvae starved for 8 days contain the same amount of chitin as larvae fed well over this period of time. Energy calculations suggest an extremely low respiration rate and a very effective reconstruction of body material in starved larvae.     

Structure and development of spines over the skin surface of the river puffer Takifugu obscurus (Tetraodontidae,Teleostei) during larval growth

The histological structure and development of spines on the skin surface of Takifugu obscurus were studied during larval development conducted artificially with an average 30‰ salinity and 18.0–20.3°C water temperature. The epidermis comprises an outermost layer, middle layer, and the stratum germinativum, and contains three types of gland cells: small spherical or flask‐shaped mucous cells, larger sacciform mucous cells, and large granular cells. The dermis and subcutis follow. The spines first appear over the ventral region at 10 days after hatching and consist of two parts: a central long tapering portion which projects into the epidermis and eventually outside of the body, and a short supporting basal portion that is embedded within the stratum compactum layer of the dermis. The central, long tapering portion has two very short processes on top until 25 days after hatching, but these two separate spines fuse into one 30 days after hatching. In contrast, the short supporting spines rooted at the base consist of three to six small spines (usually four to five spines) and are present even in the adult stage. Therefore, calcareous spines consisting of one central long spine and three to six smaller supporting spines form tetra‐ and septaradiate spines (mainly penta‐ and hexaradiate). The spines first appear over the ventral region.     

Tetracha hope 1838 of the Turks and Caicos Islands (coleoptera, carabidae, cicindelinae)

A new species, Tetracha (Neotetracha) naviauxi, and a new subspecies, Tetracha (Tetracha) sobrina caicosensis, are described from the Turks and Caicos Islands. The key to Tetracha species in Naviaux (2007) is adapted to accommodate Tetracha naviauxi. Tetracha sobrina caicosensis is compared to other Caribbean subspecies of Tetracha sobrina.     

Tecto-thalamo-telencephalic visual system of the brain in 13-day-old chick embryos

Light and electron microscopic studies have been made of the nervous tissue in three parts of the tecto-thalamo-telencephalic visual system--i.e. tectum opticum, nucleus rotundus of thalamus and ectostriatum of telencephalon--of 13-day chick embryos. Neuroblasts and neurones at various stages of differentiation were described together with various types of synaptic and nonsynaptic intercellular contacts in the neuropil of these brain structures. Heterochronous maturation of these parts of the visual system in embryogenesis was noted which reflects the level of their phylogenetic maturity. Being phylogenetically more ancient structures, tectum opticum and nucleus rotundus reveal differentiation earlier than ectostriatum which is phylogenetically younger.