The organization and structure of nerve and muscle in the jellyfish Cyanea capillata (coelenterata; scyphozoa)

The perirhopalial tissue and swimming muscle of Cyanea were examined with light microscopical and electron microscopical techniques. The perirhopalial tissue is a thin, triangular septum found on the subumbrellar surface of the animal. It separates part of the gastric canal system from the surrounding seawater, and is bound on two sides by radial muscle bands and on the third, the shorter side, by a rhopalium and the margin of the bell. The ectoderm of the perirhopalial tissue is composed of large, somewhat cuboidal, vacuolated, myoepithelial cells. The muscle tails of these cells form a single layer of radial, smooth muscle. Neurons of the “giant fiber nerve net” (GFNN), which form an extensive net over the perirhopalial tissue, lie at the base of the vacuolated portion of the myoepithelial cells. These neurons are visible in living tissue. The morphology of individual GFNN neurons was examined following intracellular injection of the fluorescent dye Lucifer Yellow. The neurons are usually bipolar and free of branches. At the electron microscope level, one usually finds that the GFNN neurons contain large vacuoles. The other characteristic feature of these cells is that they form symmetrical, or nonpolarized, synapses; that is, synaptic vesicles are found on both sides of the synapse. The swimming muscle is striated and composed of myoepithelial cells. Each myoepithelial cell has several muscle tails, and those of adjacent cells are linked to gether by desmosomes. The endoderm of the perirhopalial tissue also was examined. This investigation of the organization and ultrastructure of the perirhopalial tissue and surrounding muscle was undertaken to provide essential background information for an ongoing physiological study of the GFNN neurons and their synapses.     

Sodium chloride treatment of amphotericin B nephrotoxicity. Standard of care?

Amphotericin B is an effective therapeutic agent for most systemic or invasive mycoses, but its usefulness is limited by the frequent occurrence of nephrotoxicity. Given the high and increasing frequency of serious fungal infections, especially in immunocompromised patients, the importance of the morbidity caused by this toxicity is substantial. Salt loading may prevent and even reverse amphotericin B-induced azotemia by an unknown mechanism. A prospective, randomized, placebo-controlled trial in a relevant patient group would strengthen the support for this simple, safe therapy, but will not likely be carried out because of practical and ethical considerations. Thus, a few prospective and limited controlled human studies may be the only supportive evidence for using this therapy. Supplementing dietary sodium chloride intake with 150 mEq of sodium chloride daily intravenously or orally beginning when or before amphotericin B therapy is initiated will likely prevent much of the observed nephrotoxicity and should be carried out routinely.     

Estimating recent growth in the cuttlefish Sepia officinalis: are nucleic acid-based indicators for growth and condition the method of choice?

A laboratory calibration study was undertaken with juvenile Sepia officinalis (80-85 g initial wet weight) to investigate the effects of different food rations and different starving intervals on RNA/dry weight (DW) ratios and RNA/DNA ratios in cephalopod mantle muscle at two different temperatures. The digestive gland index was also used as an additional indicator of recent growth. High food rations and low temperature went along with high RNA/DW ratios and high RNA/DNA ratios. Starving resulted in a linear decline in growth performance and a concomitant decrease in RNA/DW and RNA/DNA ratio, with RNA/DNA ratios representing the growth data better. RNA/DNA ratios decreased faster at higher temperatures. A fluorimetric assay for nucleic acid analysis was optimized for cephalopod mantle tissues and yielded reproducible RNA/DNA ratios with a relative variance below 10%. Thus, it may be possible to use this estimator of recently encountered feeding regime for the evaluation of mortality rates of early teuthid paralarvae to eventually support stock management. Also, log relative digestive gland weight showed a strong relationship with starving time, but, surprisingly, not with temperature. Data from the two temperatures analyzed could be combined to form a common regression line of relative digestive gland index with starving time. This indicator for recent growth might be especially suitable for large specimens with a well-developed digestive gland.     

Chitin biosynthesis during pupal development of Drosophila melanogaster and the effect of the lethalcryptocephal mutation

Estimation of chitin deposition in the pupal and adult cuticles of adult Drosophila melanogaster during the pupal period is described. The timing of the periods of chitin deposition is compared with that deduced by previous workers using electron microscopy. The hypothesis that lethalcryptocephal mutant homozygotes are unable to evert their cephalic complexes at pupation because of excess chitin deposition is examined. The data obtained show no evidence that the mutation has any effect on chitin deposition.     

Active site mutations in DNA topoisomerase I distinguish the cytotoxic activities of camptothecin and the indolocarbazole, rebeccamycin.

DNA topoisomerase I (Top1p) catalyzes topological changes in DNA and is the cellular target of the antitumor agent camptothecin (CPT). Non-CPT drugs that target Top1p, such as indolocarbazoles, are under clinical development. However, whether the cytotoxicity of indolocarbazoles derives from Top1p poisoning remains unclear. To further investigate indolocarbazole mechanism, rebeccamycin R-3 activity was examined in vitro and in yeast. Using a series of Top1p mutants, where substitution of residues around the active site tyrosine has well-defined effects on enzyme catalysis, we show that catalytically active, CPT-resistant enzymes remain sensitive to R-3. This indolocarbazole did not inhibit yeast Top1p activity, yet was effective in stabilizing Top1p-DNA complexes. Similar results were obtained with human Top1p, when Ser or His were substituted for Asn-722. The mutations altered enzyme function and sensitivity to CPT, yet R-3 poisoning of Top1p was unaffected. Moreover, top1delta, rad52delta yeast cells expressing human Top1p, but not catalytically inactive Top1Y723Fp, were sensitive to R-3. These data support hTop1p as the cellular target of R-3 and indicate that distinct drug-enzyme interactions at the active site are required for efficient poisoning by R-3 or CPT. Furthermore, resistance to one poison may potentiate cell sensitivity to structurally distinct compounds that also target Top1p.     

APOLAR EMBRYOS OF FUCUS RESULTING FROM OSMOTIC AND CHEMICAL TREATMENT

Embryos of the brown alga Fucus vesiculosas L. were grown as populations in glass petri dishes in seawater at 15 C in continuous low-intensity unilateral fluorescent illumination for periods up to 2 weeks. A quantitative estimate of increase in nuclear number was made from acetocarmine squash preparations of samples taken at 12-or-24 hr intervals. Over the period of 2-6 days embryos showed a doubling time of about 12-18 hr. Under normal seawater culture conditions each embryo formed a single rhizoid. When grown in seawater supplemented with sugar concentrations above 0.4 m , Fucus embryos developed as multicellular spherical embryos lacking rhizoids. In 0.6 m sucrose-seawater, 97% of the embryos were apolar at 2 days; only 37% were apolar at 4 days, many having recovered from the sucrose inhibition. Some embryos remained apolar after growth in 0.6 m sucrose for 2 weeks. Nuclear counts showed that sucrose-seawater markedly inhibited the rate of cell division. Other sugars including D-glucose, D-fructose, D-galactose and the sugar alcohol D-mannitol were also effective. When apolar embryos grown in sucrose-seawater were returned to seawater, embryo growth resumed at the normal seawater rate, judged from nuclear counts. Such embryos formed multiple rhizoids, varying from two to eight rhizoids per embryo, which developed on the embryo quadrant or half away from the unilateral light. Each of the multiple rhizoids originated from a single small cell in the periphery of the multicellular spherica embryo. Thus the rhizoid-forming stimulus apparently had been subdivided among a number of the cells of the apolar embryos. The implications of this finding are discussed. Attempts to produce multiple rhizoids by treatment of embryos with indoleacetic acid or 2,4-dichlorophen-oxyacetic acid failed. However, embryos treated with 10⁻⁴ M or 5 × 10⁻⁵ m 2,3,5-triiodobenzoic acid formed 40 and 30% multiple rhizoids, respectively, suggesting that some chemical, perhaps hormonal, mechanism is involved in polarization and rhizoid initiation in Fucus embryogenesis.     

Book reviews

Environmental Biology of Fishes -