Development of the large nucleolus in the oocytes of the copepod Acanthocyclops vernalis: an electron microscope study

A central feature of oogenesis in the copepod crustacean, Acanthocyclops vernalis, is the development of a very large nucleolus in the oocytes. This nucleolus appears to be the only source of rRNA for the oocyte, as no helper cells are present. Previous work has suggested that ribosomal DNA sequences other than those found at the morphological nucleolar organizers are participating in the elaboration of this nucleolus. It has been hypothesized that chromatin diminution, which occurs during early embryonic development, may involve the loss of these rDNA sequences, which are needed only for the production of ribosomes during oogenesis. The present study examines the development of the large oocyte nucleolus at the electron microscopic level. Nucleologenesis in A. vernalis was found to proceed through 5 stages. During the first 3 stages nucleolar morphology resembled that described in other organisms. In the last 2, however, nucleolar morphology changed radically and the nucleolus was seen to increase greatly in size while breaking up into multiple subunits. The subunits initially resemble active nucleoli, although in the last stage, synthesis appears to stop, as the nucleolus was found to consist only of dense areas containing ribosome-like particles. These observations are consistent with the hypothesis that diminuted DNA contains ribosomal RNA genes.     

Age and growth assessment of western North Atlantic spiny butterfly ray <Emphasis Type="Italic">Gymnura altavela</Emphasis> (L. 1758) using computed tomography of vertebral centra

Life history strategies of batoid fishes have evolved within dynamic marine ecosystems. Adaptations in reproductive and developmental biology are paramount to the survival of species, and therefore knowledge of growth rates to maturity is fundamental for identifying constraints on the conservation of populations. The butterfly rays (Myliobatiformes: Gymnuridae) are highly derived batoids with generally low reproductive potentials for which age and growth information remains unknown. In this study we applied high-resolution X-ray computed tomography (HRXCT) to vertebral centra from a stingray for the first time to estimate age, and used a multimodel approach to investigate growth of spiny butterfly ray, Gymnura altavela. Estimated ages of the oldest male and female were 11 and 18 yrs. at disk widths (WD) 1355 mm and 2150 mm, respectively. Disk width-at-age data were analyzed using three growth models (von Bertalanffy, logistic, Gompertz), and the most parsimonious and empirically supported model was the logistic function with sex treated as a fixed effect on asymptotic disk width (WD _∞ ) and k parameters. Model parameter estimates were (males) WD _∞  = 1285.46 ± 67.27 mm, k = 0.60 ± 0.10, and (females) WD _∞  = 2173.51 ± 129.78 mm, k = 0.27 ± 0.04. Results indicated sexually dimorphic growth patterns, with males growing faster and reaching asymptotic size at earlier ages than females. These age and growth results are the first reported for the genus, and suggest that G. altavela grows at a similar rate as some teleosts and batoids, and relatively fast among chondrichthyans.     

Long-term use of high-efficiency vacuum cleaners and residential airborne fungal-spore exposure

Exposure to fungal allergens is an important contributor to allergic respiratory disease, but information on the efficacy of residential fungal allergen-avoidance in allergic-disease management is lacking. Using vacuum cleaners with high-efficiency exhaust filtration is one method recommended for reducing residential allergen exposure levels, but their use to reduce fungal-spore exposure levels has not been evaluated. To evaluate the effectiveness of high-efficiency vacuuming to control airborne fungal-spore levels, fungal bioaerosols were repeatedly assessed over the course of 10 months in homes randomly assigned to groups using either conventionally filtered (control) or high-efficiency-filtered vacuum cleaners for routine vacuum cleaning. Air samples were analyzed for three fungal-spore categories representing taxa with predominantly outdoor sources and one representing taxa that commonly have indoor sources. In a two-way analysis of variance, sampling period had a significant effect on mean levels of all fungal-spore categories. Vacuum cleaner type had a marginally significant effect on the indoor spore category, with one high-efficiency vacuum group mean (of three) significantly lower than one control mean. No effect was observed of vacuum cleaner type on outdoor spore categories. Including home-environment variables in analysis of covariance models strengthened the effect of the vacuum-type treatment on the indoor spore category, with no effect on the three outdoor spore categories. Decreased indoor spore levels vs. controls were only observed in high-efficiency vacuum groups during the last sampling period, at the end of the heating season. The results suggest that using a vacuum with high-efficiency filtered exhaust could have some modest effectiveness in controlling airborne fungal-spore exposure in homes when infiltration of outdoor air is very limited.     

Unit membrane structural changes following cell association in Dictyostelium

1. 1. A study of the plasma membranes of Dictyostelium discoideum during development was conducted by freeze-fracture and thin-section electron microscopy.

2. 2. The plasma membranes exhibited paniculate structures ranging from 41–188 Å in diameter. The particles increase significantly in average size from the vegetative stage until mature spore formation at which time a decrease occurs.

3. 3. The increase in particle size during development has been attributed to the fusion of mobile particles within the matrix of the membrane.

4. 4. The possibility that cell differentiation is dependent upon an adhesive-stimulatory mechanism provided by the plasma membranes upon aggregation is discussed.

     

Monostotic fibrous dysplasia in the temporal bone: A late prehistoric occurrence

Fibrous dysplasia, characterized by benign osteolytic and osteoblastic lesions may involve one or several bones. Recent investigators have suggested that it may be merely a phase of what have previously been thought to be several different bone disease. Isolated fibrous dysplasia in the temporal bone is infrequent. Several reports of this disease have appeared in the literature of paleopathology, but none involved only the temporal bone. Monostotic involvement of the right temporal bone was discovered in the skull of an adult male recovered from an archeological site dating from the Late Mississippian period (A. D. 1,350–A. D. 1,650). It will provide an opportunity for preliminary documentation of the antiquity of this disease in the southeastern portion of the United States.     

Identification and characterization of coenzyme B12-dependent glycerol dehydratase- and diol dehydratase-encoding genes from metagenomic DNA libraries derived from enrichment cultures

To isolate genes encoding coenzyme B(12)-dependent glycerol and diol dehydratases, metagenomic libraries from three different environmental samples were constructed after allowing growth of the dehydratase-containing microorganisms present for 48 h with glycerol under anaerobic conditions. The libraries were searched for the targeted genes by an activity screen, which was based on complementation of a constructed dehydratase-negative Escherichia coli strain. In this way, two positive E. coli clones out of 560,000 tested clones were obtained. In addition, screening was performed by colony hybridization with dehydratase-specific DNA fragments as probes. The screening of 158,000 E. coli clones by this method yielded five positive clones. Two of the plasmids (pAK6 and pAK8) recovered from the seven positive clones contained genes identical to those encoding the glycerol dehydratase of Citrobacter freundii and were not studied further. The remaining five plasmids (pAK2 to -5 and pAK7) contained two complete and three incomplete dehydratase-encoding gene regions, which were similar to the corresponding regions of enteric bacteria. Three (pAK2, -3, and -7) coded for glycerol dehydratases and two (pAK4 and -5) coded for diol dehydratases. We were able to perform high-level production and purification of three of these dehydratases. The glycerol dehydratases purified from E. coli Bl21/pAK2.1 and E. coli Bl21/pAK7.1 and the complemented hybrid diol dehydratase purified from E. coli Bl21/pAK5.1 were subject to suicide inactivation by glycerol and were cross-reactivated by the reactivation factor (DhaFG) for the glycerol dehydratase of C. freundii. The activities of the three environmentally derived dehydratases and that of glycerol dehydratase of C. freundii with glycerol or 1,2-propanediol as the substrate were inhibited in the presence of the glycerol fermentation product 1,3-propanediol. Taking the catalytic efficiency, stability against inactivation by glycerol, and inhibition by 1,3-propanediol into account, the hybrid diol dehydratase produced by E. coli Bl21/pAK5.1 exhibited the best properties of all tested enzymes for application in the biotechnological production of 1,3-propanediol.     

Discovery of inhibitors of the channel-activating protease prostasin (CAP1/PRSS8) utilizing structure-based design

Structure-based design was utilized to guide the early stage optimization of a substrate-like inhibitor to afford potent peptidomimetic inhibitors of the channel-activating protease prostasin. The first X-ray crystal structures of prostasin with small molecule inhibitors bound to the active site are also reported.