The emergence of a new chlorophytan system,and Dr. Kornmann's contribution thereto

In traditional chlorophytan systems the organizational level was the primary character for the distinction of main groups (classes and orders). For instance, in Fott (1971), the flagellate level corresponds with the Volvocales, the coccoid level with the Chlorococcales, the filamentous level with the Ulotrichales, the siphonocladous level with the Siphonocladales, and the siphonous level with the Bryopsidales. The new system presented here is an elaboration and emendation of recently proposed taxonomies and their underlying phylogenetic hypotheses, and it is mainly based on ultrastructural features which have become available over the last 15 years. The following criteria are used for the distinction of classes and orders: (1) architecture of the flagellate cell (flagellate cells are considered as the depositories of primitive characters); (2) type of mitosis-cytokinesis; (3) place of meiosis in the life history and, consequently, the sexual life history type; (4) organizational level and thallus architecture; (5) habitat type (marine versus feshwater and terrestrial); (6) chloroplast type. The following classes are presented: Prasinophyceae, Chlamydophyceae, Ulvophyceae (orders Codiolales, Ulvales, Cladophorales, Bryopsidales, Dasycladales), Pleurastrophyceae (?), Chlorophyceae s.s. (orders Cylindrocapsales, Oedogoniales, Chaetophorales), Zygnematophyceae, Trentepohliophyceae, Charophyceae (orders Klebsormidiales, Coleochaetales, Charales). The new system no longer reflects the traditional hypothesis of a stepwise evolutionary progression of organizational levels in which the flagellate level represents the most primitive lineage, the coccoid and sarcinoid levels lineages of intermediate derivation, and the filamentous, siphonocladous and siphonous levels the most derived lineages. Instead, it is now hypothesized that these levels have arisen over and over again in different chlorophytan lineages which are primarily characterized by their type of flagellate cell. The flagellate green algal classes Prasinophyceae (with organic body scales) and Chlamydophyceae probably represent bundles of highly conservative lineages that diverged very long ago. Consequently, extant genera and species in these classes can be expected to have emerged long ago. Fossil evidence points to a minimum age of 600 Ma of certain extant Prasinophycean genera, and molecular evidence to a minimum age of 400–500 Ma of a fewChlamydomonas species. On the contrary, the most derived “green algal” lineage, the Angiosperms, can be expected to consist of, on average, much younger genera and species. Fossil evidence points to a minimum age of genera of 5–60 Ma. Lineages of intermediate evolutionary derivation (Ulvophyceae, Chlorophyceae, Charophyceae) can be expected to encompass genera and species of intermediate age. Fossil and (limited) molecular evidence point to a minimum age of 230–70 Ma of extant genera in Bryopsidales, Dasycladales and Cladophorales (Ulvophyceae) and of 250–80 Ma of extant genera in Charales (Charophyceae).     

Photo-bleaching and photon saturation in flow cytometry.

In flow cytometry, small particles travel at a high speed through a bright light spot. The high light intensity at the point of measurement causes measurable photon saturation. This observation indicates that the rate at which individual dye molecules emit photons is close to the maximum emission rate. Despite the short exposure time, individual molecules may go through a few hundred excitation cycles while they are in the light beam. The absorbed light dose causes significant dye destruction. This article presents experimental procedures to determine the extent of photon saturation and photo-bleaching of dyes bound to cell nuclei in a flow cytometer. Measurements of Hoechst and propidium iodide bound to chromatin show that the amount of dye bleached per emitted photon is the same at low and high illumination intensities. This finding indicates that photon emission and dye destruction are both the result of the absorption of single excitation photons. The experimental observations allow rough estimates of the lifetime of the excited state and the lifetime of the molecule. The lifetime of the Hoechst 33258 bound to DNA is estimated to be 100 excitation-relaxation cycles. The average propidium iodide molecule lasts approximately 200 excitation-relaxation cycles. The theoretical considerations show that the optimal illumination conditions are different for bleaching and nonbleaching dyes. An optical arrangement for high precision measurements of bleaching dyes is presented.     

Kinetics of nitrite oxidation in two Nitrobacter species grown in nitrite-limited chemostats

The influence of growth rate, the presence of acetate and variation in the dissolved oxygen concentration on the kinetics of nitrite oxidation was studied in suspensions of intact cells of Nitrobacter winogradskyi and Nitrobacter hamburgensis. The cells were grown in nitrite-limited chemostats at different dilution rates under chemolithotrophic and mixotrophic conditions. Growth of N. hamburgensis in continuous culture was dependent on the presence of acetate. Acetate hardly affected the maximal nitrite oxidation rate per cell (V _max), but displayed a distinctly negative effect on the saturation constants for nitrite oxidation (K _m ) of both Nitrobacter species. This effect was reversible; when acetate was removed from the suspensions the K _m -values for nitrite oxidation returned to their original values. A reduction of the dissolved oxygen concentration from 100% to 18% air saturation slightly decreased the V _max of chemolithotrophically grown N. winogradskyi cells, whereas a 2.3 fold increase was observed with mixotrophically grown cells of N. hamburgensis. It is suggested that the large variation in K _m encountered in field samples could be due to this observed phenotypic variability. The V _max per cell is not a constant, but apparently is dependent on growth rate and environmental conditions. This implies that potential nitrite oxidation activity and numbers of cells are not necessarily related. Considering their kinetic characteristics, it is unlikely that N. hamburgensis is able to compete succesfully with N. winogradskyi for limiting amounts of nitrite under mixotrophic conditions. However, at reduced partial oxygen tensions, N. hamburgensis may become the better competitor.     

A threshold result for an epidemiological model

A threshold parameter R ₀ is identified for an SIRS epidemiological model which has nonlinear incidence and a distributed delay for transfer out of the removed class. For R ₀ < 1, the disease free equilibrium is proved to be the global attractor for all solutions.Research supplied in part by NSERC A-8965     

The QM gene is X-linked and therefore not involved in suppression of tumorigenesis in Wilms' tumor

Summary Inactivation of one or more tumor-suppressor genes on the short arm of chromosome 11 is thought to play a role in the etiology of Wilms' tumor. A candidate gene, QM, was recently isolated by subtractive hybridization between a tumorigenic cell line (deleted for part of 11p) and a non-tumorigenic cell line (the tumorigenic cell line carrying an extra t(X;11)copy). We show here with an exon-specific polymerase chain reaction that the genomic homolog of the QM cDNA is located in the G6PD-color vision genes region in Xq28. No homologous sequences could be detected on 11p. Our experiments indicate that the QM gene is not involved in the suppression of Wilms' tumor.     

Structure,development and function of the branchial sieve of the common bream,Abramis brama,white bream,Blicca bjoerkna and roach,Rutilus rutilus

Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach.     

Prediction of various grades of cervical neoplasia on plastic-embedded cytobrush samples. Discriminant analysis with qualitative and quantitative predictors.

The purpose of this study was to investigate whether discrimination into five groups of various grades of cervical preneoplasia and neoplasia is possible using discriminant analysis models. Data were analyzed for 242 cases diagnosed as either slight dysplasia (n = 50), moderate dysplasia (n = 50), severe dysplasia (n = 50), carcinoma in situ (n = 50) or invasive carcinoma (n = 42) and consisted of qualitative and quantitative features of cells derived from a repeat sample taken from the ectocervix as well as the endocervix using Cytobrushes. The samples were embedded in plastic, and thin sections were prepared, resulting in a monolayer of cut nuclei. The percentages of expected correct prediction were obtained by using 10,000 double cross-validation samples; the mean percentage of correct prediction into five groups using cross-validation was 65% (in the original analysis, 72%) and into two groups (dysplasia versus carcinoma in situ and invasive carcinoma) was 91% (93%). The results reflect group discrimination potential; we do not claim reliability of prediction for an individual patient. The patients were not a representative sample of the population; to investigate whether groups of patients could be discriminated on the basis of both qualitative and quantitative features, the data analyzed contain an almost equal number of observations in each of the five groups. The results indicate that features do not classify the cases in the same way; the discriminant analyses suggest that quantitative features play an important role in the discrimination of dysplasia from carcinoma cases, while the majority of the qualitative features are important in discrimination within the three dysplasia groups.     

Expression of bovine herpesvirus 1 glycoprotein gIV by recombinant baculovirus and analysis of its immunogenic properties.

The gene encoding the gIV glycoprotein of bovine herpesvirus 1 has been inserted into the genome of Autographa californica baculovirus in lieu of the coding region of the A. californica baculovirus polyhedrin gene. Recombinant protein was identified by its reactivity with gIV-specific monoclonal antibodies and expressed at high levels (about 85 micrograms per 2.5 x 10(6) cells) in Spodoptera frugiperda (SF9) cells. The recombinant glycoprotein had an apparent molecular mass of 63 kDa, indicating that it was incompletely glycosylated. However, it was transported to and expressed on the cell surface of infected SF9 cells. Furthermore, reactivity with polyclonal and monoclonal antibodies specific for gIV suggested that most epitopes were functionally unaltered on the recombinant gIV. Immunization of cattle with recombinant gIV in crude, partially purified, or pure form resulted in the induction of neutralizing antibodies to BHV-1, which were reactive with authentic gIV. However, the neutralizing antibody titers were lower than those elicited by an equivalent amount of affinity-purified authentic gIV, which appeared to be mainly due to reduced recognition of one of the neutralizing antigenic domains of gIV, designated domain I. The potential use of this recombinant gIV glycoprotein as a vaccine to bovine herpesvirus 1 infection in cattle is discussed.     

Polyphosphoinositol lipids inChlamydomonas eugametos gametes

InChlamydomonas eugametos gametes, phosphatidylinositol 4-phosphate (PtdInsP) and phosphatidylinositol 4,5-bisphosphate (PtdInsP₂) comprised 0.4 and 0.3% of the whole-cell phospholipids. They were concentrated in the plasma membrane around the cell body and were present in low concentrations in the flagellar membrane. When gametes were fed³²PO ₄ ^- , the label was rapidly incorporated into PtdInsP and PtdInsP₂ and only slowly incorporated into structural lipids such as phosphatidylethanolamine and phosphatidylglycerol. Similarly, when a pulse of³²PO ₄ ^- was chased with PO ₄ ^- , the label was rapidly lost from the polyphosphoinositol lipids but not from the structural lipids. The major fatty acids in the polyphosphoinositides were C-22 carbon polyenoic acids (70%). The significance of these results in relationship to intracellular signalling via inositol phosphates and Ca²⁺ is discussed.Abbreviations InsP₃ inositol 1,4,5-trisphosphate - mt^–/mt⁺ mating-type plus or minus - PtdA phosphatidic acid - PtdEtn phosphatidylethanolamine - PtdGro phosphatidylglycerol - PtdIns phosphatidylinositol - PtdInsP phosphatidylinositol 4-phosphate; - PtdInsP₂ phosphatidylinositol 4,5-bisphosphate - TCA trichloroacetic acid We thank Frank Schuring for Fig. 5A and Susan Kenter, Hans Kruisselbrink, Saskia Bijvank and Nelleke Corbett for their enthousiastic assistance.