Mathematical modelling, simulation and prediction of tumour-induced angiogenesis

Angiogenesis, the formation of blood vessels from a pre-existing vasculature, is a process whereby capillary sprouts are formed in response to externally supplied chemical stimuli. The sprouts then grow and develop, driven by endothelial cell migration and proliferation, and organise themselves into a dendritic structure. Angiogenesis occurs during embryogenesis, wound healing, arthritis and during the growth of solid tumours. In this paper we present a novel mathematical model which describes the formation of the capillary sprout network in response to chemical stimuli (tumour angiogenesis factors, TAF) supplied by a solid tumour. The model also takes into account endothelial cell-extracellular matrix interactions via the inclusion of fibronectin in the model. The model consists of a system of nonlinear partial differential equations describing the response in space and time of endothelial cells to the TAF and the fibronectin (migration, proliferation, anastomosis, branching). Using the discretized system of partial differential equations, we use a deterministic cellular automata (DCA) model, which enables us to track individual endothelial cells and incorporate branching explicity into the model. Numerical simulations are presented which are in very good qualitative agreement with experimental observations. Certain experiments are suggested which could be used to test the hypotheses of the model and various extensions and developments of the model with particular applications to anti-angiogenesis strategies are discussed.     

Corneal glycoconjugates: an ultrastructural lectin-gold study

Continuous human leukemia-lymphoma cell lines have become invaluable tools for hematological research as they provide an unlimited amount of cellular material. The first human lymphoma cell line Raji was established in 1963; since then several hundred leukemia-lymphoma cell lines spanning almost the whole spectrum of hematopoietic cell lineages (except for dendritric cells) have been described. The cardinal features of leukemia-lymphoma cell lines are their monoclonal origin, arrest of differentiation, and (growth factor-independent or -dependent) unlimited proliferation. Categorization of cell lines usually follows the physiological stages of hematopoietic differentiation in the various cell lineages. For an adequate classification, a detailed characterization of both primary and cultured cells in absolutely necessary. New cell lines, in particular, must be adequately, characterized; while cell culture data and immunological and cytogenetic features are essential, cell lines should be described in as much detail as possible. In addition to this recommended multiparameter characterization and the obligatory immortality of the culture, authentication of the true origin of the cells, novelty, scientific significance and availability of the cell line for other investigators are of utmost importance. It is still extremely difficult to establish new leukemia-lymphoma cell lines (except for some subtypes), and most attempts fail. Paramount to the lack of our understanding as to why certain cells start to proliferate in culture and others do not (thus implying a random process), is probably the difficulty of mimicking in vitro the physiological in vivo microenvironment. Attempts to improve the efficiency of cell line establishment should focus on examining the appropriateness of the in vitro culture conditions; these conditions should emulate as closely as possible the in vivo situation. In summary, leukemia-lymphoma cell lines have the potential to greatly facilitate diverse studies of normal and malignant hematopoiesis; to that end, these cell lines must be extensively characterized and adequately described.     

Pitfalls in the management of preauricular sinuses

A total of 159 operations for the excision of a preauricular sinus carried out in 117 patients over an 8-year period were reviewed. Previous excision, the use of a probe to delineate the sinus and operating under local anaesthesia all increased the chance of recurrence. The condition recurred more often in patients who developed post-operative wound sepsis than in those who healed primarily. Means of decreasing the recurrence rate include: (1) meticulous dissection of the sinus by an experienced head and neck surgeon under general anaesthesia; (2) the use of an extended preauricular incision; (3) clearance down to the temporalis fascia to ensure complete removal of all epithelial components; (4) avoidance of sinus rupture; and (5) closure of wound dead space.     

Kinetics of duck hepatitis B virus infection following low dose virus inoculation: one virus DNA genome is infectious in neonatal ducks

Using pooled serum from congenitally duck hepatitis B virus (DHBV)-infected ducks as inoculum, we examined the effect of virus dose on the incubation period of infection and on the patterns of spread of virus infection in the liver. The pooled serum inoculum contained 9.5 x 10(9) DHBV genomes per milliliter and had an infectivity titre (ID50) in newly hatched ducks of 1.5 x 10(10) per milliliter with a 95% confidence interval of 3.0 x 10(9) to 6.3 x 10(10) ID50/ml, indicating the equivalence between one DHBV genome and one infectious unit within the limits of the assays. The incubation period of infection was inversely related to the dose of inoculum and the onset of viraemia ranged from Day 6 with the highest dose to Day 14 or 29 with the lowest dose inoculum. To study the spread of virus infection from a low percentage of initially infected cells we inoculated newly hatched ducks intravenously with sufficient DHBV (1.5 x 10(3) ID50) to infect only approximately 0.0001% of total liver cells. DHBV infection first reached detectable levels on Day 4 postinoculation (p.i.) and was detected in approximately 0.035% of hepatocytes, most of which occurred as single cells or pairs of cells, indicating that a number of rounds of infection had occurred with the spread of virus both to adjoining cells, i.e., by cell-to-cell spread, and to cells located in other parts of the liver lobule. Despite some bird-to-bird variation in timing, the percentage of infected hepatocytes increased exponentially with a mean doubling time of 16 hr from Day 4 to Day 14 p.i., by which time replication was seen in > 95% of hepatocytes. This rapid dissemination from a small number of infected hepatocytes suggests that, in neonatal ducks, there are no major delays in virus replication within the liver, that any innate and adaptive defence mechanisms operating during the first 10 to 14 days of infection are insufficient to contain virus spread, and that even a small number of infected hepatocytes produce enough progeny to rapidly infect the remaining hepatocytes.     

The modified bitegard: a method for administering supplemental oxygen and measuring carbon dioxide

HUGE is a database for human large proteins newly identified by Kazusa cDNA project, which aims to predict protein primary structures from sequences of human large cDNAs (>4 kb). In particular, cDNA clones capable of coding for large proteins (>50 kDa) are current targets of the project. More than 700 sequences of human cDNAs (average size, 5.1 kb) have been determined to date and deposited in the public databases. Notable information implied from the cDNAs and the predicted protein sequences can be obtained through HUGE via the World Wide Web at URL http://www.kazusa.or.jp/huge     

Yeast silencers create domains of nuclease-resistant chromatin in an SIR4-dependent manner

Previous analysis of the repression of the silent mating type loci in Saccharomyces cerevisiae has linked the mechanism of silencing to the formation of a chromatin domain at the silenced loci. In this study, a TRP1 reporter gene was used to examine changes in chromatin structure in a neutral environment. This enabled the chromatin structure organized by yeast silencers to be compared directly with changes effected by the yeast alpha2 repressor. It was found that silencers mediate the formation of lengthy nuclease-resistant domains on the DNA, rather than specifically positioning nucleosomes over promoter regions as the alpha2 repressor does. Silencing at the TRP1 reporter gene closely resembled silencing at the HMR and HML loci. Repression of the test gene was optimal when two silencers flanking the reporter gene were used, mimicking the situation at the silent loci. In addition, both repression of the reporter gene and the formation of nuclease-resistant chromatin domains was SIR4 dependent.