Modelling the spatial patterning of teeth primordia in the alligator

We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator, Alligator mississippiensis. Detailed embryological studies by Westergaard and Ferguson (1986, 1987, 1990) have shown that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a dynamic patterning mechanism, which crucially includes domain growth. The mechanism can reproduce the spatial pattern development of the first seven teeth primordia in each half jaw of A. mississippiensis. The results for the precise spatio-temporal sequence compare well with experiment. Simulation of the model also predicts that certain transplantations can alter the spatial sequence of teeth primordia initiation.     

A mathematical model of glioma growth: the effect of chemotherapy on spatio-temporal growth

During the past two decades computerized tomography (CT) and magnetic resonance imaging (MRI) have permitted the detection of tumours at much earlier stages in their development than was previously possible. In spite of this earlier diagnosis the effects of earlier and more extensive treatments have been difficult to document. This failure has led to an increasing awareness of the importance of infiltration of glioma cells into surrounding grossly normal brain tissue such that recurrence still occurs. In this paper a simple mathematical model for the proliferation and infiltration of such tumours is introduced, based in part on quantitative image analysis of histological sections of a human brain glioma and especially on cross-sectional area/volume measurements of serial CT images while the patient was undergoing chemotherapy. The model parameters were estimated using optimization techniques to give the best fit of the simulated tumour area to the CT scan data. Numerical solution of the model on a two-dimensional domain, which took into account the geometry of the brain and its natural barriers to diffusion, was used to determine the effect of chemotherapy on the spatiotemporal growth of the tumour.     

Travelling waves in a tissue interaction model for skin pattern formation

Tissue interaction plays a major role in many morphogenetic processes, particularly those associated with skin organ primordia. We examine travelling wave solutions in a tissue interaction model for skin pattern formation which is firmly based on the known biology. From a phase space analysis we conjecture the existence of travelling waves with specific wave speeds. Subsequently, analytical approximations to the wave profiles are derived using perturbation methods. We then show numerically that such travelling wave solutions do exist and that they are in good agreement with our analytical results. Finally, the biological implications of our analysis are discussed.     

The Lignicolous Fungus <Emphasis Type="Italic">Coniochaeta pulveracea</Emphasis> and Its Interactions with Syntrophic Yeasts from the Woody Phylloplane

The yeast-like fungus Coniochaeta pulveracea was studied with regard to its novel lignocellulolytic activities and the possible effect thereof on yeasts from the woody phylloplane. An enrichment procedure was used to isolate C. pulveracea from a decaying Acacia tree, and the identity of the isolate was confirmed using morphology, as well as molecular and phylogenetic techniques. This isolate, as well as strains representing C. pulveracea from different geographical regions, were compared with regard to optimum growth temperature and enzyme activity to representatives of closely related species. These include strains of Coniochaeta boothii, Coniochaeta rhopalochaeta, and Coniochaeta subcorticalis. Plate assays for cellulase and xylanase activity indicated that all representatives of the above-mentioned species were able to produce extracellular hydrolytic enzymes and were also able to degrade birchwood toothpicks during a 50-day incubation period at 30°C. To test the ability of these fungi and their enzymes to release simple sugars from complex cellulosic substrates, filtrates obtained from liquid cultures of Coniochaeta, cultivated on carboxymethyl cellulose (CMC) as sole carbon source, were analyzed using high-performance liquid chromatography analysis. Consequently, the presence of mono- and disaccharides such as glucose and cellobiose was confirmed in these culture filtrates. Two subsequent experiments were conducted to determine whether these simple sugars released from woody material by Coniochaeta may enhance growth of phylloplane yeasts. In the first experiment, representatives of Coniochaeta were co-cultured with selected yeasts suspended in agar plates containing birchwood toothpicks, followed by examination of plates for colony formation. Results indicated that Coniochaeta growth on the toothpicks enhanced growth of nearby yeast colonies in the agar plates. In the second experiment, representatives of selected yeasts and Coniochaeta species were co-cultured on CMC and xylan-containing plates where after yeast colony formation was recorded on the plates. Saccharomyces cerevisiae strains, engineered to utilize specific wood degradation products, i.e., cellobiose or xylose, as sole carbon source were used as positive controls. While it was found that cellobiose released from CMC was assimilated by the yeasts, no evidence could be obtained that xylose released from xylan was used as carbon source by the yeasts. These ambiguous results could be ascribed to secretion of nutritious metabolic end products, other than the products of fungal xylanases.     

Major Streptomyces species associated with fissure scab of potato in South Africa including description of Streptomyces solaniscabiei sp. nov

Streptomyces species are the causal agents of several scab diseases on potato tubers. A new type of scab symptom, caused by Streptomyces species, was observed in South Africa from 2010 onwards. The disease was initially thought to be caused by a single Streptomyces species, however, subsequent isolations from similar symptoms on other potato tubers revealed diversity of the Streptomyces isolates. The objective of this study was to characterise these isolates in order to determine what are the major species involved in the disease. This was done by sequencing and phylogenetic analyses of the 16S rDNA as well as five housekeeping genes, investigation of growth on different culture media, standard phenotypic tests and scanning electron microscopy of culture morphology. The presence of the pathogenicity island (PAI) present in plant pathogenic Streptomyces species was also investigated. The genomes of eight isolates, selected from the three main clades identified, were sequenced and annotated to further clarify species boundaries. Three isolates of each of the three main clades were also inoculated onto susceptible potato cultivars in order to establish the pathogenicity of the species. The results of the phylogenetic and genome analyses revealed that there are three main species involved, namely, Streptomyces werraensis, Streptomyces pseudogriseolus and a novel Streptomyces species that is described here as Streptomyces solaniscabiei sp. nov., with strain FS70^T (=?PPPPB BD 2226^T?=?LMG 32103^T) as the type strain. The glasshouse trial results showed that all three of the Streptomyces species are capable of producing fissure scab symptoms. None of the Streptomyces isolates from fissure scab contained the full PAI and the mechanism of disease initiation still needs to be determined. Genomic comparisons also indicated that S. gancidicus Suzuki 1957 (Approved Lists 1980) is a later heterotypic synonym of S. pseudogriseolus Okami and Umezawa 1955 (Approved Lists 1980).

     

On a Model Mechanism for the Spatial Patterning of Teeth Primordia in the Alligator

We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator,Alligator mississippiensis. Detailed embryological studies by Westergaard & Ferguson (1986, 1987, 1990) show that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a reaction-diffusion mechanism, which crucially includes domain growth. The model can reproduce the spatial pattern development of the first seven teeth primordia in the lower half jaw ofA. mississippiensis. The results for the precise spatio-temporal sequence compare well with detailed developmental experiments.