CDEV Subgroup Contributed Talks

David Holloway

British Columbia Institute of Technology

"Controlling the number of cotyledons in conifer embryos"

Conifers, unlike flowering plants, generate variable numbers of cotyledons (embryonic 'seed leaves'). Conifer cotyledons do not form all over the dome-shaped embryo, but form in a single ring at a particular distance from the tip. A 3-fold increase in this ring radius from 55 to 180 µm corresponds to the experimentally observed range of 2 to 10 regularly-spaced cotyledons. In the flowering plant Arabidopsis, leaves are also initiated at a particular distance from the growing tip. Molecularly, this is at a 'trough' between two expression domains, of REV (an HD-ZIP III protein) above the leaves and KAN below the leaves. REV and KAN are mutually inhibitory via miRNAs (tasiARF from REV, miR166 from KAN). This is at least partly shared by conifers: overexpression of miR166 in larch decreases HD-ZIP III expression and affects cotyledon formation. We have developed a model for HD-ZIP III (H), KAN (K) regulation to investigate how their interface position is controlled - in particular, what allows for the 3-fold natural variability in conifer cotyledon ring radius. Simulating Arabidopsis H/K experimental perturbations contributes to a general mechanism for radial positioning, as well as quantitatively predicting radial shifts in new conifer experiments.

Tamsin Spelman

Sainsbury Laboratory, University of Cambridge, UK

"Links between microtubules and nucleus shape in a plant root hair cell"

Root hair cells develop out of Trichoblast cells in the plant root epidermis and are characterised by a long thin protrusion which in Arabidopsis is ≈10μm wide and can grow to ≈1mm in length [1]. For growth of this protrusion, nucleus migration up the root hair is necessary, with the nucleus positioned ≈80μm back from the growing tip [2]. Our aim is to understand nucleus shape and position in the root hair, particularly focusing on how it is affected by the cytoskeleton (microtubules and actin). By segmenting experimental data, we analyse 3D nucleus shape and motion before and after treatment with drugs effecting osmolarity and microtubule organisation: Mannitol and Oryzalin. To further understand the relationship between the nucleus and microtubules, we then analyse the microtubule distribution in the nucleus-tip region of the root hair. Using 3D microtubule simulations and simple nuclear dynamics models, we analyse the microtubule density distributions and organisation for a range of conditions in the root hair cell and compare these to the distributions obtained experimentally. [1] Grierson C et. al. (2014) Root hairs. Arabidopsis Book. 12:e0172. [2]T. Ketelaar et. al. (2002) Positioning of Nuclei in Arabidopsis Root Hairs. The Plant Cell, 14(11):2941-2955;

Daniel Koch

King's College London

"Information Processing by Homo-Oligomeric Proteins: From First Principles to Cardiac Arrhythmias"

Reversible protein homo-oligomerisation, i.e. the formation of larger protein complexes out of identical subunits, is observed for 30-50% of all vertebrate proteins. Despite being a ubiquitous phenomenon, the specific function of protein homo-oligomerisation remains poorly understood. I previously demonstrated theoretically that homo-oligomerisation could be a versatile mechanism for a range of signal processing capabilities such as dynamic signal encoding, homeostasis and bistability via pseudo-multisite modification. In this talk I will present the first dynamical systems model of phospholamban (PLN), a crucial mediator protein of β-adrenergic signaling and regulator of calcium cycling in heart muscle cells. Importantly, PLN forms homo-pentamers whose function remained unclear for decades. Simulations and model analyses demonstrate that pentamers enable bistable phosphorylation and further constitute substrate competition based low-pass filters for phosphorylation of monomeric PLN. I confirmed both predictions of my model experimentally by demonstrating substrate competition in vitro and hysteresis of pentamer phoshorylation in cardiomyocytes. These non-linear phenomena could ensure consistent monomer phosphorylation and calcium cycling despite noisy signaling activity in the upstream network and are likely impaired by a genetic mutation that causes arrhythmogenic heart disease. These studies show that homo-oligomerisation can play unanticipated and potentially disease relevant roles in biochemical signaling networks.

Adriana Zanca

The University of Melbourne

" Cell proliferation and migration during wound healing"

Experiments have suggested that during skin wound healing, the wound front is comprised of a hyperproliferative region behind a non-proliferating migrating tongue at the wound edge. Mathematical and computational models allow us to efficiently explore the effects of changing the characteristics of these proposed regions in order to suggest plausible hypotheses about the mechanics of the regions, and wound healing in general. In this work we use cell-based computational modelling to investigate competing experimental findings regarding whether the regions spatially overlap. Furthermore, we examine the effect of changing the size, location and cell characteristics, such as proliferation and migration rate, of each region on the behaviour of the wound edge.