ABSTRACT
The kinetics of lipofuscin growth in diseased retinal pigment epithelium cells is investigated using Monte Carlo simulations and scaling theory on a cluster aggregation model. The model captures the essential physics of lipofuscin growth in the cells. A remarkable feature is that small particles may be removed from the cells while the larger ones become fixed and grow by aggregation. Model simulations are compared to the number of lipofuscin granules in eyes with early age-related degeneration.
Subject(s)
Choroidal Neovascularization/metabolism , Lipofuscin/biosynthesis , Lipofuscin/chemical synthesis , Models, Biological , Models, Chemical , Retinal Pigment Epithelium/chemistry , Retinal Pigment Epithelium/metabolism , Cells, Cultured , Choroidal Neovascularization/pathology , Computer Simulation , Humans , Retinal Pigment Epithelium/pathologyABSTRACT
The segmentation of vertebrate embryos, a process known as somitogenesis, depends on a complex genetic network that generates highly dynamic gene expression in an oscillatory manner. A recent proposal for the mechanism underlying these oscillations involves negative-feedback regulation at transcriptional translational levels, also known as the "delay model" [J. Lewis Curr. Biol. 13, 1398 (2003)]. In addition, in the zebrafish a longitudinal positional information signal in the form of an Fgf8 gradient constitutes a determination front that could be used to transform these coupled intracellular temporal oscillations into the observed spatial periodicity of somites. Here we consider an extension of the delay model by taking into account the interaction of the oscillation clock with the determination front. Comparison is made with the known properties of somite formation in the zebrafish embryo. We also show that the model can mimic the anomalies formed when progression of the determination wave front is perturbed and make an experimental prediction that can be used to test the model.
Subject(s)
Biological Clocks/physiology , Gene Expression Regulation, Developmental , Models, Biological , Somites/embryology , Animals , Fibroblast Growth Factors/metabolism , Zebrafish/embryology , Zebrafish Proteins/metabolismABSTRACT
A simple model of deposition of particles and growth of point islands in a two-dimensional substrate is introduced and studied. The detachment of particles from islands with an odd number of particles can occur with a probability P. The power-law scalings of the island, monomer, and odd island densities are analytically obtained and verified by Monte Carlo simulations. The universality class of the model depends on P, and the island density exponent chi changes from chi=1/3 (for P=0 ) to chi=0 (for P>0 ).
