MORPHOGENESIS morphogenesis CONTEXT Introduction Factors affecting morphogenesis Morphogenetic

MORPHOGENESIS

morphogenesis CONTEXT � Introduction � Factors affecting morphogenesis � Morphogenetic Movements � Genetic basis of morphogenesis � Cellular basics of morphogenesis

Introduction “IT IS THE BIOLOGICAL PROCESS THAT CAUSES AN ORGANISM TO ITS DEVELOP SHAPE” The word morphogenesis is derived from the Greek word morphê-Shape Genesis-Creation � Which literally means "beginning of the shape" �

� � is the biological process that causes an organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation, The process controls the organized spatial distribution of cells during the embryonic development of an organism Morphogenesis can take place also in a mature organism, in cell culture or inside tumor cell masses Morphogenesis also describes the development of unicellular life forms that do not have an embryonic stage in their life cycle, or describes the evolution of a body structure within a taxonomic group

Factors affecting morphogenesis Factors affecting Morphogenesis in organism(naturally) Morphogenetic responses may be induced in organisms by hormones, by environmental chemicals ranging from substances produced by other organisms to toxic chemicals or radionuclides released as pollutants, and other plants, or by mechanical stresses induced by spatial patterning of the cells. � Factors affecting Morphogenesis in vitro Several factors influence the phenomenon of morphogenesis considerably during a culture. They are: genotypes, explant, growth regulators, nutrients, other additives and physical environment. �

Invagination During invagination, an epithelial sheet bends inward to form an inpocketing. One way to think of this in three dimensions is to imagine that you are poking a partially deflated beach ball inward with your finger. The resulting bulge or tube is an invagination. If the apical side of the epithelium forms the lumen (central empty space) of the tube, then the movement is termed invagination. If the lumen is formed by basal surfaces, then the movement is termed an evagination. Ingression During ingression, cells leave an epithellial sheet by transforming from wellbehaved epithellial cells into freely migrating mesenchyme cells. To do so, they must presumably alter their cellular architecture, alter their program of motility, and alter their adhesive relationship(s) to the surrounding cells. Primary mesenchyme cells are an example of a mesenchymal cell type that emigrates out of an epithelium (do you know which one? ). Involution During involution, a tissue sheet rolls inward to form an underlying layer via bulk movement of tissue. One helpful image here is of a tank tread or conveyor belt. As material moves in from the edges of the sheet, material originally at the sites of inward rolling (shown in blue here) is free to move further up underneath the exterior tissue

Epiboly During epiboly, a sheet of cells spreads by thinning. i. e. , the sheet thins, while its overall surface area increases in the other two directions. Epiboly can involve a monolayer (i. e. a sheet of cells one cell layer thick), in which case the individual cells must undergo a change in shape. In other cases, however, a sheet that has several cell layer can thin by changes in position of its cells. In this case, epiboly occurs via intercalation, one of the other movements described on this page. Intercalation During intercalation, two or more rows of cells move between one another, creating an array of cells that is longer (in one or more dimensions) but thinner. The overall change in shape of the tissue results from cell rearrangement. Intercalation can be a powerful means of expanding a tissue sheet. A specialized form of intercalation is convergent extension, which is described on this page. Convergent Extension During convergent extension, two or more rows of cells intercalate, but the intercalation is highly directional. Cells converge by intercalating perpendicular to the axis of extension, resulting in the overall extension of the tissue in a preferred direction. If we had a way to label cells from rows on either side of the axis of extension, they would be found to mix with one another as a result of these oriented intercalation events.

Genetic basis of morphogenesis Morphogens MORPHOGENS : A morphogen is a substance whose non-uniform distribution governs the pattern of tissue development in the process of morphogenesis or pattern formation, one of the core processes of developmental biology, establishing positions of the various specialized cell types within a tissue. More specifically, a morphogen is a signaling molecule that acts directly on cells to produce specific cellular responses depending on its local concentration. Typically, morphogens are produced by source cells and diffuse through surrounding tissues in an embryo during early development, such that concentration gradients are set up. These gradients drive the process of differentiation of unspecialised stem cells into different cell types, ultimately forming all the tissues and organs of the body

Cellular basics of morphogenesis � � � � cell sorting Differential Adhesion Hypothesis Epithelial-mesenchymal transition Cell-cell adhesion Cell Adhesion Molecules (CAMs) Extracellular matrix Cell contractility