Development of Dicty ostelium discoid eum (cellular slime mold) Biology 4361 September 13, 2007Cellular Slime Molds Fuligo septica G. Zabka Physarum polycephalum G. ZabkaDictyostelium discoideumDictyostelium discoideum Life CycleQuestions How do myxamoebae find each other? (How do cells communicate?) How do cells in the pseudoplasmodium decide whether they are prestalk or prespore cells? (differentiation, morphogenesis, organogenesis) What take place in the cells to change them into stalk and spore cells? (differentiation, reproduction) How do the myxamoebae move? (gastrulation, morphogenesis) How do the prestalk and prespore know where to go when forming fruiting body? (gastrulation, morphogenesis) These types of questions can be asked during the development of virtually all multicellular organisms. What signals trigger the switch from myxamoebae to pseudoplasmodium? (What controls growth?)Chemotaxis (Intercellular Signaling) ATP cAMP PPi Chemotactic signal: cyclic adenosine 3’,5’monophosphate (cAMP) 1) Myxamoebae secrete cAMP. 3) Later (~3 min), the receiving myxamoebae secrete cAMP of their own. Chemot axis – movement induced by a chemical myxamoebae move in response to a chemical signal sent by other myxamoebae! 4) This process results in movement of myxamoebae towards a central location. But… 2) Other myxamoebae receive cAMP signal with specific receptors and move toward the cAMP source. cAMP stimulates organization of actin filaments in the membrane cortex….with all myxamoebae secreting and receiving cAMP, how do the know which way to travel? Chemotaxis 2 Required: a mechanism to reset the system cAMP AMP phosphodiesterase 5) Phosphodiesterase breaks down cAMP shuts down chemotaxis. clears receptors for next round of binding, movement, and cAMP productionDictyostelium Motility actin red myosin green overlap yellow Myosin (motor protein) uses actin microfilaments to move cells. polymerization establishes polarity of microfilaments (i.e. defines anterior and posterior) cAMP stimulates polymerization of globular (g)actin to filamentous (f)actin (microfilaments)Regulation Anterior cells are destined to become stalk. Posterior cells are destined to become spores. However, cut the slug in half… both halves form stalks and spores Therefore, identities of stalk and spore cells must be somewhat flexible! Regulation: the ability of cells to change their developmental fates according to their location. This gives the developing organism the ability to compensate for environmentally induced changes in structure. Also, it implies that cells must “sense” their position within the organism.Cell Adhesion in Dictyostelium gp24 gp80 gp150 starvation +10 h streaming amoebae migrating pseudoplasmodium Active mitoticallydividing cells can’t stick to each other. Migrating pseudoplasmodium cells must stick to each other. Stalk prespore cells have to slide over one another. gp = glycoproteins developmentallyregulated adhesion
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