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Aggregation of amoebae generally takes place in converging streams. The amoebae move using filose pseudopods , and are attracted to chemicals produced by other amoebae. In Dictyostelium discoideum , aggregation is signalled by cAMP , but others use different chemicals.
In D. discoideum, the amoeba secretes the signal, cAMP, out of the cell, attracting other amoebae to migrate toward the source. Every amoeba moves toward a central amoeba, the one dispensing the greatest amount of cAMP secretions. The secretion of the cAMP is then exhibited by all amoebae and is a call for them to begin aggregation.
Dictyostelium aggregations on a culture plate Dictyostelium colony in process of aggregation Pseudoplasmodium or "slug" of a Dictyostelium Single amoeboid cell of Dictyostelium, showing the contractile vacuole. Dictyostelium is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores.
During the aggregation phase of their life cycle, Dictyostelium discoideum amoebae communicate with each other using traveling waves of cyclic AMP. [51] [52] [53] There is an amplification of cyclic AMP when they aggregate. [54] Pre-stalk cells move toward cyclic AMP, but pre-spore cells ignore the signal. [55]
Clockwise from top right: Amoeba proteus, Actinophrys sol, Acanthamoeba sp., Nuclearia thermophila., Euglypha acanthophora, neutrophil ingesting bacteria. An amoeba (/ ə ˈ m iː b ə /; less commonly spelled ameba or amœba; pl.: amoebas (less commonly, amebas) or amoebae (amebae) / ə ˈ m iː b i /), [1] often called an amoeboid, is a type of cell or unicellular organism with the ability ...
Chromatoidal bodies are aggregations of ribosomes found in cysts of some amoebae including Entamoeba histolytica and Entamoeba coli. They exist in the cytoplasm and are dark staining. In the early cystic stages of E. histolytica, chromatid bodies arise from aggregation of ribosomes forming polycrystalline masses. As the cyst matures, the masses ...
Over time, an envelope of a mucus-like substance begins to surround the aggregated amoebae. [2] The amoebae at the top of the aggregation begin to project upward, and a hyaline membrane is laid down onto the projection, as development occurs. Stalk material is secreted while the amoebae move upwards within the projection.
When the amoebae are stressed, typically by a shortage of food, they form a grex. According to species and circumstances, details of the shape of the grex and how it may form will vary but typically the stressed amoebae first produce pheromones that stimulate the flock to vertically assemble in a column. When the column of aggregated cells ...