Concept

Dictyostelid

Summary
The dictyostelids (Dictyostelia/Dictyostelea, ICZN, or Dictyosteliomycetes, ICBN) are a group of cellular slime molds, or social amoebae. When food (normally bacteria) is readily available dictyostelids behave as individual amoebae, which feed and divide normally. However, when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium, grex, or slug (not to be confused with the gastropod mollusc called a slug). The grex has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate. Under the correct circumstances the grex matures forming a sorocarp (fruiting body) with a stalk supporting one or more sori (balls of spores). These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available. In Acytostelium, the sorocarp is supported by a stalk composed of cellulose, but in other dictyostelids the stalk is composed of cells, sometimes taking up the majority of the original amoebae. With a few exceptions, these cells die during stalk formation, and there is a definite correspondence between parts of the grex and parts of the fruiting body. 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 the species Dictyostelium purpureum, the grouping is by kinship, not just by proximity. Dictyostelium has been used as a model organism in molecular biology and genetics, and is studied as an example of cell communication, differentiation, and programmed cell death. It is also an interesting example of the evolution of cooperation and cheating. A large body of research data concerning D. discoideum is available on-line at DictyBase. The mechanism behind the aggregation of the amoebae relies on cyclic adenosine monophosphate (cAMP) as a signal molecule.
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Related concepts (7)
Dictyostelium discoideum
Dictyostelium discoideum is a species of soil-dwelling amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, D. discoideum is a eukaryote that transitions from a collection of unicellular amoebae into a multicellular slug and then into a fruiting body within its lifetime. Its unique asexual life cycle consists of four stages: vegetative, aggregation, migration, and culmination. The life cycle of D. discoideum is relatively short, which allows for timely viewing of all stages.
Amoeba
An amoeba (əˈmiːbə; less commonly spelled ameba or amœba; : am(o)ebas or am(o)ebae əˈmiːbi), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, and animals.
Mycetozoa
Mycetozoa is a polyphyletic grouping of slime molds. It was originally thought to be a monophyletic clade, but recently it was discovered that protostelia are a polyphyletic group within Conosa. It can be divided into dictyostelid, myxogastrid, and protostelid groups. The mycetozoan groups all fit into the unikont supergroup Amoebozoa, whereas most other slime molds fit into various bikont groups (fonticulids are opisthokonts). The dictyostelids are used as examples of cell communication and differentiation, and may provide insights into how multicellular organisms develop.
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