September 17, 2006

From Single to Multiple Cells

Human and animal egg cells are astonishingly similar to those of an amoeba. They both have a nucleus, they share all the same kinds of membranes and organelles. They both divide using the same mechanism (mitosis). The difference is that once the human egg cell starts dividing, the resulting cells stick together, and eventually start 'differentiating' - i.e. becoming different kinds of cells which results in the different types of structures and organs we can see in a human. But the question is can a single celled amoeba develop into a multicelled creature? The answer is yes, and scientists have seen it happen.

The social amoebae are exceptional in their ability to alternate between unicellular and multicellular forms. The best-studied member of this group is Dictyostelium discoideum, known as Dicty to researchers, spends most of its time living alone in the soil as a single-celled amoeba. However, in a food shortage the individual cells communicate, aggregate and then develop into a multicellular organism that produces spores, the only survivors of the time of hunger. Its development from single cell to true multicellular organism makes it valuable as a model, allowing biologists to define the ways in which cells in complex organisms develop. Cell communication is an absolute requirement for multicellular life. The genome sequence consists of 34 million base pairs - letters of genetic code - that contain the instructions for 12,500 proteins - about half as many as the human genome and more than twice as many as simple yeasts. Among these are genes involved in complex processes characteristic of multicellular life - communication, adhesion, movement - that cannot be modeled in simpler species. "The genome of Dictyostelium discoideum is one of the most distinctive analyzed so far, reflecting the intriguing biology of this organism," commented Marie-Adele Rajandream, leader of the sequencing component at the Wellcome Trust Sanger Institute. For several decades, Dictyostelium has been studied in laboratories around the world as a perfect test-bed in which to study processes such as how cells move and how individual cells specialize and coordinate to form complex organisms. The solitary amoeba shares many features with our own cells, particularly those that patrol our bodies and engulf harmful bacteria.

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