Want to see multicellular life emerge from unicellular life before your eyes?
First, let’s begin with some background information that will help you understand what you are about to see:
The dictyostelids are a group of cellular slime molds, or social amoebae. When food, normally bacteria, is readily available they are individual amoebae, which feed and divide normally. However when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium or slug (not to be confused with the gastropod mollusc called a slug). The slug has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate. Under the correct circumstances the slug matures forming a fruiting body with a stalk supporting one or more balls of spores. These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available.
Okay, so let’s look at some videos of this.
The first video is described as follows: A starved cell population of ~120 Dictyostelium cells develops on agar to form a slime mold and eventually a fruiting body (latter not shown). Fluorescence microscopy is used to visualize a ubiquitously expressed GFP-fusion protein. The movie shows how the cells aggregate via chemotaxis.
This video represents about 8 hours in real time:
Next, let’s watch the slug form and crawl away. Here’s the description: A starved cell population of ~10000 Dictyostelium cells develops on agar in a 1mm wide hole to form a slime mold (and eventually a fruiting body, not shown). Fluorescence microscopy is used to visualize a ubiquitously expressed RFP-fusion protein. The movie shows how cells aggregate via chemotaxis….The 15 second movie is roughly 5 hours in real time.
Finally, let’s see the waves of cAMP that precede the formation of the multicellular slugs. This one is described as follows: A lawn of starved Dictyostelium cells is imaged using phase contrast microscopy. Cells signal via spiral waves of cAMP, and population territories form with a fruiting body in the center of each. To visualize the spirals, use has been made of the fact that when the cells experience a high concentration of cAMP surrounding them, they elongate (called polarization). When that happens the optical density of the cells changes which can be captured by the specific type of microscopy used.