Crystal Jellies

The write-up

A nearly invisible jelly whose glow lit up biology. Aequorin makes blue light; GFP turns it green.

1. Exhibit A

   Not a true jelly

   The crystal jelly is a hydrozoan. Its free-swimming stage is a hydromedusa, which buds off a tiny polyp. Most hydromedusae are under about 1 cm across, but this one is unusually large.

2. Exhibit B

   Range and size

   It is found from the Bering Sea to Baja California and in the Gulf of California, mostly in nearshore waters and large bays. Reported adult bell diameters vary by source: 8 to 25 cm in the Scripps guide, and up to 16 inches at the Oregon Coast Aquarium.

3. Exhibit C

   Body plan

   It is almost entirely transparent. Up to about 100 radial canals run to the bell margin, which carries up to about 150 tentacles in fully grown specimens. The light comes from more than 100 tiny organs along the bell's edge.

4. Exhibit D

   Blue to green

   In 1962 Shimomura and colleagues reported aequorin, a protein that gives off blue light when it binds calcium. They also reported a separate green-fluorescent protein. GFP produces no light on its own. It takes energy from aequorin and re-emits it as green light peaking near 510 nm, which is why the jelly's glow looks green.

5. Exhibit E

   From jelly to Nobel

   The specimens were collected at Friday Harbor, Washington. GFP's gene was sequenced in 1992 (238 amino acids), and the protein became a widely used marker in cell biology. Shimomura, Martin Chalfie and Roger Tsien shared the 2008 Nobel Prize in Chemistry for its discovery and development.