REFERENCE ABSTRACT

TITLE: Jellyfish's glow reveals head's beginnings
AUTHOR: Elizabeth Pennisi
JOURNAL: SCIENCE NEWS, 145(23), 6/4/94
ABSTRACT: A fluorescing protein from the jellyfish, produced by a gene known as GFP, has been used as an excellent biological tracer allowing biologic processes to be easily visualized. When this GFP gene was joined to the fruit fly gene for "exu", scientists were able to examine the role of exu in fruit fly egg development. Every molecule of exu was "tagged" with a fluorescent protein.

We know that, in cells, DNA passes the instructions for protein manufacture to RNA, which then leaves the cell nucleus and carries those instructions to the ribosomes, the actual protein factories. Fruit flies add an interesting twist to this process. In the egg chambers of fruit flies, RNA also moves from special cells ("nurse cells") to the maturing egg, traveling through cytoplasmic pathways called ring canals. Once in the egg, these RNA molecules are briefly stored, until the embryo begins to develop. Then, those RNA segments become active and direct the manufacture of a protein called bicoid. A high concentration of bicoid in one part of the embryo activates genes that control development of the head and thorax.

These RNA molecules need the help of a protein called exuperantia (exu) to get to where they need to go in the necessary quantities. Without exu, the RNA diffuses evenly through the egg and the embryo may not develop a head or thorax. For this experiment, researchers joined the jellyfish GFP gene to the fruit fly gene that codes for exu. This hybrid gene combination was then inserted into mutant fruit fly germ (reproductive) cells that lacked the exu gene. With this new gene, the germ cells developed nurse cells and egg cells. The exu made by the nurse cells remained "tagged" with the fluorescent GFP gene. By "lighting up" the exu protein in this way, scientists could visually track exu's progress through molecular interactions and therefore determine its role in the development of embryonic fruit flies. The traditional method of "marking" molecules involves the use of targeted antibodies. But antibodies sometimes miss their targets or show up where no target exists. Also, to use labeled antibodies, scientists must kill the cell being studied. With GFP, we can study living cells. GFP may be superior to luciferase, the firefly bioluminescent protein, because it needs no helper enzymes to cause it to fluoresce.

KEY WORDS/PHRASES
Bicoid
Exuperantia (exu)
Fluorescing protein
GFP gene
Luciferase
Nurse cells
Ring canals
Targeted antibodies