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Structure and Function of Neuropeptides in Flatworms
Only 20 years ago, David Price and Mike Greenberg discovered that a small peptide, Phe-Met-Arg-Phe-amide (FMRFamide) was acting as cardioexcitatory transmitter in clams. Since then, FMRFamide and FMRFamide-related peptides have been found to be fundamental in the biology of early invertebrates, including the both major types of parasitc worms.
We want to understand the role that small neuropeptides play as neurotransmitters in these worms. We have found that FMRFamide-related peptides potently myoexcitatory in flatworms, eliciting contractions of individual muscle fibers and muscle strip preparations.
In addition to FMRFamide-related peptides, we know that flatworms possess a peptide that is an ancestor of the vertebrate neuropeptide Y family. The flatworm homologue is a 36-39 amino acid called neuropeptide F, and it is the most abundant peptide in every flatworm that has been examined. The role of this abundant neuropeptide of flatworms remains unknown.
(Left) Image of a schistosome. The red staining is immunoreactivity to a flatworm neuropeptide, and the green staining is actin in muscle. The red mass is the clump of neurons in the head region of the worm--it is a brain! (Right) Aaron Maule of the Queen's University of Belfast produced this amazing schistosome image. Here, Aaron stands with Tim near the 18th green at Pebble Beach. Tim typically beats Aaron in golf and indulges in wild celebrations on the 17th green, often stepping in the line in which Aaron must putt.
The role of neuropeptides in flatworms is the pimary focus of our laboratory work. As such, there are a broad range of ongoing and planned projects. Alomst all of our work on neuropeptides in flatworms is done in collaboration with Aaron Maule's laboratory at the Queen's University of Belfast. Here are a few of the ongoing projects.
- Structural characterization of neuropeptides in schistosomes
For over two years, our lab tried to determine the structure of neuropeptides in schistosomes--particularly have been interested in one known as Neuropeptide F. Finally, we figured it out (but, we can't tell you yet). We still want to know the FMRFamide-related peptides that are present.
Judith is laughing, because she finally knows the primary structure of schistosome Neuropeptide F! Jessie is laughing because she thinks it is weird that Judith cares so much about Neuropeptide F. - Molecular cloning and characterization of neuropeptide receptors in schistosomes and other flatworms
These efforts are ongoing in schistosomes and a number of other free-living flatworms. Cloning the FMRFamide-related peptide receptors is going to be a very difficult task, because there is very little information to start with--there are only two examples of cloned FMRFamide-related peptide receptors from any animals.
On the other hand, we have made great progress towards characterization of neuropeptide F receptors using molecular approaches based on receptor homology. Judith has a full open reading frame for at least one G-protein coupled receptor from schistosomes that looks like a neuropeptide receptor. We are presently expressing that receptor in mammalian cells to define its activity.
- Peptide-induced currents in flatworm muscle
Although we know that flatworm FMRFamide-related peptides have dramatic effects on flatworm muscle, almost nothing is known about how those effects are mediated. We are characterizing the effects of flatworm peptides on the whole cell currents in flatworm muscle fibers.
- The role of proteases inactivating myoexcitatory FMRFamide-related peptides
A major project in our lab is focused on the role that proteases play in the termination of peptidergic signaling in early animals. In other animals, termination of peptide transmitter signaling occurs by protease-mediated degradation of the transmitter. Peptide transmitters are metabolized by proteases most often located on the cell surface in a manner very similar to the degradation of acetylcholine by the cell-surface hydrolase acetylcholinesterase. We have evidence that the excitatory action of FMRFamide-related peptides on flatworm muscle is limited by protease mediated degradation.
