University of Utah biologists found a gene that controls rhythmicevents in a worm's life: swallowing food, laying eggs and pooping.
If the gene is disabled, the worms can't swallow, so theydie. If the gene is partly restored so the worms can swallow, they havetrouble reproducing and get constipated.
"We have found a gene that is important for the control offundamental rhythms in nematode worms," says biology professor andphysician Andres Villu Maricq, a member of the Brain Institute at theUniversity of Utah. "The same gene products that control thefundamental processes of life in mammals also are found in the worm, soour study suggests this gene and related genes may have critical rolesin controlling rhythmic behaviors in humans and other animals."
Discovery of the gene is reported in the Oct. 7, 2005,issue of the journal Cell. The study deals with seconds- to hours-longultradian rhythms that control such body functions as heart rate,breathing, swallowing and contraction of the intestines. Much less isknown about ultradian rhythms than about circadian rhythms, whichregulate the 24-hour cycle of sleeping, waking and activity, Maricqsays.
The gene that controls ultradian rhythms in worms is related toother genes that, when mutated, cause uncontrolled growth of mammaliancells – a hallmark of cancer. By learning how the gene works,researchers may learn how to interfere with it – a possible way to findnew cancer drugs
Maricq and colleagues studied Caenorhabditis elegans, amillimeter-long (one 25th of an inch) nematode worm that is found insoil, eats bacteria and frequently is used by geneticists. Theresearchers discovered a worm gene they named vav-1 – which is relatedto three similar human genes. The study showed that the gene controlledthe rhythmic contractions of smooth muscle in three parts of the worm'sbody by regularly raising and lowering calcium levels in the musclecells:
- The pharynx, which is the worm equivalent of the throat and must undergo a wave-like expansion and contraction every one or two seconds so the worm can swallow.
- The gonadal sheath, a tube-like smooth muscle structure that contracts every seven seconds during ovulation, squeezing out eggs so they can be fertilized by sperm.
- The intestines, which must pressurize and then release so the worm can defecate every 45 to 50 seconds.
When the scientists disabled the vav-1 gene, the worms could notswallow food and died before the end of the first of four larvalstages, or 10 to 12 hours into their normal two-week lifespan.
When the researchers restored the vav-1 gene just in thepharynx so worm larvae could eat, survive and grow to adulthood, theworms rarely were able to produce offspring and their 50-seconddefecation cycle became irregular, with the mean time between poopsincreasing to 195 seconds, or 3¼ minutes.
"The worm can swallow and live and grow up to be an adultwith really bad constipation," Maricq says. "Mutants sometimes have towait six to 10 minutes."
The Brain Institute "is interested in the molecular controlof behavior – how our nervous system works," Maricq says. "Vav is foundin the brain, and we now show this gene, vav-1, is of centralimportance for the control of rhythmic behaviors [in worms]."
Scientists do not know if vav genes control humanswallowing, ovulating or defecating, "but it will be an obvious avenuefor further research," he adds. "Almost all of our behaviors arerhythmic: breathing, swallowing, heartbeats and brain activity."
Maricq conducted the study with biologist Mary Beckerle,deputy director and senior director for laboratory research at theUniversity of Utah's Huntsman Cancer Institute; Kenneth Norman, apostdoctoral fellow; and Robert Fazzio and Jerry Mellem, both biologygraduate students when the study was conducted. Other coauthors areMaria Espelt and Kevin Strange at Vanderbilt University in Nashville,Tenn. The study was funded by the American Cancer Society, NationalInstitutes of Health, National Science Foundation, American HeartAssociation and the Huntsman Cancer Foundation.
The Cancer Connection
The cancer groups financed thestudy because the worm vav-1 gene is analogous to known"proto-oncogenes" in mammals – genes that are used by the body forvarious normal processes, but, when mutated, may become an oncogene, orcancer-causing gene.
Mutant vav genes have been shown to cause cancer-likechanges in cells, but it has not yet been shown they cause cancer inhumans, who have three vav genes.
"We don't know that much about what they do," except thatwhen immune cells are stimulated by bacteria or other invaders, vavgenes help increase the cells' calcium levels, which sends a wake-upsignal to the rest of the immune system, Maricq says.
Other genes and their proteins turn vav-1 on and off. Whensuch control is eliminated, vav-1 is unleashed, so cells grow out ofcontrol and may become cancerous.
Thus, vav-1 is one of the "players in the cascade of eventsthat may lead to cancer," Maricq says. "The reason you want to know theplayers is that each one represents a potential target for drugs, apotential way to stop the process."
Worms with cancer-causing vav-1 might be used to testpossible new anti-cancer drugs. If the oncogene causes a change in theworm's rhythmic behavior, then drugs that stop the behavior change alsomight work against cancer, Maricq says.
Finding the Rhythm Gene
Maricq's team discovered thevav-1 gene in worms by starting with the mammal version of the gene,then looking in the worm's genetic blueprint, for similar genes.
Next, the researchers determined where vav-1 worked bytagging it with green fluorescent protein. The pharynx, gonadal sheathand intestines glowed green.
To test what the vav-1 gene did, the researchers bred wormsthat lacked the gene. "They were born, but died soon thereafter becausethey couldn't eat," Maricq says.
The worms were not missing the mouth or other body parts,"but there was no pumping of the pharynx," he adds. As a test, thebiologists inserted the gene back into the pharynx, but not the rest ofthe worm. As a result, the worms could eat and develop to adulthood,but then developed defects in ovulating and pooping.
C. elegans worms are hermaphrodites – both male and female– and make their own sperm and eggs. Rhythmic contractions control howthe eggs are pushed down the tube-like gonadal sheath and into thespermatheca, which contains sperm.
When vav-1 is disabled, the worms "have almost no progeny,"Maricq says. "They don't have the proper synchronized ovulation. Theegg has to be timed to enter the spermatheca at the right time becausethe spermatheca is contracting. It can cut eggs up when timing is off."And without proper rhythmic contractions, eggs also may be too young ortoo old to be fertilized when they reach the spermatheca.
As part of the study, the researchers shut down variousgenes to demonstrate the chain of molecular events in which vav-1 actslike a switch to control calcium levels in cells and thus thecontractions responsible for swallowing, ovulating and defecating.
The chain begins when the vav-1 gene is used to make theprotein VAV-1. The protein activates other proteins made by what areknown as Rho/Rac genes. Then the Rho/Rac proteins turn other genes andproteins on and off.
The study found that when Rho/Rac proteins are turned on,levels of a chemical named IP3 increase in cells. IP3 attaches to"receptors" on the endoplasmic reticulum, a calcium-filled membrane baginside each cell. IP3 makes the endoplasmic reticulum release calciuminto the cell. Ups and downs in calcium levels control the rhythmiccontractions responsible for swallowing, ovulating and pooping inworms.
For more on the Brain Institute at the University of Utah, see http://brain.utah.edu
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