Study of planarians offers insight into germ cell development

April 24, 2007

The planarian is not as well known as other, more widely used subjects of scientific study - model creatures such as the fruit fly, nematode or mouse. But University of Illinois cell and developmental biology professor Phillip Newmark thinks it should be. As it turns out, the tiny, seemingly cross-eyed flatworm is an ideal subject for the study of germ cells, precursors of eggs and sperm in all sexually reproducing species.

The planarian Newmark studies, Schmidtea mediterranea, is a tiny creature with a lot of interesting traits. Cut it in two (lengthwise or crosswise) and each piece will regenerate a new planarian, complete with brains, guts and - in most cases - gonads. Even when the planarian's brain is severed from its body, it can regenerate all that is removed, including the reproductive organs.

In a new study published this month in the Proceedings of the National Academy of Sciences, Newmark and his colleagues at the U. of I. report that planarians share some important characteristics with mammals that may help scientists tease out the mechanisms by which germ cells are formed and maintained. Newmark's team made a few discoveries related to a gene, called nanos, which was previously known to play a critical role in germ cell development in several other model organisms.

Unlike fruit flies and nematodes, which show signs of germ cell initiation in the earliest stages of their embryonic development, planarians do not generally express nanos or produce germ cells until several days after hatching. This delayed initiation of germ cell growth is called inductive specification, and is common to mammals and a number of other animals.

Graduate student Yuying Wang and the other team members were able to show that nanos is essential for inductive specification in planarians. Blocking nanos expression by means of RNA interference immediately after the planarians hatched prevented the emergence and development of germ cells. Blocking nanos in mature adults caused their ovaries and testes to disappear. And when the researchers blocked nanos expression in planarians that had had their bodies and reproductive organs detached from their brains, the planarians regenerated new bodies, but with no reproductive cells.

"This is the first time that nanos gene function has been studied in a non-traditional model organism," Newmark said. "This is important because planarians, like mammals, seem to make their germ cells by an inductive mechanism. So we're hoping that we can use the molecular biological tools available for studying planarians to get at the mechanisms that tell a cell: 'You're going to be a germ cell.' "

S. mediterranea also has the ability to reproduce asexually: It clones itself by means of fission. In looking at nanos in asexual individuals of this species, the researchers made the surprising discovery that these asexual individuals also express nanos and produce germ cells. Some other mechanism, as yet unknown, prevents these germ cells from developing into functional testes and ovaries.

"Having a simple organism that also uses inductive signaling is going to help us tease apart the more conserved mechanisms (of germ cell development and maintenance)," Newmark said. "We hope that this information will also prove informative for understanding these processes in higher organisms."
-end-
Editor's note: To reach Phillip Newmark, call 217-244-4674; e-mail: pnewmark@uiuc.edu.

University of Illinois at Urbana-Champaign

Related Fruit Fly Articles from Brightsurf:

What can you learn by peering into a fruit fly's gut? It turns out a lot!
They say a picture is worth 1,000 words. But what about a real-time window into the complexity of the gastrointestinal system?

Study gives the green light to the fruit fly's color preference
In a study published in the journal Nature on Wednesday, University of Miami researchers made two unexpected discoveries.

Maleness-on-the-Y: A novel male sex determiner in major fruit fly pests
Becoming a male Mediterranean fruit fly relies on the newly identified Y-chromosome linked gene -- Maleness-on-the-Y (MoY) -- which encodes the small protein required to signal male sex determination during development, a new study shows.

Why so fly: MU scientists discover some fruit flies learn better than others
Fruit flies could one day provide new avenues to discover additional genes that contribute to a person's ability to learn and remember.

Fruit fly wing research reshapes understanding of how organs form
How do fruit flies grow their wings? Rutgers scientists discovered a surprising answer that could one day help diagnose and treat human genetic diseases.

Fruit fly promiscuity alters the evolutionary forces on males
Researchers in the Department of Zoology at Oxford University have demonstrated for the first time what effect female fruit flies having multiple partners has on sexual selection -- before and after mating.

Fruit fly protein could be new tool in tackling disease-carrying mosquitos
An insulin-binding protein in fruit flies could provide new opportunities for tackling disease-carrying mosquitos, such as malaria and yellow fever, scientists at the University of York have found.

Guiding flight: The fruit fly's celestial compass
Fruit flies use the sun to avoid flying in circles, according to new research.

When confronted, a single neuron helps a fruit fly change course
In the fruit fly, a single pair of brain neurons command backward locomotion in both larvae and adults, researchers report.

Fecal deposits reveal the fruit fly's pheromone flag
Fruit flies have a rich language of smell messages that they exchange, but now their secret is out.

Read More: Fruit Fly News and Fruit Fly Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.