Navigation Links
Chemical signaling helps regulate sensory map formation in the brain

Researchers from the University of Chicago have uncovered an important mechanism used by the developing brain to pattern nerve connections in the part of the brain that interprets visual signals. In the process, they have provided the first experimental evidence for a decades-old model of how nerve cells establish distant connections in a way that can consistently relay spatial information.

In the January 5, 2006, issue of the journal Nature, the researchers show that a gradient of a molecule known as Wnt3 counterbalances another force provided by the EphrinB1-EphB signaling system. The balance between these two signaling systems, they show, is necessary to establish the carefully controlled pattern of nerve connections required to convey spatial information in the correct order from the eye to the brain.

"This is the first biological validation of a computational model developed in the early 1980s that suggested that two such forces would be necessary to guide axons as they establish the connections that relay spatial information from one part of the nervous system to another," said study author Yimin Zou, Ph.D., assistant professor of neurobiology at the University of Chicago.

Neurobiologists refer to this type of neuronal connection ?in which the spatial order of neurons of one part of the nervous system is "copied" onto another -- as "topographic mapping." The term describes the creation of a coordinated connection that allows positional information from a grid of sensors, in this case the light-sensitive cells in the retina, to be smoothly and systematically transferred to their target, the structures in the brain that interpret information from the eyes.

"Without an orderly and faithful connection," said Zou, "information from the eyes could not be properly deciphered by the brain."

"Topographic maps are a very common wiring strategy in our brains," he said. Similar systems are thought to regulate other sensory system s -- such as hearing and touch, as well as motor systems -- but the visual system has been the predominant model system for studying the development of such maps and the gradients of guidance molecules that control their formation.

Scientists have searched for these gradients, the global positioning system of the brain, for more than forty years.

In 1963, neurobiologist Roger Sperry (who won the Nobel Prize in 1981) proposed the "chemoaffinity hypothesis." Sperry suggested that chemical signals, probably present in concentration gradients, serve as positional landmarks within the brain. Theses landmarks are then recognized by growth cones at the tip of axons ?the projections that grow out from the retinal neurons and into the brain. The wandering axons use these signals to locate their destinations in the map.

Twenty years later, in 1983, Alfred Gierer developed computational models of this process. His models indicated that at least two counterbalancing signaling systems were required to push and pull the growing and branching axons as they searched for their ultimate topographic positions within the brain.

In the 1990s, scientists found the first of those signaling systems, a family of ephrin proteins that are present in graded fashion in the brain and are involved in axon guidance. The A-class ephrins are required for map formation along the anterior-posterior (front-to-back) axis and the B-class for medial-lateral (side-to-side) axis.

For several years, Zou's lab has been studying a different family of proteins, known at the Wnts. Although Wnts were better known because of their role as morphogens -- proteins that pattern bodily structures and determine cell fates -- Zou recently showed how members of the Wnt family served to guide pathfinding axons up and down the spinal cord by attracting or repelling receptors on the growth cones of sensory or motor nerves.

In this paper, Zou and colleagues reveal a new ro le for Wnts. They show that a gradient of Wnt3 along the medial-lateral axis within the developing brain is the opposing regulating force, working along with ephrinB1 to specify the topographic target selection in the optic tectum, a brain region that processes information from the eye.

At the molecular-signaling level, Wnt3 acts through two different classes of growth-cone receptors, Ryk and the Frizzled(s), to pattern topographic connections in the brain. Disrupting either the Wnt or ephrin pathway throws the growing axons off their targets, shifting the map from side to side.

This counterbalancing force has two components, Zou's team discovered, with one receptor drawn toward certain concentrations of Wnt3 and the other driven away. "A repulsive Wnt-Ryk pathway competes with an attractive Wnt-Frizzled interaction," the authors write, "to titrate the response to Wnt3 protein at different concentrations." The net outcome of the competition, they conclude, "determines the topographic connections by providing a lateral directed mapping force."


'"/>

Source:University of Chicago Medical Center


Related biology news :

1. Chemicals in tattoo inks need closer scrutiny
2. Roots Engage in Underground Chemical Warfare
3. Chemical Engineer Kao Explores Antibiotic Synthesis With DNA Chips
4. Chemical band-aid prevents heart failure in mice with muscular dystrophy
5. Chemical compound inhibits tumor growth, size in new mouse study
6. T-rays: New imaging technology spotlighted by American Chemical Society
7. Chemical warfare agent detection technology used to treat lung disease
8. Chemical guidance of T cells leads to immunologic memory and long-term immunity
9. Chemical in many air fresheners may reduce lung function
10. Chemical tests of cell growth enter third dimension
11. Chemicals in brown algae may protect against skin cancer
Post Your Comments:
*Name:
*Comment:
*Email:


(Date:4/19/2016)... April 20, 2016 The new ... a compact web-based "all-in-one" system solution for all door ... reader or the door interface with integration authorization management ... control systems. The minimal dimensions of the access control ... the building installations offer considerable freedom of design with ...
(Date:3/31/2016)... , March 31, 2016 ... ) ("LegacyXChange" or the "Company") LegacyXChange is ... users of its soon to be launched online site ... https://www.youtube.com/channel/UCyTLBzmZogV1y2D6bDkBX5g ) will also provide potential shareholders ... of DNA technology to an industry that is notorious ...
(Date:3/22/2016)... and SANDY, Utah , ... which operates the highest sample volume laboratory in ... Genomics and UNIConnect, leaders in clinical sequencing informatics and ... launch of a project to establish the informatics infrastructure ... NSO has been contracted by the Ontario ...
Breaking Biology News(10 mins):
(Date:5/25/2016)... ... 2016 , ... The Ankle Plating System 3 and Small ... fractures of the distal tibia and fibula. This system marks Acumed's continued commitment ... is composed of seven plate families that span the lateral, medial, and posterior ...
(Date:5/25/2016)... ... May 25, 2016 , ... ... (RFI) issued by the Office of the National Coordinator for Health IT (ONC) ... determines if clinically relevant data were available when and where it was needed. ...
(Date:5/25/2016)... CITY, UTAH. (PRWEB) , ... May 25, 2016 , ... ... in healthcare information exchange, today announced that Charles W. Stellar has been named by ... WEDI’s interim CEO since January 2016. As an executive leader with more than 35 ...
(Date:5/25/2016)... ... May 25, 2016 , ... ... Drug Administration (FDA) has granted the company’s orphan drug designation request covering BHV-4157 ... drug designation granted by the FDA. , Spinocerebellar ataxia is a rare, ...
Breaking Biology Technology: