Featured Research

from universities, journals, and other organizations

Exploring how the nervous system develops

Date:
June 19, 2014
Source:
University of California - Santa Barbara
Summary:
The circuitry of the central nervous system is immensely complex and, as a result, sometimes confounding. When scientists conduct research to unravel the inner workings at a cellular level, they are sometimes surprised by what they find. The findings give scientists an idea of how individual cell types are generated, how they differentiate and how they form appropriate connections with one another.

Schematic of twelve retinal neurons quantified in the study, including the rod photoreceptor (orange), the cone photoreceptor (purple), the horizontal cell (pink), four bipolar cell types (light green) and five amacrine cell types (dark green).
Credit: Image courtesy of University of California - Santa Barbara

The circuitry of the central nervous system is immensely complex and, as a result, sometimes confounding. When scientists conduct research to unravel the inner workings at a cellular level, they are sometimes surprised by what they find.

Related Articles


Patrick Keeley, a postdoctoral scholar in Benjamin Reese's laboratory at UC Santa Barbara's Neuroscience Research Institute, had such an experience. He spent years analyzing different cell types in the retina, the light-sensitive layer of tissue lining the inner surface of the eye that mediates the first stages of visual processing. The results of his research are published today in the journal Developmental Cell.

Using a rodent model, Keeley and his colleagues quantified the number of cells present in each retina for 12 different retinal cell types across 30 genetically distinct lines of mice. For every cell type the team investigated, the researchers found a remarkable degree of variation in cell number across the strains. More surprising, the variation in the number of different cell types was largely independent of one another across the strains. This has substantial implications for retinal wiring during cellular development.

"These cells are connected to each other, and their convergence ratios are believed to underlie various aspects of visual processing," Keeley explained, "so it was expected that the numbers of these cell types might be correlated. But that was not the case at all. We found very few significant correlations and even the ones we did find were modest."

Using quantitative trait locus (QTL) analysis -- a statistical method that links two types of information, in this case cell number and genetic markers -- Keeley's team compared not only the covariance between different types of cells but also the genetic co-regulation of their number. When they mapped the variation in cell number to locations within the genome, the locations were rarely the same for different types of cells. The result was entirely unexpected.

"Current views of retinal development propose that molecular switches control the alternate fates a newborn neuron should adopt, leading one to expect negative correlations between certain cell types," said Reese, who is also a professor in UCSB's Department of Psychological and Brain Sciences. "Still others have proposed that synaptically connected nerve cells 'match' their pre- and post-synaptic numbers through a process of naturally occurring cell death, leading one to expect positive correlations between connected cell types. Neither expectation was borne out."

"If the cell types are not correlated, then some mice will have retinas with a lot of one cell type -- say, photoreceptors -- but not a lot of another cell type to connect to, in this case bipolar cells, or vice versa," Keeley added. "So how does the developing retina accommodate this variation?"

The authors posit that since the ratios of pre- to post-synaptic cell number are not precisely controlled, the rules for connecting them should offer a degree of plasticity as they wire their connections during development.

Take bipolar cells as an example. To test this assumption, the scientists looked at the morphology of their dendrites, the threadlike extensions of a neuron that gather synaptic input. Keeley and coworkers examined their size, their branching pattern and the number of contacts they formed as a function of the number of surrounding bipolar cells and the number of photoreceptors across these different strains.

"We found that the extent of dendritic growth was proportional to the local density of bipolar cells," Keeley explained. "If there are more, they grow smaller dendrites. If there are fewer, they grow larger dendrites.

"Photoreceptor number, on the other hand, had no effect upon the size of the dendritic field of the bipolar cells but determined the frequency of branching made by those very dendrites," he added. "This plasticity in neural circuit assembly ensures that the nervous system modulates its connectivity to accommodate the independent variation in cell number."

This research gives scientists an idea of how individual cell types are generated, how they differentiate and how they form appropriate connections with one another. Researchers in the Reese lab are trying to understand the genes that control these processes.

"I think that's important when we discuss cellular therapeutics such as transplanting stem cells to replace cells that are lost," Keeley said. "We're going to need this sort of fundamental knowledge about neural development to promote the differentiation and integration of transplanted stem cells. This focus on genetic and cellular mechanisms is going to be important for developing new therapies to treat developmental disorders affecting the eye."


Story Source:

The above story is based on materials provided by University of California - Santa Barbara. The original article was written by Julie Cohen. Note: Materials may be edited for content and length.


Journal Reference:

  1. PatrickW. Keeley, IreneE. Whitney, NilsR. Madsen, AceJ. St.John, Sarra Borhanian, StephanieA. Leong, RobertW. Williams, BenjaminE. Reese. Independent Genomic Control of Neuronal Number across Retinal Cell Types. Developmental Cell, 2014; DOI: 10.1016/j.devcel.2014.05.003

Cite This Page:

University of California - Santa Barbara. "Exploring how the nervous system develops." ScienceDaily. ScienceDaily, 19 June 2014. <www.sciencedaily.com/releases/2014/06/140619125539.htm>.
University of California - Santa Barbara. (2014, June 19). Exploring how the nervous system develops. ScienceDaily. Retrieved October 30, 2014 from www.sciencedaily.com/releases/2014/06/140619125539.htm
University of California - Santa Barbara. "Exploring how the nervous system develops." ScienceDaily. www.sciencedaily.com/releases/2014/06/140619125539.htm (accessed October 30, 2014).

Share This



More Health & Medicine News

Thursday, October 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Fauci Says Ebola Risk in US "essentially Zero"

Fauci Says Ebola Risk in US "essentially Zero"

AP (Oct. 30, 2014) NIAID Director Anthony Fauci said the risk of Ebola becoming an epidemic in the U.S. is essentially zero Thursday at the Washington Ideas Forum. He also said an Ebola vaccine will be tested in West Africa in the next few months. (Oct. 30) Video provided by AP
Powered by NewsLook.com
Nurse Defies Ebola Quarantine With Bike Ride

Nurse Defies Ebola Quarantine With Bike Ride

AP (Oct. 30, 2014) A nurse who vowed to defy Maine's voluntary quarantine for health care workers who treated Ebola patients followed through on her promise Thursday, leaving her home for an hour-long bike ride. (Oct. 30) Video provided by AP
Powered by NewsLook.com
Microsoft Launches Fitness Band After Accidental Reveal

Microsoft Launches Fitness Band After Accidental Reveal

Newsy (Oct. 30, 2014) Microsoft accidentally revealed its upcoming fitness band on Wednesday, so the company went ahead and announced it. Video provided by Newsy
Powered by NewsLook.com
Studying Effects of Music on Dementia Patients

Studying Effects of Music on Dementia Patients

AP (Oct. 30, 2014) The University of Wisconsin-Milwaukee is studying the popular Music and Memory program to see if music, which helps improve the mood of Alzheimer's patients, can also reduce the use of prescription drugs for those suffering from dementia. (Oct. 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins