Do Ovaries Continue to Produce Eggs During Adulthood?

ScienceDaily (July 26, 2012) — A compelling new genetic study tracing the origins of immature egg cells, or ‘oocytes’, from the embryonic period throughout adulthood adds new information to a growing controversy. The notion of a “biological clock” in women arises from the fact that oocytes progressively decline in number as females get older, along with a decades-old dogmatic view that oocytes cannot be renewed in mammals after birth.


 

After careful assessment of data from a recent study published in PLoS Genetics, scientists from Massachusetts General Hospital and the University of Edinburgh argue that the findings support formation of new eggs during adult life; a topic that has been historically controversial and has sparked considerable debate in recent years.

Eggs are formed from progenitor germ cells that exit the mitotic cycle, thereby ending their ability to proliferate through cell division, and subsequently enter meiosis, a process unique to the formation of eggs and sperm which removes one half of the genetic material from each type of cell prior to fertilization.

While traditional thinking has held that female mammals are born with all of the eggs they will ever have, newer research has demonstrated that adult mouse and human ovaries contain a rare population of progenitor germ cells called oogonial stem cells capable of dividing and generating new oocytes. Using a powerful new genetic tool that traces the number of divisions a cell has undergone with age (its ‘depth’) Shapiro and colleagues counted the number of times progenitor germ cells divided before becoming oocytes; their study was published in PLoS Genetics in February this year.

If traditional thinking held true, all divisions would have occurred prior to birth, and thus all oocytes would exhibit the same depth regardless of age. However, the opposite was found — eggs showed a progressive increase in depth as the female mice grew older.

In their assessment of the work by Shapiro and colleagues — published recently in a PLoS Genetics Perspective article — reproductive biologists Dori Woods, Evelyn Telfer and Jonathan Tilly conclude that the most plausible explanation for these findings is that progenitor germ cells in ovaries continue to divide throughout reproductive life, resulting in production of new oocytes with greater depth as animals age.

Although these investigations were performed in mice, there is emerging evidence that oogonial stem cells are also present in the ovaries of reproductive-age women, and these cells possess the capacity, like their mouse counterparts, to generate new oocytes under certain experimental conditions. While more work is needed to settle the debate over the significance of oocyte renewal in adult mammals, Woods and colleagues emphasize that “the recent work of Shapiro and colleagues is one of the first reports to offer experimental data consistent with a role for postnatal oocyte renewal in contributing to the reserve of ovarian follicles available for use in adult females as they age.”

 

Journal Reference:

  1. Woods DC, Telfer EE, Tilly JL. Oocyte Family Trees: Old Branches or New Stems? PLOS Genet, 2012 DOI: 10.1371/journal.pgen.1002848

Citation:

Public Library of Science (2012, July 26). Do ovaries continue to produce eggs during adulthood?. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726180259.htm

One Act of Remembering Can Influence Future Acts

ScienceDaily (July 26, 2012) — Can the simple act of recognizing a face as you walk down the street change the way we think? Or can taking the time to notice something new on our way to work change what we remember about that walk? In a new study published in the journal Science, New York University researchers show that remembering something old or noticing something new can bias how you process subsequent information.


This novel finding suggests that our memory system can adaptively bias its processing towards forming new memories or retrieving old ones based on recent experiences. For example, when you walk into a restaurant or for the first time, your memory system can both encode the details of this new environment as well as allow you to remember a similar one where you recently dined with a friend. The results of this study suggest that what you did right before walking into the restaurant can determine which process is more likely to occur.

Previous scholarship has demonstrated that both encoding new memories and retrieving old ones depend on the same specific brain region — the hippocampus. However, computational models suggest that encoding and retrieval occur under incompatible network processes. In other words, how can the same part of the brain perform two tasks that are at odds with each other?

At the heart of this paradox is distinction between encoding, or forming a new memory, and memory retrieval, or recalling old information. Specifically, encoding is thought to rely on pattern separation, a process that makes overlapping, or similar, representations more distinct, whereas retrieval is thought to depend on pattern completion, a process that increases overlap by reactivating related memory traces.

With this in mind, the researchers saw a potential resolution to this neurological paradox — that the hippocampus can be biased towards either pattern completion or pattern separation, depending on the current context?

To address this question, the researchers conducted an experiment in which participants rapidly switched between encoding novel objects and retrieving recently presented ones. The researchers hypothesized that processing the novel objects would bias participants’ memory systems towards pattern separation while processing the old ones would evoke pattern completion biases.

Specifically, they were shown a series of objects that fell into three categories: novel objects (i.e., an initial presentation of an image, such as an apple or a face), repeated objects, or objects that were similar but not identical to previously presented ones (e.g., an apple with slightly different shape from the initial image). Participants were then asked to identify each as new (first presentation), old (exact repetition), or similar (not exact repetition). The similar items were the critical study items since they contained a little old and little new information. Thus, participants could either notice the novel details or incorrectly identify these stimuli as old.

The researchers found that participants’ ability to notice the new details and correctly label those stimuli as ‘similar’ depended on what they did on the previous trial. Specifically, if they encountered a new stimulus on the preceding trial, participants were more likely to notice the similar trials were similar, but not old, items.

By contrast, in another experiment, the researchers demonstrated that the same manipulation can also influence how we form new memories. In this study, the researchers tested how well participants were able to form links between overlapping memories. They found that participants were more likely to construct these links when the overlapping memories were formed immediately after retrieving an unrelated old object as compared to identifying a new one. This suggests that after processing old objects, participants were more likely to retrieve the associated memories and link them to an ongoing experience.

“We’ve all had the experience of seeing an unexpected familiar face as we walk down the street and much work has been done to understand how it is that we can come to recognize these unexpected events,” said Lila Davachi, an associate professor in NYU’s Department of Psychology and the study’s senior author. “However, what has never been appreciated is that simply seeing that face can have a substantial impact on your future state of mind and can allow you, for example, to notice the new café that just opened on the corner or the new flowers in the garden down the street.”

“We spend most of our time surrounded by familiar people, places, and objects, each of which has the potential to cue memories,” added Katherine Duncan, the study’s first author who was an NYU doctoral student at the time of the study and is now a postdoctoral researcher at Columbia University. “So why does the same building sometimes trigger nostalgic reflection but other times can be passed without notice? Our findings suggest that one factor maybe whether your memory system has recently retrieved other, even unrelated, memories or if it was engaged in laying down new ones.”

Co-author Arhanti Sadanand assisted with the research as an NYU undergraduate. She begins medical school at Virginia Commonwealth University this fall.

Link:

http://www.newswise.com/articles/one-act-of-remembering-can-influence-future-acts-nyu-researchers-find

Journal Reference:

  1. K. Duncan, A. Sadanand, L. Davachi. Memory’s Penumbra: Episodic Memory Decisions Induce Lingering Mnemonic Biases. Science, 2012; 337 (6093): 485 DOI: 10.1126/science.1221936

Citation:

New York University (2012, July 26). One act of remembering can influence future acts. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726142045.htm

Biological Mechanism for Growing Massive Animal Weapons, Ornaments Discovered

ScienceDaily (July 26, 2012) — In the animal kingdom, huge weapons such as elk antlers or ornaments like peacock feathers are sexy. Their extreme size attracts potential mates and warns away lesser rivals.


 

Now researchers led by scientists at the University of Montana and Washington State University have discovered a developmental mechanism they think may be responsible for the excessive growth of threatening horns or come-hither tail feathers. Published in the July 26 online edition of Science, the research reveals a mechanism to explain both the size of these traits, and the incredible variation among males of the same species — why some beetles, for instance, grow massive horns while their fellows grow nothing but nubbins.

“Our research explains how these enormous traits get to be so enormous,” said Doug Emlen, a professor and evolutionary biologist in UM’s Division of Biological Sciences. “People have known for 100 years that the best males produce the biggest structures, but nobody has really understood how. Our work looks under the hood to explain why so many sexually selected structures get so massive.”

The researchers discovered when they disturbed the insulin-signaling pathway in Japanese rhinoceros beetles — big insects that can grow horns two-thirds the length of their bodies — the horns were far less likely to grow. In fact, horn growth was stunted eight times as much as growth of the wings, or the rest of the body. They interpret this to mean that the exaggerated structures — the horns — are more sensitive to signaling through this physiological pathway than are other traits.

“If you have a lot of food, you have a lot of insulin,” said Laura Corley Lavine, a Washington State University entomologist and co-principle investigator with Emlen. “You respond to that by making a really giant, exaggerated horn. Then the female can tell she wants to mate with you because you are truthfully advertising your condition.”

The researchers injected a cocktail of double-stranded RNA into the beetle larvae to shut down the desired insulin pathway gene. Within 72 hours normal insulin signaling had resumed, but by then horn growth was stunted. Genitalia grew normally despite the shutdown, and the wings and bodies were slightly affected. The horns, however, experienced major changes.

The experiment confirmed what the researchers thought the insulin pathway was doing to the beetles. “We’re the first ones to make the link by explicitly tying the insulin pathway to the evolution of these kinds of male weapons,” Lavine said. “The discovery of the actual mechanism might now open new avenues of study for how exaggerated traits evolved, their genetic basis and the evolution of animal signals.”

“There is a hormone signal secreted by the brain that circulates through the whole animal,” Emlen said. “It communicates to the different cells and tissues and essentially tells them how much to grow.” Hormone levels reflect the physiological condition of each animal, with high circulating levels in well-fed, dominant individuals and lower levels in poorly fed or less-fit individuals. When tissues are sensitive to these signals, as most tissues are, their final sizes scale with the overall quality and size of the animal. Because of this mechanism, big beetles have larger eyes, legs and wings than smaller beetles.

Emlen said the horns are exquisitely sensitive to these insulin signals — more sensitive than other structures. Developing horns in big, fit, well-fed males are drenched with the hormone, spurring exaggerated horn growth. On the flip side, a small, less-fit male receive less of the horn-boosting hormone, stunting growth of its weapon.

Emlen said this process explains how horns can range from massive to nonexistent among male beetles of the same species and why the size of such exaggerated, showy traits accurately reflects the overall quality of the males who wield them. He said the results likely are applicable to other species beyond rhinoceros beetles, since additional studies have tied this same physiological pathway to growth of red deer antlers and crab pincer claws.

“Horns and antlers matter,” Emlen said. “Animals pay attention to them when they size each other up for battle. And females pay attention to horns or are attracted to males with really big tails. Why? Because only the best of the best can have really big horns or tails.”

 

Link:

http://www.eurekalert.org/pub_releases/2012-07/wsu-rdb072512.php

Journal Reference:

  1. Douglas J. Emlen,    Ian A. Warren,    Annika Johns,    Ian Dworkin,    and Laura Corley Lavine. A Mechanism of Extreme Growth and Reliable Signaling in Sexually Selected Ornaments and Weapons. Science, 26 July 2012 DOI: 10.1126/science.1224286

Citation:

Washington State University (2012, July 26). Biological mechanism for growing massive animal weapons, ornaments discovered. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726142202.htm

Connectomics: Mapping the Neural Network Governing Male Roundworm Mating

ScienceDaily (July 26, 2012) — In a study published July 26 online in Science, researchers at Albert Einstein College of Medicine of Yeshiva University have determined the complete wiring diagram for the part of the nervous system controlling mating in the male roundworm Caenorhabditis elegans, an animal model intensively studied by scientists worldwide.


 

The study represents a major contribution to the new field of connectomics — the effort to map the myriad neural connections in a brain, brain region or nervous system to find the specific nerve connections responsible for particular behaviors. A long-term goal of connectomics is to map the human “connectome” — all the nerve connections within the human brain.

Because C. elegans is such a tiny animal- adults are one millimeter long and consist of just 959 cells — its simple nervous system totaling 302 neurons make it one of the best animal models for understanding the millions-of-times-more-complex human brain.

The Einstein scientists solved the structure of the male worm’s neural mating circuits by developing software that they used to analyze serial electron micrographs that other scientists had taken of the region. They found that male mating requires 144 neurons — nearly half the worm’s total number — and their paper describes the connections between those 144 neurons and 64 muscles involving some 8,000 synapses. A synapse is the junction at which one neuron (nerve cell) passes an electrical or chemical signal to another neuron.

“Establishing the complete structure of the synaptic network governing mating behavior in the male roundworm has been highly revealing,” said Scott Emmons, Ph.D., senior author of the paper and professor in the department of genetics and in the Dominick P. Purpura Department of Neuroscience at Einstein. “We can see that the structure of this network has spatial characteristics that help explain how it exerts neural control over the multi-step decision-making process involved in mating.”

In addition to determining how the neurons and muscles are connected, Dr. Emmons and his colleagues for the first time accurately measured the weights of those connections, i.e., an estimate of the strength with which one neuron or muscle communicates with another.

The research was supported by the Medical Research Council (U.K.); the National Institute of Mental Health (R21MH63223) and the Office of Behavioral and Social Sciences Research (OD010943), both of the National Institutes of Health; and the G. Harold and Leila Y. Mathers Charitable Foundation.

Link:

http://www.einstein.yu.edu/news/releases/814/connectomics-mapping-the-neural-network-governing-male-roundworm-mating/

Journal Reference:

  1. T. A. Jarrell, Y. Wang, A. E. Bloniarz, C. A. Brittin, M. Xu, J. N. Thomson, D. G. Albertson, D. H. Hall, S. W. Emmons. The Connectome of a Decision-Making Neural Network. Science, 2012; 337 (6093): 437 DOI: 10.1126/science.1221762

Citation:

Albert Einstein College of Medicine of Yeshiva University (2012, July 26). Connectomics: Mapping the neural network governing male roundworm mating. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726142043.htm

Actinobacteria as the Base of the Evolutionary Tree

ScienceDaily (July 26, 2012) — Ever since Darwin first published The Origin of the Species, scientists have been striving to identify a last universal common ancestor of all living species. Paleontological, biochemical, and genomic studies have produced conflicting versions of the evolutionary tree. Now a team of researchers, led by a professor at the State University of New York at Buffalo and including area high school students, has developed a novel method to search the vast archives of known gene sequences to identify and compare similar proteins across the many kingdoms of life. Using the comparisons to quantify the evolutionary closeness of different species, the researchers have identified Actinobacteria, a group of single membrane bacteria that include common soil and water life forms, as the base of the evolutionary tree.


 

They will present their findings at the annual meeting of the American Crystallographic Association (ACA), held July 28 — Aug. 1 in Boston, Mass.

“Today the gene banks are enormous. They contain more than 600,000 genes from the genomes of more than 6,000 species,” says William Duax, a physical chemist and lead researcher on the team. However, many of the gene sequences, and the proteins they encode, are not systematically identified. Proteins that are structurally similar and perform the same function could be labeled with different numbers that obscure the fact that they belong to the same protein family. “Our first challenge is to make sure that we are comparing apples to apples and oranges to oranges,” says Duax.

Duax and his team have developed efficient ways to search through the gene banks looking for all copies of the same family of protein. They concentrated their efforts on proteins that are found on the surface of cell components called ribosomes. The ribosomal proteins are among the most accurately identified proteins, and because they are not transferred between individuals independent of reproduction, are good candidates for tracing the evolution of all species.

Ribosomal proteins in the same family twist into the same shape. The sequence of amino acids in a protein determines what 3D structure it folds into and Duax and his colleagues identified patterns that marked specific types of turns. They used these marker sequences to identify and almost perfectly align the proteins, similar to the way you could use five points to identify the shape of a star and align its orientation to match other star shapes.

Structurally aligning the proteins allowed the researchers to easily spot small differences that indicate organisms belong on different branches of the evolutionary tree. For example, a single amino acid difference in one ribosomal protein separates bacteria with one cell membrane from those with two.

At the ACA meeting, the researchers will present the results from the analysis of two different ribosomal protein families, called S19 and S13. Duax will present the analysis of protein S19, while high school student Alexander Merriman will present analysis of protein S13. Merriman joined Duax’s lab through a scientific mentorship program designed to give teenagers hands-on experience with cutting-edge research. “They are enthusiastic researchers and do great work,” Duax says of the students he welcomes into his lab each Friday.

Both analyses point to Actinobacteria as the last universal common ancestor. This agrees with previous work done by the group on proteins named S9 and S12. The researchers will continue to search for more evidence to add to their developing picture of the evolutionary tree. The group plans to analyze additional proteins, as well as DNA and RNA. “We are applying a systematic approach to make sense of a sometimes messy gene bank,” says Duax.

First Photo Evidence of Snub-Nosed Monkey Species in China

ScienceDaily (July 26, 2012) — Chinese researchers have published the first evidence that a population of the recently discovered snub-nosed monkey, Rhinopithecus Strykeri, live in China. Until now researchers have been unable to photograph the monkey, whose upturned nostrils are said to make it sneeze in the rain.


 

The paper is published in the American Journal of Primatology. The species was first discovered by a team led by Ngwe Lwin from the Myanmar Biodiversity and Nature Conservation Association and described by Dr Thomas Geissman in the American Journal of Primatology in October 2010. It was believed that the species was isolated to the Kachin State of north eastern Myanmar. However, this new discovery reveals the international range of this critically endangered species.

The new expedition, led by Yongcheng Long from the Nature Conservancy China Program, travelled to the Yunnan province of China after a forest guard, Liu Pu, took photos of a group of snub-nosed monkeys in a forest in near Pianma, in Yunann’s Lushui County.

“The population of this species is hard to estimate, but based on our contacts with the monkey group both in October 2011 and in March 2012 we estimate the population to be less than 100 individuals,” said Long. “However, while we now know the home range to be far greater than previously believed, we still do not yet know the true population number or the extent of their home range as the monkeys are shy and very hard to access.”

In local dialects the species is called mey nwoah, ‘monkey with an upturned face’, although it was officially named ‘Rhinopithecus Strykeri’ in honour of Jon Stryker, President and Founder of the Arcus Foundation, which supported the initial project.

Local hunters claim the monkey is easy to find when it is raining because they often get rainwater in their upturned noses causing them to sneeze. However, long term observations did not show that they spend rainy days sitting with their heads tucked between their knees as the hunters also claim.

Thomas Geissmann, who led the taxonomic description, described the monkey as having almost entirely blackish fur with white fur only on ear tufts, chin beard and perineal area. It also has a relatively long tail, approximately 140% of its body size. The new photos confirm this description.

“After the discovery of the new species of Snub-nosed Monkey in Myanmar we conducted hunter interview surveys along the Chinese-Myanmar border which suggest at least one group in contiguous forest across the border in Yunnan. I contacted Long Yongchen my friend and colleague from the IUCN primate specialist group who followed and organised the first surveys that document the presence of the Myanmar ‘snubby’ in China,” said Frank Momberg, Fauna & Flora International, Myanmar Program Director. “The discovery of Rhinepithecus strykeri in China gives a bit more hope for the species survival, however the population is still considered critically endangered, due to the high level of threats and very small population.”

With a range crossing national borders efforts to conserve this endangered species will no longer by isolated to Myanmar. The country is currently experiencing political reform, which is expected to lead to economic and industrial development, which may impact natural areas. The researchers are calling for action from China, Myanmar and the international conservation community to protect the area’s rich biodiversity.

“This monkey group was actually found in an area designated as a nature reserve 30 years ago and while local people have been hunting the species for ages, local managers knew nothing about it,” concluded Long. “This highlights the need to improve wildlife management in China, as it is likely quite a few new species of plants and animals may be discovered in the border areas between China and Myanmar.”

Link:

http://www.wiley.com/WileyCDA/PressRelease/pressReleaseId-104277.html?cid=RSS_PRESSROOM2_BREAKING_NEWS

Journal Reference:

  1. Yongcheng Long, Frank Momberg, Jian Ma, Yue Wang, Yongmei Luo, Haishu Li, Guiliang Yang, Ming Li. Rhinopithecus strykeri Found in China!. American Journal of Primatology, 2012; DOI: 10.1002/ajp.22041

Citation:

Wiley (2012, July 26). First photo evidence of snub-nosed monkey species in China. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726101715.htm

Expectations Lead to Less but More Efficient Processing in the Human Brain

ScienceDaily (July 26, 2012) — Even though we have the impression that we see the world around us as it really is, our perception is strongly influenced by our expectations. Our knowledge of the world helps us recognise objects and people quickly and accurately, even when the image we receive is noisy or unclear, such as cyclists in the park at dusk, or football players on a television set with poor reception.


Until now, knowledge of the way the brain combines prior expectations with information from the outside world has been lacking. A recent study at the Radboud University, at the Donders Institute for Brain, Cognition, and Behaviour in Nijmegen, sheds light on this process.

During the study, participants were presented with both expected and unexpected images, while their brain activity was recorded with an MRI scanner. When participants viewed expected images, regions of the brain known to be involved in visual processing were less active than when they viewed unexpected images. Surprisingly though, at the same time, these regions contained a clearer representation of the expected images than of the unexpected ones. This latter finding was established through use of a so-called brain-decoder; a computer algorithm that tried to decode which image a participant saw from their brain activity. It turned out that the brain-decoder was more successful at decoding expected than unexpected images, an indication that the activity in these brain regions contained a clearer representation for expected images.

Therefore, expectations lead to less but more efficient processing in the human brain.

Link:

http://www.ru.nl/english/general/news_agenda/news/redactionele/expectations-lead/

Journal Reference:

  1. Peter Kok, Janneke F.M. Jehee, Floris P. de Lange. Less Is More: Expectation Sharpens Representations in the Primary Visual Cortex. Neuron, 2012; 75 (2): 265 DOI: 10.1016/j.neuron.2012.04.034

Citation:

Radboud University Nijmegen (2012, July 26). Expectations lead to less but more efficient processing in the human brain. ScienceDaily. Retrieved July 28, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120726094506.htm