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Researchers have found the relations between genetic differences and left handedness

Researchers have found the relationship between genetic differences and left-handedness

Scientists for the first time have been able to identify the specific gene regions which have an influence on being left-handed. They have also found connections to differences in the structure of the brain in those having these variations.

It has been established before that being left or right-handed has an approximate dependence of 25 percent on the genetic code at birth. However, until now, researchers have not been able to locate the specific areas of the genome that are responsible.

The latest study involved nearly 400,000 individual records in a national database of the United Kingdom. Four genetic regions were found that were associated with handedness out of which three were linked to the proteins in the development and structure of the brain. These proteins are related to the cytoskeleton which is responsible for the construction and functionality of the cells. The study appears in the Brain Journal.

Brain scans were performed on 10,000 participants through which researchers were able to link the variations in the genetic code with white matter tracts between the language-processing regions. The cytoskeleton of the brain is present in the white matter tracts. Akira Wiberg, physician said that the large datasets from the UK Biobank helped in a deep understanding of the processes responsible for left-handedness. The language areas in the left and right sides of the brain coordinate with each other in a coordinated manner for participants with left-handedness. This might translate to left-handers having better language and verbal skills.

Human beings have an imbalance between the left-handed and right-handed individuals which is a ratio of 1:9. Cytoskeletal differences like a coil of a snail’s shell can be highly influenced by genetics. Hence scientists think the indications of the development of handedness might be initiated in the mother’s womb.

We are still at an early stage of the research to say conclusively that handedness and genes are related however this research has provided significant associations between the two instances. Scientists are now starting to understand how a dominant hand is influenced by genetic coding. This also helps in preventing any misconceptions that left-handedness is a sign of being unlucky or that being a right-handed individual is somehow superior.

Dominic Furniss, a plastic surgeon researching in molecular genetics said that through this study it has been demonstrated that left-handedness is a result of the brain’s developmental biology which is also influenced by the complex genetic interplay.

Journal Reference: Brain

A comprehensive catalogue of human digestive tract bacteria

A comprehensive catalogue of human digestive tract bacteria

The human digestive tract is home to thousands of different strains of bacteria. Many of these are beneficial, while others contribute to health problems such as inflammatory bowel disease. Researchers from MIT and the Broad Institute have now isolated and preserved samples of nearly 8,000 of these strains, while also clarifying their genetic and metabolic context.

This data set (BIO-ML), which is available to other researchers who want to use it, should help to shed light on the dynamics of microbial populations in the human gut and may help scientists develop new treatments for a variety of diseases, says Eric Alm, director of MIT’s Center for Microbiome Informatics and Therapeutics and a professor of biological engineering and of civil and environmental engineering at MIT.

“There’s a lot of excitement in the microbiome field because there are associations between these bacteria and health and disease. But we’re lacking in being able to understand why that is, what’s the mechanism, and what are the functions of those bacteria that are causing them to associate with disease,” says Alm, who is the senior author of the study.

The researchers collected stool samples from about 90 people, for up to two years, allowing them to gain insight into how microbial populations change over time within individuals. This study focused on people living in the Boston area, but the research team is now gathering a larger diversity of samples from around the globe, in hopes of preserving microbial strains not found in people living in industrialized societies.

“More than ever before, modern techniques allow us to isolate previously uncultured human gut bacteria. Exploring this genetic and functional diversity is fascinating — everywhere we look, we discover new things. I’m convinced that enriching biobanks with a large diversity of strains from individuals living diverse lifestyles is essential for future advancements in human microbiome research,” says Mathilde Poyet, a senior postdoc at MIT and one of the lead authors of the study.

MIT research associate Mathieu Groussin and former postdoc Sean Gibbons are also lead authors of the study, which appears in the Sept. 2 issue of Nature Medicine. Ramnik Xavier, a professor of medicine at Harvard Medical School and member of the Broad Institute, is a senior author of the study along with Alm.

Microbiome dynamics

Humans have trillions of bacterial cells in their digestive tracts, and while scientists believe that these populations change and evolve over time, there has been little opportunity to observe this. Through the OpenBiome organization, which collects stool samples for research and therapeutic purposes, Alm and his colleagues at MIT and the Broad Institute had access to fecal samples from about 90 people.

For most of their analysis, the researchers focused on microbes found in about a dozen individuals who had provided samples over an extended period, up to two years.

“That was a unique opportunity, and we thought that would be a great set of individuals to really try to dig down and characterize the microbial populations more thoroughly,” Alm says. “To date there hadn’t been a ton of longitudinal studies, and we wanted to make that a key focus of our study, so we could understand what the variation is day-to-day.”

The researchers were able to isolate a total of 7,758 strains from the six major phyla of bacteria that dominate the human GI tract. For 3,632 of these strains, the researchers sequenced their full genomes, and they also sequenced partial genomes of the remaining strains.

Analyzing how microbial populations changed over time within single hosts allowed the researchers to discover some novel interactions between strains. In one case, the researchers found three related strains of Bacteroides vulgatus coexisting within a host, all of which appeared to have diverged from one ancestor strain within the host. In another case, one strain of Turicibacter sanguinis completely replaced a related strain of the same species nearly overnight.

“This is the first time we’re getting a glimpse of these really different dynamics,” Alm says.

Population variation

The researchers also measured the quantities of many metabolites found in the stool samples. This analysis revealed that variations in amino acid levels were closely linked with changes in microbial populations over time within a single person. However, differences between the composition of microbial populations in different people were more closely associated with varying levels of bile acids, which help with digestion.

The researchers don’t know exactly what produces these differences in amino acid and bile acid levels, but say they could be influenced by diet — a connection that they hope to investigate in future studies. They have also made all of their data available online and are offering samples of the strains of bacteria they isolated, allowing other scientists to study the functions of these strains and their potential roles in human health.

“Comprehensive and high-resolution collections of bacterial isolates open the possibility to mechanistically investigate how our lifestyle shapes our gut microbiome, metabolism, and inflammation. We aim to provide such a resource to the research community worldwide, including to lower-income research institutions,” Groussin says.

The researchers have also begun a larger-scale project to collect microbiome samples from a greater diversity of populations around the world. They are especially focusing on underrepresented populations who live in nonindustrialized societies, as their diet and microbiomes are expected to be very different from those of people living in industrialized societies.

“It may be that as populations that have been living traditional lifestyles start to switch to a more industrialized lifestyle, they may lose a lot of that biodiversity. So one of the main things we want to do is conserve it, and then later we can go back and characterize it as well,” Alm says.

Materials provided by Massachusetts Institute of Technology

Skeletons in Roopkund Lake

DNA analysis of the Roopkund skeletons makes its mystery even more complex

Roopkund lake amidst the Himalayan mountains has been a place of mystery. It is a shallow lake which is filled with the bones of human beings, due to which it is also known as Skeleton Lake and the reason behind the presence of skeletons is not yet known. 

One hypothesis is that a large number of people died due to a single catastrophe. However, this idea is now challenged by DNA analysis of 38 skeletons present there. It reveals that different groups of people from distant places such as the Mediterranean came to the lake over a period of 1000 years. The paper appears in the journal Nature Communications

David Reich, a geneticist from Harvard Medical School said that biomolecular analysis including radiocarbon dating and stable isotope dietary reconstruction reveals the history of the lake to be more complex than imagined. Geneticist Kumarasamy Thangaraj, CSIR Centre for Cellular and Molecular Biology sequenced mitochondrial DNA of 72 skeletons a decade ago. Some skeletons had DNA of a local Indian origin however several appeared to have come from West Eurasia. This led to a deeper analysis of genome sequencing in which genome-wide DNA was produced for 38 persons. These were compared against 1521 ancient and 7985 current persons from all over the world. 23 persons had similar DNA to that of people from India however 14 persons had similar DNA to that of residents in current Greece and Crete. And one person had DNA from Southeast Asian origin. 

Eadaoin Harney, Harvard University said that scientists are highly surprised by this variation in the genetics of the skeletons. That the DNAs of the skeletons reveal similarities with the eastern Mediterranean suggests that the Lake attracted visitors from all over the world. Isotope analysis supports these findings. Some stable isotopes can be absorbed in plants which are then eaten by people. These replace some calcium in bones and teeth which can be matched suitably to specific locations. 

Ayushi Nayak, archaeologist of Max Planck Institute for Science of Human History said that persons with Indian origins had a diet mainly depending on C3 and C4 derived food sources. It is consistent with the genetic evidence that they belonged to several socioeconomic groups in South Asia. However, people connected to the eastern Mediterranean had a diet with a lesser amount of millet. 

What is even more mind-boggling is the time of arrival of these groups. Radiocarbon dating estimates that the bones related to Indian ancestry came between the 7th and 10th centuries and those from the Mediterranean and Southeast Asia were dated between the 17th and 20th centuries. It is very much possible that skeletons not tested could belong to other regions from different time periods.

We still do not know how these persons came to the Lake and what is the cause of their death. Scientists have to dig deeper to find the answers. 

Journal Reference: Nature Communications