Spin This News: Parental Chromosomes Develop Apart During Embryo's First Division

       Genetic researchers at the European Molecular Biology Lab (EMDL) have shown that mammalian life begins differently than originally suspected.

     It was long hypothesized that during a mammal embryo's first cell division, one spindle is responsible for segregating the embryo's chromosomes into two cells. Researchers now show that there are actually two spindles (as shown below), one for each set of parental chromosomes, meaning that the genetic information from each parent is kept apart throughout the first division.

     The publication Science published the results (which are likely to change biology textbooks) on 7/12/18. {Are there still textbooks?!}.

     This dual spindle formation may explain the high error rate in the early developmental stages of mammals, spanning the first few cell divisions. "The aim of this project was to find out why so many mistakes happen in those first divisions," says Dr. Jan (a guy!) Ellenberg, the group leader at EMBL who led the project. "We already knew about dual spindle formation in simpler organisms like insects, but we never thought (why not?!) this would be the case in mammals like mice. This finding was a big surprise, showing that you should always be prepared for the unexpected."

     Researchers have heretofore seen parental chromosomes occupying two half-moon-shaped parts in the nucleus of two-cell embryos, but it wasn't clear how this could be explained. "First, we were looking at the motion of parental chromosomes only, and we couldn't make sense of the cause of the separation," said Dr. Judith Reichmann. "Only when focusing on the microtubules -- the dynamic structures that spindles are made of -- could we see the dual spindles for the first time. This allowed us to provide an explanation for this 20-year-old mystery."

      Mitosis is the process of cell division, when one cell splits into two daughter cells. It occurs throughout the lifespan of multi-cellular organisms but is particularly important when the organism grows and develops. The key step of mitosis is to pass an identical copy of the genome to the next cell generation. For this to happen, DNA is duplicated and organised into dense thread-like structures known as chromosomes. The chromosomes are then attached to long protein fibres -- organised into a spindle -- which pulls the chromosomes apart and triggers the formation of two new cells. {The following diagram is one which will likely be updated in future embryology textbooks.}

     The spindle is made of thin, tube-like protein assemblies known as microtubules. During mitosis of animal cells, groups of such tubes grow dynamically and self-organize into a bi-polar spindle that surrounds the chromosomes. The microtubule fibres grow towards the chromosomes and connect with them, in preparation for chromosome separation to the daughter cells. Normally there is only one bi-polar spindle per cell, however, this research suggests that during the first cell division there are two: one each for the maternal and paternal chromosomes.

     "The dual spindles provide a previously unknown mechanism -- and thus a possible explanation -- for the common mistakes we see in the first divisions of mammalian embryos," Dr. Ellenberg explains. Such mistakes can result in cells with multiple nuclei, terminating development. "Now, we have a new mechanism to go after and identify new molecular targets. It will be important to find out if it works the same in humans, because that could provide valuable information for research on how to improve human infertility treatment, for example."

      In addition, the knowledge from this paper might impact legislation. In some countries, the law states that human life begins -- and is thus protected -- when the maternal and paternal nuclei fuse after fertilization. If it turns out that the dual spindle process works the same in humans, this definition is not fully accurate, as the union in one nucleus happens slightly later, after the first cell division.

     This discovery would have been impossible without the light-sheet microscopy technology (as seen above) developed at EMBL, which is now available through the spin-off company Luxendo. This allows for real-time and 3D imaging of the early stages of development, when embryos are very sensitive to light and would be damaged by conventional light microscopy methods. The high speed and spatial precision of light-sheet microscopy drastically reduce the amount of light that the embryo is exposed to, making a detailed analysis of these formerly hidden processes possible.

This is one spin we can stay with for awhile.
Steph

Earthquake experiment with brownies representing the stable craton of Canada and jello representing the tectonic plate boundary in Haiti.

The kids made "earthquake-proof" structures and observed the differences of the structures on "Canada" and "Haiti."

DNA of Ancient Canaanites: Levant, Lebanon, and Lines

      Researchers have deciphered the complete DNA of five Canaanite skeletons. By comparing these five Canaanite genomes with those of other ancient and modern populations, the scientists identified the Canaanites’ ancestors and discovered their descendants were modern Lebanese people.

     The results, reported July 27 in the American Journal of Human Genetics, give new insight into the origins and fate of a people whose story has largely been told through the secondhand accounts of its contemporaries.

     "The Canaanites emerged in the Levant, a region east of the Mediterranean Sea, 3,000 to 4,000 years ago. This cultural group, which established extensive trade networks and colonies across the Mediterranean region, left behind few written records, perhaps because they wrote on papyrus rather than clay. So most knowledge of the Canaanites comes from ancient Egyptian, Hebrew and Greek documents."

     "But, doubt surrounds some of those accounts. For one thing, Greek historians thought the Canaanites originated near the Persian Gulf, whereas archaeological records suggest they arose from farming communities that settled the Levant up to 10,000 years ago. For another, the Old Testament makes reference to the destruction of Canaanite communities, but some of their cities, such as Sidon in Lebanon, appear to have been continually inhabited through the present day."

      
     "Researchers reconstructed the genomes of the 3,700-year-old remains of five Canaanites unearthed in Sidon. Comparisons of these genomes with those of other ancient Eurasian peoples indicate that Canaanite ancestry was split roughly 50-50 between the early farmers who settled the Levant and immigrants of Iranian descent who arrived later, between 6,600 and 3,550 years ago."

     “You’d need a lot of migration for roughly half of the population to be replaced by the incoming Iranian-related populations,” says Iosif Lazaridis, a geneticist at Harvard Medical School who was not involved in the study. “This must have been some important event in the history of the Near East.” One possibility is the spread of the Akkadian Empire, which controlled a region spanning from the Levant to Iran between 4,400 and 4,200 years ago. That connection may have presented the opportunity for interbreeding between these far-flung populations."

     "The researchers also determined that modern Lebanese people can attribute about 93 percent of their ancestry to the Canaanites. The other 7 percent comes from Eurasians who probably arrived in the Levant 3,700 to 2,200 years ago. Study coauthor Chris Tyler-Smith, was surprised by how much Canaanite heritage dominated modern Lebanese DNA. He says he expected to see a more mixed gene pool because so many populations have crossed through the Levant in the last few thousand years."

     "This study alone may not paint the complete picture of the Canaanite lineage, says Aaron Burke, an archaeologist at UCLA, because the researchers examined the genomes of only five Canaanites."

      "However, the study’s Canaanite genetic data do provide “a snapshot of history in the area,” Lazaridis said. Identifying which populations crop up in the Canaanite lineage — and when — can help trace the historical movements of people throughout the Near East. With DNA analyses of enough ancient people, Lazaridis says, “I think it will be possible to reconstruct the whole timeline of what happened in Lebanon and other parts of the world.” 

No lamentations; looking forward to more data!
Steph

DNA Ties between Indigenous People of Australasia and Amazon: Free Shipping Included?

     

     Yesterday, Harvard University researchers published research in the journal Nature which shows close DNA connection between indigenous peoples of the Amazon Basin of South America and aboriginal people of Australasia (including Australia, New Zealand, Papua, New Guinea and surrounding islands).

       The researchers looked at the data several times because it differed from their previous models of the spread of the human population. Skoglund et al found the genomic evidence to be even stronger as they looked harder to show there was not a tie between the two population groups.

        This summary article from Science Daily includes these paragraphs:

        "Skoglund and colleagues from HMS, the Broad and several universities in Brazil analyzed publicly available genetic information from 21 Native American populations from Central and South America. They also collected and analyzed DNA from nine additional populations in Brazil to make sure the link they saw hadn't been an artifact of how the first set of genomes had been collected. The team then compared those genomes to the genomes of people from about 200 non-American populations."

      "The link persisted. The Tupí-speaking Suruí and Karitiana and the Ge-speaking Xavante of the Amazon had a genetic ancestor more closely related to indigenous Australasians than to any other present-day population. This ancestor doesn't appear to have left measurable traces in other Native American groups in South, Central or North America."

      "The genetic markers from this ancestor don't match any population known to have contributed ancestry to Native Americans, and the geographic pattern can't be explained by post-Columbian European, African or Polynesian mixture with Native Americans, the authors said. They believe the ancestry is much older--perhaps as old as the First Americans."

        "The team named the mysterious ancestor Population Y, after the Tupí word for ancestor, 'Ypykuéra.' "

          The researchers propose that Population Y and First Americans came down from the ice sheets to become the two founding populations of the Americas.

       "About 2 percent of the ancestry of Amazonians today comes from this Australasian lineage that's not present in the same way elsewhere in the Americas," said David Reich, one of the contributing authors.

        An Australasian heritage for Amazonian people is one of the last connections that would come to my mind, given the geographical isolation of Australasia for such a long time period. What's your thinking about this migration pattern?

Two additional links on this topic from The New York Times and The Smithsonian.

Scratching my head over this one,
Steph

This world map projection is helpful:

     You can just about see Gilligan in the middle of the Pacific. . .

      And with the wind patterns:

Your Genetic Constitution, My Genetic Constitution: Friends Sharing DNA

     

     The company you keep may include similar genetic material--up to 1 percent shared DNA amongst your friends--according to a new study from scientists at the University of California--San Diego and Yale University published in the Proceedings of the National Academy of Sciences.

     "Looking across the whole genome," co-author James Fowler said, "we find that, on average, we are genetically similar to our friends. We have more DNA in common with the people we pick as friends than we do with strangers in the same population."

     The researchers focused on 1,932 subjects from the Framingham Heart study; they compared pairs of unrelated friends against pairs of unrelated strangers. The same people, who were neither biologically related nor spouses, were used in both types of samples. The only thing that differed between them was their social relationship.
 
   The study controlled for ancestry (see study link below) and is a genome-wide analysis of nearly 1.5 million markers of gene variation. The researchers concluded that friends have similar genetic material to 4th cousins and that the shared genetic material is statistically significant.

    The strongest correlation between friends was sense of smell and the least correlated was resistance to diseases.

     The study is described in the 7-14-14 edition of Science Daily:

GENOME ANALYSIS AMONG FRIENDS

     So, mes amis, what are your favorite smells?! Least favorite smells? Do you suppose the study would be valid for on-line friends?

      My favorites smells are petriclor, lilacs, lemon, coffee, newly mown grass, pine trees, cinnamon, and baby-head smell. Least favorites? Mold, old sour milk, and ammonia.


      

      The paper also lends support to the view of human beings as 'metagenomic,'" co-author Nicholas Christakis said, "not only with respect to the microbes within us but also to the people who surround us. It seems that our fitness depends not only on our own genetic constitutions, but also on the genetic constitutions of our friends."
 
      So how's your genome profile? We all depend on each other, after all. . .

     And lastly, this misspelling of Quatorze de Juillet was too good to pass up. Happy Bastille Day, Julliet, Juliette, Julius, et al! 

Vive mes amis,
Steph
(Femme des Mots)

Any guesses as to what these are?

Franklin, my dear, we DO give a damn!

                

                  "Franklin, my dear, we DO give a damn!"

     Rosalind Franklin's First Photograph of DNA structure

 

  

           Rosalind Franklin's extraordinary 1953 photograph of the DNA double helix was the impetus for Watson and Crick realizing the helix supports were on the outside of the structure with the phosphate "rungs" pointing inward. Until then, both Watson and Crick, Linus Pauling, and other researchers hypothesized the phosphates were on the outside. Franklin's research and extraordinary photograph 51 (shown below)

 were pivotal in understanding the double helix model. Yet, Rosalind Franklin received no credit for her pioneering work in x-ray crystallography of the DNA, or for the amazing photograph. Watson and Crick both later wrote that her photograph was "key" to their understanding of the structure of DNA. PBS has chronicled her story in a documentary entitled "Secret of Photograph 51:"

                                http://www.pbs.org/wgbh/nova/photo51/

            And Brenda Maddox has also written Rosalind Franklin: The Dark Lady of DNA.

            My Halloween costume will be of Rosalind Franklin, complete with photo 51 emblazoned on a t-shirt, microscope, a DNA model, and a lab coat.

          I decided this was a wise choice after making DNA models with the kindergarteners on Friday. They asked me more than once "Was she a girl?" Yes, Rosalind Franklin was a girl/woman who, sadly, died at age 37 of complications from ovarian cancer. She did not receive credit for her amazing x-ray crystallography work on the DNA helix. Most (but not all) people I have shared her story with over the past week or so were completely unaware of her contributions.

           The kids and I also worked together on one giant table making a very long double helix. I (oh so subtly) mentioned that working on scientific discoveries and models together is the way to go.

          To you, Rosalind Franklin, thank you for your extraordinary x-ray crystallography, your methodical, detailed research, and for Photograph 51.  

           Frankly/Franklin, my dear, we DO give a damn!

 I would enjoy hearing your thoughts about Rosalind Franklin (1920-1958).

Fifty-one-derfully,

Word Woman (aka Scientific Steph)

P.S. My trusty canine pup is considering accompanying me as Helix, the Dog. :-)