MSGID: 1:317/3 64927cfb   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Scientists discover new embryonic cell type that self-destructs to   
   protect the developing embryo    
      
     Date:   
         June 20, 2023   
     Source:   
         University of Bath   
     Summary:   
         Scientists have uncovered a new quality control system that removes   
         damaged cells from early developing embryos.   
      
      
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   FULL STORY   
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   Scientists studying gene activity data of the early human embryo have   
   discovered an overlooked type of cell which self-destructs within   
   days of forming, as part of a quality control process to protect the   
   developing foetus.   
      
   The findings give insights on what happens at the very first stages of   
   life after fertilisation which could in the future help improve IVF or   
   regenerative medicine treatments.   
      
   A new study published on 20 June 2023 in PLoS Biology by an international   
   team of scientists including researchers at the University of Bath,   
   finds that our earliest development in the womb may be rather different   
   to what we have always assumed.   
      
   While human adults are made up of trillions of cells, we all started   
   out as just one cell, the fertilized egg. This divides to become 2 cells   
   which in turn divide to become four, which become 8 and so on. At some   
   point the cells then start to specialise in their function. Like trains   
   sent to different end stations, some will be shunted off to become the   
   placenta while others will become the embryo.   
      
   Self-destructing embryonic cell The team of scientists analysed previously   
   published data on gene activity of each individual cell from 5-day old   
   embryos and discovered around a quarter of the cells didn't fit the   
   profile of any of the known cell types (pre-embryo, pre-placenta etc).   
      
   Investigating further, they discovered that these cells contained   
   so-called "Young transposable elements" or "jumping genes." These are   
   rogue elements of DNA that can copy themselves and insert themselves   
   back into our DNA, often causing damage in the process.   
      
   Staining of embryos by project collaborators in Spain confirmed the   
   existence of the cells with proteins derived from the jumping genes.   
      
   Looking a little further forward in time, the team found their descendants   
   both have DNA damage and undergo a process of programmed cell death.   
      
   Quality control mechanism This process, the researchers suggest, looks   
   like a form of quality control: selection between cells in favour of   
   the good ones.   
      
   Dr Zsuzsanna Izsva?k, co-senior author from the Max Delbru"ck Center   
   and an expert on mobile DNA, said: "Humans, like all organisms, fight   
   a never-ending game of cat and mouse with these harmful jumping genes.   
      
   "While we try and suppress these jumping genes by any means possible,   
   very early in development they are active in some cells, probably because   
   we cannot get our genetic defences in place fast enough."  Co-lead author   
   Professor Laurence Hurst, from the Milner Centre for Evolution at the   
   University of Bath, said: "If a cell is damaged by the jumping genes - -   
   or any other sort of error such as having too few or too many chromosomes   
   - - then the embryo is better off removing these cells and not allowing   
   them to become part of the developing baby.   
      
   "We are used to the idea of natural selection favouring one organism over   
   another. What we are seeing within embryos also looks like survival of   
   the fittest but this time between almost identical cells. It looks like   
   we've uncovered a novel part of our arsenal against these harmful genetic   
   components."  Using old genetic enemies to fight new ones Conversely, the   
   single-cell data showed that the key cells that will become the embryo   
   (the inner cell mass or ICM) don't contain jumping genes but instead   
   express a virus-like gene called human endogenous virus H. This helps   
   suppress the young jumping genes in the inner cell mass, fitting with   
   an emerging pattern that we use our old genetic enemies to fight our   
   new ones.   
      
   The authors suggest that if the quality control process is too sensitive,   
   the embryo as a whole may die. This might explain why some mutations   
   in our system to detect damage in early embryos are also associated   
   with infertility.   
      
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   Story Source: Materials provided by University_of_Bath. Note: Content   
   may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Manvendra Singh, Aleksandra M. Kondrashkina, Thomas J. Widmann,   
      Jose L.   
      
         Cortes, Vikas Bansal, Jichang Wang, Christine Ro"mer, Marta   
         Garcia- Canadas, Jose L. Garcia-Perez, Laurence D. Hurst,   
         Zsuzsanna Izsva'k. A new human embryonic cell type associated   
         with activity of young transposable elements allows definition   
         of the inner cell mass. PLOS Biology, 2023; 21 (6): e3002162 DOI:   
         10.1371/journal.pbio.3002162   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230620174450.htm   
      
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