• Cell division in microalgae: Mitosis rev

    From ScienceDaily@1:317/3 to All on Mon Mar 7 21:30:48 2022
    Cell division in microalgae: Mitosis revealed in detail

    Date:
    March 7, 2022
    Source:
    Bielefeld University
    Summary:
    Cell division ensures growth or renewal and is thus vital for
    all organisms. However, the process differs somewhat in animals,
    bacteria, fungi, plants, and algae. Until now, little was known
    about how cell division occurs in algae. Researchers have used
    confocal laser scanning microscopy (CLSM) to capture the very
    first high-resolution three- dimensional images of cell division
    in live cells of the microalga Volvox carteri, and have identified
    new cellular structures involved in the process.



    FULL STORY ==========================================================================
    Cell division ensures growth or renewal and is thus vital for all
    organisms.

    However, the process differs somewhat in animals, bacteria, fungi,
    plants, and algae. Until now, little was known about how cell division
    occurs in algae.

    Researchers at Bielefeld University have used confocal laser
    scanning microscopy (CLSM) to capture the very first high-resolution three-dimensional images of cell division in live cells of the microalga
    Volvox carteri, and have identified new cellular structures involved in
    the process. Professor Dr Armin Hallmann from the Faculty of Biology is
    leading the study. The findings have now been published open access in
    the journal The Plant Cell.


    ==========================================================================
    The cell is the smallest organisational unit of life. It contains the
    necessary building blocks of life in a compact form and is the place
    where vital biochemical reactions take place. With the help of enzymes, substance and energy transformations take place, which are processes also
    known as metabolism. The cell interior is separated and thus protected
    from the environment by the cell membrane. Genetic material, the cell's information store, is often located in the cell nucleus as DNA. When a
    cell divides by mitosis, it first divides its nucleus into two identical daughter nuclei with the same genetic material. Then the rest of the
    cell divides and two identical daughter cells are produced. The complex, genetically determined process of mitosis in particular must take place
    very precisely: the entire genetic material, divided into chromosomes,
    must be segregated accurately into the two daughter cell nuclei.

    Cell division of the alga Volvox carteri combines animal and plant characteristics 'Cell division is one of the most fundamental processes in living organisms. It has basically been preserved over countless millions
    of years of evolution and can be found in all organisms,' says Professor
    Dr Armin Hallmann, head of the Cellular and Developmental Biology of
    Plants research group at Bielefeld University. Yet the mechanisms of cell division in animals, fungi, plants, and algae each have characteristic features. The multicellular green alga Volvox carteri is a particularly interesting case in point. 'It exhibits both animal and plant features
    in mitosis,' says Hallmann. The researchers have now been able to clarify
    this phenomenon in their study. 'Until now, researchers knew very little
    about the exact process of mitosis in this green alga.' Mitosis in the microalga Volvox carteri With their analyses, the scientists have been
    able to identify five characteristics that are crucial for mitosis in
    the microalga Volvox carteri.



    ==========================================================================
    The first two features concern the envelope of the microalgal
    nucleus. 'The nuclear envelope does not disintegrate at the beginning
    of mitosis, as is often the case, but remains in place until shortly
    before nuclear division is completed,' says Armin Hallmann. 'Instead, it becomes porous and permeable, so that cellular components are exchanged
    between the inside of the cell nucleus and the cytosol -- a fluid that surrounds the cell nucleus. Hence, for a certain period of time, the
    cell nucleus loses its typical property as a confined reaction space,
    although the nuclear envelope is still present.' The third feature is
    related to the centrosomes of the cell. These are cell structures that
    play a central role in the organisation of the mitotic spindle here. The mitotic spindle arranges the chromosomes in such a way that they can
    be segregated accurately into the two newly forming cell nuclei. 'We
    have been able to show that the centrosomes play a crucial role in
    the mitosis of Volvox carteri even though they are located outside
    the nuclear envelope. They form the basic structure for organising the
    precise division of the genetic material with the help of the nuclear
    division spindle within the nuclear envelope.

    Until now, we only knew about an organisation of the spindle by
    centrosomes from cell division in animals,' says Hallmann.

    A fourth feature is the formation of a specific filamentous structure,
    the phycoplast, at the end of mitosis. After the cell nucleus has divided,
    the rest of the cell must also divide so that the newly formed cells can finally separate from each other. The dynamic phycoplast is the basis
    for the formation of a cleavage furrow which ultimately divides the
    cell, whereas plants form a different structure which ultimately leads
    to the formation of a separating, solid cell wall. 'The special thing
    about algae is that the phycoplast is formed directly by recycling the
    nuclear division spindle, which is then no longer required,' explains
    the scientist.

    Finally, the researchers were able to detect an enormous dynamic of the
    entire inner architecture of the cell as well as of the nuclear envelope
    during cell division.

    Making molecular processes visible The researchers were able to record the
    cell division processes by producing fluorescent proteins (proteins that
    glow when exposed to light) and tracking them in the cell using confocal
    laser scanning microscopy (CLSM). For the first time, scientists have
    succeeded in imaging the mitosis of microalgae in three dimensions in live cells and characterising it in detail, using Volvox carteri as an example.



    ==========================================================================
    'The question we posed ourselves was: how exactly does cell division
    work in green algae? Which structures are involved in mitosis and what
    role do they play in the process?' says first author Dr Eva Laura von
    der Heyde. She previously conducted research in Hallmann's research
    group as a doctoral student and is now a postdoc. In order to be able to localise important proteins involved in cell division in the cell, their
    genes are linked to the gene of a fluorescent protein using molecular
    biology techniques. The proteins involved in cell division thus become fluorescent, which makes them distinguishable from all other proteins
    in the cell. 'We used a special laser to excite different fluorescent
    proteins to glow. Using a confocal laser scanning microscope, we were
    able to detect the yellow-green glow of the microstructures formed by
    the proteins in live cells,' says Eva Laura von der Heyde.

    The researchers also recorded on video how the proteins move during
    cell division, how they form microstructures, and how these structures
    are rebuilt.

    In a time-lapse video, which condenses 30 minutes of mitosis to nine
    seconds and shows it simultaneously in ten optical section planes, it
    becomes clear how the centrosomes organise the formation of the nuclear division spindle and how the nuclear division spindle finally transforms
    into the phycoplast after the chromosomes have separated.

    Insights into evolution In the long term, Armin Hallmann and Eva Laura
    von der Heyde hope to be able to build on these new findings to learn
    more about the evolution of cell division.

    How did the different variants of cell division that are found today in animals, fungi, plants, and algae come about? 'In evolution, the first
    land plants developed from primordial green algae. This is why the green
    alga Volvox carteri also possesses properties that it has in common with
    land plants growing today. However, it is striking that Volvox carteri
    also possesses properties that can be found in animals living today. Other
    of their characteristics are again only found in green algae. These
    special characteristics also make this model organism so important for
    our understanding of the evolution of cell division,' says Hallmann.

    ========================================================================== Story Source: Materials provided by Bielefeld_University. Note: Content
    may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Eva Laura von der Heyde, Armin Hallmann. Molecular and cellular
    dynamics
    of early embryonic cell divisions in Volvox carteri. The Plant Cell,
    2022; DOI: 10.1093/plcell/koac004 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220307091729.htm

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