Protein complex SMC ensures the dynamics of holocentromeres

Date:
August 6, 2021
Source:
Leibniz Institute of Plant Genetics and Crop Plant Research
Summary:
Monocentromeres are typical for the chromosomes of most animals
and plants. The centromere is necessary for the transport of
the chromosomes and represents the connection point between the
chromatids. This is how the classic X-shape of the chromosome
is formed. However, in an estimated 350,000 species, including
butterflies, nematodes and some plants, the centromeres are
distributed along the entire length of the chromosome.

For this reason, they are called holocentromeres. A research team
has now used modelling to investigate how the centromere changes
dynamically in the course of a cell division in these species.



FULL STORY ========================================================================== Holocentric plant species such as Cyperus papyrus were already of great importance to the ancient Egyptians. "This fibre plant was used to
make one of the first papers back then," says Prof. Dr. Andreas Houben,
head of the Chromosome Structure and Function research group at the IPK
Leibniz Institute.

What all these species have in common is an evolutionary advantage. If a
piece of the chromosome breaks off due to mutagenesis, the corresponding fragment is lost in monocentric species. "This does not happen in
holocentric species, because there the centromere extends over the entire chromosome," explains the IPK scientist.


========================================================================== However, the research team now wanted to know how the process of cell
division takes place in these species. First, the spindle fibres dock
onto the centromere and then pull the two chromatids apart. "This works
like a rubber band," explains Prof. Dr. Andreas Houben. In the so-called interphase, the holocentromere falls apart and innumerable centromeric
units are formed, which are evenly distributed in the cell nucleus. In
the subsequent mitosis, the chromosome condenses and the centromeric
units form step by step a linear centromere along the chromatids.

With the help of modelling, IPK junior scientist Dr. Amanda Ca^mara from
the Domestication Genomics research group led by Dr. Martin Mascher was
able to prove that a so-called SMC protein complex plays a decisive role
in this process.

"When the protein complex comes close to a centromeric unit, it becomes
fixed on the chromatin thread," explains Dr. Amanda Ca^mara. As a
result, several loops are formed, the chromosome is thus condensed
and a centromeric line is formed, which ultimately gives rise to the
new holocentromere. "This makes the SMC complex quite essential for the dynamics of holocentromeres. This possible function of the SMC discovered through modelling was previously unknown," says the IPK scientist.

In the next step, the researchers at IPK will try to confirm the results
of the modelling experimentally.

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


========================================================================== Journal Reference:
1. Amanda Souza Ca^mara, Veit Schubert, Martin Mascher, Andreas
Houben. A
simple model explains the cell cycle-dependent assembly of
centromeric nucleosomes in holocentric species. Nucleic Acids
Research, 2021; DOI: 10.1093/nar/gkab648 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210806104319.htm

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