The SMC protein complex ensures the dynamics of holocentromers


The SMC protein complex ensures the dynamics of holocentromers. Credit: IPK

Monocentromers are typical of the chromosomes of most animals and plants. The centromere is necessary for the transport of chromosomes and represents the point of connection between chromatids. This is how the classic X-shape of the chromosome is formed. However, in about 350,000 species, including butterflies, nematodes, and some plants, centromeres are distributed throughout the length of the chromosome. For this reason, they are called holocentromers.

A research team from the IPK Leibniz Institute has now used modeling to study how the centromere changes dynamically during cell division in these species. The results are now published in the journal Nucleic Acid Research.

Holocentric plant species such as Cyperus papyrus were already of great importance to the ancient Egyptians. “This fiber factory was used to make one of the first papers at the time,” explains Professor Andreas Houben, head of the chromosome structure and function research group at the IPK Leibniz Institute. What all of these species have in common is an evolutionary advantage. If a piece of the chromosome breaks 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 cell division process takes place in these species. First, the fibers of the spindle attach to the centromere, then separate the two chromatids. “It works like a rubber band,” explains Professor Dr Andreas Houben. In what is called the interphase, the holocentromer breaks up and countless centromeric units are formed, which are evenly distributed throughout the cell nucleus. In the next mitosis, the chromosome condenses and the centromere units gradually form a linear centromere along the chromatids.

Using modeling, IPK junior scientist Dr Amanda Câmara of the Domestication Genomics research group led by Dr Martin Mascher was able to prove that a protein complex called SMC plays a decisive role in this process. .

“When the protein complex approaches a centromeric unit, it attaches to the chromatin thread, explains Dr. Amanda Câmara. 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 holocentromer. “This makes the SMC complex quite essential for the dynamics of holocentromers. This possible function of SMC discovered through modeling was previously unknown,” explains the IPK scientist.

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

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More information:
Amanda Souza Câmara et al, A Simple Model Explains the Cell Cycle Dependent Assembly of Centromeric Nucleosomes in Holocentric Species, Nucleic Acid Research (2021). DOI: 10.1093 / nar / gkab648

Provided by the Leibniz Institute of Plant Genetics and Crop Plant Research

Quote: SMC protein complex demonstrated to support holocentromeric dynamics (2021, August 6) retrieved August 6, 2021 from

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