What is it about?
DNA methylation is what we call an epigenetic marks. Epigenetic marks on DNA are chemical modifications harboured by a DNA molecule without changing the sequence of the DNA. Therefore, the protein coded by the DNA remains the same and has the same activity but the epigenetic marks have an impact on how much the DNA is supposed to be expressed. Those modifications are placed by specific enzymes called DNA-methyltransferases. In the genome of the parasite Leishmania we found the sequence potentially coding for one of these DNA-methyltransferase. So at first, we gene the protein to check if it was essential for the parasite life and it is not. So we used a specific DNA sequencing technique that indicates exactly on the DNA where this methyl chemical modification is. We sequenced the DNA of the parasite with and without the protein and we did not find any difference indicating that Leishmania, despite having a protein coding for DNA-methyltransferase, does not methylate its DNA. Human DNA is methylated, so we made mixes of Leishmania and human DNA to a point where it mimics the ratio of a normal infection. Using a method that capture methylated DNA we were able to remove most of the human DNA allowing us to have access to the parasite DNA.
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Why is it important?
In a previous study we performed, we showed that the DNA of the parasite was showing different features (but the sequence remains unchanged) if the parasite is in vitro in a petri dish or in vivo inside a mammal. The present study is important because so far the DNA of the parasite inside a clinical sample is too diluted inside the human DNA for us to obtain its sequence with conventional sequencing technique. Here we found a technique to use prior to perform the DNA sequencing that is greatly enriching in parasite DNA. This quantity is enough to be sequenced and to get the genetic information of the parasite directly from the patient sample without having to go for in vitro culture and to have the parasite to adapt to an new environment.
Perspectives
The results of this study potentially allows us to get access to the parasite's genome structure inside the patient. Therefore, not having to cultivate the parasite in vitro and loose the genome structure information. Another study shows the use of a technique called SureSelect which involve the design of specific RNA probes to extract the genome of the parasite from a complex sample. This technique has some great results at calling genome structure(Domagalska M et al 2020). But this method is much more expensive than using beads to remove methylated DNA from the sample. The method described in our study is cheap and fast and can be used in every simple laboratory settings everywhere in the world.
Dr Franck Dumetz
University of Maryland
Read the Original
This page is a summary of: C-5 DNA methyltransferase 6 does not generate detectable DNA methylation in Leishmania, August 2019, Cold Spring Harbor Laboratory Press,
DOI: 10.1101/747063.
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