Silenced X chromosome genes reawaken in new mouse model | Spectrum

Silenced X chromosome genes reawaken in new mouse mannequin | Spectrum


Prepared riser: Mouse cells that harbor a bioluminescent model of MECP2 additionally categorical a purple fluorescent tag after pharmacological reactivation of the X chromosome (backside), which is often silenced.
Courtesy of Mira-Bontembal and Tan, et al.

A brand new mouse mannequin might speed up the invention of gene-activating therapies to deal with Rett syndrome, a situation associated to autism, its makers say.

Rett syndrome arises from mutations in MECP2, a gene on the X chromosome. Such mutations are often deadly shortly after delivery in boys, who’ve just one X chromosome and thus no backup copy of the gene. Women have two X chromosomes, however a course of referred to as random X inactivation silences considered one of them in about half of their cells. Because of this, their backup copy of MECP2 can’t compensate for a mutated one — resulting in the syndrome’s core traits, which embrace mental incapacity and seizures.

Researchers have been making an attempt to awaken the silenced copy to deal with the situation. To check their methods, they usually couple the MECP2 gene to DNA that encodes a fluorescent jellyfish protein. Nevertheless, the fluorescent sign is weak and should not detect delicate modifications in gene activation. Alternatively, the gene is fused with luciferase — the bioluminescent enzyme present in fireflies. That is brighter and extra delicate, however the cumbersome protein can disrupt the perform of the MECP2 protein.

Within the new mouse mannequin, researchers fused the MECP2 gene to DNA that encodes a nanosized model of luciferase that, regardless of being extra compact, emits 100 occasions as a lot gentle as the unique. It could detect smaller modifications in MECP2 reactivation and is much less prone to disrupt the perform of the MECP2 protein, says examine investigator Antonio Bedalov, professor of drugs on the Fred Hutchinson Most cancers Analysis Middle in Seattle, Washington. The mice additionally categorical a purple fluorescent protein when the bioluminescent model of MECP2 is energetic; that tag allows the researchers to trace which cells carry the modified gene.

Bedalov and his colleagues bred feminine mice to harbor the bioluminescent model of MECP2 on their silenced copy of the X chromosome. The workforce then extracted neural stem cells from the mice, grew them in tradition dishes and handled them with 4 compounds identified to reactivate MECP2.

Researchers usually use mouse fibroblasts in such experiments, however neural stem cells are extra related to Rett syndrome, says examine investigator Hegias Mira-Bontenbal, affiliate professor at Erasmus Medical Centre in Rotterdam, the Netherlands.

Solely one of many compounds Mira-Bontenbal and his colleagues used, referred to as 5-azacytidine, efficiently lit up the neural stem cells, signaling MECP2 reactivation. The drug works by blocking an enzyme from including to DNA repressive tags that flip genes off. Combining the drug with quick nucleotide strands that inhibit a molecule concerned in silencing the X chromosome boosted MECP2 expression additional.

To find out what number of different genes alongside the X chromosome have been additionally reactivated by the remedy, the researchers took benefit of genetic variation between the 2 X chromosomes — the bred mice inherited one X from an Algerian mouse pressure referred to as Solid/EiJ and the opposite X from a typical C57BL/6 laboratory mouse. These two units of mice are as genetically comparable to one another as persons are to chimpanzees, Bedalov says.

Sequencing the energetic genes from the X chromosome and looking for stretches of nucleotides distinctive to the Algerian mice revealed reactivation of 85 different genes. The examine was revealed in February in Stem Cell Reviews.

Other teams are already utilizing the mouse-derived cell traces, Mira-Bontenbal says, to analyze how completely different MECP2 mutations have an effect on how nicely the protein works and the way rapidly it’s degraded, shedding gentle on how the situation progresses on the mobile stage.

Mira-Bontenbal says that he and his colleagues purpose to check a whole lot of chemical compounds to evaluate their capacity to reactivate MECP2, an in any other case labor-intensive course of. The workforce is creating an identical nano-luciferase system in human cells to see whether or not pharmacological therapies translate to folks.

In the meantime, Bedalov and his colleagues are utilizing a modified model of CRISPR to take away the repressive tags on MECP2, within the hope of reactivating MECP2 with out switching on different genes. They plan to check the effectiveness of that technique utilizing the mouse mannequin, Bedalov says.

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