How a blood-loving parasite gave us a better understanding of Rett Syndrome

By Lisa Willemse; co-published at www.medium.com/the-expression

On the surface, there is very little to connect the parasite responsible for Chagas disease with Rett Syndrome, an X-linked neurodegenerative disorder. One is a tiny organism carried by insects and transmitted to humans via bites, and the other is a human disease caused by genetic mutation. 
 
Strangely, though, it took an expert in one to discover more about the other. The result is another vital clue to how Rett Syndrome develops – through the misregulation of a key protein – an advance that might allow us to find a way to stop it. 
 
It turns out, it’s not so much about the diseases or their origin, but how you study them. 
 
Deivid Rodrigues, a postdoc in the James Ellis lab at the SickKids Hospital, began his scientific career in parasitology, contributing some key insights on Trypanosoma cruzi (the parasite) before turning his attention to MECP2 (the mutated gene in Rett Syndrome). The jump from studying tiny protozoa to making a discovery in human neural development is surprisingly less of a leap than one might think. In fact, what goes on inside the cells at the biological level is not all that different between species. 
 
“My particular interests are the post-transcriptional regulation mechanisms,” says Rodrigues. “You know the information for making proteins is written in the genes and the genes are first transcribed into RNA molecules and the RNA molecules are then translated to make proteins.” (This is the Central Dogma of biology, as explained in this animated video.) “And we know a lot about the mechanisms that regulate transcription; the first step, making RNA molecules from the DNA. But we don’t know a lot about the mechanisms that regulate the stability of the RNA molecules once made or how efficiently they are translated into proteins. There’s a lot going on there.”
 
In 2012, Rodrigues moved to Toronto from Rio to take a position at the Ellis lab. He was intent on improving methods of generating induced pluripotent stem cells (iPSC; created by taking adult cells, i.e. skin cells, and applying specific genetic factors to revert them to a more primitive, stem-cell state), and the Ellis lab was among the first in Canada to begin working with iPSC. 
 
“Deivid’s background involved working on control of RNA in parasites,” recalls Ellis. “He came in with these particular skills – skills nobody else in the lab had -- and when he arrived, he just started checking out the interesting sequences in the MECP2 gene and he noticed that it’s hugely conserved across species which means it must be important.”
 
Based on this preliminary work, Rodrigues quickly secured a highly competitive grant from RettSyndrome.org where he began to pick apart the mechanism of how MECP2 is regulated.  
 
It’s long been known that Rett Syndrome is linked to mutation of the MECP2 gene but the disease can also be triggered by MECP2 gene duplication. Rett Syndrome almost exclusively affects girls, who have one normal and one mutant MECP2 gene on their X chromosomes, and begin to show the characteristic developmental delays of the disease within the first few years of life. 
 
“What Deivid has allowed us to do is get into the molecular biology behind the abundance of MECP2 protein because if a child has a duplication of MECP2, and therefore twice as much protein, it’s enough to cause the disease,” says Ellis. 
 
Rodrigues’ studies have identified a shift in the control mechanism of MECP2 protein production between the very low levels produced by embryonic stem cells (very early development) and later stage neural cells, which maintains higher, but controlled levels of MECP2 protein.
 
But between the translation of RNA to protein is a whole host of factors that dictate if a protein gets made, and if so, at what level of output. 
 

“We know protein levels are really important to get right and that’s probably why the MECP2 gene is regulated so tightly,” says Ellis. “The focus that everyone’s had for so long has been RNA levels, but it’s the proteins that do the work.”
 
Rodrigues was able to identify two specific players that directly affect the level of protein production; one that leads to degradation of RNA in embryonic stem cells, and another that activates translation in neural cells. 
 
“We are proposing a model that keeps that level of MECP2 protein very tightly regulated,” says Rodrigues.
 
This model of regulation is the subject of a paper the lab is currently working on, but it has implications that go beyond a possible way to control or treat Rett Syndrome, to a host of other neurodevelopmental disorders, such as autism spectrum disorder – at least, this is what Ellis and Rodrigues have thought. The hypothesis was strong enough to win a New Ideas Grant from the Ontario Institute for Regenerative Medicine (OIRM).
 
The OIRM grant allowed Rodrigues and Ellis to look more broadly at the mechanism of MECP2 protein regulation across a wider range of genes that are important in development. The work is now entering its final stage of study before the data can be analysed and written up. 
 
“MECP2 is a master regulator of neurological development. It controls the transcription of many, many genes,” says Rodrigues. The team hopes that they will find many more genes that possess the same mechanism that keeps low levels of protein in embryonic stem cells and higher, controlled levels in neural cells. This analysis will provide insight into what that extra level of control is doing in cells and what its potential impact is in disease. 
 
If strong data emerges from the OIRM study, Ellis is already thinking about the implications of these findings in other tissues and is planning the next phase of grant applications that will emerge from it.
 
“We see this work as the cornerstone of something much bigger,” says Ellis. “For example, let’s say we see the same phenomena in cardiac cells – maybe there are a bunch of genes that get expressed in embryonic stem cells but don’t make the protein and once you differentiate them into cardiomyocytes maybe this protein gets made and maybe this is important during normal development. If we understand the mechanism in normal development, we will also better understand what is happening when it goes awry in disease,” he says.
 
It’s the kind of knowledge that could lead to better management and treatment, not just for Rett Syndrome, but for many other diseases. If so, we may one day owe that parasite, and the basic study of how biological processes work, a debt of gratitude.