Mek1Y130C mice recapitulate aspects of human cardio-facio-cutaneous syndrome

ABSTRACT The RAS/MAPK signaling pathway is one of the most investigated pathways, owing to its established role in numerous cellular processes and implication in cancer. Germline mutations in genes encoding members of the RAS/MAPK pathway also cause severe developmental syndromes collectively known as RASopathies. These syndromes share overlapping characteristics, including craniofacial dysmorphology, cardiac malformations, cutaneous abnormalities and developmental delay. Cardio-facio-cutaneous syndrome (CFC) is a rare RASopathy associated with mutations in BRAF, KRAS, MEK1 (MAP2K1) and MEK2 (MAP2K2). MEK1 and MEK2 mutations are found in ∼25% of the CFC patients and the MEK1Y130C substitution is the most common one. However, little is known about the origins and mechanisms responsible for the development of CFC. To our knowledge, no mouse model carrying RASopathy-linked Mek1 or Mek2 gene mutations has been reported. To investigate the molecular and developmental consequences of the Mek1Y130C mutation, we generated a mouse line carrying this mutation. Analysis of mice from a Mek1 allelic series revealed that the Mek1Y130C allele expresses both wild-type and Y130C mutant forms of MEK1. However, despite reduced levels of MEK1 protein and the lower abundance of MEK1 Y130C protein than wild type, Mek1Y130C mutants showed increased ERK (MAPK) protein activation in response to growth factors, supporting a role for MEK1 Y130C in hyperactivation of the RAS/MAPK pathway, leading to CFC. Mek1Y130C mutant mice exhibited pulmonary artery stenosis, cranial dysmorphia and neurological anomalies, including increased numbers of GFAP+ astrocytes and Olig2+ oligodendrocytes in regions of the cerebral cortex. These data indicate that the Mek1Y130C mutation recapitulates major aspects of CFC, providing a new animal model to investigate the physiopathology of this RASopathy. This article has an associated First Person interview with the first author of the paper.


First person -Rifdat Aoidi
First Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Rifdat Aoidi is first author on 'Mek1 Y130C mice recapitulate aspects of human cardio-faciocutaneous syndrome', published in DMM. Rifdat conducted the work in this article while a PhD student in the lab of Jean Charron in Laval University, Canada. She is now a postdoctoral training fellow in Victor Tybulewicz's lab at the Francis Crick Institute, London, UK, working on analyzing the congenital heart defects in Down syndrome mouse model.

How would you explain the main findings of your paper to non-scientific family and friends?
Cardio-facio-cutaneous syndrome (CFC) is part of the RASopathy, a group of rare genetic developmental syndromes. CFC syndrome is caused by mutations in genes called BRAF (~75% of patients), MEK1 and MEK2 (~25% of patients). These mutations result in a range of defects including craniofacial dysmorphology, cardiac malformations, cutaneous abnormalities and neurocognitive delay. We wanted to generate a mouse model in order to understand the syndrome and uncover the pathological mechanisms that lead to these defects. Knowing that among MEK1 and MEK2 mutations, MEK1 Y130C mutation is the most common, we decided to generate a mouse model carrying this mutation in order to investigate its molecular and developmental consequences. Analysis of these mice showed that Mek1 Y130C mutant mice exhibited pulmonary artery stenosis, cranial dysmorphia and neurological anomalies. Our data indicate that the Mek1 Y130C mutation recapitulates major aspects of CFC syndrome, providing a new animal model to investigate the physiopathology of this RASopathy.
What are the potential implications of these results for your field of research?
To our knowledge, no mouse model carrying RASopathy-linked Mek1 or Mek2 gene mutations has been reported. Here, we generated the first mouse model for the most common MEK1 mutation, which gives a tool that can be used to analyze the mechanisms underlying the defects observed in CFC syndrome.
What are the main advantages and drawbacks of the model system you have used as it relates to the disease you are investigating?
CFC syndrome is a disorder associated with various developmental abnormalities. In order to investigate the causes and the mechanisms underlying defects observed in CFC syndrome, we have to analyze its development in genetically modified animals. Because of its high similarity with human in terms of anatomy, development and genetics, the mouse is the most frequently used mammalian model for human disease. I believe that the mouse is the most appropriate species because of the availability of the most developed genetic manipulation techniques and of the huge wealth of information about developmental biology. Mice are small, have a relatively short "Having a network of postdoctoral fellows can allow early career-scientists to meet more experienced postdocs in order to share our common experiences and discuss the issues that we all face." What has surprised you the most while conducting your research?
Analysis of our Mek1 Y130C allele revealed that both wild type and Y130C mutant protein were expressed, and the MEK1 Y130C protein has lower expression that the wild type. These findings suggest that a duplication of the Mek1 gene might have happened when generating the Mek1 Y130C allele. One of the strengths of our model is that despite reduced levels of MEK1 Y130C protein compared with wild type, Mek1 Y130C mutants showed increased activation of ERK (MAPK) in response to growth factors, supporting a role for MEK1 Y130C in hyperactivation of the RAS/MAPK pathway, leading to CFC. These findings are in agreement with previous findings suggesting that CFC mutations are gain-of-function that hyperactivate the RAS/MAPK pathway.

What changes do you think could improve the professional lives of early-career scientists?
For early-career scientists, the most challenging thing is to know to which funding bodies to apply in order to fund your research. Having a network of postdoctoral fellows can allow early-career scientists to meet more experienced postdocs in order to share our common experiences and discuss the issues that we all face.

What's next for you?
My long-term aim is to become an independent investigator studying human genetic diseases that result in developmental defects. To achieve this goal, I am currently undergoing postdoctoral training at the Francis Crick Institute in London, UK, working on analyzing the causes of congenital heart defects in Down syndrome mouse model.