Mek1 Y130C mice recapitulate aspects of the 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..

The impact of RASopathy-associated mutations on CNS development in mice and humans

“…The RAS-ERK signaling pathway also regulates the expression of transcription factors, such as cell fate determinants. Numerous studies demonstrated that the enhanced activity of RAS-ERK signaling induces the expression of the transcription factor OLIG2, which promotes the fate of NSCs to the glial lineage [85,90,108]. Furthermore, the activation of RAS-ERK signaling promotes the expression of the pro-neural gene Achaete scute-like 1 (Ascl1) but blocks pro-neural gene Neurogenin 2 (Neurog2) expression.…”

“…Raf1 heterozygous knockout Small granule cell volume, increased cell death, reduced neuronal maturation [105] Postnatal lethality, growth retardation, apoptosis in the lung and liver, limbs coordination problems [106] Raf1 L613V heterozygous knock-in Increased density of astrocytes, enhanced OPCs density [107] Enhanced learning and memory [107] Mek1/2 Mek1 Y130C homozygous knock-in Increased astrocyte density, increased number of cortical oligodendrocytes [108] Pulmonary artery stenosis, cranial dysmorphia [108] Nestin-dependent Mek1/2 ablation Decrease of astrocyte precursors and OPCs, failure of gliogenesis [109] Early postnatal lethality [109] hGFAP-dependent Mek1/2 ablation Suppressed generation of astrocyte precursors and OPCs, failure of gliogenesis [109] Postnatal lethality [109] hGFAP-dependent Mek1 S218E,S222E Increase in astrocyte precursors and mature astrocytes, reduction of neuron number [109] Not described…”

“…Nf1 mutant mice mimic most of the CNS features found in NF1 human patients, including increased brain volume, enlarged corpus callosum and cortical area, and especially, enhanced gliogenesis, which may be closely associated with structural abnormalities. Despite compelling evidences of the expression of glial lineage transcription factors such as Olig2 increasing as RAS-ERK highly activates [85,90,108], yet it is unclear how RAS-ERK pathway regulates cell fate determinants. Thus, for understanding CNS abnormalities in NF1 patients, it is worth investigating the expression regulations of cell fate determinants with regard to RAS-ERK activity.…”

“…Although it is known that transcription factors for glial lineage become highly expressed in accordance with increasing RAS-ERK activity [85,90,108], RAS-activating mutation SHP2 D61G promotes neuronal lineage rather than glial lineage, by direct interaction with JAK-STAT pathway [96]; however, the expression of glial transcription factors that may have been affected by the increase in RAS-ERK activity is yet to be examined. On the contrary, other NS-linked mutations such as Raf1 L613V rather enhanced glial lineage [107].…”

Hyperactive MEK1 signaling in cortical GABAergic neurons causes embryonic parvalbumin-neuron death and defects in behavioral inhibition

“…Coordinated interactions between multiple cell types are necessary for normal brain function, but deficits in select cellular subtypes often mediate specific neurodevelopmental phenotypes. Past work has shown that ERK/MAPK signaling regulates the development of dorsal cortex-derived glutamatergic cortical projection neurons (PNs) and glia (Aoidi et al, 2018; Ehrman et al, 2014; Ishii et al, 2013; Li et al, 2012). Upstream regulators, such as Syngap1 , are also crucial for the early development of cortical glutamatergic neuron structure, excitability, and cognition (Clement et al, 2012; Ozkan et al, 2014).…”