Cardio-facio-cutaneous (CFC) syndrome is caused by germline mutations in KRAS, BRAF and MEK1/2. The highly selective and potent MEK inhibitors that have been developed as anti-cancer agents hold potential as therapeutics for CFC syndrome. We have previously shown that the effects of CFC mutations on zebrafish gastrulation can be prevented by a 1-hour treatment with MEK inhibitors within a specific developmental time-window. However, MEK activity is essential for normal development and PD0325901 treatment outside this treatment window leads to additional developmental defects in MEK-dependent tissues. We now test ten different doses of PD0325901 at six developmental time points and assess the effects on body axis length, heart development and craniofacial structures in zebrafish embryos. Notably, we find that a continuous low-level dose of PD0325901 that has only minor inhibition of MEK activity can prevent the action of both the common CFC BRAF(Q257R) kinase-active allele and the BRAF(G596V) kinase-impaired mutant allele through the first 5 days of development. These results provide a detailed study of the effects of PD0325901 in development and show that, unlike in cancer, which requires robust inhibition of MAPK signalling, a partial reduction in phospho-ERK1/2 activity is sufficient to moderate the developmental effects of BRAF(CFC) mutations.
"Defects in neural crest are associated with cardiofaciocutaneous syndromes such as Noonan's syndrome, Costello syndrome, and LEOPARD syndrome. Notably, germline mutations that result in constitutive Erk activation cause many of these overlapping developmental syndromes, sometimes termed ''Rasopathies'' (Anastasaki et al., 2012). These abnormal developmental syndromes have several features in common, including heart defects, skin abnormalities, and distinctive facial features. "
[Show abstract][Hide abstract] ABSTRACT: Proper neural crest development and migration is critical during embryonic development, but the molecular mechanisms regulating this process remain incompletely understood. Here, we show that the protein kinase Erk, which plays a central role in a number of key developmental processes in vertebrates, is regulated in the developing neural crest by p21-activated protein kinase 1 (Pak1). Furthermore, we show that activated Erk signals by phosphorylating the transcription factor Gata6 on a conserved serine residue to promote neural crest migration and proper formation of craniofacial structures, pigment cells, and the outflow tract of the heart. Our data suggest an essential role for Pak1 as an Erk activator, and Gata6 as an Erk target, during neural crest development.
[Show abstract][Hide abstract] ABSTRACT: Cardio-facio-cutaneous syndrome (CFC) is a RASopathy that is characterized by craniofacial, dermatologic, gastrointestinal, ocular, cardiac, and neurologic anomalies. CFC is caused by activating mutations in the Ras/mitogen-activated protein kinase (MAPK) signaling pathway that is downstream of receptor tyrosine kinase (RTK) signaling. RTK signaling is known to play a central role in craniofacial and dental development, but to date, no studies have systematically examined individuals with CFC to define key craniofacial and dental features. To fill this critical gap in our knowledge, we evaluated the craniofacial and dental phenotype of a large cohort (n = 32) of CFC individuals who attended the 2009 and 2011 CFC International Family Conferences. We quantified common craniofacial features in CFC which include macrocephaly, bitemporal narrowing, convex facial profile, and hypoplastic supraorbital ridges. In addition, there is a characteristic dental phenotype in CFC syndrome that includes malocclusion with open bite, posterior crossbite, and a high-arched palate. This thorough evaluation of the craniofacial and dental phenotype in CFC individuals provides a step forward in our understanding of the role of RTK/MAPK signaling in human craniofacial development and will aid clinicians who treat patients with CFC.
[Show abstract][Hide abstract] ABSTRACT: The RASopathies are a clinically defined group of medical genetic syndromes caused by germline mutations in genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) pathway. These disorders include neurofibromatosis type 1, Noonan syndrome, Noonan syndrome with multiple lentigines, capillary malformation-arteriovenous malformation syndrome, Costello syndrome, cardio-facio-cutaneous syndrome, and Legius syndrome. Because of the common underlying Ras/MAPK pathway dysregulation, the RASopathies exhibit numerous overlapping phenotypic features. The Ras/MAPK pathway plays an essential role in regulating the cell cycle and cellular growth, differentiation, and senescence, all of which are critical to normal development. Therefore, it is not surprising that Ras/MAPK pathway dysregulation has profound deleterious effects on both embryonic and later stages of development. The Ras/MAPK pathway has been well studied in cancer and is an attractive target for small-molecule inhibition to treat various malignancies. The use of these molecules to ameliorate developmental defects in the RASopathies is under consideration. Expected final online publication date for the Annual Review of Genomics and Human Genetics Volume 14 is August 31, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Annual review of genomics and human genetics 07/2013; 14(1). DOI:10.1146/annurev-genom-091212-153523 · 8.96 Impact Factor
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