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Background Cardio-facio-cutaneous (CFC) syndrome is a human multiple congenital anomaly syndrome that is caused by activating heterozygous mutations in either BRAF, MEK1, or MEK2, three protein kinases of the Ras/mitogen-activated protein kinase (MAPK) pathway. CFC belongs to a group of syndromes known as RASopathies. Skeletal muscle hypotonia is a ubiquitous phenotype of RASopathies, especially in CFC syndrome. To better understand the underlying mechanisms for the skeletal myopathy in CFC, a mouse model with an activating BrafL597V allele was utilized. Results The activating BrafL597V allele resulted in phenotypic alterations in skeletal muscle characterized by a reduction in fiber size which leads to a reduction in muscle size which are functionally weaker. MAPK pathway activation caused inhibition of myofiber differentiation during embryonic myogenesis and global transcriptional dysregulation of developmental pathways. Inhibition in differentiation can be rescued by MEK inhibition. Conclusions A skeletal myopathy was identified in the CFC BrafL597V mouse validating the use of models to study the effect of Ras/MAPK dysregulation on skeletal myogenesis. RASopathies present a novel opportunity to identify new paradigms of myogenesis and further our understanding of Ras in development. Rescue of the phenotype by inhibitors may help advance the development of therapeutic options for RASopathy patients.

Costello syndrome (CS) is a congenital disorder caused by heterozygous activating germline HRAS mutations in the canonical Ras/mitogen-activated protein kinase (Ras/MAPK) pathway. CS is one of the RASopathies, a large group of syndromes caused by mutations within various components of the Ras/MAPK pathway. An important part of the phenotype that greatly impacts quality of life is hypotonia. To gain a better understanding of the mechanisms underlying hypotonia in CS, a mouse model with an activating HrasG12V allele was utilized. We identified a skeletal myopathy that was due, in part, to inhibition of embryonic myogenesis and myofiber formation, resulting in a reduction in myofiber size and number that led to reduced muscle mass and strength. In addition to hyperactivation of the Ras/MAPK and PI3K/AKT pathways, there was a significant reduction in p38 signaling, as well as global transcriptional alterations consistent with the myopathic phenotype. Inhibition of Ras/MAPK pathway signaling using a MEK inhibitor rescued the HrasG12V myopathy phenotype both in vitro and in vivo, demonstrating that increased MAPK signaling is the main cause of the muscle phenotype in CS., Summary: A Costello syndrome (CS) mouse model carrying a heterozygous Hras p.G12V mutation was utilized to investigate Ras pathway dysregulation, revealing that increased MAPK signaling is the main cause of the muscle phenotype in CS.

Noonan syndrome (NS) is one of the common RASopathies. While the clinical phenotype in NS is variable, it is typically characterized by distinctive craniofacial features, cardiac defects, reduced growth, bleeding disorders, learning issues, and an increased risk of cancer. Several different genes cause NS, all of which are involved in the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway. Juvenile xanthogranuloma (JXG) is an uncommon, proliferative, self-limited cutaneous disorder that affects young individuals and may be overlooked or misdiagnosed due to its transient nature. A RASopathy that is known to be associated with JXG is neurofibromatosis type 1 (NF1). JXG in NF1 has also been reported in association with a juvenile myelomonocytic leukemia (JMML). As RASopathies, both NS and NF1 have an increased incidence of JMML. We report a 10-month-old female with NS who has a PTPN11 pathogenic variant resulting in a heterozygous SHP2 p.Y62D missense mutation. She was found to have numerous, small, yellow-pink smooth papules that were histopathologically confirmed to be JXG. In understanding the common underlying pathogenetic dysregulation of the Ras/MAPK pathway in both NS and NF1, this report suggests a possible molecular association for why NS individuals may be predisposed to JXG.

Cardio-facio-cutaneous (CFC) syndrome is a human multiple congenital anomaly syndrome that is caused by activating heterozygous mutations in either BRAF, MEK1, or MEK2, three protein kinases of the Ras/mitogen-activated protein kinase (MAPK) pathway. CFC belongs to a group of syndromes known as RASopathies. Skeletal muscle hypotonia is a ubiquitous phenotype of RASopathies, especially in CFC syndrome. To better understand the underlying mechanisms for the skeletal myopathy in CFC, a mouse model with an activating BrafThe activating BrafA skeletal myopathy was identified in the CFC Braf

Cardio-facio-cutaneous syndrome (CFC) is one of the RASopathies and is caused by germline mutations that activate the Ras/mitogen-activated protein kinase (MAPK) pathway. CFC is due to heterozygous germline mutations in protein kinases BRAF, MEK1, or MEK2 and rarely in KRAS, a small GTPase. CFC is a multiple congenital anomaly disorder in which individuals may have craniofacial dysmorphia, heart issues, skin and hair anomalies, and delayed development. Pathogenic variants for CFC syndrome are usually considered de novo because vertical transmission has only been reported with MEK2 and KRAS. The index case was a 3-year-old male with features consistent with the clinical diagnosis of CFC. Sequencing revealed a previously reported heterozygous likely pathogenic variant BRAF p.G464R. Upon detailed family history, the index case's pregnant mother was noted to have similar features to her son. Targeted familial testing of the BRAF pathogenic variant was performed on the mother, confirming her diagnosis. Prenatal genetic testing for the fetus was declined, but postnatal molecular testing of the index case's sister was positive for the familial BRAF p.G464R variant. Functional analysis of the variant demonstrated increased kinase activity. We report the first identified vertically transmitted functional BRAF pathogenic variant. Our findings emphasize the importance of obtaining a comprehensive evaluation of family members and that activating pathogenic variants within the canonical MAPK cascade mediated by BRAF are compatible with human reproduction.

The RASopathies are defined as a group of medical genetics syndromes that are caused by germ-line mutations in genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) pathway. Taken together, the RASopathies represent one of the most prevalent groups of malformation syndromes affecting greater than 1 in 1,000 individuals. The Ras/MAPK pathway has been well studied in the context of cancer as it plays essential roles in growth, differentiation, cell cycle, senescence and apoptosis, all of which are also critical to normal development. The consequence of germ-line dysregulation leads to phenotypic alterations of development. RASopathies can be caused by several pathogenetic mechanisms that ultimately impact or alter the normal function and regulation of the MAPK pathway. These pathogenetic mechanisms can include functional alteration of GTPases, Ras GTPase-activating proteins, Ras guanine exchange factors, kinases, scaffolding or adaptor proteins, ubiquitin ligases, phosphatases and pathway inhibitors. Although these mechanisms are diverse, the common underlying biochemical phenotype shared by all the RASopathies is Ras/MAPK pathway activation. This results in the overlapping phenotypic features among these syndromes.

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.

The Ras/mitogen activated protein kinase (MAPK) pathway is essential in the regulation of the cell cycle, differentiation, growth and cell senescence, all of which are critical to normal development. It is therefore not surprising that its dysregulation has profound effects on development. A class of developmental disorders, the “RASopathies”, is caused by germline mutations in genes that encode protein components of the Ras/MAPK pathway. The vast majority of these mutations result in increased signal transduction down the Ras/MAPK pathway, but usually to a lesser extent than somatic mutations associated with oncogenesis. Each syndrome exhibits unique phenotypic features, however, since they all cause dysregulation of the Ras/MAPK pathway, there are numerous overlapping phenotypic features between the syndromes, including characteristic facial features, cardiac defects, cutaneous abnormalities, neurocognitive delay and a predisposition to malignancies. Here we review the clinical and underlying molecular basis for each of these syndromes.

Costello syndrome (CS) is a complex developmental disorder involving characteristic craniofacial features, failure to thrive, developmental delay, cardiac and skeletal anomalies, and a predisposition to develop neoplasia. Based on similarities with other cancer syndromes, we previously hypothesized that CS is likely due to activation of signal transduction through the Ras/MAPK pathway [Tartaglia et al., 2003]. In this study, the HRAS coding region was sequenced for mutations in a large, well-characterized cohort of 36 CS patients. Heterogeneous missense point mutations predicting an amino acid substitution were identified in 33/36 (92%) patients. The majority (91%) had a 34G --> A transition in codon 12. Less frequent mutations included 35G --> C (codon 12) and 37G --> T (codon 13). Parental samples did not have an HRAS mutation supporting the hypothesis of de novo heterogeneous mutations. There is phenotypic variability among patients with a 34G --> A transition. The most consistent features included characteristic facies and skin, failure to thrive, developmental delay, musculoskeletal abnormalities, visual impairment, cardiac abnormalities, and generalized hyperpigmentation. The two patients with 35G --> C had cardiac arrhythmias whereas one patient with a 37G --> T transversion had an enlarged aortic root. Of the patients with a clinical diagnosis of CS, neoplasia was the most consistent phenotypic feature for predicating an HRAS mutation. To gain an understanding of the relationship between constitutional HRAS mutations and malignancy, HRAS was sequenced in an advanced biphasic rhabdomyosarcoma/fibrosarcoma from an individual with a 34G --> A mutation. Loss of the wild-type HRAS allele was observed, suggesting tumorigenesis in CS patients is accompanied by additional somatic changes affecting HRAS. Finally, due to phenotypic overlap between CS and cardio-facio-cutaneous (CFC) syndromes, the HRAS coding region was sequenced in a well-characterized CFC cohort. No mutations were found which support a distinct genetic etiology between CS and CFC syndromes.

Prader-Willi syndrome (PWS) is caused by lack of expression of paternally inherited genes on chromosome 15q11-->15q13. Most cases result from microdeletions in proximal chromosome 15q. The remainder results from maternal uniparental disomy of chromosome 15, imprinting center defects, and rarely from balanced or unbalanced chromosome rearrangements involving chromosome 15. We report a patient with multiple congenital anomalies, including craniofacial dysmorphology, microcephaly, bilateral cryptorchidism, and developmental delay. Cytogenetic analysis showed a de novo 45,XY,der(5)t(5;15)(p15.2;q13), -15 karyotype. In effect, the proband had monosomies of 5p15.2-->pter and 15pter-->15q13. Methylation polymerase chain reaction analysis of the promoter region of the SNRPN gene showed only the maternal allele, consistent with the PWS phenotype. The proband's expanded phenotype was similar to other patients who have PWS as a result of unbalanced translocations and likely reflects the contribution of the associated monosomy. Array comparative genomic hybridization (array CGH) confirmed deletions of both distal 5p and proximal 15q and provided more accurate information as to the size of the deletions and the molecular breakpoints. This case illustrates the utility of array CGH in characterizing complex constitutional structural chromosome abnormalities at the molecular level.

The timing of myogenic differentiation of hypaxial muscle precursor cells in the somite lags behind that of epaxial precursors. Two hypotheses have been proposed to explain this delay. One attributes the delay to the presence of negative-acting signals from the lateral plate mesoderm adjacent to the hypaxial muscle precursor cells located in the ventrolateral lip of the somitic dermomyotome (Pourquié et al. [1995] Proc. Natl. Acad. Sci. USA 92:3219-3223). The second attributes the delay to an absence of positive-acting inductive signals, similar to those from the axial structures that induce epaxial myotome development (Pownall et al. [1996] Development 122:1475-1488). Because both studies relied principally upon changes in the expression pattern of mRNAs specific to early muscle precursor cell markers, we revisited these experiments using two methods to assess muscle terminal differentiation. First, injection of fluorescent dyes before surgery was used to determine whether ventrolateral lip cells transform from epithelial cells to elongated myocytes. Second, an antibody to a terminal differentiation marker and a new monoclonal antibody that recognises avian and mammalian Pax3 were used for immunohistochemistry to assess the transition from precursor cell to myocyte. The results support both hypotheses and show further that placing axial structures adjacent to the somite ventrolateral lip induces an axial pattern of myocyte terminal differentiation and elongation.

The enzymatic transfer of ADP-ribose from NAD to histone H(1) [defined as trans(oligo-ADP-ribosylation)] or to PARP-1 [defined as auto(poly-ADP-ribosylation)] requires binding of coenzymic DNA. The preceding paper [Kun, E., et al. (2004) Biochemistry 43, 210-216] shows that oligonucleotides of dsDNA can serve as coenzymic DNA for PARP-1 trans- or auto-modification activity. Results of DNA-protein binding (EMSA) experiments reported here demonstrate that short DNA oligonucleotides containing the 5'-TGTTG-3' nucleotide sequence motif preferentially bind to cloned PARP-1 in vitro. The same nucleotide sequence motif is responsible for striated myocyte-selective transcription of a contractile protein gene encoding cardiac troponin T (cTnT). Results of experiments reported here demonstrate that mutation of this motif also abolishes the differentiation-dependent activation of the transfected cTnT promoter in myoblasts cultured in vitro, indicating that nucleotide sequence-dependent binding of PARP-1 to promoter DNA of the cTnT gene is also necessary for differentiation-dependent activation. Thus, PARP-1 has two types of dsDNA binding activity: (1) nucleotide sequence-dependent binding, analyzed here with EMSA experiments, and (2) coenzymic binding, measured catalytically, which does not depend on the nucleotide sequence of the dsDNA. We hypothesize that the well-known association of PARP-1 with chromatin can be attributed to its stable binding to chromosomal dsDNA, some portion of which is likely to be nucleotide sequence-dependent binding. According to this hypothesis, the distribution of this protein-modifying enzyme in chromatin may be targeted to specific genomic loci and vary according to cell type and developmental stage.

The chicken cardiac troponin T (cTnT) gene is representative of numerous cardiac and skeletal muscle-specific genes that contain muscle-CAT (MCAT) elements within their promoters. We examined the regulation of the chicken cTnT gene in vivo in zebrafish embryos, and in vitro in cardiomyocyte, myoblast, and fibroblast cultures. Defined regions of the cTnT promoter were linked to the green fluorescent protein (GFP) gene for in vivo analysis, and the luciferase gene for in vitro analysis. Injection of the cTnT promoter constructs into fertilized zebrafish eggs resulted in GFP expression in both heart and skeletal muscle cells reproducing the pattern of expression of the endogenous cTnT gene in the chicken embryo. Promoter deletion analysis revealed that the cis-regulatory regions responsible for cardiac and skeletal muscle-specific expression functioned in an equivalent manner in both in vitro and in vivo environments. In addition, we show that mutation of the poly-ADP ribose polymerase-I (PARP-I) binding site adjacent to the distal MCAT element in the chicken cTnT promoter produced a non-cell-specific promoter in vitro and in the zebrafish. Thus, the PARP-I transcriptional regulatory mechanism that governs muscle specificity of the chicken cTnT promoter is conserved across several chordate classes spanning at least 350 million years of evolution.

The expression of fast myosin heavy chain (MyHC) genes was examined in vivo during fast skeletal muscle development in the inbred White Leghorn chicken (line 03) and in adult muscles from the genetically related dystrophic White Leghorn chicken (line 433). RNA dotblot and northern hybridization was employed to monitor MyHC transcript levels utilizing specific oligonucleotide probes. The developmental pattern of MyHC gene expression in the pectoralis major (PM) and the gastrocnemius muscles was similar during embryonic development with three embryonic MyHC isoform genes, Cemb1, Cemb2, and Cemb3, sequentially expressed. Following hatching, MyHC expression patterns in each muscle differed. The expression of MyHC genes was also studied in muscle cell cultures derived from 12-day embryonic pectoralis muscles. In vitro, Cvent, Cemb1, and Cemb2 MyHC genes were expressed; however, little if any Cemb3 MyHC gene expression could be detected, even though Cemb3 was the predominant MyHC gene expressed during late embryonic development in vivo. In most adult muscles other than the PM and anterior latissimus dorsi (ALD), the Cemb3 MyHC gene was the major adult MyHC isoform. In addition, two general patterns of expression were identified in fast muscle. The fast muscles of the leg expressed neonatal (Cneo) and Cemb3 MyHC genes, while other fast muscles expressed adult (Cadult) and Cemb3 MyHC genes. MyHC gene expression in adult dystrophic muscles was found to reflect the expression patterns found in corresponding normal muscles during the neonatal or early post-hatch developmental period, providing additional evidence that avian muscular dystrophy inhibits muscle maturation.

RASopathies are syndromes caused by gain-of-function mutations in the Ras signaling pathway. One of these conditions, Costello syndrome (CS), is typically caused by an activating de novo germline mutation in HRAS and is characterized by a wide range of cardiac, musculoskeletal, dermatological and developmental abnormalities. We report that a majority of individuals with CS have hypo-mineralization of enamel, the outer covering of teeth, and that similar defects are present in a CS mouse model. Comprehensive analysis of the mouse model revealed that ameloblasts, the cells that generate enamel, lacked polarity, and the ameloblast progenitor cells were hyperproliferative. Ras signals through two main effector cascades, the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K) pathways. To determine through which pathway Ras affects enamel formation, inhibitors targeting either PI3K or MEK 1 and 2 (MEK 1/2), kinases in the MAPK pathway, were utilized. MEK1/2 inhibition rescued the hypo-mineralized enamel, normalized the ameloblast polarity defect and restored normal progenitor cell proliferation. In contrast, PI3K inhibition only corrected the progenitor cell proliferation phenotype. We demonstrate for the first time the central role of Ras signaling in enamel formation in CS individuals and present the mouse incisor as a model system to dissect the roles of the Ras effector pathways in vivo.

Introduction: RASopathies are a group of genetic conditions due to alterations of the Ras/MAPK pathway. Neurocutaneous findings are hallmark features of the RASopathies, but musculoskeletal abnormalities are also frequent. The objective was to evaluate handgrip strength in the RASopathies. Methods: Individuals with RASopathies (e.g., Noonan syndrome, Costello syndrome, cardio-facio-cutaneous [CFC] syndrome, and neurofibromatosis type 1 [NF1]) and healthy controls were evaluated. Two methods of handgrip strength were tested: GRIP-D Takei Hand Grip Dynamometer and the Martin vigorimeter. A general linear model was fitted to compare average strength among the groups, controlling for confounders such as age, gender, height, and weight. Results: Takei dynamometer: handgrip strength was decreased in each of the syndromes compared with controls. Decreased handgrip strength compared with sibling controls was also seen with the Martin vigorimeter (P < 0.0001). Conclusions: Handgrip strength is decreased in the RASopathies. The etiology of the reduced muscle force is unknown, but likely multifactorial. Muscle Nerve 46: 394–399, 2012

A class of clinically related developmental disorders, the RASopathies, has recently been shown to be caused by germline mutations in genes that encode components, or regulators, of the Ras/mitogen-activated protein kinase (MAPK) pathway. Neurofibromatosis type 1, the first syndrome identified to be caused by a germline mutation in this pathway, was followed by other syndromes including Noonan, Noonan with multiple lentigines, capillary malformation–AV malformation, Costello, cardio-facio-cutaneous, and Legius. The Ras/MAPK pathway plays an essential role in the regulation of the cell cycle, differentiation, growth, and cell senescence, all of which are critical to normal development. As a result, Ras/MAPK pathway dysregulation has been shown to have profound deleterious effects on both embryonic and later stages of development. Because the underlying molecular mechanism for these syndromes is dysregulation of the Ras/MAPK pathway, the RASopathies exhibit numerous overlapping phenotypic features, including reduced growth, characteristic facial features, cardiac defects, cutaneous abnormalities, neurocognitive delay, and a predisposition to neoplasia, both benign and malignant. As a group, the RASopathies are one of the largest recognizable patterns of malformation syndromes known, affecting approximately 1:1,000 individuals.

Cardio-facio-cutaneous syndrome (CFC) and Costello syndrome (CS) are two of the more rare RASopathies caused by altered signal transduction of the Ras/mitogen-activated protein kinase (MAPK) pathway. All of the RASopathies exhibit some degree of hypotonia, but CS and CFC are more severe. To determine if individuals with CS and CFC have an underlying skeletal myopathy, we systematically evaluated skeletal muscle pathology in both conditions. We reviewed pathology reports from six individuals who had undergone a skeletal muscle biopsy, and we reviewed histology slides on two cases with CS and one case with CFC. All patients in the cohort had histopathologic findings, and two consistent abnormalities were identified. The first was the presence of abnormal muscle fiber size and variability, and the second was the presence of type 2 fiber predominance. Given the degree of hypotonia typically present in these patients, the overall architecture of the muscle was relatively normal, without showing indications of severe structural histopathology or metabolic abnormalities. Because the Ras/MAPK pathway is vital for skeletal myogenesis, we evaluated the effects of CS and CFC mutations on myogenesis using C2C12 myoblasts. All CS/CFC mutations inhibited myoblast differentiation as indicated by fewer myosin heavy chain expressing cells and a decrease in the number of myotubes as compared to controls. These findings indicate that CS and CFC may have a true myopathy related to an inherent dysregulation of skeletal myogenesis, which further expands our understanding of the consequences of germline Ras/MAPK mutations. © 2011 Wiley-Liss, Inc.

The Ras/mitogen-activated protein kinase (MAPK) pathway is essential in regulation of the cell cycle, cell differentiation, growth, and cell senescence, each of which are critical to normal development. A class of developmental disorders, the "RASopathies," is caused by germline mutations in genes that encode protein components of the Ras/MAPK pathway which result in dysregulation of the pathway and profound deleterious effects on development. One of these syndromes, cardiofaciocutaneous (CFC) syndrome, is caused by germline mutations in BRAF, MAP2K1 (MEK1) and MAP2K2 (MEK2), and possibly KRAS genes. Here, we describe the laboratory protocols and methods that we used to identify mutations in BRAF and MEK1/2 genes as causative for CFC syndrome. In addition, we present the techniques used to determine the effect these mutations have on activity of the Ras/MAPK pathway through Western blot analysis of the phosphorylation of endogenous ERK1/2, as well as through the use of an in vitro kinase assay that measures the phosphorylation of Elk-1.

Cardio-facio-cutaneous (CFC) syndrome is one of the RASopathies and is caused by alteration of activity through the Ras/mitogen-activated protein kinase (MAPK) pathway due to heterozygous de novo mutations in protein kinases BRAF, MEK1, or MEK2. CFC is a rare multiple congenital anomaly disorder in which individuals have characteristic dysmorphic features, cardiac defects, ectodermal anomalies and developmental delay.We report a 7(1/2)-month-old boy with a clinical diagnosis of CFC. Bidirectional sequence analysis of MEK2 revealed a novel c.383C-->A transversion in exon 3 resulting in a nonsynonymous missense substitution, p.P128Q. Other family members, including the proband's mother and half-sibling, displayed phenotypic features of CFC and were also screened for the MEK2 mutation identified in the proband. Sorting Intolerant From Tolerant (SIFT) analysis determined the novel MEK2 p.P128Q to be deleterious. To corroborate the functional alteration of the novel mutant protein, transient transfection of HEK 293T cells with subsequent Western analysis was used to demonstrate increased kinase activity, as measured by ERK phosphorylation. This first reported case of a vertically transmitted functional CFC MEK mutation further expands our understanding of germline mutations within the Ras/MAPK pathway.

The Ras/mitogen-activated protein kinase (MAPK) pathway is essential in regulation of the cell cycle, cell differentiation, growth, and cell senescence, each of which are critical to normal development. A class of developmental disorders, the "RASopathies," is caused by germline mutations in genes that encode protein components of the Ras/MAPK pathway which result in dysregulation of the pathway and profound deleterious effects on development. One of these syndromes, cardiofaciocutaneous (CFC) syndrome, is caused by germline mutations in BRAF, MAP2K1 (MEK1) and MAP2K2 (MEK2), and possibly KRAS genes. Here, we describe the laboratory protocols and methods that we used to identify mutations in BRAF and MEK1/2 genes as causative for CFC syndrome. In addition, we present the techniques used to determine the effect these mutations have on activity of the Ras/MAPK pathway through Western blot analysis of the phosphorylation of endogenous ERK1/2, as well as through the use of an in vitro kinase assay that measures the phosphorylation of Elk-1.

cDNAs encoding the rod region of four different fast myosin heavy chains (MYCHs) in the chicken were identified, using anti-MYCH monoclonal antibodies, in two expression libraries prepared from 19-day embryonic and adult chicken muscle. These clones were used to determine the amino acid sequences that encompass the epitopes of five anti-MYHC monoclonal antibodies. Additionally, the amino acid sequences were compared to each other and to a full length embryonic MYHC. Although there is extensive homology in the chicken fast myosin rods, sequences within the hinge, within the central portion of the light meromyosin fragment, and at the carboxy terminus exhibit the largest number of amino acid substitutions. We propose that divergence within these subdomains may contribute to isoform-specific properties associated with skeletal myosin rods.

Comparisons of the nucleotide sequences of the light meromyosin (LMM) region of developmentally regulated fast chicken myosin heavy chain (MHC) isoforms indicates that chicken MHC isoforms are more similar to each other than to MHC isoforms in other species. The sequence data provide evidence that gene conversion events have occurred recently among the isoforms. An embryonic (C emb1 ) isoform and neonatal isoform have the most extensive regions of sequence identity. Similar gene conversion events are present in the rat α- and β-cardiac MHCs, but were not obvious in the LMM of developmentally regulated fast human MHC isoforms. The data suggest that gene conversion events can play a significant role in the evolution of the MHC multigene families and that concerted evolution of the chicken multigene family occurred after the divergence of mammals and avians.

A class of developmental disorders caused by dysregulation of the Ras-induced mitogen-activated protein kinase (MAPK) cascade (the Ras–MAPK pathway) has emerged. Three of these disorders – Noonan, Costello and cardio–facio–cutaneous syndromes – have overlapping phenotypic features characterised by distinctive facial dysmorphia, cardiac defects, musculoskeletal and cutaneous abnormalities, and neurocognitive delay. The germline mutations associated with these disorders are in genes that encode proteins of the Ras–MAPK pathway. In vitro studies have determined that the overwhelming majority of these mutations result in increased signal transduction down the pathway, but usually to a lesser degree than somatic mutations in the same genes that are associated with cancer. The Ras–MAPK pathway is essential in the regulation of the cell cycle, differentiation, growth and senescence, so it is not surprising that germline mutations that affect its function have profound effects on development. Here we review the clinical consequences of the known molecular lesions associated with Noonan syndrome, Costello syndrome and cardio–facio–cutaneous syndrome, and explore possible therapeutic modalities for treatment.

Interstitial deletions of chromosome 12q are rare, with only 11 reported cases in the literature. We recently described two cases with cytogenetically identical interstitial deletions of the long arm of chromosome 12. Here, we report on a third patient, a 26-month-old male with a cytogenetically-identical interstitial deletion: 46,XY,del(12)(q21.2q22). Phenotypic features of this male proband included craniofacial and ectodermal anomalies, genitourinary anomalies, minor cardiac abnormalities, mild ventriculomegaly on brain MRI, hyperopia, and developmental delay. To further define the extent of the chromosomal aberration, microarray-based comparative genomic hybridization (array CGH) analysis was performed and the array data was compared to one of our previously reported cases. Although cytogenetic analysis of the two patients was concordant, molecular analysis by array CGH revealed that the patients had discordant distal breakpoints. The determination of molecular breakpoints and phenotypic analyses in these two patients, in conjunction with previously reported cases, leads us to propose a 12q deletion phenotype and a possible genetic locus for hyperkeratosis pilaris/ulerythema ophryogenes.

Sequence comparisons of avian and mammalian skeletal and cardiac myosin heavy-chain isoforms are used to examine the evolutionary relationships of sarcomeric myosin multigene families. Mammalian fast-myosin heavy-chain isoforms from different species, with comparable developmental expression, are more similar to each other than they are to other fast isoforms within the same genome. In contrast, the developmentally regulated chicken fast isoforms are more similar to each other than they are to myosin heavy-chain isoforms in other species. Extensive regions of nucleotide identity among the chicken fast myosin heavy chains and in the mouse and rat alpha- and beta-cardiac myosin heavy-chain sequences suggest that gene-conversion-like mechanisms have played a major role in the concerted evolution of these gene families. We also conclude that the chicken fast myosin heavy-chain multigene family has undergone recent expansion subsequent to the divergence of birds and mammals and that both the developmental regulation and the specialization of myosin isoforms have likely developed independently in birds and mammals.

Costello syndrome (CS; MIM 214080) is a rare multiple congenital anomaly disorder in which individuals have characteristic dysmorphic craniofacial features, cardiac abnormalities, ectodermal and musculoskeletal anomalies, endocrinopathy, developmental delay, and a predisposition to neoplasia both benign and malignant. In this study, we examined a large, well-characterized cohort of patients with the clinical diagnosis of CS. We sequenced HRAS in 36 unrelated individuals with the clinical diagnosis of CS and three sets of parents and 10 normal controls. We screened for HRAS coding region mutations in an effort to define HRAS mutations in CS and attempt to establish a possible genotype-phenotype correlation. In addition, we sequenced HRAS to establish loss of heterozygosity in a rhabdomyosarcoma and fibrosarcoma from a CS patient. HRAS mutations were identified in 33 out of 36 (92%) patients with the clinical diagnosis of CS. Mutations were found in codon 12 or 13. Two different missense point mutations were identified in codon 12: 34G9A and 35G9C, predicting an amino acid substitution of gly12ser and gly12ala, respectively. The 34G9A transition mutation, the most common mutation observed in this cohort of patients, was found in 30 of 33 patients. Two patients were found to have a codon 12 35G9C transversion. One patient in the cohort had a codon 13 mutation: 37G9T transversion, predicting an amino acid substitution of gly13cys. Parental DNA samples from three CS patients with the 34G9A mutation did not harbor a mutation. HRAS was sequenced from DNA isolated from a rhabdomyosarcoma and fibrosarcoma from a patient who had the germline activating mutation 34GA. Sequence analysis demonstrated LOH of the wild-type allele of HRAS as demonstrated by detection of only 34A in exon 1. Our data show that the majority of Costello syndrome patients have de novo heterogeneous HRAS mutations. Furthermore, tumorigenesis in Costello syndrome patients is accompanied by additional somatic changes affecting the HRAS gene.