Rhabdomyosarcoma-associated locus and MYOD1 are syntenic but separate loci on the short arm of human chromosome 11

Novel Peptide Inhibitors for Lactate Dehydrogenase A (LDHA): A Survey to Inhibit LDHA Activity via Disruption of Protein-Protein Interaction

Lactate dehydrogenase A (LDHA) is a critical metabolic enzyme belonging to a family of 2-hydroxy acid oxidoreductases that plays a key role in anaerobic metabolism in the cells. In hypoxia condition, the overexpression of LDHA shifts the metabolic pathway of ATP synthesis from oxidative phosphorylation to aerobic glycolysis and the hypoxia condition is a common phenomenon occurred in the microenvironment of tumor cells; therefore, the inhibition of LDHA is considered to be an excellent strategy for cancer therapy. In this study, we employed in silico methods to design inhibitory peptides for lactate dehydrogenase through the disturbance in tetramerization of the enzyme. Using peptide as an anti-cancer agent is a novel approach for cancer therapy possessing some advantages with respect to the chemotherapeutic drugs such as low toxicity, ease of synthesis, and high target specificity. So peptides can act as appropriate enzyme inhibitor in parallel to chemical compounds. In this study, several computational techniques such as molecular dynamics (MD) simulation, docking and MM-PBSA calculation have been employed to investigate the structural characteristics of the monomer, dimer, and tetramer forms of the enzyme. Analysis of MD simulation and protein-protein interaction showed that the N-terminal arms of each subunit have an important role in enzyme tetramerization to establish active form of the enzyme. Hence, N-terminal arm can be used as a template for peptide design. Then, peptides were designed and evaluated to obtain best binders based on the affinity and physicochemical properties. Finally, the inhibitory effect of the peptides on subunit association was measured by dynamic light scattering (DLS) technique. Our results showed that the designed peptides which mimic the N-terminal arm of the enzyme can successfully target the C-terminal domain and interrupt the bona fide form of the enzyme subunits. The result of this study makes a new avenue to disrupt the assembly process and thereby oppress the function of the LDHA.

Cardiotrophic Growth Factor-Driven Induction of Human Muse Cells Into Cardiomyocyte-Like Phenotype

Multilineage-differentiating stress-enduring (Muse) cells are endogenous nontumorigenic stem cells collectable as stage-specific embryonic antigen 3 (SSEA-3) + from various organs including the bone marrow and are pluripotent-like. The potential of human bone marrow-derived Muse cells to commit to cardiac lineage cells was evaluated. We found that (1) initial treatment of Muse cells with 5'-azacytidine in suspension culture successfully accelerated demethylation of cardiac marker Nkx2.5 promoter; (2) then transferring the cells onto adherent culture and treatment with early cardiac differentiation factors including wingless-int (Wnt)-3a, bone morphogenetic proteins (BMP)-2/4, and transforming growth factor (TGF) β1; and (3) further treatment with late cardiac differentiation cytokines including cardiotrophin-1 converted Muse cells into cardiomyocyte-like cells that expressed α-actinin and troponin-I with a striation-like pattern. MLC2a expression in the final step suggested differentiation of the cells into an atrial subtype. MLC2v, a marker for a mature ventricular subtype, was expressed when cells were treated with Dickkopf-related protein 1 (DKK-1) and Noggin, inhibitors of Wnt3a and BMP-4, respectively, between steps (2) and (3). None of the steps included exogenous gene transfection, making induced cells feasible for future clinical application.

DNMT3B in vitro knocking-down is able to reverse embryonal rhabdomyosarcoma cell phenotype through inhibition of proliferation and induction of myogenic differentiation

Aberrant DNA methylation has been frequently observed in many human cancers, including rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children. To date, the expression and function of the de novo DNA methyltransferase (DNMT) 3B in RMS have not yet been investigated. Our study show for the first time a significant up-regulation of DNMT3B levels in 14 RMS tumour samples and 4 RMS cell lines in comparison to normal skeletal muscle. Transfection of RD and TE671 cells, two in vitro models of embryonal RMS (ERMS), with a synthetic DNMT3B siRNA decreased cell proliferation by arresting cell cycle at G1 phase, as demonstrated by the reduced expression of Cyclin B1, Cyclin D1 and Cyclin E2, and by the concomitant up-regulation of the checkpoint regulators p21 and p27. DNMT3B depletion also impaired RB phosphorylation status and decreased migratory capacity and clonogenic potential. Interestingly, DNMT3B knock-down was able to commit ERMS cells towards myogenic terminal differentiation, as confirmed by the acquisition of a myogenic-like phenotype and by the increased expression of the myogenic markers MYOD1, Myogenin and MyHC. Finally, inhibition of MEK/ERK signalling by U0126 resulted in a reduction of DNMT3B protein, giving evidence that DNMT3B is a down-stream molecule of this oncogenic pathway.Taken together, our data indicate that altered expression of DNMT3B plays a key role in ERMS development since its silencing is able to reverse cell cancer phenotype by rescuing myogenic program. Epigenetic therapy, by targeting the DNA methylation machinery, may represent a novel therapeutic strategy against RMS.

A recurrent neomorphic mutation in MYOD1 defines a clinically aggressive subset of embryonal rhabdomyosarcoma associated with PI3K-AKT pathway mutations

Rhabdomyosarcoma, a cancer of skeletal muscle lineage, is the most common soft-tissue sarcoma in children. Major subtypes of rhabdomyosarcoma include alveolar (ARMS) and embryonal (ERMS) tumors. Whereas ARMS tumors typically contain translocations generating PAX3-FOXO1 or PAX7-FOXO1 fusions that block terminal myogenic differentiation, no functionally comparable genetic event has been found in ERMS tumors. Here we report the discovery, through whole-exome sequencing, of a recurrent somatic mutation encoding p.Leu122Arg in the myogenic transcription factor MYOD1 in a distinct subset of ERMS tumors with poor outcomes that also often contain mutations altering PI3K-AKT pathway components. Previous mutagenesis studies had shown that MYOD1 with a p.Leu122Arg substitution can block wild-type MYOD1 function and bind to MYC consensus sequences, suggesting a possible switch from differentiation to proliferation. Our functional data now confirm this prediction. Thus, MYOD1 p.Leu122Arg defines a subset of rhabdomyosarcomas eligible for high-risk protocols and the development of targeted therapeutics.

In vitro indeterminate teleost myogenesis appears to be dependent on Pax3

The zebrafish (Danio rerio) has been used extensively as a model system for developmental studies but, unlike most teleost fish, it grows in a determinate-like manner. A close relative, the giant danio (Devario cf. aequipinnatus), grows indeterminately, displaying both hyperplasia and hypertrophy of skeletal myofibers as an adult. To better understand adult muscle hyperplasia, a postlarval/postnatal process that closely resembles secondary myogenesis during development, we characterized the expression of Pax3/7, c-Met, syndecan-4, Myf5, MyoD1, myogenin, and myostatin during in vitro myogenesis, a technique that allows for the complete progression of myogenic precursor cells to myotubes. Pax7 appears to be expressed only in newly activated MPCs while Pax3 is expressed through most of the myogenic program, as are c-Met and syndecan-4. MyoD1 appears important in all stages of myogenesis, while Myf5 is likely expressed at low to background levels, and myogenin expression is enriched in myotubes. Myostatin, like MyoD1, appears to be ubiquitous at all stages. This is the first comprehensive report of key myogenic factor expression patterns in an indeterminate teleost, one that strongly suggests that Pax3 and/or Myf5 may be involved in the regulation of this paradigm. Further, it validates this species as a model organism for studying adult myogenesis in vitro, especially mechanisms underlying nascent myofiber recruitment.

Update on rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a malignant childhood tumor of mesenchymal origin that currently has a greater than 70% overall 5-year survival. Multimodality treatment is determined by risk stratification according to pretreatment stage, postoperative group, histology, and site of the primary tumor. Pretreatment staging is dependent on primary tumor site, size, regional lymph node status, and presence of metastases. Unique to RMS is the concept of postoperative clinical grouping that assesses the completeness of disease resection and takes into account lymph node evaluation. At all tumor sites, the clinical grouping, and therefore completeness of resection, is an independent predictor of outcome. Overall, the prognosis for RMS is dependent on primary tumor site, patient age, completeness of resection, extent of disease, including the presence and number of metastatic sites and histology and biology of the tumor cells. Therefore, the surgeon plays a vital role in RMS by contributing to risk stratification for treatment, local control of the primary tumor, and outcome. The current state-of-the-art treatment is determined by treatment protocols developed by the Soft Tissue Sarcoma Committee of the children's Oncology Group.

Reverse transcriptase-polymerase chain reaction as an ancillary molecular technique in the diagnosis of small blue round cell tumors by fine-needle aspiration cytology

We evaluated the feasibility and usefulness of reverse transcriptase-polymerase chain reaction (RT-PCR) on fine-needle aspirates for categorization of small blue round cell tumors (SBRCTs). A total of 51 cases, including 25 Ewing sarcoma/peripheral primitive neuroectodermal tumors (PNETs), 11 rhabdomyosarcomas, 13 neuroblastomas, and 2 desmoplastic small round cell tumors (DSRCTs) were analyzed. The detection of the EWS-FLI1 (20/25) and EWS-ERG (4/25) fusion transcripts resolved 24 of 25 cases of Ewing sarcoma/PNET. The PAX3/7-FKHR fusion transcript was detected in 2 of 4 cases of alveolar rhabdomyosarcoma and the EWS-WT1 transcript in both cases of DSRCT. Tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (dopa) decarboxylase transcripts were demonstrated in 10 of 13 cases of neuroblastoma. In comparison, immunocytochemical analysis resolved 19 (76%) of 25 Ewing sarcomas, 9 (82%) of 11 rhabdomyosarcomas, 6 (46%) of 13 neuroblastomas, and 1 (50%) of 2 DSRCTs. Overall, RT-PCR resolved 38 (86%) of 44 vs 35 (69%) of 51 cases by immunocytochemical analysis. RT-PCR is easily applied to fine-needle aspirates of SBRCT and greatly facilitates accurate tumor typing.

Pediatric surgical oncology: management of rhabdomyosarcoma

A malignant tumor of striated muscle origin, Rhabdomyosarcoma (RMS) is a childhood tumor that has benefited from 30 years of multimodality therapeutic trials culminating in a greater than 70% overall current 5-year survival. Prognosis for RMS is dependent on anatomic primary tumor site, age, completeness of resection, presence and number of metastatic sites, histology and biology of the tumor cells. Multimodality treatment is based on risk stratification according to pretreatment stage, postoperative group, histology and site. Therefore, pretreatment staging is vital for assessment and is dependent on primary tumor site, size, regional lymph node status, and presence of metastases. Unique to RMS is the concept of postoperative clinical grouping that assesses the completeness of disease resection and takes into account lymph node evaluation both at the regional and metastatic basins. At all sites, if operative resection of all disease is accomplished, including microscopic disease, survival is improved. Therefore, the surgeon plays a vital role in determining risk stratification for treatment and local control of the primary tumor for RMS.

Rhabdomyosarcomas in adults and children: an update

CONTEXT

Rhabdomyosarcomas comprise a relatively common diagnostic entity among childhood cancers and a relatively rare one among adult tumors. They may possess a variety of histologies that generally differ among age groups. These lesions appear to be separate biologic entities as well as morphologic categories, with embryonal tumors having genetic lesions related to loss of heterozygosity and aberrant parental imprinting, alveolar tumors containing genetic fusions between PAX and forkhead genes, and pleomorphic tumors showing an accumulation of genetic lesions similar to other adult high-grade sarcomas.

OBJECTIVE

To present guidelines for diagnosis of rhabdomyosarcoma and recent finding concerning the biology and classification of these lesions.

DATA SOURCES

Review of recent and older published literature and distillation of the authors' experience.

CONCLUSIONS

Infants and young children tend to have embryonal rhabdomyosarcomas, adolescents and young adults tend to have alveolar rhabdomyosarcomas, and older adults tend to have pleomorphic rhabdomyosarcomas, although there is some overlap. Newer rare entities, including spindle cell rhabdomyosarcoma and sclerosing rhabdomyosarcoma, have been described in children and adults. Fusion-positive tumors have a distinct molecular signature with downstream activation of a number of myogenic and tumorigenic factors. Genetic testing may be successfully used for diagnosis and may guide therapy in future clinical trials. Differential diagnosis has become simpler than in previous years, because of use of myogenic factors in immunohistochemistry, but classification based solely on histologic features remains challenging.

The molecular diagnosis of metabolic myopathies

The metabolic myopathies are distinguished by extensive clinical and genetic heterogeneity within and between individual disorders. There are a number of explanations for the variability observed that go beyond single gene mutations or degrees of heteroplasmy in the case of mitochondrial DNA mutations. Some of the contributing factors include protein subunit interactions, tissue-specificity, modifying genetic factors, and environmental triggers. Advances in the molecular analysis of metabolic myopathies during the last decade have not only improved the diagnosis of individual disorders but also helped to characterize the contributing factors that make these disorders so complex.

Duplication of ATR inhibits MyoD, induces aneuploidy and eliminates radiation-induced G1 arrest

Chromosome 3q alterations occur frequently in many types of tumours. In a genetic screen for loci present in rhabdomyosarcomas, we identified an isochromosome 3q [i(3q)], which inhibits muscle differentiation when transferred into myoblasts. The i(3q) inhibits MyoD function, resulting in a non-differentiating phenotype. Furthermore, the i(3q) induces a 'cut' phenotype, abnormal centrosome amplification, aneuploidy and loss of G1 arrest following gamma-irradiation. Testing candidate genes within this region reveals that forced expression of ataxia-telangiectasia and rad3-related (ATR) results in a phenocopy of the i(3q). Thus, genetic alteration of ATR leads to loss of differentiation as well as cell-cycle abnormalities.

Methylation alterations of the MyoD1 upstream region are predictive of subclassification of human rhabdomyosarcomas

MyoD1 expression is a distinguishing characteristic of rhabdomyosarcoma. In this study, distinct methylation alterations were identified in the 5' flanking region of the MyoD1 gene from the two major subtypes, ie, alveolar and embryonal rhabdomyosarcoma. The MyoD1 methylation patterns of 26 rhabdomyosarcomas were compared with that of normal skeletal muscle and nonmuscle specimens by Southern blot analysis using methylation-sensitive restriction enzymes HhaI and HpaII. A 5-kb region immediately upstream of the MyoD1 coding sequence was found to be methylated in adult muscle and all nonmuscle tissues tested. The MyoD1 upstream region was unmethylated in the majority of the alveolar rhabdomyosarcomas (13 of 15, 87%) examined in this study. In contrast, 10 of 11 (91%) embryonal rhabdomyosarcomas showed a methylation pattern that was also observed in fetal muscle cells, in which the CpG sites in the MyoD1 upstream region were partially methylated. Our data suggest that the methylation status of the MyoD1 upstream CpG sites may be related to rhabdomyosarcoma tumorigenesis and may have valuable implications for its differential diagnosis.

Detection of the MyoD1 transcript in rhabdomyosarcoma cell lines and tumor samples by reverse transcription polymerase chain reaction

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood. Diagnosis of RMS can be difficult when it appears as a small round-cell tumor without evidence of differentiation. Recently, a set of regulatory proteins expressed during skeletal muscle development has been described. Among them, MyoD1 has been detected by Northern blot and immunohistochemical analyses in normal skeletal muscle and RMS. Given the relevance of this marker in the diagnosis of RMS, we developed an assay to evaluate the expression of MyoD1 mRNA in small tissue specimens by reverse transcription polymerase chain reaction. Specificity and sensitivity of the assay was determined in a series of 25 tumor cell lines and 39 pediatric tumor samples, including 35 RMSs. Subsequently, we studied the expression of MyoD1 in bone marrow and peripheral blood stem cell specimens. We detected the MyoD1 transcript in normal skeletal muscle and in almost all RMSs, whereas no expression was found in non-RMS samples or in normal hematopoietic tissues. This assay showed high sensitivity and specificity, and it could be a useful molecular tool for the diagnosis of RMS within small roundcell tumors of childhood and for the detection of minimal bone marrow and peripheral blood stem cell involvement in children with RMS, regardless of the histological subtype.

Amplification of MDM2 inhibits MyoD-mediated myogenesis

One obvious phenotype of tumor cells is the lack of terminal differentiation. We previously classified rhabdomyosarcoma cell lines as having either a recessive or a dominant nondifferentiating phenotype. To study the genetic basis of the dominant nondifferentiating phenotype, we utilized microcell fusion to transfer chromosomes from rhabdomyosarcoma cells into C2C12 myoblasts. Transfer of a derivative chromosome 14 inhibits differentiation. The derivative chromosome 14 contains a DNA amplification. MDM2 is amplified and overexpressed in these nondifferentiating hybrids and in the parental rhabdomyosarcoma. Forced expression of MDM2 inhibits MyoD-dependent transcription. Expression of antisense MDM2 restores MyoD-dependent transcriptional activity. We conclude that amplification and overexpression of MDM2 inhibit MyoD function, resulting in a dominant nondifferentiating phenotype.

Diagnosis in neuromuscular diseases

The diagnosis of neuromuscular diseases can be challenging and successful in the majority of patients, due to advancements in electrophysiology, muscle and nerve biopsy immunohistochemistry, and cytogenetics. This article reviews diverse topics, highlighting these recent achievements, with an emphasis on how they affect the clinical and laboratory diagnosis of specific neuromuscular disorders.

Molecular analysis of 36 mutations at the mouse pink-eyed dilution (p) locus

Thirty-six radiation- or chemically induced homozygous-lethal mutations at the p locus in mouse chromosome 7 have been analyzed at 17 loci defined by molecular probes to determine the types of lesions, numbers of p-region markers deleted or rearranged, regions of overlap of deletion mutations, and genetic distances between loci. A linear deletion map of the [Myod1, Ldh3]-[Snrpn, Znf127] region has been constructed from the molecular analyses of the p-locus deletions. The utility of these deletions as tools for the isolation and characterization of the genes specifying the neurological, reproductive, and developmental phenotypes genetically mapped to this region will grow as more detailed molecular analyses continue.

Complementation analyses for 45 mutations encompassing the pink-eyed dilution (p) locus of the mouse

The homozygous and heterozygous phenotypes are described and characterized for 45 new pink-eyed dilution (p) locus mutations, most of them radiation-induced, that affect survival at various stages of mouse development. Cytogenetically detectable aberrations were found in three of the new p mutations (large deletion, inversion, translocation), with band 7C involved in each case. The complementation map developed from the study of 810 types of compound heterozygotes identifies five functional units: jls and jlm (two distinct juvenile-fitness functions, the latter associated with neuromuscular defects), pl-1 and pl-2 (associated with early-postimplantation and preimplantation death, respectively), and nl [neonatal lethality associated with cleft palate (the frequency of rare "escapers" from this defect varied with the genotype)]. Orientation of these units relative to genetic markers is as follows: centromere, Gas-2, pl-1, jls, jlm p, nl (equatable to cp 1 = Gabrb3); pl-2 probably resides in the c-deletion complex. pl-1 does not mask preimplantation lethals between Gas2 and p; and no genes affecting survival are located between p and cp1. The alleles specifying mottling or darker pigment (generically, pm and px, respectively) probably do not represent deletions of p-coding sequences but could be small rearrangements involving proximal regulatory elements.

Pleiotropy in microdeletion syndromes: neurologic and spermatogenic abnormalities in mice homozygous for the p6H deletion are likely due to dysfunction of a single gene

Variability and complexity of phenotypes observed in microdeletion syndromes can be due to deletion of a single gene whose product participates in several aspects of development or can be due to the deletion of a number of tightly linked genes, each adding its own effect to the syndrome. The p6H deletion in mouse chromosome 7 presents a good model with which to address this question of multigene vs. single-gene pleiotropy. Mice homozygous for the p6H deletion are diluted in pigmentation, are smaller than their littermates, and manifest a nervous jerky-gait phenotype. Male homozygotes are sterile and exhibit profound abnormalities in spermiogenesis. By using N-ethyl-N-nitrosourea (EtNU) mutagenesis and a breeding protocol designed to recover recessive mutations expressed hemizygously opposite a large p-locus deletion, we have generated three noncomplementing mutations that map to the p6H deletion. Each of these EtNU-induced mutations has adverse effects on the size, nervous behavior, and progression of spermiogenesis that characterize p6H deletion homozygotes. Because EtNU is thought to induce primarily intragenic (point) mutations in mouse stem-cell spermatogonia, we propose that the trio of phenotypes (runtiness, nervous jerky gait, and male sterility) expressed in p6H deletion homozygotes is the result of deletion of a single highly pleiotropic gene. We also predict that a homologous single locus, quite possibly tightly linked and distal to the D15S12 (P) locus in human chromosome 15q11-q13, may be associated with similar developmental abnormalities in humans.

Molecular genetic studies of muscle lactate dehydrogenase deficiency in white patients

We identified two new mutations in 2 white patients with muscle lactate dehydrogenase deficiency. Both patients had exercise intolerance, cramps, and recurrent myoglobinuria. One patient was homozygous for a 2-bp deletion in exon 5, resulting in a frameshift with premature termination of translation. The second patient was homozygous for a G-->A substitution at the 3' end of exon 2, leading to exon skipping and splicing of exon 1 to exon 3; the aberrantly spliced messenger RNA contains a frameshift, resulting in premature termination of translation. The present report provides evidence of molecular genetic heterogeneity in white patients with muscle lactate dehydrogenase deficiency.

Malignant rhabdoid tumor. A study with two established cell lines

BACKGROUND

Malignant rhabdoid tumor (MRT), originally described as a rare renal sarcoma in childhood, has been known to express phenotypic diversity. In this study, unique characteristics of the MRT cells were investigated by using established cell lines.

METHODS

Immunocytochemical, ultrastructural, cytogenetic, and molecular (by polymerase chain reaction, PCR) analyses were done for two MRT cell lines, one of renal and one of extrarenal origin, before and after differentiation-induction with either 12-O-tetradecanoyl phorbol-13-acetate (TPA) or transretinoic acid (RA).

RESULTS

The proliferating cells in the original tumor tissues as well as in the established cell lines demonstrated neural, epithelial, and mesenchymal markers morphologically. Both cell lines had karyotypic abnormalities including chromosome 22q11.2. The cell line from the extrarenal MRT, Tm87-16, demonstrated distinct morphologic changes with neuroblastic differentiation and produced numerous neuritic processes after treatment with either TPA or RA. The cell line from the renal MRT, STM91-01, suggested schwannian differentiation but did not change morphologically after chemical induction. Both cell lines expressed c-myc, but did not express N-myc, MyoD1, tyrosine hydroxylase, or neural cell adhesion molecule (N-CAM). With PCR and immunocytochemical study, a high level of chromogranin expression was detected by the cells of Tm87-16 only after TPA induced differentiation.

CONCLUSIONS

MRT cells demonstrated diverse phenotype of neuro-ecto-mesenchymal differentiation. The results of this study suggest that MRT may be derived from a primitive pluripotential cell, such as neural crest or equivalent. MRT, therefore, might be categorized as one of the subsets of primitive neuroectodermal tumor.

Evaluation of potential models for imprinted and nonimprinted components of human chromosome 15q11-q13 syndromes by fine-structure homology mapping in the mouse

Prader-Willi and Angelman syndromes are complex neurobehavioral contiguous gene syndromes whose expression depends on the unmasking of genomic imprinting for different genetic loci in human chromosome 15q11-q13. The homologous chromosomal region in the mouse genome has been fine-mapped by using interspecific (Mus spretus) crosses and overlapping, radiation-induced deletions to evaluate potential animal models for both imprinted and nonimprinted components of these syndromes. Four evolutionarily conserved sequences from human 15q11-q13, including two cDNAs from fetal brain (DN10, D15S12h; DN34, D15S9h-1), a microdissected clone (MN7; D15F37S1h) expressed in mouse brain, and the gene for the beta 3 subunit of the gamma-aminobutyric acid type A receptor (Gabrb3), were mapped in mouse chromosome 7 by analysis of deletions at the pink-eyed dilution (p) locus. Three of these loci are deleted in pre- and postnatally lethal p-locus mutations, which extend up to 5.5 +/- 1.7 centimorgans (cM) proximal to p; D15S9h-1, which maps 1.1 +/- 0.8 cM distal to p and is the mouse homolog of the human gene D15S9 (which shows a DNA methylation imprint), is not deleted in any of the p-locus deletion series. A transcript from the Gabrb3 gene, but not the transcript detected by MN7 at the D15F37S1h locus, is expressed in mice homozygous for the p6H deletion, which have an abnormal neurological phenotype. Furthermore, the Gabrb3 transcript is expressed equally well from the maternal or paternal chromosome 7 and, therefore, its expression is not imprinted in mouse brain. Deletions at the mouse p locus should serve as intermediate genetic reagents and models with which to analyze the genetics and etiology of individual components of human 15q11-q13 disorders.

A gene for the mouse pink-eyed dilution locus and for human type II oculocutaneous albinism

The mouse pink-eyed dilution (p) locus on chromosome 7 is associated with defects of skin, eye and coat pigmentation. Mutations at p cause a reduction of eumelanin (black-brown) pigment and altered morphology of black pigment granules (eumelanosomes), but have little effect on pheomelanin (yellow-red) pigment. We show here that the human complementary DNA DN10, linked to the p locus in mice, identifies the human homologue (P) of the mouse p gene, and appears to encode an integral membrane transporter protein. The expression pattern of this gene in various p mutant mice correlates with the pigmentation phenotype; moreover, an abnormally sized messenger RNA is detected in one mutant, p(un), which reverts to the normal size in p(un) revertants. The human P gene corresponds to the D15S12 locus within the chromosome segment 15q11-q13, which is typically deleted in patients with Prader-Willi and Angelman syndrome (see ref. 5 for review). These disorders are phenotypically distinct, depending on the parent of origin of the deleted chromosome, but both syndromes are often associated with hypopigmentation of the skin, hair and eyes (see ref. 8 for review), and deletion of the P gene may be responsible for this hypopigmentation. In addition, we report a mutation in both copies of the human P gene in one case of tyrosinase-positive (type II) oculocutaneous albinism, recently linked to 15q11-q13 (ref. 9).

Cytogenetic study of botryoid rhabdomyosarcoma of the uterine cervix

We report a case of sarcoma botryoides of the uterine cervix occurring in a 19-year-old woman. By light microscopy the tumor showed round and spindle cells with hyperchromatic nuclei and, focally, a cambium layer subjacent to the surface epithelium and surrounding endocervical glands. Strap-shaped cells with and without cross-striations and small foci of immature cartilage were also present. Immunohistochemical studies showed positive staining within the tumor cells for myoglobin, desmin, vimentin, muscle-specific actin and CD56. By electron microscopy, tumor cells showed cytoplasmic filaments in an alternating pattern of thick and thin filaments. Chromosomal analysis demonstrated deletion of the short arm of chromosome 1, and trisomies 13 and 18. To our knowledge, this is the first reported case of sarcoma botryoides of the endocervix with chromosomal analysis.

Cytogenetic abnormalities in non-small cell lung carcinoma: similarity of findings in conventional and feeder cell layer cultures

Primary tumors from 39 patients with non-small cell lung carcinoma (NSCLC) were examined for cytogenetic abnormalities by conventional short-term harvest (1-39 days) of primary cultures of minced solid-tumor tissues and by harvest of monolayer cultures of tumor tissue (6 days to 5 months) on murine fibroblast feeder layers. A successful karyotype was obtained with both methods in nine of 39 cases. Among the remaining 30 cases, a successful karyotype was obtained in eight cases by the conventional method only and in three cases by the feeder cell method only. The success rates were 44% for the conventional method, and 31% for the feeder cell method, and the combined success rate was 51% for one or the other method. The feeder culture method, in which harvests were usually performed at later times than with the conventional method, generally produced metaphases with superior banding, which allowed clearer definition of cytogenetic abnormalities. In addition, cell lines were established in eight of these cases by the feeder cell method. Karyotypes from the longer-term harvests typically were very similar to those from short-term conventional cultures. Minor numerical differences and/or a few additional structural abnormalities were noted in seven of the nine cases analyzed by both methods. Overall, however, even in karyotypes from 5-month cultures, the prominent recurrent changes and modal chromosome numbers observed in short-term cultures were still present. The results indicate that long-term culture with fibroblast feeder cells is a valid means of obtaining cells from solid lung tumors for cytogenetic and molecular analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of myogenic regulatory genes, MyoD1 and myogenin, in human rhabdomyosarcoma sublines

A cell line (SCMC-MM-1) was established from a human abdominal tumor that was initially diagnosed as a malignant mesenchymoma by histological, immunohistochemical and clinical criteria. The cell line was composed of 2 morphologically and immunohistochemically distinct cell types, one with a small polygonal phenotype (P-type), characterized by the immunostaining of vimentin and the presence of a few electron-microscopically visible organelles, and the other with a giant tubular phenotype (T-type), characterized by the immunostaining of desmin, alpha-sarcomeric actin and skeletal-muscle myosin, and the presence of thick and thin myofilaments and Z-line materials. The parental cell line was cloned into 2 sublines, a P-type clone (SCMC-MM-1-19P) and a T-type clone (SCMC-MM-1-1T), which shared both 2q37 and 11p15 translocations, the characteristic chromosomal aberrations for rhabdomyosarcoma, with the parental SCMC-MM-1 cell line. Northern-blot analyses of the myogenic regulatory genes, including MyoD1 and myogenin, demonstrated the expression of MyoD1 in both of these sublines. Myogenin was very weakly expressed in the SCMC-MM-1-19P subline, but strongly expressed in the SCMC-MM-1-1T subline. Chromosomal and myogenic-regulatory-gene analyses revealed that both of these sublines were rhabdomyosarcoma cell lines. Furthermore, the regulatory-gene analyses indicated that these 2 sublines represented 2 distinct differentiation stages of myoblasts, and that MyoD1 and myogenin could serve as the lineage marker and the differentiation marker, respectively, of human rhabdomyosarcoma.

Chromosomal sublocalization of the 2;13 translocation breakpoint in alveolar rhabdomyosarcoma

A characteristic balanced reciprocal chromosomal translocation [t(2;13)(q35;q14)] has been identified in more than 50% of alveolar rhabdomyosarcomas. As the first step in characterization of the genes involved in this translocation, we constructed somatic cell hybrids that retained either the derivative chromosome 2 or the derivative chromosome 13 without a normal chromosome 13 homologue. Ten linked DNA probes known to be located within bands 13q13-q14 were mapped relative to the breakpoint on chromosome 13, allowing localization of the breakpoint region between two loci separated by 5.5 cM. A long-range restriction map extending approximately 2,300 kb around these loci failed to provide evidence of rearrangement. Additionally, we confirmed that the FMS-like tyrosine kinase gene (FLT), previously localized to 13q12 by in situ hybridization, is located proximal to the breakpoint, and we demonstrated that FLT is not a target for disruption by this tumor-specific translocation.

Regulation of muscle cell growth and differentiation by the MyoD family of helix-loop-helix proteins

The skeletal muscle cell system provides a powerful model for exploring the mechanistic basis for the antagonism between cell growth and differentiation. The recent identification of the MyoD family of muscle-specific transcription factors now offers opportunities to dissect at the molecular level of the mechanisms through which defined cell type-specific transcription factors can activate an entire differentiation program as well as to unravel the mechanisms through which growth factor and oncogenic signals can disrupt cellular differentiation. Because the mechanisms for growth factor signaling and induction of cell proliferation are conserved in diverse cell types, it is tempting to speculate that the molecular mechanisms responsible for the antagonism between cell proliferation and differentiation in muscle cells are also operative in other cell types. Resolution of this question, however, must await identification of the regulatory factors that specify cell fate in other lineages.

The myoD gene family: nodal point during specification of the muscle cell lineage

The myoD gene converts many differentiated cell types into muscle. MyoD is a member of the basic-helix-loop-helix family of proteins; this 68-amino acid domain in MyoD is necessary and sufficient for myogenesis. MyoD binds cooperatively to muscle-specific enhancers and activates transcription. The helix-loop-helix motif is responsible for dimerization, and, depending on its dimerization partner, MyoD activity can be controlled. MyoD senses and integrates many facets of cell state. MyoD is expressed only in skeletal muscle and its precursors; in nonmuscle cells myoD is repressed by specific genes. MyoD activates its own transcription; this may stabilize commitment to myogenesis.

The human MyoD1 (MYF3) gene maps on the short arm of chromosome 11 but is not associated with the WAGR locus or the region for the Beckwith-Wiedemann syndrome

The human gene encoding the myogenic determination factor myf3 (mouse MyoD1) has been mapped to the short arm of chromosome 11. Analysis of several somatic cell hybrids containing various derivatives with deletions or translocations revealed that the human MyoD (MYF3) gene is not associated with the WAGR locus at chromosomal band 11p13 nor with the loss of the heterozygosity region at 11p15.5 related to the Beckwith-Wiedemann syndrome. Subregional mapping by in situ hybridization with an myf3 specific probe shows that the gene resides at the chromosomal band 11p14, possibly at 11p14.3.