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Biomedical subjects

M P Scott

Publications and source records attributed to M P Scott.

At least 19 recordsLinked to original sources
PubMed2000

Distinct hox protein sequences determine specificity in different tissues.

Hox genes encode evolutionarily conserved transcription factors that control the morphological diversification along the anteroposterior (A/P) body axis. Expressed in precise locations in the ectoderm, mesoderm, and endoderm, Hox proteins have distinct regulatory activities in different tissues. How Hox proteins achieve tissue-specific functions and why cells lying at equivalent A/P positions but in different germ layers have distinctive responses to the same Hox protein remains to be determined. Here, we examine this question by identifying parts of Hox proteins necessary for Hox function in different tissues. Available genetic markers allow the regulatory effects of two Hox proteins, Abdominal-A (AbdA) and Ultrabithorax (Ubx), to be distinguished in the Drosophila embryonic epidermis and visceral mesoderm (VM). Chimeric Ubx/AbdA proteins were tested in both tissues and used to identify protein sequences that endow AbdA with a different target gene specificity from Ubx. We found that distinct protein sequences define AbdA, as opposed to Ubx, function in the epidermis vs. the VM. These sequences lie mostly outside the homeodomain (HD), emphasizing the importance of non-HD residues for specific Hox activities. Hox tissue specificity is therefore achieved by sensing distinct Hox protein structures in different tissues.

Animals↗
PubMed2000

naked cuticle encodes an inducible antagonist of Wnt signalling.

During animal development, cells have to respond appropriately to localized secreted signals. Proper responses to Hedgehog, transforming growth factor-beta, epidermal growth factor and fibroblast growth factor/Ras signals require cognate inducible antagonists such as Patched, Dad, Argos and Sprouty. Wnt signals are crucial in development and neoplasia. Here we show that naked cuticle (nkd), a Drosophila segment-polarity gene, encodes an inducible antagonist for the Wnt signal Wingless (Wg). In fly embryos and imaginal discs nkd transcription is induced by Wg. In embryos, decreased nkd function has an effect similar to excess Wg; at later stages such a decrease appears to have no effect. Conversely, overproduction of Nkd in Drosophila and misexpression of Nkd in the vertebrate Xenopus laevis result in phenotypes resembling those of loss of Wg/Wnt function. nkd encodes a protein with a single EF hand (a calcium-binding motif) that is most similar to the recoverin family of myristoyl switch proteins. Nkd may therefore link ion fluxes to the regulation of the potency, duration or distribution of Wnt signals. Signal-inducible feedback antagonists such as nkd may limit the effects of Wnt proteins in development and disease.

Amino Acid Sequence↗
PubMed2000

Evidence that haploinsufficiency of Ptch leads to medulloblastoma in mice.

The PTCH gene encodes a putative tumor suppressor protein; germline alterations in PTCH have been found in patients with the nevoid basal cell carcinoma syndrome (NBCCS). Medulloblastoma, a brain tumor, develops in about 3% of NBCCS patients, and mutations in PTCH have also been described in a subset of sporadic medulloblastomas. The search for the causes of medulloblastoma has been hindered by the lack of an appropriate model system for this tumor type. Recently, a transgenic mouse hemizygous for the Ptch gene was generated by homologous recombination. Medulloblastomas were found in about 19% of these mice within the first 25 weeks after birth. The status of the wild-type PTCH allele in these tumors has not been investigated. For clearer definition of the role of PTCH as a tumor suppressor in medulloblastoma, 13 cerebellar tumors from transgenic Ptch(+/-) mice were examined for alterations in the remaining Ptch allele. A single mutation was found in one tumor, a C-to-A substitution changing a tyrosine to a stop codon; all other tumors exhibited a wild-type sequence. Two tumors with normal Ptch cDNA were examined by in situ hybridization. Ptch cDNA was found in tumor cells but not in associated tumor stroma. We also examined the mRNA expression levels for the remaining Ptch allele, as well as for Gli1, a gene known to be transcriptionally activated by Ptch inactivation. Blot analysis of RNA from the 13 tumors shows that Ptch mRNA of appropriate size is expressed in all tumors at varying levels. Expression of Gli1 was increased in tumors compared to normal cerebellum. These results suggest that deletion of one copy of Ptch may be sufficient to promote medulloblastoma development in mice.

Alleles↗
PubMed1999

Vertebrate homologs of Drosophila suppressor of fused interact with the gli family of transcriptional regulators.

The hedgehog (Hh) signaling pathway is crucial for pattern formation during metazoan development. Although originially characterized in Drosophila, vertebrate homologs have been identified for several, but not all, genes in the pathway. Analysis of mutants in Drosophila demonstrates that Suppressor of fused [Su(fu)] interacts genetically with genes encoding proteins in the Hh signal transduction pathway, and its protein product physically interacts with two of the proteins in the Hh pathway. We report here the molecular cloning and characterization of chicken and mouse homologs of Su(fu). The chick and mouse proteins are 27% identical and 53% similar at the amino acid level to the Drosophila melanogaster and Drosophila virilis proteins. Vertebrate Su(fu) is widely expressed in the developing embryo with higher levels in tissues that are known to be patterned by Hh signaling. The chick Su(fu) protein can physically interact with factors known to function in Hh signal transduction including the Drosophila serine/threonine kinase, Fused, and the vertebrate transcriptional regulators Gli1 and Gli3. This interaction may be significant for transcriptional regulation, as recombinant Su(fu) enhances the ability of Gli proteins to bind DNA in electrophoretic mobility shift assays.

Amino Acid Sequence↗
PubMed1999

Overexpression of ptc1 inhibits induction of Shh target genes and prevents normal patterning in the neural tube.

Patched (Ptc) is a human tumor suppressor protein and a candidate receptor for Hedgehog (Hh) proteins, which regulate growth and patterning in embryos. Ptc represses expression of Hh target genes such as Gli1 and ptc1 itself. Localized secretion of Hh appears to induce transcription of target genes in specific patterns by binding to Ptc and preventing it from functioning in recipient cells. People who are heterozygous for PTC1 exhibit a range of developmental defects, suggesting that some genes are inappropriately expressed when there is not enough Ptc protein. To test the idea that a balance between Hh and Ptc activities is essential for normal development, we overexpressed Ptc in the neural tube. We find that excess Ptc is sufficient to inhibit expression of Gli1 and ptc1, suggesting that Sonic hedgehog (Shh) cannot signal effectively. This leads to partial dorsalization of the neural tube and a wide spectrum of neural defects, ranging from embryonic lethality to hydrocephaly.

Animals↗
PubMed1999

Recruitment of a hedgehog regulatory circuit in butterfly eyespot evolution.

The origin of new morphological characters is a long-standing problem in evolutionary biology. Novelties arise through changes in development, but the nature of these changes is largely unknown. In butterflies, eyespots have evolved as new pattern elements that develop from special organizers called foci. Formation of these foci is associated with novel expression patterns of the Hedgehog signaling protein, its receptor Patched, the transcription factor Cubitus interruptus, and the engrailed target gene that break the conserved compartmental restrictions on this regulatory circuit in insect wings. Redeployment of preexisting regulatory circuits may be a general mechanism underlying the evolution of novelties.

Animals↗
PubMed1999

Femoral neck stress fracture presenting as gluteal pain in a marathon runner: case report.

A case is described of a 50-year-old man with a femoral neck stress fracture presenting as gluteal pain. An operative pinning procedure of the femoral neck was performed for stabilization. Femoral neck stress fractures are often misdiagnosed early in their presentation. The signs and symptoms can mimic those of more commonly seen disorders. Appropriate physiatric history and physical examination, along with indicated studies, will help prevent misdiagnosis and potentially serious complications associated with musculoskeletal pathology.

Athletic Injuries↗
PubMed1999

Control of neuronal precursor proliferation in the cerebellum by Sonic Hedgehog.

Cerebellar granule cells are the most abundant type of neuron in the brain, but the molecular mechanisms that control their generation are incompletely understood. We show that Sonic hedgehog (Shh), which is made by Purkinje cells, regulates the division of granule cell precursors (GCPs). Treatment of GCPs with Shh prevents differentiation and induces a potent, long-lasting proliferative response. This response can be inhibited by basic fibroblast growth factor or by activation of protein kinase A. Blocking Shh function in vivo dramatically reduces GCP proliferation. These findings provide insight into the mechanisms of normal growth and tumorigenesis in the cerebellum.

Animals↗
PubMed1999

Ultraviolet and ionizing radiation enhance the growth of BCCs and trichoblastomas in patched heterozygous knockout mice.

Basal cell carcinomas, the commonest human skin cancers, consistently have abnormalities of the hedgehog signaling pathway and often have PTCH gene mutations. We report here that Ptch+/- mice develop primordial follicular neoplasms resembling human trichoblastomas, and that exposure to ultraviolet radiation or ionizing radiation results in an increase in the number and size of these tumors and a shift in their histologic features so that they more closely resemble human basal cell carcinoma. The mouse basal cell carcinomas and trichoblastoma-like tumors resemble human basal cell carcinomas in their loss of normal hemidesmosomal components, presence of p53 mutations, frequent loss of the normal remaining Ptch allele, and activation of hedgehog target gene transcription. The Ptch mutant mice provide the first mouse model, to our knowledge, of ultraviolet and ionizing radiation-induced basal cell carcinoma-like tumors, and also demonstrate that Ptch inactivation and hedgehog target gene activation are essential for basal cell carcinoma tumorigenesis.

Animals↗
PubMed1999

A putative Drosophila homolog of the Huntington's disease gene.

The Huntington's disease (HD) gene encodes a protein, huntingtin, with no known function and no detectable sequence similarity to other proteins in current databases. To gain insight into the normal biological role of huntingtin, we isolated and sequenced a cDNA encoding a protein that is a likely homolog of the HD gene product in Drosophila melanogaster. We also determined the complete sequence of 43 125 contiguous base pairs of genomic DNA that encompass the Drosophila HD gene, allowing the intron-exon structure and 5'- and 3'-flanking regions to be delineated. The predicted Drosophila huntingtin protein has 3583 amino acids, which is several hundred amino acids larger than any other previously characterized member of the HD family. Analysis of the genomic and cDNA sequences indicates that Drosophila HD has 29 exons, compared with the 67 exons present in vertebrate HD genes, and that Drosophila huntingtin lacks the polyglutamine and polyproline stretches present in its mammalian counterparts. The Drosophila HD mRNA is expressed in a broad range of developmental stages and in the adult, a temporal pattern of expression similar to that observed for mammalian HD transcripts. We can discern five regions of high similarity from multiple sequence alignments between Drosophila and vertebrate huntingtins. These regions may define functionally important domains within the protein.

Amino Acid Sequence↗
PubMed1999

Cytokeratin 20: a marker for diagnosing Merkel cell carcinoma.

Merkel cell carcinoma is an aggressive cutaneous neoplasm that is often difficult to diagnose because of its histologic and immunohistochemical similarity to metastatic oat cell carcinomas and other cutaneous neoplasms. Our purpose was to determine the utility of immunoperoxidase staining of cytokeratin 20 (CK 20), a newly discovered intermediate filament protein, in Merkel cell carcinomas and other cutaneous tumors. Sixty-one tumors were sectioned and stained with antibodies directed at CK 20. The staining of Merkel cell carcinomas was compared with metastatic oat cell carcinomas, lymphomas, squamous cell carcinomas, basal cell carcinomas, melanomas, metastatic carcinoids, spiradenomas, eccrine carcinomas, adenoidcystic carcinoma, sebaceous carcinomas, hidradenomas, sebaceous epitheliomas, trichoblastomas, mixed tumors, and metastatic adenocarcinomas. Nine of 10 Merkel cell carcinomas stained with antibody to CK 20. Two metastatic carcinomas to the skin were also positive. One hidradenoma and one squamous carcinoma exhibited focal staining, but were otherwise negative. All other tumors were nonstaining. Cytokeratin 20 is a sensitive and specific marker for Merkel cell carcinoma and is helpful in distinguishing between Merkel cell carcinoma and other malignant and benign neoplasms.

Biomarkers, Tumor↗
PubMed1999

Mouse patched1 controls body size determination and limb patterning.

Hedgehog (Hh) proteins control many developmental events by inducing specific cell fates or regulating cell proliferation. The Patched1 (Ptc1) protein, a binding protein for Hh molecules, appears to oppose Hh signals by repressing transcription of genes that can be activated by Hh. Sonic hedgehog (Shh), one of the vertebrate homologs of Hh, controls patterning and growth of the limb but the early embryonic lethality of ptc1(-)(/)(-) mice obscures the roles of ptc1 in later stages of development. We partially rescued ptc1 homozygous mutant embryos using a metallothionein promoter driving ptc1. In a wild-type background, the transgene causes a marked decrease in animal size starting during embryogenesis, and loss of anterior digits. In ptc1 homozygotes, a potent transgenic insert allowed survival to E14 and largely normal morphology except for midbrain overgrowth. A less potent transgene gave rise to partially rescued embryos with massive exencephaly, and polydactyly and branched digits in the limbs. The polydactyly was preceded by unexpected anterior limb bud transcription of Shh, so one function of ptc1 is to repress Shh expression in the anterior limb bud.

Animals↗
PubMed1999

Defects in mouse mammary gland development caused by conditional haploinsufficiency of Patched-1.

In vertebrates, the hedgehog family of cell signaling proteins and associated downstream network components play an essential role in mediating tissue interactions during development and organogenesis. Loss-of-function or misexpression mutation of hedgehog network components can cause birth defects, skin cancer and other tumors. The mammary gland is a specialized skin derivative requiring epithelial-epithelial and epithelial-stromal tissue interactions similar to those required for development of other organs, where these interactions are often controlled by hedgehog signaling. We have investigated the role of the Patched-1 (Ptc1) hedgehog receptor gene in mammary development and neoplasia. Haploinsufficiency at the Ptc1 locus results in severe histological defects in ductal structure, and minor morphological changes in terminal end buds in heterozygous postpubescent virgin animals. Defects are mainly ductal hyperplasias and dysplasias characterized by multilayered ductal walls and dissociated cells impacting ductal lumens. This phenotype is 100% penetrant. Remarkably, defects are reverted during late pregnancy and lactation but return upon involution and gland remodeling. Whole mammary gland transplants into athymic mice demonstrates that the observed dysplasias reflect an intrisic developmental defect within the gland. However, Ptc1-induced epithelial dysplasias are not stable upon transplantation into a wild-type epithelium-free fat pad, suggesting stromal (or epithelial and stromal) function of Ptc1. Mammary expression of Ptc1 mRNA is both epithelial and stromal and is developmentally regulated. Phenotypic reversion correlates with developmentally regulated and enhanced expression of Indian hedgehog (Ihh) during pregnancy and lactation. Data demonstrate a critical mammary role for at least one component of the hedgehog signaling network and suggest that Ihh is the primary hedgehog gene active in the gland.

Alagille Syndrome↗
PubMed1999

The Drosophila kismet gene is related to chromatin-remodeling factors and is required for both segmentation and segment identity.

The Drosophila kismet gene was identified in a screen for dominant suppressors of Polycomb, a repressor of homeotic genes. Here we show that kismet mutations suppress the Polycomb mutant phenotype by blocking the ectopic transcription of homeotic genes. Loss of zygotic kismet function causes homeotic transformations similar to those associated with loss-of-function mutations in the homeotic genes Sex combs reduced and Abdominal-B. kismet is also required for proper larval body segmentation. Loss of maternal kismet function causes segmentation defects similar to those caused by mutations in the pair-rule gene even-skipped. The kismet gene encodes several large nuclear proteins that are ubiquitously expressed along the anterior-posterior axis. The Kismet proteins contain a domain conserved in the trithorax group protein Brahma and related chromatin-remodeling factors, providing further evidence that alterations in chromatin structure are required to maintain the spatially restricted patterns of homeotic gene transcription.

Amino Acid Sequence↗