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Biomedical subjects

J G Davis

Publications and source records attributed to J G Davis.

At least 37 records · Page 2Linked to original sources
PubMed1997

Relationship of p215BRCA1 to tyrosine kinase signaling pathways and the cell cycle in normal and transformed cells.

We have analysed the relationship of the products of two genes, neu and BRCA1, known to be important in human breast cancer. Highly specific antibodies that recognized both the rodent and human form of the BRCA1 gene product (Mr 215 kDa, p215BRCA1) were developed to facilitate these efforts. p215BRCA1 was identified as a tyrosine phosphorylated protein primarily localized in the nucleus of several breast cancer cell lines. In transformed murine and human cells, levels of p215BRCA1 tyrosine phosphorylation were inversely correlated with the activity of the erbB family receptor-tyrosine-kinases and with the transformed growth features of these cells. Regulation of p215BRCA1 tyrosine phosphorylation was also related to events in the cell cycle. Increased levels of p215BRCA1 phosphotyrosine content were observed in NIH3T3 cells arrested at the G2/M transition. These findings indicate that the products of BRCA1, neu, and erbB breast cancer genes participate in a common or shared signaling pathway important in cell growth and its regulation.

3T3 Cells↗
PubMed1997

Trans receptor inhibition of human glioblastoma cells by erbB family ectodomains.

Our aim has been to understand the features of erbB receptor homo- and heterodimer assembly to develop approaches to disrupt receptor activation. We have developed a general approach to cause erbB receptor-specific trans inhibition of human neoplasia. The clonal progression of human astrocytomas to a more malignant phenotype often involves the amplification and overexpression of the epidermal growth factor receptor (EGFr) gene. We have selectively targeted the EGFr in human glioblastoma cells with kinase-deficient mutants of the erbB family derived from the ectodomain of the Neu oncogene that are able to form heterodimers with EGFr and inhibit EGFr-dependent phenotypes. In EGFr-positive U87MG human glioblastoma cells, expression of the Neu ectodomain inhibits EGF-, but not platelet-derived growth factor-, induced DNA synthesis; inhibits cell proliferation in the presence of EGF, but not platelet-derived growth factor; inhibits the ability of U87MG to form colonies in soft agar; and inhibits transforming efficiency in athymic mice. These studies establish that EGFr-mediated signal transduction is important in the maintenance of malignant glioma, and that trans receptor inhibition is a novel way to abrogate abnormal growth of these tumors. Neu ectodomains will be useful in determining the manner in which the EGFr contributes to glial tumorigenesis and in the design of pharmaceuticals that disable erbB family oncoproteins. In addition, these studies provide a rationale for the application of the Neu ectodomain in gene therapy approaches to human malignant glioma and, potentially, to other systemic epithelial malignancies expressing erbB family receptors.

Animals↗
PubMed1997

Identification of a structural constituent and one possible site of postembryonic formation of a teleost otolithic membrane.

A gelatinous otolithic membrane (OM) couples a single calcified otolith to the sensory epithelium in the bluegill sunfish (Lepomis macrochirus) saccule, one of the otolithic organs in the inner ear. Though the OM is an integral part of the anatomic network of endorgan structures that result in vestibular function in the inner ear, the identity of the proteins that make up this sensory accessory membrane in teleosts, or in any vertebrate, is not fully known. Previously, we identified a cDNA from the sunfish saccular otolithic organ that encoded a new member of the collagen family of structural proteins. In this study, we examined biochemical features and the localization of the saccular collagen (SC) protein in vivo using polyclonal antisera that recognize the noncollagenous domains of the SC protein. The SC protein, in vivo, was identified as a 95-kDa glycoprotein in sunfish whole-saccule lysate and in homogenates of microdissected saccular OMs. Immunohistochemical analyses demonstrated that the SC protein was localized within one of the two distinct layers of the sunfish saccular OM. The SC protein was also detected within the cytoplasm of supporting cells at the edges of the saccular sensory epithelium, indicating that these cells are a primary site for the synthesis of this structural protein. Further studies of the organization of this matrix molecule in the OM may help clarify the role of this sensory accessory membrane in vestibular sensory function.

Animals↗
PubMed1997

Diagnosis of Fanconi anemia in patients without congenital malformations: an international Fanconi Anemia Registry Study.

Data were analyzed from 419 Fanconi anemia (FA) patients enrolled in the American Registry of the International Fanconi Anemia Registry (IFAR) to determine whether Fanconi anemia (FA) patients without major congenital malformations (CM) have distinguishing characteristics that can lead to an earlier diagnosis. These included 377 patients reported by physicians to the IFAR and 42 patients examined by us. The number of FA patients in each group without CM was 128 and 16, respectively; one third of all patients lacked CM. We found that height, weight, and head circumference were < or = 5th centile in 26.6%, 18.0%, and 8.6% of FA patients without CM referred to the IFAR, and in 43.8%, 25.0%, and 43.8% of FA patients without CM examined by us. Minor anomalies were reported in 9.4% of FA patients without CM referred to the IFAR and 100% of FA patients without CM examined by us. Most FA patients without CM have alterations in growth parameters, skin pigmentation abnormalities, or microphthalmia. Increased awareness of the complete spectrum of FA by clinicians will enable an earlier diagnosis to be made.

Congenital Abnormalities↗
PubMed1997

Murine thioredoxin peroxidase delays neuronal apoptosis and is expressed in areas of the brain most susceptible to hypoxic and ischemic injury.

Thioredoxin peroxidase (TPx) is an antioxidant protein that limits the activity of reactive oxygen species (ROS). We cloned the cDNA encoding the mouse homolog of TPx from an E14.5 brain cDNA library and analyzed its distribution and function in murine tissues. Comparison of the amino acid sequence of mouse TPx with those of other species revealed that TPx was highly conserved across all species. Mouse TPx had broad tissue distribution, but its expression was especially marked in cells that metabolize oxygen molecules at high levels such as erythroid cells, renal tubular cells, cardiac and skeletal muscle cells, and certain types of neurons. Levels of increased expression of TPx in the brain were coincident with regions known to be especially sensitive to hypoxic and ischemic injury in humans. Models of erythroid differentiation and neuronal survival were employed to study the function of TPx. Murine erythroleukemia cells (MEL cells) increased TPx transcription when in a chemically differentiated state. Furthermore, expression of mouse TPx in PC12 pheochromocytoma cells prolonged their survival in the absence of nerve growth factor (NGF) and serum, indicating that TPx could promote neuronal cell survival. We propose that TPx contributes to antioxidant defense in erythrocytes and neuronal cells by limiting the destructive capacity of oxygen radicals. These findings identify a novel gene that appears to be relevant to hypoxic brain injury and may be of importance in development of new approaches to abrogate the effects of ischemic- and hypoxic-related injury in the central nervous system (CNS).

Amino Acid Sequence↗
PubMed1997

Definition of the critical interval for Smith-Magenis syndrome.

Smith-Magenis syndrome (SMS) comprises a complex physical and behavioral phenotype that is associated with an interstitial deletion of chromosome 17p11.2. The deletions observed in patients can range from <2 to >9 megabases of DNA and may include more than 100 genes. In order to determine the critical deletion interval responsible for the syndrome phenotype, we have examined several patients with varying deletions involving 17p11.2 by somatic cell hybrid analyses. We have binned 112 markers along 17p11.2, including 27 markers within the critical interval for SMS, which is bound proximally by D17S29 and distally by cCI17-638. In addition, we present two patients who carry deletions involving 17p11.2 but do not exhibit the typical features of SMS. Patients such as these will allow genotype:phenotype correlations to be made and the gene(s) responsible for the SMS phenotype to be determined.

Abnormalities, Multiple↗
PubMed1996

Cloning of m-ehk2 from the murine inner ear, an eph family receptor tyrosine kinase expressed in the developing and adult cochlea.

To identify receptor tyrosine kinases (RTKs) present in the murine inner ear, a degenerate polymerase chain reaction (PCR) methodology was employed to clone partial cDNAs encoding RTKs from embryonic day-17.5 mouse whole inner ear RNA. At least 20 distinct TKs were identified within the first 50 subcloned PCR products obtained by this analysis (Davis/Lee et al., 1996). One of the receptor RTKs identified encoded an eph-related kinase not previously described in the mouse. Analysis of full-length cDNAs revealed that this RTK is the mouse homolog of the rat ehk-2 gene product (Maisonpierre et al., 1993). Differences in the carboxyl terminal of the mouse and rat ehk2 RTKs suggest that differential splicing of this gene may occur resulting in transcripts encoding truncated and nontruncated forms of the ehk2 RTK. Multiple transcripts corresponding to this RTK were detected by Northern blot analysis only in the mouse brain. RT-PCR analysis revealed the presence of transcripts encoding this kinase in adult mouse brain, inner ear, testes, ovary, thymus, and spleen. Transcripts encoding this kinase were localized using in situ hybridization to the postembryonic day 1 cochlear ganglion neurons in the inner ear and to neurons in discrete regions of the nervous system. This is the first report of eph-related RTK in inner ear tissue that is present in both the developing and adult inner ear tissue. Because this is a member of a family of RTKs that is implicated in establishing the specificity of neuron-target cell interactions (Garrity and Zipursky, 1995), additional studies to determine if the ehk-2 gene product is involved in such processes in the murine cochlea are warranted.

Amino Acid Sequence↗
PubMed1995

Molecular cloning and characterization of an inner ear-specific structural protein.

Molecular biological studies of the mammalian inner ear have been limited by the relatively small size of the sensory endorgans contained within. The saccular otolithic organ in teleostian fish is structurally similar to its mammalian counterpart but can contain an order of magnitude more sensory cells. The prospect of the evolutionary conservation of proteins utilized in the vertebrate inner ear and the relative abundance of teleostian saccular sensory tissue made this an attractive system for molecular biological studies. A complementary DNA obtained by differential screening of a saccular complementary DNA library was identified that encodes an inner ear-specific collagen molecule.

Amino Acid Sequence↗
PubMed1995

Substitution of alanine543 with a threonine residue at the carboxy terminal end of the beta-chain is associated with thermolabile hexosaminidase B in a Jewish family of Oriental ancestry.

Thermolabile forms of the lysosomal enzyme beta-hexosaminidase B (Hex B), likely to result from different genetic defects, have been described. Ten individuals in five generations of a family of Oriental Jewish ancestry were identified biochemically as carriers of a thermolabile Hex B form. The beta-chain thermolability was found to be associated with the presence of a G --> A transition at nucleotide 1627 of the HEX B gene causing the substitution of Ala543 with a threonine. Oriental Jew whose Hex B was heat labile. Since thermolabile Hex B has been shown to occur more frequently among Jews of Oriental origin, the Ala543 --> Thr mutation may be the common mutation associated with beta-chain thermolability in this ethnic group.

Alanine↗
PubMed1995

Use of the teleost saccule to identify genes involved in inner ear function.

The vertebrate inner ear sensory epithelia contain different types of hair cells and supporting cells. The teleost saccule is anatomically similar to the mammalian saccule and is primarily involved in the detection of translational acceleration and orientation with respect to gravity. To facilitate molecular studies of the teleost saccule cDNA libraries were constructed from microdissected Lepomis macrochirus (bluegill sunfish) saccular maculae. To our knowledge, this is the first report of cDNA libraries constructed from the saccule. In one instance, a non-polymerase chain reaction-based method of amplifying a mRNA population from limited amounts of starting tissue was employed that allowed construction of cDNA libraries from nanogram amounts of tissue mRNA. Conventional cDNA libraries were constructed from the sunfish saccular maculae as well. These cDNA libraries enriched in hair cell and supporting cell transcripts should facilitate molecular biological studies of inner ear sensory epithelia. As an example of their utility, efforts to identify tyrosine kinases expressed in the saccular endorgan using low-stringency hybridization screening of these cDNA libraries and the partial sequence of a cDNA found to encode an erbB-2-related tyrosine kinase are also reported.

Amino Acid Sequence↗
PubMed1994

Fanconi's anemia.

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Abnormalities, Multiple↗
PubMed1994

Molecular cloning of a chick cochlea cDNA encoding a subunit of DNA replication factor C/activator 1.

A chick cochlea cDNA library was constructed to clone molecules involved in peripheral auditory transduction and in the maintenance and regeneration of the sensory neuroepithelium following damage. Characterization of the library showed it to be of high complexity, to contain a high proportion of full-length cDNA inserts, and to contain a representative proportion of clones derived from hair cell transcripts. A cDNA clone encoding the chick homolog of the 40-kD subunit of the human replication factor C (also called activator 1) was isolated and the complete cDNA sequence determined. The predicted amino acid sequence is about 90% identical to that of the human homolog. Expression of the message for this replication factor was detected in brain and liver as well as in the cochlea. Expression levels in the brain are relatively high and are similar in developing and adult chicken nervous tissue. This suggests that replication factor C message expression, unlike that for the functionally associated factor proliferating cell nuclear antigen (PCNA), may be constitutive rather than cell cycle dependent. Although likely to be involved in DNA replication within the receptor neuroepithelium, expression of this replication factor message is not likely to constitute a marker for proliferation.

Amino Acid Sequence↗
PubMed1993

Effect of three preservatives on the growth of Bacillus cereus, Vero cytotoxigenic Escherichia coli and Staphylococcus aureus, on plates with gradients of pH and sodium chloride concentration.

The effect of temperature, pH, sodium chloride concentration and a preservative (sodium benzoate, sodium nitrite or potassium sorbate) on the growth of three foodborne bacterial pathogens (Bacillus cereus, Vero cytotoxigenic Escherichia coli and Staphylococcus aureus) was studied using gradient gel plates. Growth, expressed in optical density units, was recorded using image analysis techniques, and was expressed as three-dimensional grids. These gave a visual indication of the effects of any three of the environmental factors on bacterial proliferation. Sorbate was completely effective against E. coli at all temperature/pH/NaCl combinations, and was the most effective preservative tested against B. cereus. Increase in the acidity and/or the NaCl concentration improved the effect of all the preservatives, except nitrite when used against St. aureus. Nitrite was the least effective preservative, particularly against St. aureus. At < 25 degrees C, sorbate was more effective than benzoate against St. aureus when used with higher concentrations of NaCl. At 35 degrees C benzoate was the most effective preservative against St. aureus, especially when used at pH < 6.

Bacillus cereus↗
PubMed1993

Reproductive technologies for prenatal diagnosis.

Reproductive genetic technology provides unprecedented opportunities for pregnant women and their families to obtain direct information about the genetic makeup of their developing fetus. Ultrasonography, maternal serum markers, amniocentesis, chorionic villus sampling and percutaneous umbilical blood sampling already offer opportunities for prenatal diagnosis in early pregnancy. New techniques, such as preimplantation, prenatal diagnosis and fetal cell sorting offer opportunities for prenatal diagnosis in even earlier stages of pregnancy.

Amniocentesis↗
PubMed1993

The need for more accurate and timely diagnosis in Fanconi anemia: a report from the International Fanconi Anemia Registry.

OBJECTIVE: The objective of this study was to address the need for early diagnosis of Fanconi anemia (FA), an autosomal recessive chromosomal instability syndrome characterized by a unique cellular hypersensitivity to DNA cross-linking agents, such as diepoxybutane, and by a high risk of malignancies. METHODS: We analyzed data from 370 FA patients enrolled in the American Registry of the International FA Registry. Of these individuals, 220 had congenital malformations; the rest were ascertained based on hematologic abnormalities only or on clinical evaluation and screening following the diagnosis of an affected family member. The probands noted to have congenital malformations at the time of diagnosis were classified into two groups on the basis of their clinical presentation: (1) patients manifesting both congenital malformations and hematologic abnormalities (159 individuals); (2) patients manifesting congenital malformations only (61 individuals). RESULTS: The mean age of diagnosis was 6.6 years and 1.1 years for Groups 1 and 2, respectively. Thus, the majority of FA patients with congenital malformations were not diagnosed until after the onset of hematologic abnormalities. We also report central nervous system, gastrointestinal, and skeletal malformations which previously have not been included as part of the FA phenotype. Our review of the patients enrolled in the International FA Registry indicates that the FA phenotype is more variable than recognized previously. CONCLUSIONS: Testing for sensitivity to diepoxybutane to rule out a diagnosis of FA needs to be applied more widely in patients with congenital malformations. All siblings of affected probands also should have testing, because a lack of concordance of phenotype in affected siblings makes clinical diagnosis unreliable even within sibships. A more timely diagnosis of FA in the preanemic phase is needed to implement appropriate therapy and to enable parents to make informed reproductive decisions.

Child↗
PubMed1992

Carboxyl-terminal deletion and point mutations decrease the transforming potential of the activated rat neu oncogene product.

The rat neu oncogene encodes a constitutively activated growth factor receptor/transmembrane tyrosine kinase, p185Tneu, that is structurally similar to yet distinct from the epidermal growth factor receptor. To explore the role of the carboxyl-terminal region and of putative autophosphorylation sites in regulating the activity of the rat p185Tneu (T, transforming) protein, we used site-directed mutagenesis to generate a p185Tneu mutant in which a putative tyrosine autophosphorylation site (residue 1253) at the extreme carboxyl terminus was replaced by a phenylalanine residue and a mutant in which the carboxyl-terminal 122 amino acids were deleted. These proteins were expressed in NIH 3T3 cells at comparable levels and exhibited similar autophosphorylation activity, exogenous substrate phosphorylation ability, oligomerization levels, and responsiveness to a partially purified neu-activating factor. However, the mutant p185Tneu proteins displayed a decreased transforming capacity both in vitro and in vivo. This analysis demonstrated that the carboxyl-terminal domain and at least one putative tyrosine autophosphorylation site of p185Tneu play a role in positively regulating the cell growth-regulating properties of the neu protein.

3T3 Cells↗