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J Merriam

Publications and source records attributed to J Merriam.

At least 19 recordsLinked to original sources
PubMed1999

The Drosophila activin receptor baboon signals through dSmad2 and controls cell proliferation but not patterning during larval development.

The TGF-beta superfamily of growth and differentiation factors, including TGF-beta, Activins and bone morphogenetic proteins (BMPs) play critical roles in regulating the development of many organisms. These factors signal through a heteromeric complex of type I and II serine/threonine kinase receptors that phosphorylate members of the Smad family of transcription factors, thereby promoting their nuclear localization. Although components of TGF-beta/Activin signaling pathways are well defined in vertebrates, no such pathway has been clearly defined in invertebrates. In this study we describe the role of Baboon (Babo), a type I Activin receptor previously called Atr-I, in Drosophila development and characterize aspects of the Babo intracellular signal-transduction pathway. Genetic analysis of babo loss-of-function mutants and ectopic activation studies indicate that Babo signaling plays a role in regulating cell proliferation. In mammalian cells, activated Babo specifically stimulates Smad2-dependent pathways to induce TGF-beta/Activin-responsive promoters but not BMP-responsive elements. Furthermore, we identify a new Drosophila Smad, termed dSmad2, that is most closely related to vertebrate Smads 2 and 3. Activated Babo associates with dSmad2 but not Mad, phosphorylates the carboxy-terminal SSXS motif and induces heteromeric complex formation with Medea, the Drosophila Smad4 homolog. Our results define a novel Drosophila Activin/TGF-beta pathway that is analogous to its vertebrate counterpart and show that this pathway functions to promote cellular growth with minimal effects on patterning.

Activin Receptors↗
PubMed1998

Ribosomal protein insufficiency and the minute syndrome in Drosophila: a dose-response relationship.

Minutes comprise > 50 phenotypically similar mutations scattered throughout the genome of Drosophila, many of which are identified as mutations in ribosomal protein (rp) genes. Common traits of the Minute phenotype are short and thin bristles, slow development, and recessive lethality. By mobilizing a P element inserted in the 5' UTR of M(3)95A, the gene encoding ribosomal protein S3 (RPS3), we have generated two homozygous viable heteroalleles that are partial revertants with respect to the Minute phenotype. Molecular characterization revealed both alleles to be imprecise excisions, leaving 40 and 110 bp, respectively, at the P-element insertion site. The weaker allele (40 bp insert) is associated with a approximately 15% decrease in RPS3 mRNA abundance and displays a moderate Minute phenotype. In the stronger allele (110 bp insert) RPS3 mRNA levels are reduced by approximately 60%, resulting in an extreme Minute phenotype that includes many morphological abnormalities as well as sterility in both males and females due to disruption of early gametogenesis. The results show that there is a correlation between reduced RPS3 mRNA levels and the severity of the Minute phenotype, in which faulty differentiation of somatic tissues and arrest of gametogenesis represent the extreme case. That heteroalleles in M(3)95A can mimic the phenotypic variations that exist between different Minute/rp-gene mutations strongly suggests that all phenotypes primarily are caused by reductions in maximum protein synthesis rates, but that the sensitivity for reduced levels of the individual rp-gene products is different.

Alleles↗
PubMed1997

Localizing the adhesive and signaling functions of plakoglobin.

Plakoglobin (PKG) is a major component of cell-cell adhesive junctions. It is also closely related to the Drosophila segment polarity gene product armadillo and can induce a WNT-like neural axis duplication (NAD) phenotype in Xenopus [Kamovsky and Klymkowsky, 1995.] To define the regions of PKG involved in cell adhesion and inductive signaling, we examined the behavior of mutated forms of PKG in Xenopus. Deletion of amino acids 22 through 39 (in the Xenopus PKG sequence increased the apparent stability of the polypeptide within the embryo and increased its ability to induce a WNT-like, NAD phenotype when expressed in the vegetal hemisphere. The N-terminal "head" and first 6 "ARM" repeats of PKG, or the C-terminal "tail" and the last 3 "ARM" repeats, could be removed without destroying the remaining polypeptide's ability to induce a NAD phenotype. The nuclear localization of mutant PKGs, however, was not strictly correlated with the ability to induce a NAD phenotype, i.e., some inactive polypeptides still accumulate in nuclei. Removal of PKG's head and first ARM repeat, which includes its alpha-catenin binding site, resulted in a polypeptide that, when expressed in the embryo, generated alpha dramatic cell adhesion defect. Removal of the next three ARM repeats abolished this adhesion defect, suggesting that the polypeptide no longer competes effectively with endogenous catenins for binding to cadherins. Expression of a form of PKG truncated after the 5th ARM repeat produced a milder cell adhesion defect, whereas expression of a polypeptide truncated after the 8th ARM repeat had little apparent effect on cellular adhesion. Based on these observations, we conclude that functions related to stability and cellular adhesion reside in the N-terminal region of the polypeptide, whereas the ability to induce a NAD phenotype lies within repeats 6-10 of the central region. The function(s) of the C-terminal domain of PKG remain uncertain at this time.

Amino Acid Sequence↗
PubMed1997

Interactions of Drosophila Ultrabithorax regulatory regions with native and foreign promoters.

The Ultrabithorax (Ubx) gene of the Drosophila bithorax complex is required to specify parasegments 5 and 6. Two P-element "enhancer traps" have been recovered within the locus that contain the bacterial lacZ gene under the control of the P-element promoter. The P insertion that is closer to the Ubx promoter expresses lacZ in a pattern similar to that of the normal Ubx gene, but also in parasegment 4 during embryonic development. Two deletions have been recovered that remove the normal Ubx promoter plus several kilobases on either side, but retain the lacZ reporter gene. The lacZ patterns from the deletion derivatives closely match the normal pattern of Ubx expression in late embryos and imaginal discs. The lacZ genes in the deletion derivatives are also negatively regulated by Ubx and activated in trans by Contrabithorax mutations, again like the normal Ubx gene. Thus, the deleted regions, including several kilobases around the Ubx promoter, are not required for long range interactions with Ubx regulatory regions. The deletion derivatives also stimulate transvection, a pairing-dependent interaction with the Ubx promoter on the homologous chromosome.

Animals↗
PubMed1996

Natural repressors of P-induced hybrid dysgenesis in Drosophila melanogaster: a model for repressor evolution.

Type I repressors control P element transposition and comprise full length elements and elements with small 3' deletions in the final exon. Using a sensitive assay for measuring the strength of repression of P element transposition in somatic and germline tissues, we have isolated and characterized a naturally occurring type I repressor element from a Q population of Drosophila melanogaster. We demonstrate that the almost complete repression of transposition in this population is a mixture of KP elements with intermediate levels of repression, and the strong contribution of a single 2.6 kb P element deletion derivative, which we call SR (Strong Repressor). A deletion in the final intron of SR allows for the constitutive production of a putative 75 kDa repressor protein in germline tissues in addition to the production of the 66 kDa repressor in the soma, which would result in a biparental mode of inheritance of repression. Based on the four observed classes of natural Q populations, we propose a model in which populations containing SR-like elements, capable of producing strong type I repressor constitutively, have a selective advantage over populations which rely either on maternally transmitted P cytotype or on KP-induced weak levels of repression. Such populations may subsequently spread and constitute an evolutionary stable strategy for the repression of hybrid dysgenesis in Drosophila melanogaster.

Amino Acid Sequence↗
PubMed1995

Nuclear and cytoplasmic dynamics of sperm penetration, pronuclear formation and microtubule organization during fertilization and early preimplantation development in the human.

This report describes spatial and temporal aspects of sperm penetration and intracytoplasmic migration, pronuclear evolution and the specificity of presyngamic opposition, stage-specific changes in cytoskeletal organization and the relative contribution of maternal and paternal components to mitotic spindle formation. These studies involved observations of living human oocytes during conventional insemination in vitro and after intracytoplasmic deposition of spermatozoa, analysis of chromatin organization and distribution during pronuclear evolution, and detection of actin and alpha-, beta- and gamma-tubulin by confocal immunofluorescence microscopy. Immature and mature oocytes, penetrated but unfertilized oocytes, fertilized but arrested eggs, and cleavage-stage embryos from normal and dispermic fertilizations were examined. The results demonstrate that sperm nuclear migration to the maternal perinuclear region is rapid and linear, occurs in the absence of a detectable cytoskeletal system and appears to be assisted by an unusual configuration of the sperm tail principal piece which results from either retained intracytoplasmic motility or the process by which the sperm tail is progressively incorporated into the oocyte. Our findings also show a specificity of pronuclear alignment that is associated with a polarized distribution of both maternal and paternal chromatin, and with the position of the sperm centrosome and the presence of microtubules nucleated from this structure. The results also indicate that a maternal microtubule nucleating capacity is present in the immature oocyte but is apparently inactive until spindle formation. The poles of the first mitotic spindle appear to be derived from the sperm centrosome, although some maternal contribution cannot be excluded. The sperm tail and centrosome persist in a single cell through the cleavage stages, and the latter serves as a prominent site of cytoplasmic microtubule nucleation. The results provide a detailed understanding of the cellular and nuclear morphodynamics of the human fertilization process and indicate subtle defects that may be responsible for early developmental failure.

Cell Nucleus↗
PubMed1994

A Drosophila third chromosome Minute locus encodes a ribosomal protein.

Minutes (M) are a group of over 50 phenotypically similar Drosophila mutations widely believed to affect ribosomal protein genes. This report describes the characterization of the P element-induced M(3)95A(Plac92) mutation [allelic to M(3)95A]. This mutation can be reversed by the mobilization of the P element, demonstrating that the mutation is caused by insertion of this transposable element. The gene interrupted by insertion of the P element was cloned by use of inverse polymerase chain reaction. Nucleotide sequence analysis revealed a 70-75% identity to the human and rat ribosomal protein S3 genes, and to the Xenopus ribosomal protein S1a gene. At the amino acid level, the overall identity is approximately 78% for all three species. This is only the second time that a Minute has been demonstrated to encode a ribosomal protein.

Amino Acid Sequence↗
PubMed1994

A retrospective analysis of unfertilized and presumed parthenogentically activated human oocytes demonstrates a high frequency of sperm penetration.

A total of 518 normal-appearing, meiotically mature human oocytes that were judged unfertilized after insemination in vitro were examined for sperm penetration by conventional fluorescence and laser scanning confocal microscopy with DNA-specific probes. A similar analysis was performed on 29 single pronuclear oocytes that were presumed to originate by spontaneous (parthenogenetic) activation. The results demonstrate that 22% of the unfertilized oocytes and 52% of the presumed parthenogenetic oocytes were actually penetrated. Sperm penetration occurred in both normozoospermic and male factor cases. The findings indicate the importance of penetration analysis in determining the causes of fertilization failure that may reside with the male or female gamete, especially when assessing the utility of and necessity for assisted fertilization in subsequent attempts. The results also suggest that the cytoplasmic capacity to decondense sperm DNA may decline more rapidly than the ability of the oocyte to be penetrated and to mount an effective block to polyspermy.

Cell Nucleus↗
PubMed1994

The developmental ability of human oocytes penetrated at the germinal vesicle stage after insemination in vitro.

This study demonstrates that sperm penetration into the ooplasm occurs at high frequency in germinal vesicle (GV) stage human oocytes which failed to resume meiosis after ovulation induction in cycles of ovarian hyperstimulation for in-vitro fertilization. The capacity of the immature human oocyte to prevent polyspermic penetration at the cell surface level was suggested by the finding that despite the presence of numerous spermatozoa within the zona pellucida and on the oocyte surface within 3 h after insemination, all normal-appearing GV stage oocytes examined in this study were penetrated by a single spermatozoon. This notion was also supported by scanning confocal microscopic analysis of oocytes double-stained for DNA and cortical granules which showed highly localized regions of cortical granule-free cytoplasm in proximity to the penetrated spermatozoon. The developmental ability of these oocytes was assessed by culture in vitro. The results show that oocytes penetrated by a spermatozoon at the GV stage resume meiosis, develop the capacity to decondense sperm DNA, abstrict both first and second polar bodies, and form a male pronucleus from the spermatozoon which enters the oocyte prior to the resumption of meiotic maturation. After penetration, sperm nuclei rapidly migrate to the centre of the oocyte and become juxtaposed with the germinal vesicle, suggesting the presence of a cellular mechanism which permits directed movement within the cytoplasm. The developmental ability of these oocytes and the normality of the resulting embryos are discussed.

Adult↗
PubMed1991

Toward cloning and mapping the genome of Drosophila.

An ultimate goal of Drosophila genetics is to identify and define the functions of all the genes in the organism. Traditional approaches based on the isolation of mutant genes have been extraordinary fruitful. Recent advances in the manipulation and analysis of large DNA fragments have made it possible to develop detailed molecular maps of the Drosophila genome as the initial steps in determining the complete DNA sequence.

Animals↗
PubMed1990

Variation in plasma halflife of gentamicin between species in relation to bodyweight and taxonomy.

Data on the plasma halflife of gentamicin during the elimination phase were collected from the literature for 30 species for analysis of the effects of bodyweight and taxonomy. Log halflife was significantly correlated to log bodyweight between species of birds (r = 0.784, n = 9, P less than 0.05) and mammals (r = 0.873, n = 13, P less than 0.001), but not among the poikilotherms (n = 9). The slopes of regressions of log halflife on log bodyweight for mammal and bird species did not differ significantly (0.27 +/- 0.045 and 0.32 +/- 0.095, respectively) but the elevations did (t = 2.73, P less than 0.05). The variations in halflife between species in relation to bodyweight and taxonomy were broadly consistent with variations in glomerular filtration rate. The results illustrate the value of interspecies comparisons of pharmacokinetic data for estimating appropriate dosage regimes for vertebrates for which no specific data are available.

Animals↗
PubMed1989

Role of cervical lymph nodes in the systemic humoral immune response to human serum albumin microinfused into rat cerebrospinal fluid.

The humoral immune response to human serum albumin (HSA) microinfused into cerebrospinal fluid (CSF) has been measured in serum, cervical lymph nodes, and spleen of Sprague-Dawley rats. Conditions were designed to promote normal brain barrier function. Serum titers of anti-HSA antibodies, primarily IgG, increased over 10 days and then persisted for at least 10 weeks. A significant role for cervical lymphatics in the systemic response to CSF-administered HSA is suggested, based on results showing that (1) cervical lymph obstruction reduces serum titers of anti-HSA antibodies, and (2) total antibody production by combined superficial and deep cervical nodes, sampled 14 days post-immunization, exceeds that by the spleen.

Animals↗
PubMed1988

Prostatic adenocarcinoma: reproducibility and correlation with clinical stages of four grading systems.

One hundred cases of adenocarcinoma of the prostate were independently examined by light microscopy by three pathologists and graded according to the Gleason, Mostofi, Böcking, and MD Anderson systems (MDAH). The results were compared in order to establish which one of these classifications was the most reproducible and then correlated to the clinical stage in order to determine how accurately each classification can predict the spread of the tumors. The MDAH system, based on the percentage of gland formation in the tumor, was the easiest to use and most reproducible system. On the other hand, the Mostofi and the Böcking systems had the best correlation between grade and stage while the MDAH system had the worst. The Böcking system was the best grading system when reproducibility and accuracy in predicting the prognosis were both taken into account.

Adenocarcinoma↗
PubMed1980

Fine needle aspiration biopsy diagnosis of neck masses.

The cytologic findings in 107 aspiration smears obtained with the fine needle technique from head and neck masses were compared with the histologic findings in permanent sections. The overall concurrence rate between cytologic and histologic findings in benign and malignant tumors was 82.2 per cent. There was a 5.6 per cent incidence of false negative findings. There were no false positive results. Fine needle aspiration was found to be safe, complication free, and most helpful in planning treatment. We recommend the technique to others who deal with head and neck masses.

Biopsy, Needle↗
PubMed1977

Phototactic and geotactic behavior of countercurrent defective mutants of Drosophila melanogaster.

Ten behavioral mutations, originally isolated in the countercurrent fractionation device, were tested in phototaxis and geotaxis mazes. While none of the mutations caused an altered ERG, they all caused photomaze behavior to differ from that seen in Canton-S controls. Eight of the mutants showed altered geotactic behavior. There was no correlation between the kind of change in phototactic behavior and the geomaze behavior of a given mutant. Certain mutations cause flies to be more photopositive and more geonegative than Canton-S; others result in behavior that is photo- and geopositive. The results suggest that certain mutations may be affecting visual components other than the ERG while other mutations may be more centrally or generally acting.

Animals↗