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S DiNardo

Publications and source records attributed to S DiNardo.

At least 37 records · Page 2Linked to original sources
PubMed1994

The making of a maggot: patterning the Drosophila embryonic epidermis.

Cell fates are instructed by signals emitted from specialized cell populations called organizers. The study of epidermal patterning in Drosophila is contributing novel insights concerning the establishment and action of such organizers. Juxtaposed rows of cells express either the wingless or hedgehog signaling molecules and thereby act as organizers of segment pattern. These signals mediate a mutually re-enforcing interaction between the two rows of cells to sustain organizer function. In a distinct and subsequent phase, wingless and hedgehog act to specify the fates of cells.

Animals↗
PubMed1994

odd-paired: a zinc finger pair-rule protein required for the timely activation of engrailed and wingless in Drosophila embryos.

The pair-rule gene, odd-paired (opa), is essential for parasegmental subdivision of the Drosophila embryo. In addition to its previously defined role in the activation of wingless (wg) in odd parasegments, we find that opa is required for the timely activation of wg in the remaining parasegments and for the timely activation of engrailed (en) in all parasegments. opa encodes a zinc finger protein with fingers homologous to those of the Drosophila segment polarity gene ciD, the human glioblastoma gene GLI and the Caenorhabditis elegans sex determination gene tra-1. Previous work showed that opa activity was essential for the establishment of alternate parasegments, suggesting opa expression or activity would be spatially restricted like other pair-rule genes. Instead, opa mRNA and protein are found throughout all segment primordia. Thus, opa does not act in a spatially restricted manner to establish the position of en and wg expression. Rather, opa must cooperate with other spatially restricted proteins to achieve proper subdivision of the Drosophila embryo.

Amino Acid Sequence↗
PubMed1993

Toward a molecular genetic analysis of spermatogenesis in Drosophila melanogaster: characterization of male-sterile mutants generated by single P element mutagenesis.

We describe 83 recessive autosomal male-sterile mutations, generated by single P element mutagenesis in Drosophila melanogaster. Each mutation has been localized to a lettered subdivision of the polytene map. Reversion analyses, as well as complementation tests using available chromosomal deficiencies, indicate that the insertions are responsible for the mutant phenotypes. These mutations represent 63 complementation groups, 58 of which are required for spermatogenesis. Phenotypes of the spermatogenesis mutants were analyzed by light microscopy. Mutations in 12 loci affect germline proliferation, spermatocyte growth, or meiosis. Mutations in 46 other loci disrupt differentiation and maturation of spermatids into motile sperm. This collection of male-sterile mutants provides the basis for a molecular genetic analysis of spermatogenesis.

Animals↗
PubMed1992

Drosophila wingless generates cell type diversity among engrailed expressing cells.

During embryogenesis, body pattern is established in a stepwise process. After specification of the body axis, the embryo is subdivided into smaller units. Within these units, a diverse array of cell types is then generated. The subdivisions of the Drosophila embryo, called parasegments, are defined by the interface between cells expressing the homeoprotein Engrailed and cells expressing the secreted protein Wingless. We have examined the generation of cell-type diversity within parasegments by focusing on the choice of cell fate made by the engrailed (en)-expressing cells. These cells differentiate as one of two alternative cell types. We report here that this choice is mediated by wingless (wg), in a function distinct from its early role maintaining en expression. Thus, en cells exhibit different responses to the wg signal at different developmental stages. Early wg input stabilizes the subdivision of the body axis by maintaining en expression, whereas later input generates cell-type diversity.

Animals↗
PubMed1992

Probing spermatogenesis in Drosophila with P-element enhancer detectors.

Formation of motile sperm in Drosophila melanogaster requires the coordination of processes such as stem cell division, mitotic and meiotic control and structural reorganization of a cell. Proper execution of spermatogenesis entails the differentiation of cells derived from two distinct embryonic lineages, the germ line and the somatic mesoderm. Through an analysis of homozygous viable and fertile enhancer detector lines, we have identified molecular markers for the different cell types present in testes. Some lines label germ cells or somatic cyst cells in a stage-specific manner during their differentiation program. These expression patterns reveal transient identities for the cyst cells that had not been previously recognized by morphological criteria. A marker line labels early stages of male but not female germ cell differentiation and proves useful in the analysis of germ line sex-determination. Other lines label the hub of somatic cells around which germ line stem cells are anchored. By analyzing the fate of the somatic hub in an agametic background, we show that the germ line plays some role in directing its size and its position in the testis. We also describe how marker lines enable us to identify presumptive cells in the embryonic gonadal mesoderm before they give rise to morphologically distinct cell types. Finally, this collection of marker lines will allow the characterization of genes expressed either in the germ line or in the soma during spermatogenesis.

Animals↗
PubMed1991

Multiple modes of engrailed regulation in the progression towards cell fate determination.

The engrailed gene product of Drosophila specifies the fate of a subset of cells in each segment. Our studies of engrailed regulation suggest that fate determination is an elaborate, multistep process. At the time in embryogenesis when the engrailed-dependent cell fate is probably determined, four modes of control act in an overlapping progression to govern engrailed expression. After activation by pair-rule genes, both an extracellular signal, wingless, and autoregulation are required for engrailed expression. Autoregulation graduates to wingless independence, but is transient, and is superseded by an engrailed-independent mode of maintenance.

Animals↗
PubMed1990

Molecular and cellular interactions responsible for intrasegmental patterning during Drosophila embryogenesis.

The elaboration of pattern within insect segments is a well-studied example of cellular patterning during development. This process requires that each cell develop appropriately for its position. Experimental embryology suggests that intercellular communication plays a key role in imparting positional information to cells. Drosophila genetics has identified numerous genes whose activity is required for patterning within segments, and whose molecular genetic analyses suggest they constitute and control cell communication circuits. Particular genes are expressed or required by cells that will follow distinct developmental pathways, and some appear to confer or interpret intercellular signals. Other patterning genes are ubiquitously required and may provide the machinery through which the signals are transmitted.

Animals↗
PubMed1988

Two-tiered regulation of spatially patterned engrailed gene expression during Drosophila embryogenesis.

A regulatory cascade, initiated during the syncytial stage of embryogenesis, culminates in the striped pattern of engrailed gene expression at the cellular blastoderm stage. The early regulatory genes, for example the pair-rule genes, are expressed transiently and as their products decay a distinct regulatory programme involving segment polarity genes takes over. This late programme maintains and perhaps modifies the striped pattern of engrailed expression through interactions that may involve cell communication.

Animals↗
PubMed1988

Temporal and spatial relationships between segmentation and homeotic gene expression in Drosophila embryos: distributions of the fushi tarazu, engrailed, Sex combs reduced, Antennapedia, and Ultrabithorax proteins.

The specification of segment number and identity in the Drosophila embryo requires the activity of several classes of genes that may be grouped according to the array of pattern elements that they control. Double-label immunofluorescence was used to simultaneously localize the products of genes representative of the pair-rule segmentation class (fushi tarazu), the segment polarity class (engrailed), and the homeotic class (Sex combs reduced, Antennapedia, and Ultrabithorax) of pattern-regulating genes. The temporal order of appearance of each class of proteins and the precise spatial relationships between the products of the different genes are described with single-cell resolution. Boundaries of gene expression, particularly the parasegmental boundaries, are established by early-acting genes such as fushi tarazu and subsequently respected by the expression patterns of later appearing gene products such as engrailed and Ultrabithorax, suggesting regulatory relationships between certain pairs of genes. In addition, the dynamic transitions observed in spatial relationship among the Sex combs reduced, Antennapedia, and Ultrabithorax homeotic protein patterns during the early period of embryogenesis may reflect cross-regulatory interactions among these genes. Finally, some cells contain a single homeotic product, whereas other cells simultaneously contain several, suggesting that certain cells may be determined by the combinatorial action of homeotic genes.

Animals↗
PubMed1987

Establishment and refinement of segmental pattern in the Drosophila embryo: spatial control of engrailed expression by pair-rule genes.

We are examining the development of the segmental body pattern of Drosophila by immunolocalization of engrailed, a developmental regulatory protein that maintains segmental subdivisions in the embryo, and is expressed in a spatially restricted (striped) manner that persists while the body pattern is being established and refined. A regulatory network among pair-rule segmentation genes establishes the striped pattern of engrailed expression. In general, mutations in particular pair-rule genes affect either even- or odd-numbered engrailed stripes. For example, fushi tarazu or odd-paired mutations delete even-numbered stripes, whereas paired mutations delete odd-numbered stripes. An analysis of engrailed expression in other mutants, including even-skipped odd-skipped double mutants, indicates that some pair-rule genes play a rule in establishing the correct width and position of engrailed stripes. Overall, the changes in engrailed pattern have consequences for final embryonic body pattern. Thus, the pair-rule loci, acting through engrailed, establish an early, general outline of body pattern. However, in several pair-rule mutants, engrailed patterns are dynamic, suggesting that as later events build upon this general rule to form the final body pattern, adjustments are made in response to the earlier pair-rule defect--that is, the pattern regulates.

Animals↗
PubMed1987

DNA topoisomerase activity is required as a swivel for DNA replication and for ribosomal RNA transcription.

Yeast strains with mutations in the genes for DNA topoisomerases I and II have been identified previously. The topoisomerase II mutants (top2) are conditional-lethal, temperature-sensitive mutants defective in the termination of DNA replication and the segregation of daughter chromosomes. The topoisomerase I mutants (top1), including strains with null mutations, are viable and exhibit no obvious growth defects, demonstrating that DNA topoisomerase I is not essential for viability in yeast. In contrast to the single mutants, top1 top2 double mutants grow poorly at the permissive temperature and stop DNA and ribosomal RNA synthesis at the restrictive temperature. Transfer RNA synthesis remains relatively normal. The rate of polyA+ RNA synthesis is down about 3-fold in the double mutant at the non-permissive temperature but the synthesis of three specific RNA polymerase II transcripts is unaffected. The results suggest that DNA replication and at least ribosomal RNA synthesis require an active topoisomerase, presumably to act as a swivel to relieve torsional stress, and that either topoisomerase can perform the required function (except for termination of DNA replication where topoisomerase II is required).

DNA Replication↗
PubMed1986

Molecular cloning and genetic mapping of the DNA topoisomerase II gene of Saccharomyces cerevisiae.

The structural gene for DNA topoisomerase II from the yeast Saccharomyces cerevisiae has been cloned. The clones were selected from a YEp13 plasmid bank of yeast DNA by complementing a temperature-sensitive mutation (top2-1) in the topoisomerase II gene, TOP2. Chromosomal integrants of the clone were derived by homologous recombination in strains lacking the 2 mu circle plasmid. Genetic analysis of these integrants indicates that we have cloned the TOP2 gene and not an extragenic suppressor. A YEp13-TOP2 hybrid plasmid integrant was used to localize the TOP2 gene to the left arm of chromosome XIV by the 2 mu circle-directed marker loss method. Results from standard meiotic mapping experiments indicate that TOP2 is about 16 centi-Morgans to the centromere proximal side of MET4. Northern blot analysis of TOP2 RNA isolated from a wild-type strain and from an rna2 mutant shows the RNA to be 4.5 kb long in both cases, thus indicating that the TOP2 gene has no large introns.

Cloning, Molecular↗
PubMed1985

Development of embryonic pattern in D. melanogaster as revealed by accumulation of the nuclear engrailed protein.

Engrailed is required to establish and maintain developmental compartments within each segment of the fly. To understand the role of the engrailed protein in this process, we have raised antibodies against engrailed and have visualized an engrailed protein in embryos by indirect immunofluorescence. The protein accumulates in the nucleus, supporting the notion that engrailed is a regulatory factor. The first pattern of expression is in alternating segments followed by expression in every segment, suggesting that engrailed may be responding to pair-rule segmentation gene products. Overall, engrailed protein levels peak in areas undergoing morphogenesis. Finally, the complex final form of the head and terminalia derive from earlier simple subdivision of these areas into developmental fields by engrailed.

Animals↗
PubMed1984

Identification of Saccharomyces cerevisiae mutants deficient in DNA topoisomerase I activity.

Mutants of the yeast, Saccharomyces cerevisiae, deficient in DNA topoisomerase I activity have been identified. One mutant has normal topoisomerase I activity when assayed at 25 degrees C and about 20% of normal activity when assayed at 36 degrees C. Strains with this mutation grow normally at all temperatures tested. The mutation has been mapped to MAK1, a gene required for maintenance of killer RNA. Three previously isolated mak1 mutants exhibit less than 1% of normal topoisomerase I activity in our assay, but yet they grow normally. The implications of these results for the role of DNA topoisomerase I in the cell are discussed.

DNA Topoisomerases, Type I↗
PubMed1984

DNA topoisomerase II mutant of Saccharomyces cerevisiae: topoisomerase II is required for segregation of daughter molecules at the termination of DNA replication.

A temperature-sensitive DNA topoisomerase II mutant of the yeast Saccharomyces cerevisiae has been identified. Genetic analysis shows that a single recessive nuclear mutation is responsible for both temperature-sensitive growth and enzymatic activity. Thus, topoisomerase II is essential for viability and the mutation is most probably in the structural gene. Experiments with synchronized mutant cells show that at the nonpermissive temperature cells can undergo one, and only one, round of DNA replication. These cells are arrested at medial nuclear division. Analysis of 2-microns plasmid DNA from these cells shows it to be in the form of multiply intertwined catenated dimers. The results suggest that DNA topoisomerase II is necessary for the segregation of chromosomes at the termination of DNA replication.

Cell Cycle↗
PubMed1982

Escherichia coli DNA topoisomerase I mutants have compensatory mutations in DNA gyrase genes.

Escherichia coli deletion mutants lacking DNA topoisomerase I have been identified previously and shown to grow at a normal rate. We show that such strains grow normally only because of spontaneously arising mutations that compensate for the topoisomerase I defect. Several of these compensatory mutations have been found to map at or near the genes encoding DNA gyrase, gyrA and gyrB. DNA gyrase assays of crude extracts show that strains carrying the mutations have lower gyrase activity. Thus the mutations are in the gyrase structural genes or in nearby regulatory sequences. These results, in conjunction with DNA supercoiling measurements of others, indicate that in vivo DNA superhelicity is a result of a balance between topoisomerase I and gyrase activities. An excess of negative supercoils due to an absence of topoisomerase I is deleterious to the cell, but a moderate gyrase deficiency is not harmful.

Chromosome Deletion↗