bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stepwise aggregation, compaction, and differentiation of uncompacted F9 cells
Authors: Littlefield John W. 
Published: May 2005

AbstractTo study the relationship between compaction and differentiation in aggregates of F9 embryonal carcinoma cells, a subline was developed which grows mostly uncompacted in monolayer culture in medium containing a low concentration of calcium (about 0.05 mM). When these cells were trypsinized and cultured in suspension in the same medium, they formed loose, open aggregates, which failed to differentiate into embryoid bodies after exposure to 10 nM retinoic acid, confirming the requirement of compaction for differentiation. If, after culture for 3 days, the uncompacted F9 aggregates were exposed to additional calcium (4 mM), all compacted within an hour. The number of days necessary for aggregates to acquire this ability to compact rapidly was reduced if the monolayer of cells from which the aggregates were derived had been exposed to additional calcium to cause compaction for several days prior to trypsinization and aggregation. Next, treatment of the compacted F9 aggregates with 10 nM retinoic acid was followed by differentiation into embryoid bodies. The number of days required for this was also reduced if the aggregates were formed from previously compacted cells, presumably because compaction of the aggregates occured sooner.The acceleration in compaction and differentiation in aggregates formed from previously compacted cells suggests that some of the proteins important for compaction, which are synthesized in a monolayer of compacted cells, persist through trypsinization and are carried over from monolayer to aggregates. Alternatively, an inhibitor of compaction is decreased in the compacted monolayer. Thus, the process of compaction in its entirety, including its relationship to subsequent differentiation, cannot be studied in aggregates formed from F9 cells grown as usual in the compacted state in monolayer culture. This work provides an alternative system in which aggregation, compaction, and differentiation of F9 cells can be made to occur in stepwise fashion and can be examined separately.
Characterization of bz1 mutants isolated from mutator stocks with high and low numbers of Mu1 elements
Authors: Hardeman Kristine J. , Chandler Vicki L. 
Published: May 2005

AbstractThe high frequency of mutations in Mutator stocks of maize is the result of transposition of Mu elements. Nine different Mu elements that share the 220 bp Mu terminal inverted repeats have been described. Mul elements have been found inserted into most of the molecularly characterized mutant alleles isolated from Mutator stocks, and most Mutator stocks contain a high number of Mul elements (10‐60). However, it is clear that additional Mu elements, which share the Mul termini but have unrelated internal sequences, can also transpose in Mutator stocks. We were interested in comparing the mutation frequency and type of elements that inserted into a particular locus when Mutator stocks with differing numbers of Mul elements were utilized. Furthermore, previous studies with Mu‐induced mutations have demonstrated that the element that inserted most frequently was Mul. Therefore, to try to obtain Mu elements different from Mul we utilized a stock that had a low number (3‐6) of Mul elements as well as a Mutator stock with a more typical number of Mul elements (20‐60).Utilizing both stocks, we isolated numerous mutants at one gene, Bronze1 (Bz1), and compared the type of elements inserted. In this paper we report that both the high and low Mu1 stocks produced bz1 mutants at frequencies characteristic of Mutator stocks, 6.6 and 4.3 ± 10−5, respectively. We describe the isolation of 20 bz1 mutations, and the initial molecular characterization of eight unstable mutations: two from the high Mu1 stock and six from the low Mu1 stock. The six alleles isolated from the low Mu1 stock appear to contain deleted Mu1 elements, and the two alleles isolated from the high Mu1 stock contain elements very similar to Mu1. When the mutants from the low Mu1 stocks were examined, it was found that the Mu1 ‐related elements increased from 3‐6 copies to 9‐20 copies in one generation. The high number of Mu1 ‐related elements was maintained in subsequent out‐crosses. This spontaneous activation and amplification of Mu ‐related elements occurred in at least 1% of the low Mu1 plants.
Quartet: A Drosophila developmental mutation affecting chromosome separation in mitosis
Authors: Zahner Joseph E. , Cheney Clarissa M. 
Published: May 2005

AbstractThe Drosophila mutation, quartet, affects development at points in the life cycle that require intense mitotic activity. Examination of embryos affected by the maternal effect of quartet has revealed defects that can be attributed to incomplete chromosome separation at mitosis. These defects include uneven spacing of nuclei, strands of DNA creating bridges between nuclei, and abnormal amounts of DNA per nucleus. Nuclei in quartet‐affected embryos also have a greater‐than‐normal number of centrosomes. Immunofluorescent examination of the spindles in quartet‐affected embryos has revealed tripolar spindles and adjacent spindles that share a common spindle pole. Finally, chromosome separation distance was measured in anaphase and telophase spindles in quartet‐affected embryos and found to be blocked in anaphase. Examination of mitotic figures in quartet larvae revealed a reduced mitotic index and an elevated frequency of abnormal mitotic figures. quartet could encode a function necessary for the disengagement of chromosomes in mitosis, for kinetochore function or for function of a spindle motor. Mutations in quartet prevent the post‐translational modification of three abundant proteins. These proteins may be involved in chromosome separation in mitosis.
Genetic alteration of normal aging processes is responsible for extended longevity in Drosophila
Authors: Arking Robert , Wells Robert A. 
Published: May 2005

AbstractThe first step in a genetic analysis of aging is to identify and characterize the genetic mutants and their controls that will be used. Such mutants or strains are initially identified by their effect on the life span. Yet many genetic interventions are known to have some effect on the life span without necessarily affecting the aging process. It is therefore necessary to prove that one is actually dealing with an aging mutant before one draws strong inferences from the data. Casarett's rules provide an operational test for doing so, relying as they do on the comparison of aging biomarkers in the experimental and reference strains. We show that our previously described genetically based long‐lived NDC‐L strain and its normal‐lived NDC‐R control strain differ only in the chronological age of expression of two behavioral and three physiological functional age biomarkers. They do not differ in the sequence or the physiological age of expression of these biomarkers. These two strains comply with the Casarett rules and thereby comprise a valid tool with which to conduct a comparative genetic analysis of aging. The implications of the available data are discussed, including the possibility that aging in these strains of Drosophila melanogaster may be the result of a multiphasic developmental process.
Chimeric genes and transgenic plants are used to study the regulation of genes involved in symbiotic plant‐microbe interactions (nodulin genes)
Authors: de Bruijn Frans J. , Szabados Laszló , Schell Jeff 
Published: May 2005

AbstractNodulin genes are plant genes specifically activated during the formation of nitrogen‐fixing nodules on leguminous plants. These genes are interesting to study since they are not only induced in a specific developmental fashion by signals coming directly or indirectly from the rhizobial symbiont, but are also expressed in a tissue‐specific manner. By examining the expression of chimeric nodulin‐reporter genes in transgenic legume plants it has been shown that nodule specific expression is mediated by DNA sequences present in the 5′upstream region of several nodulin genes. Here we summarize the available data on these cis‐acting elements and the trans‐acting factors interacting with them. We also review experiments designed to identify rhizobial “signals” which may play a role in nodule specific gene expression.
Regulation of nuclear genes encoding chloroplast proteins in transgenic plants
Authors: Fluhr Robert 
Published: May 2005

AbstractTransgenic plants have been particularly useful in studying nuclear genes encoding for photosynthetic functions. The expression of these genes and their chimeric constructs in transgenic plants faithfully mimics their natural counterparts. The use of sensitive chimeric reporter genes has enabled localizing the activity of genes encoding photosynthetic proteins to individual cells. Cab and rbcS transgenes have been shown to retain sensitivity to light quality, which is modulated by phytochrome. Conditional light activation under the influence of a circadian rhythm has been shown for Cab transgenes. Transgenic plants containing truncated promoters have helped delineate cis‐regulatory positive and negative elements involved in light‐mediated transcriptional induction and tissue specificity.
Gametic imprinting and the manifestation of the fused gene in the house mouse
Authors: Ruvinsky Anatoly O. , Agulnik Alexander I. 
Published: May 2005

AbstractThe phenomenon of gametic imprinting in mammals has raised developmentally relevant questions concerning the manifestation and inheritance of genes with variable penetrance. The dominant fused (Fu) gene located on chromosome 17 is one of the few good cases demonstrating the phenomenon in mice. The Fu mutation has a maternal effect.We have previously shown that the † 12 haplotype significantly lowers the penetrance of Fuin ♀ ♀ Fu/†12 offspring. Results of recipiocal matings of the heterozygotes for Fu indicated that the Fu of maternal origin has a lowered level of penetrance. The dominant suppressors locotad outside chromosome 17, in contrast to †12 residing in it, had stronger effects on the manifestation of Fu, decreasing its penetrance to 8–17%. Experimental evidence is presented that the pathway via which Fu passes to the zygote nucleus during gametogenesis through successive generations has a marked effect on its penetrance. Based on this evidence, patterns of genetic imprinting are described. A survey of genetic imprinting allowed us to distinguish two developmental phases, gametic and zygotic. The hypothesis for the gametic phase of the development of multicellular organisms suggests that it proceeds from initialization, a process thought to ensure the freeing of chromosomes from redundant epigenetic information and their preparation for the consecutive developmental cycle.
Recent advances in the molecular genetics of Dictyostelium
Authors: Knecht D. A. , Kessin R. H. 
Published: May 2005

AbstractDNA mediated transformation is a critical technique for uniting genetic, molecular genetic and reverse genetic approaches to a wide range of problems in cell and molecular biology. In Dictyostelium, there is now the capability not only to manipulate DNA sequences in vitro and put them back into the cell, but also to alter the sequences of endogenous chromosomal genes through high frequency homologous recombination. This means that the range of gene manipulation techniques that have made yeast such a useful system should now be applicable in Dictyostelium. For studying problems such as cellular motility, morphogenesis, and gene regulation, few organisms have the combination of features offered by Dictyostelium.
Establishment of conditions for the transformation of nonaxenic Dictyostelium strains
Authors: Lloyd Malgorzata M. , Ceccarelli Adriano , Williams Jeffrey G. 
Published: May 2005

AbstractWe have studied the transient expression, in Dictyostelium cells growing on a bacterial food source, of a construct containing the coding region of the firefly luciferase gene inserted downstream of a Dictyosteliumactin promoter. The fusion gene is not detectably expressed when DNA is introduced by calcium phosphate precipitation or by electroporation, but it is expressed when introduced using cationic liposomes (lipofectin). Using this latter procedure, we are able to transform cells with a G418 resistance vector and select stable, drug‐resistant transformants at a relatively low, but workable, efficiency. This technique will allow molecular genetics to be applied to the many important nonaxenic Dictyostelium strains.
Regulatory gene interactions controlling discoidin lectin expression in Dictyostelium discoideum
Authors: Alexander Stephen , Leone Sandra , Ostermeyer Elizabeth , Sydow Lisa M. 
Published: May 2005

AbstractGenetic studies have revealed a network of three unlinked regulatory genes that control the developmental expression of the family of endogenous lectins in Dictyostelium discoideum. Mutations in the disA and disB loci have a null phenotype and do not express the discoidin I or II lectins. The third mutation, drsA, is a second‐site suppressor of the disB mutation, which restores expression of all lectin species. Cells carrying this mutation express the discoidin lectins during growth, which is in contrast to wild‐type cells in which lectin synthesis is developmentally regulated. In addition to this basic level of genetic control, the conditions of growth dramatically influence the patterns of discoidin expression. Growth‐phase wild‐type cells do not express lectin if the cells are grown on plates in association with bacteria. However, wild‐type cells growing in bacterial suspensions express high levels of lectin during growth. Synthesis of the discoidin lectins in growing cells is sensitive to the levels of extracellular cyclic adenosine monophosphate (cAMP) and folic acid. These results suggest that the drsA mutation renders cells insensitive to cAMP and/or folate and thus allows expression of lectin during growth.
Homology cloning of protein kinase and phosphoprotein phosphatase sequences of Dictyostelium discoideum
Authors: Haribabu Bodduluri , Dottin Robert P. 
Published: May 2005

AbstractReversible protein phosphory‐lation appears to be important of several stages in the signal transduction pathways in Dictyostelium discoideum. To elucidate its role, we have isolated sequences encoding putative protein kinases and phosphoprotein phosphatases by homology clon‐ ing using polymerase chain reactions (PCRs). Oli‐gonucleotide primers were synthesized for use as forward and reverse primers with their nucleotide sequences deduced from the amino acid sequences of conserved domains of several protein kinases and phosphoprotein phosphatases. The fragments amplified by PCR were cloned, sequenced, and shown to encode parts of five different protein kinases and two phosphoprotein phos‐phatases. Several features such as the deduced amino acid sequence homology, location of invariant amino acids, GC content, and the codon usage confirmed that one set of clones encode parts of different protein kinases of Dictyostelium. Two clones derived from phosphoprotein phosphatase primers encode fragments of type 1 and type 2A phosphoprotein phosphatases. Amplified fragments were used to screen a Xgtll bank, and several cDNA clones for protein kinases were isolated. Some of these show differential expression during development or in response to exogenous cAMP.
Gene expression and chromatin structure in the cellular slime mold, Dictyostelium discoideum
Authors: Blumberg Daphne D. , Agarwal Ameeta K. , Sloger Marcia S. , Yoder Bradley K. 
Published: May 2005

AbstractMicrococcal nuclease digestion of chromatin from growing cells reveals a structural organization which differs for genes transcribed at diverse rates. The late cAMP dependent prespore genes which are not transcribed in growing cells are found in growing cells in a regular nucleosomal repeat with an average spacing of 168 nucleotides. By contrast genes expressed at a low level in growing cells show an irregular pattern of bands with an average distance between bands of 80 nucleotides. The sizes of the bands generated from the transcribed genes are consistent with the concept that transcription results in the loss of the linker region histone H1 with concomitant sliding of nucleosomes to generate close packed (“slipped”) di, tri, and tetra nucleosomes lacking the linker region. Further analysis of dinucleosomes released by micrococcal nuclease digestion reveals that transcriptionally active genes are found associated with dinucleosome species which may be lacking histone H1. The length of DNA protected by these dinucleosomes is heterogeneous, ranging from 250 to 300 nucleotides.Methodology is described which has been adapted to allow two dimensional hybridization mapping of nucleoprotein complexes on single copy Dictyostelium genes.
Analysis of the multiple transcripts of the Dd ras gene during Dictyostezium discoideum development
Authors: Reymond Christophe D. , Thompson Nancy A. 
Published: May 2005

AbstractTranscripts from the Dd ras gene can only be detected once starved cells have begun to aggregate (Reymond et al., Cell 39: 141–148, 1984). We show in this report that the three transcripts which originate from Dd ras during nor‐ mal development differ in their 5′ ends. In suspen‐ sion of starved single cells, one major Dd ras RNA accumulates upon addition of CAMP. It seems that the CAMPregulation of Dd ras expression happens both at the transcriptional and post‐transcriptional level. An RNA secondary structure present in the 5′ untranslated region of the gene is proposed to be important in this post‐transcriptional regulation.
The relative importance of transcriptional and post transcriptional regulation of Drosophila chorion gene expression during oogenesis
Authors: Romano Charles P. , Martinez‐Cruzado Juan Carlos , Kafatos Fotis C. 
Published: May 2005

AbstractTo determine the relative roles of transcriptional and post‐transcriptional events in establishing the temporal pattern of chorion gene expression in Drosophila, we have examined chorion gene transcription, RNA accumulation, and protein synthesis in follicles of selected pre‐early‐ and late‐choriogenic stages. Chorion gene transcription was assayed in follicle cell nuclei by nuclear run‐on reactions. For the s 15, s 16, s 18, s36, and s38 chorion genes, the periods of intense transcription are as predicted from the dynamics of RNA accumulation and protein synthesis, indicating that these genes are primarily regulated at the transcriptional level. In contrast, gene s19 appears subject to post‐transcriptional control at stage 14, when transcription rates are substantially higher than predicted from the observed RNA levels.Transcription of regions between the clustered and tandemly oriented chorion genes was also examined. In contrast to many RNA polymerase II transcribed genes, for the s18 and s36 chorion genes run‐on transcription appears to terminate within about 100 base pairs downstream of the polyadenylation sites, corroborating previous reports based on electron microscopy of s36 [Osheim et al., EMBO J 5:3591–3596, 1986].
Developmental regulation of the sheep β‐lactoglobulin gene in the mammary gland of transgenic mice
Authors: Harris S. , McClenaghan M. , Simons J. P. , Ali S. , Clark A. J. 
Published: May 2005

Abstractβ‐Lactoglobulin (BLG) is the most abundant whey protein in sheep milk but it is not present in mouse milk. We have previously shown that transgenic mice carrying the BLG gene express it specifically in the mammary gland and secrete BLG into milk at high concentrations. Here we demonstrate that BLG transcription is correctly initiated in mice and that BLG synthesis is restricted to the secretory epithelial cells of the mammary gland. We have also determined the temporal pattern of milk protein gene expression and find that the BLG transgene is regulated coordinately with mouse β‐casein and that the patterns of regulation of BLG in mouse and sheep share some similarities.
Formation of functionally active chloroplasts is determined at a limited stage of leaf development in virescent mutants of rice
Authors: Iba Koh , Takamiya Ken‐Ichiro , Toh Yoshihiro , Satoh Hikaru , Nishimura Mitsuo 
Published: May 2005

AbstractThe ability to form functionally active chloroplasts is determined at a certain early stage of leaf development in three non‐allelic temperature‐sensitive virescent mutants of rice. Temperature‐shift analysis, together with anatomical observations, indicates that the intrinsic developmental signals of the virescent genes are expressed at the stage immediately following the formation of basic leaf structure, but just before the onset of leaf elongation. These signals control the expression of chloroplast‐encoded genes but do not affect the subsequent morphological development of the leaf or the photo‐regulation of the expression of nuclear genes encoding chloroplast proteins.
Embryonic mutants of Arabidopsis thaliana
Authors: Meinke David W. 
Published: May 2005

AbstractGenetic analysis of plant em‐bryogenesis has been approached in part through the isolation and characterization of recessive embryonic mutants. The most extensive studies have dealt with maize and Arabidopsis. The high frequency of mutants defective in plant embryogenesis is consistent with the presence of many target genes with essential functions at this stage of the life cycle. Some mutants are likely to be defective in genes with general housekeeping functions. Others should facilitate the identification of genes with a more direct role in the regulation of morphogesis. Over 300 embryonic mutants of Arabidopsis isolated following chemical mutagenesis and T‐DNA insertional mutagenesis are currently being analyzed. This collection includes embryonic le‐thals, defectives, and pattern mutants. Developmental abnormalities include the presence of fused cotyledons, twin embryos, abnormally large suspensors, distorted epidermal layers, single cotyledons, enlarged shoot apices, pattern deletions and duplications, embryos with altered patterns of symmetry, bloated embryos with giant vacuolated cells, reduced hypocotyls that fail to produce roots, and embryos that protrude through the seed coat late in maturation. This review describes the isolation and characterization of embryonic mutants of Arabidopsis and their potential application to plant biology. © 1992 Wiley‐Liss, Inc.
In vitro transcription in isolated nucleoli ofTetrahymena pyriformis
Authors: Matsuura Tadashi , Higashinakagawa Toru 
Published: May 2005

AbstractAn in vitro transcription system was established using extrachromosomal nucleoli from Tetrahymena pyriformis macronuclei as a template. Ribosomal precursor RNA (pre‐rRNA) and nascent pre‐rRNA chains were removed from isolated nucleoli by treatment with RNase T1 and Sarkosyl. Nucleoli were then incubated in a RNA synthetic cocktail containing a cellular extract from Tetrahymena thermophila. The transcription product was examined for the presence of transcripts from T. pyriformis ribosomal DNA (rDNA) by P1 nuclease protection mapping using a DNA probe from a T. pyriformis rDNA clone. A sequence difference between T. pyriformis and T. thermophila in the 5′ region of their 35S pre‐rRNAs permitted exclusive detection of T. pyriformis transcripts. The results showed that faithful transcription initiation occurred in vitro from the in vivo initiation site of the nucleolar template and that the nucleolar template had a much higher efficiency of transcription than that of the purified rDNA clone. This system may offer unique advantages for future studies of tran‐scriptional control during development and differentiation. © 1992 Wiley‐Liss, Inc.