bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular phylogeny of ciliates: What does it tell us about the evolution of the cytoskeleton and of developmental strategies?
Authors: Fleury Anne , Delgado Pilar , Iftode Francine , Adoutte André 
Published: May 2005

AbstractAn rRNA phylogeny of 22 species of ciliates belonging to seven of Small and Lynn's eight classes has been obtained by distance and parsimony methods. It displays good congruence with classical systematics at low taxonomic levels and several major surprises at higher levels: (1) The species analyzed group into five major branches, four of which emerge almost simultaneously: hypotrichs, oligohymenophorans, lito‐stomes, and nassophoreans corresponding to four of Small and Lynn's classes. The simultaneous emergence of these groups contradicts the long accepted view that litostomes (a group with “simple”, symmetrical, apical oral apparatus) are “primitive,” while hypotrichs are “highly evolved.” (2) Heterotrichs group with a karyorelictid, together forming the first emerging branch. While this supports the view that karyorelictids may be early‐emerging ciliates, it completely explodes the traditional “spirotrichs” taxon, which united heterotrichs and hypotrichs. Instead, this reinforces the concept of Postciliodesmatophora and suggests that asymmetric oral apparatuses (i.e., with distinct paroral and adoral ciliatures) may be primitive in ciliates. The global topology of the tree therefore does not fit with the classical views of ciliate evolution, from “simple” oral apparatus and stomatogenesis to “complex” ones. Instead, a rather striking agreement with the strategy adopted to construct the cortical framework was disclosed. We noted that the cytoskeletal elements used to strengthen the cell surface could be subdivided into four main types: epiplasm, filaments, continuous microtu‐bules, or basal body derived fibers. These four types fitted quite well with the major evolutionary lines disclosed by the molecular phylogeny. We therefore discuss unorthodox hypotheses assuming an early explosive radiation of ciliates into a small number of major lineages differing essentially in the solution adopted to subtend the cell surface and anchor the infraciliature. © 1992 Wiley‐Liss, Inc.
Early gene interaction during prepupal expression of Drosophila arginine kinase
Authors: James Judith M. , Collier Glen E. 
Published: May 2005

AbstractArginine kinase displays a distinctive rise and fall in specific activity and specific protein levels during the prepupal stage of Drosophila development with maximal activity occurring at morphological stage P3. This developmentally regulated peak is under the influence of ecdysone. Altered doses of the major ecdysone‐inducible “early” genes at cytological regions 75B and 2B5 alter this pattern of expression while altered doses of another major “early” gene at 74EF have no effect. We hypothesize that a product of the 2B5 locus and a product of the 75B locus interact to effect this developmental pattern of expression of Drosophila arginine kinase. © 1992 Wiley‐Liss, Inc.
The differential expression of the G surface antigen alleles in Paramecium primaurelia heterozygous cells correlates to macronuclear DNA rearrangement
Authors: Keller Anne‐Marie , Mouël Anne Le , Caron François , Katinka MichaëL , Meyer Eric 
Published: May 2005

AbstractThe Paramecium primaurelia cell surface is covered with a high molecular weight protein called the surface antigen. Several genes encode alternative surface antigens, but only one is expressed at a time. In addition, each of these genes shows a high degree of allelic polymorphism. Paramecium primaurelia strains 156 and 168 have different alleles of the G antigen gene whose respective antigens can be distinguished in vivo using specific antibodies. An interallelic exclusion phenomenon has been previously described: 94% of the 156/168 heterozygotes express only the 156 allele of the G gene; 6% express both the 156 and the 168 alleles. The phenotype of the heterozygotes is determined at the time of macronuclear differentiation. We have investigated the molecular basis for the different heterozygous phenotypes. Both mRNAs are always produced, and the 156 mRNA is always more abundant than the 168 mRNA. The relative amounts of these messages, however, vary greatly between different heterozygotes and parallel their phenotype. Pushing the analysis further, we show that the copy number of each allele in the macronucleus correlates with the relative amounts of the mRNAs. However, allelic dosage alone is not sufficient to explain the variations of the mRNA ratio. The G antigen gene is located near a telomere in the macronucleus. We show that the distance between the 156G gene and the telomere is different in homozygotes and heterozygotes. It also varies among heterozygotes and is correlated with the mRNA ratio. Thus, we have identified two different parameters, both linked to the genome rearrangements occurring during macronuclear differentiation, that correlate with the relative expression of the two alleles. Two hypotheses concerning the influence of the telomere position on the expression of the gene are discussed. © 1992 Wiley‐Liss, Inc.
Localization in situ of polyhomeotic transcripts in Drosophila embryos reveals spatially restricted expression beginning at the blastoderm stage
Authors: Deatrick Janet 
Published: May 2005

Abstractpolyhomeotic is a member of a group of genes, the Pc‐group responsible for the maintenance of gene expression during development. In particular, the Pc‐group of genes is involved in the correct expression of homeotic genes of the bithorax and Antennapedia complexes.Molecular analysis reveals that the Pc‐group genes function relatively late in development, once homeotic gene expression has been correctly initiated. This initiation of homeotic gene expression depends on interaction between genes in the segmentation gene hierarchy, the gap and pair‐rule genes.The in situ analysis presented here indicates that polyhomeotic transcripts are expressed in a spatially restricted fashion early in development. This blastoderm expression is under the control of genes in the segmentation hierarchy. Given these results, and the role of polyhomeotic in the correct maintenance of homeotic gene expression, I propose that polyhome otic expression may relay the initiation of homeotic gene expression with other mechanisms involved in the maintenance of this expression, involving the other Pc‐group genes. © 1992 Wiley‐Liss, Inc.
The rad3‐1 mutant is defective in axial core assembly and homologous chromosome pairing during meiosis in the basidiomycete Coprinus cinereus
Authors: Pukkila Patricia J. , Skrzynia Cécile , Lu Benjamin C. 
Published: May 2005

AbstractWe have utilized spreading methods as well as serial sectioning three‐dimensional reconstruction to examine meiotic chromosome behavior in cells homozygous for the rad3‐1 mutation in Coprinus cinereus. Comparison of 42 wild‐type nuclei that had been spread, stained with silver, and viewed by electron microscopy with 30 mutant nuclei treated in the same manner revealed several defects in the mutant. Axial core formation was defective in the mutant, although limited side‐by‐side association of axial cores was observed. To detect any differences in three‐dimensional architecture between the wild‐type and mutant nuclei, we reconstructed three of the former and six of the latter after serial sectioning. It was not possible to trace the expected number of axial cores from section to section in the mutant, although some tripartite synaptonemal complex was observed. Many axial core ends failed to terminate in the nuclear envelope in the mutant. This spectrum of defects (incomplete axial core assembly with some tripartite synaptonemal complex formation) had not been observed previously in either C. cinereus or other systems. We conclude that this combination of spreading and sectioning methods is very useful for analysis of meiotic mutants. © 1993 Wiley‐Liss, Inc.
Effects of several meiotic mutations on female meiosis in maize
Authors: Golubovskaya Inna , Avalkina Nadezhda A. , Sheridan William F. 
Published: May 2005

AbstractA modified enzyme digestion technique of ovary isolation followed by staining and squash preparation has allowed us to observe female meiosis in normal maize meiotically dividing megaspore mother cells (MMCs). The first meiotic division in megasporogenesis of maize is not distinguishable from that in mi‐crosporogenesis. The second female meiotic division is characterized as follows: (1) the two products of the first meiotic division do not simultaneously enter into the second meiotic division; as a rule, the chalazal‐most cell enters division earlier than the micropylar one, (2) often the second of the two products does not proceed with meiosis, but degenerates, and (3) only a single haploid meiotic product of the tetrad remains alive, and this cell proceeds with three rounds of mitoses without any intervening cell wall formation to produce the eight‐nucleate embryo sac. This technique has allowed us to study the effects of five meiotic mutations (aml, aml‐pral, afdl, dsy *‐9101, and dvl) on female meiosis in maize. The effects of the two alleles of the aml gene (aml and aml‐pral) and of the afdl and dsy *‐9101mutations are the same in both male and female meiosis. The aml allele prevents the entrance of MMCs into meiosis and meiosis is replaced by mitosis; the aml‐pral permits MMCs to enter into meiosis, but their progress is stopped at early prophase I stages. The afdl gene is responsible for substitution of the first meiotic (reductional) division by an equational division including the segregation of sister chromatid centromeres at anaphase I. The dsy * ‐9101 gene exhibits abnormal chromosome pairing; paired homologous chromosomes are visible at pachytene, but only univalents are observed at diakinesis and metaphase I stages. These mutation specific patterns of abnormal meiosis are responsible for the bisexual sterility of these meiotic mutants.The abnormal divergent shape of the spindle apparatus and the resulting abnormal segregation of homologous chromosomes observed in micro‐sporogenesis in plants homozygous for the dv1 mutation have not been found in meiosis of megasporogenesis. Only male sterility is induced by the dv1 gene in the homozygous condition. © 1993 Wiley‐Liss, Inc.
Temporal and spatial distribution of meiotin‐1 in anthers of Lilium longiflorum
Authors: Hasenkampf Clare , Qureshi Misbah , Horsch Andrea , Riggs C. Daniel 
Published: May 2005

AbstractMeiotin‐1 is a chromatin associated, conserved protein found in meiocytes immediately preceding and during meiosis and is thought to have a role in determining the higher order structure of meiotic chromosomes [Riggs and Hasenkampf: Chromosoma 101:92–98, 1991]. In the studies reported here we utilized immunoblotting and immunocytochemical techniques to examine the temporal and spatial distribution of meiotin‐1 in the anthers of Lilium longiflorum. The results with the anti‐meiotin‐1 immune serum were compared with those obtained using an anti‐his‐tone Hl immune serum. The anti‐histone Hl immune serum gave constant immunostaining in all cell types of the anther at all of the stages tested. In contrast, the anti‐meiotin‐1 immune serum only gave immunostaining with the microsporocytes and to a lesser extent with the nutritive layer, the tapetum. It did not react with the cells of the anther wall. Meiotin‐1 immunostaining was first present in significant quantities in the microsporocytes as they accumulated in the G1 phase before the onset of premeiotic S phase and reached peak levels in the time interval between leptotene and pachytene—the same interval when chromosome synapsis occurs and when reciprocal genetic exchange is thought to occur. Immunostaining for both meiotin‐1 and histone H1 uniformly decorates the longitudinal axes of the chromosomes. Our data are consistent with the idea that the role of meiotin‐1 may be to tag certain sequences or to limit the degree of chromosome condensation that occurs during meiotic prophase. © 1993 Wiley‐Liss, Inc.
Promoter‐containing ribosomal DNA fragments function as X‐Y meiotic pairing sites in D. melanogaster males
Authors: Merrill Cynthia J. , Chakravarti Dhrubajyoti , Habera Ledare , Das Suchita , Eisenhour Lynn , McKee Bruce D. 
Published: May 2005

AbstractThe Drosophila melanogaster ribosomal DNA (rDNA) functions as an X‐Y meiotic pairing site. Deletions encompassing the X chromosomal rDNA block (located in the heterochromatin) disrupt X‐Y pairing and disjunction. Insertions of single, complete rRNA genes at ectopic locations on the heterochromatically deficient X partially restore X‐Y pairing capacity. This study was undertaken to test fragments of an rDNA repeat for the ability to stimulate X‐Y pairing and disjunction and to test for relationships between pairing capacity and two other phenotypes associated with rDNA insertions: transcription and the ability to organize a nucleolus. Insertions of three different fragments, all of which retained the rDNA promoter and upstream spacer sequences and which differed among each other in the length of downstream sequences, were obtained by P‐element mediated transformation. One of the fragments is truncated only 140bp downstream from the promoter. Insertions of all three fragments proved capable of stimulating X‐Y disjunction. Double insertions were substantially more effective than single insertions. RNA/PCR analysis was used to show that transcripts initiated at the inserted rDNA promoters are present in testis RNA from all insertions. Treatment with an antinucleolar antibody revealed that none of the insertions was associated with a mininucleolus. Thus promoter‐containing rDNA fragments are autonomously capable of being transcribed and of functioning as X‐Y pairing sites, but not of forming a mini‐nucleolus. © 1993 Wiley‐Liss, Inc.
Pulsed‐field gel analysis of the pattern of DNA double‐strand breaks in the Saccharomyces genome during meiosis
Authors: Game John C. 
Published: May 2005

AbstractPulsed‐field gel electrophoresis (PFGE) has been used to study the timing, frequency, and distribution of double‐strand breaks (DSBs) in chromosomal‐sized DNA during meiosis in yeast. It has previously been shown that DSBs are associated with some genetic hotspots during recombination, and it is important to know whether meiotic recombination events routinely initiate via DSBs. Two strains have been studied here—a highsporulating homothallic wild type and a congenic mutant strain carrying a rad50S mutation. This mutant has previously been reported to accumulate broken molecules in meiosis to much higher frequencies than wild type and to abolish the characteristic wild‐type processing of DNA that has been observed at the break sites. When whole chromosomes are resolved by PFGE, both strains show some broken molecules starting at the time that cells commit to genetic recombination. Breakage has been assessed primarily on Chromosome III and Chr. XV, using Southern hybridization to identify these chromosomes and their fragments. At any one time, break frequency in wild type is much lower than the cumulative frequency of recombination events that occur during meiosis. However, there is suggestive evidence that each break is short‐lived, and it is therefore difficult to estimate the total number of breaks that may occur. In rad50S, chromosome breaks accumulate to much higher levels, which are probably broadly consistent with the estimated number of recombination events in wild type. However, since rad50S is substantially defective in completing recombination, it is not known for certain if it initiates events at wild‐type frequencies.A surprising feature of the data is that a strong banding pattern is observed in the fragment distribution from broken chromosomes in both strains, implying that at least much of the breakage occurs at specific sites or within short regions. However, with the exception of the rDNA region on Chr. XII, assessment of the genetic map indicates that recombination can occur almost anywhere in the genome, although some regions are much hotter than others. Possible reasons for this apparent paradox are discussed. It may in part result from breakage levels too low for adequate detection in cold regions but may also imply that recombination events are localized more than previously realized. Alternatively, there may be a more indirect relationship between break sites and the associated recombination events. © 1993 Wiley‐Liss, Inc.
Minimal extent of homology required for completion of meiotic recombination in Saccharomyces cerevisiae
Authors: Hayden Martha S. , Byers Breck 
Published: May 2005

AbstractThe minimal length of contiguous homology required for successful completion of meiotic recombination was investigated by using heterologous insertions to delimit homologous segments of chromosome III in the yeast Saccharomyces cerevisiae. Constructs created in vitro by insertion of selectable markers into the LEU2 locus were transplaced into haploid strains, which were then mated to create diploids containing pairs of insertion heterologies at various distances. Analysis of the meiotic products from these diploids revealed a gradient in the frequency of both reciprocal and nonreciprocal recombination declining monotonically from the 5′ end of LEU2. Both types of event were found to be restricted by the presence of the insertion heterologies. The spo 13 single division meiosis was exploited to develop a plating assay in which LEU2 diploid spores containing reciprocally recombinant strands derived from events occurring completely within the interval flanked by the insertion heterologies were selected by random spore methods. Reciprocal recombination frequencies measured with this assay decreased linearly with extent, extrapolating to a minimal homology requirement of 150–250 nucleotides. When homology was most severely restricted, unexpected flanking marker configurations among reciprocal recombinants within LEU2 demonstrated the occurrence of complex recombination events. In addition to detecting reciprocal recombinants, the system is capable of measuring the probability that a non‐reciprocal recombination event will have one endpoint between the heterologous inserts and the other lying outside the interval. The minimal length of homology required for this aspect of recombination was found to be 25–60 nucleotides. © 1993 Wiley‐Liss, Inc.
Regulation of two different hsp70 transcript populations in steroid hormone‐induced fungal development
Authors: Silver Julie C. , Brunt Shelley A. , Kyriakopoulou Garyfallia , Borkar Monica , Nazarian‐Armavil Vigen 
Published: May 2005

AbstractIn the filamentous oomycete fungus Achlya, the differentiation of gamete bearing structures on vegetative hyphae of the male mating type, is induced by the Achlya steroid hormone, antheridiol. Among the several metabolically labeled intracellular proteins whose synthesis or accumulation is altered by hormone treatment are steroid‐induced 85‐kDa and 68‐ to 78‐kDa proteins. The 85‐kDa protein was previously shown to be the Achlya heat shock protein hsp85 [Brunt et al., 1990; Brunt and Silver, 1991], a component of the putative Achlya steroid hormone receptor. It was of interest to determine if the antheridiol‐induced “70‐kDa” proteins were hsp70‐family heat shock proteins and if hormone treatment‐induced changes in the level of hsp70 transcripts. Two different Achlya hsp70 genomic sequences were cloned and used to investigate these questions. The two hsp70 sequences recognized two different mycelial transcript populations, one of which was regulated also by decreased glucose. Of note, both of the two hsp70 transcript populations were found to be regulated by antheridiol. The hormone‐induced chcnges in hsp70 transcript levels were temporally correlated with the onset of massive lateral hyphal branching and alterations in the pattern of secreted N‐linked glycoproteins which occur in hormone‐treated mycelia. To our kncwledge, this represents one of the first reports on changes in hsp70 proteins and transcripts during fungal differentiation. Our results may have implications for the role of heat shock proteins in hyphal branching and secretion in filamentous fungi and perhaps other cell types. © 1993Wiley‐Liss, Inc. Inc.
Characterization of two Maize HSP90 heat shock protein genes: Expression during heat shock, embryogenesis, and pollen development
Authors: Marrs Kathleen A. , Casey Elena Silva , Capitant Sherry A. , Bouchard Robert A. , Dietrich Paul S. , Mettler Irvin J. , Sinibaldi Ralph M. 
Published: May 2005

AbstractWe have isolated two genes from Zea mays encoding proteins of 82 and 81 kD that are highly homologous to the Drosophila 83‐kD heat shock protein gene and have analyzed the structure and pattern of expression of these two genes during heat shock and development. Southern blot analysis and hybrid select translations indicate that the highly homologous hsp82 and hsp81 genes are members of a small multigene family composed of at least two and perhaps three or more gene family members. The deduced amino acid sequence of these proteins based on the nucleotide sequence of the coding regions shows 64‐88% amino acid homology to other hsp90 family genes from human, yeast, Drosophila, and Arabidopsis. The promoter regions of both the hsp82 and hsp81 genes contain several heat shock elements (HSEs), which are putative binding sites for heat shock transcription factor (HSF) commonly found in the promoters of other heat shock genes. Gene‐specific oligonucleotide probes were synthesized and used to examine the mRNA expression patterns of the hsp81 and hsp82 genes during heat shock, embryogenesis, and pollen development. The hsp81 gene is only mildly heat inducible in leaf tissue, but is strongly expressed in the absence of heat shock during the premeiotic and meiotic prophase stages of pollen development and in embryos, as well as in heat‐shocked embryos and tassels. The hsp82 gene shows strong heat inducibility at heat‐shock temperatures (37–42°C) and in heat shocked embryos and tassels but is only weakly expressed in the absence of heat shock. Promoter‐GUS reporter gene fusions made and analyzed by transient expression assays in Black Mexican Sweet (BMS) Maize protoplasts also indicate that the hsp82 and hsp81 are regulated differentially. The hsp82 promoter confers strong heat‐inducible expression of the GUS reporter gene in heat‐treated cells (60‐ to 80‐fold over control levels), whereas the hsp81 promoter is only weakly heat inducible (5‐ to 10‐fold over control levels). © 1993Wiley‐Liss, Inc.