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Armin Hallmann - One of the best experts on this subject based on the ideXlab platform.
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targeted migration of pherophorin s indicates extensive extracellular matrix dynamics in Volvox carteri
Plant Journal, 2020Co-Authors: Benjamin Von Der Heyde, Armin HallmannAbstract:Hydroxyproline-rich glycoproteins (HRGPs) constitute a major group of proteins of the extracellular matrix (ECM). The multicellular green alga Volvox carteri is a suitable model organism in which to study the evolutionary transition to multicellularity, including the basic principles and characteristics of an ECM. In Volvox, the ECM is dominated by a single HRGP family: the pherophorins. Our inventory amounts to 117 pherophorin-related genes in V. carteri. We focused on a pherophorin with an unexpected characteristic: pherophorin-S is a soluble, non-cross-linked ECM protein. Using transformants expressing a YFP-tagged pherophorin-S we observed the synthesis and secretion of pherophorin-S by somatic cells in vivo, and we then traced the protein during its conspicuous migration to the ECM around prehatching juveniles and its localized concentration there. Our results provide insights into how an ECM zone surrounding the progeny is remotely affected by distantly located parental somatic cells. In view of the properties and migration of pherophorin-S, we conclude that pherophorin-S is likely to act as an ECM plasticizer to allow for dynamic ECM remodeling.
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whole transcriptome rna seq analysis reveals extensive cell type specific compartmentalization in Volvox carteri
BMC Biology, 2017Co-Authors: Benjamin Klein, Daniel Wibberg, Armin HallmannAbstract:One of evolution’s most important achievements is the development and radiation of multicellular organisms with different types of cells. Complex multicellularity has evolved several times in eukaryotes; yet, in most lineages, an investigation of its molecular background is considerably challenging since the transition occurred too far in the past and, in addition, these lineages evolved a large number of cell types. However, for volvocine green algae, such as Volvox carteri, multicellularity is a relatively recent innovation. Furthermore, V. carteri shows a complete division of labor between only two cell types – small, flagellated somatic cells and large, immotile reproductive cells. Thus, V. carteri provides a unique opportunity to study multicellularity and cellular differentiation at the molecular level. This study provides a whole transcriptome RNA-Seq analysis of separated cell types of the multicellular green alga V. carteri f. nagariensis to reveal cell type-specific components and functions. To this end, 246 million quality filtered reads were mapped to the genome and valid expression data were obtained for 93% of the 14,247 gene loci. In the subsequent search for protein domains with assigned molecular function, we identified 9435 previously classified domains in 44% of all gene loci. Furthermore, in 43% of all gene loci we identified 15,254 domains that are involved in biological processes. All identified domains were investigated regarding cell type-specific expression. Moreover, we provide further insight into the expression pattern of previously described gene families (e.g., pherophorin, extracellular matrix metalloprotease, and VARL families). Our results demonstrate an extensive compartmentalization of the transcriptome between cell types: More than half of all genes show a clear difference in expression between somatic and reproductive cells. This study constitutes the first transcriptome-wide RNA-Seq analysis of separated cell types of V. carteri focusing on gene expression. The high degree of differential expression indicates a strong differentiation of cell types despite the fact that V. carteri diverged relatively recently from its unicellular relatives. Our expression dataset and the bioinformatic analyses provide the opportunity to further investigate and understand the mechanisms of cell type-specific expression and its transcriptional regulation.
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The inducible nitA promoter provides a powerful molecular switch for transgene expression in Volvox carteri.
BMC Biotechnology, 2015Co-Authors: Eva Laura Von Der Heyde, Benjamin Klein, Lars Abram, Armin HallmannAbstract:Background The multicellular green alga Volvox carteri represents an attractive model system to study various aspects of multicellularity like cellular differentiation, morphogenesis, epithelial folding and ECM biogenesis. However, functional and molecular analyses of such processes require a wide array of molecular tools for genetic engineering. So far there are only a limited number of molecular tools available in Volvox.
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genome wide analysis of alternative splicing in Volvox carteri
BMC Genomics, 2014Co-Authors: Arash Kianianmomeni, Cheng Soon Ong, Gunnar Ratsch, Armin HallmannAbstract:Alternative splicing is an essential mechanism for increasing transcriptome and proteome diversity in eukaryotes. Particularly in multicellular eukaryotes, this mechanism is involved in the regulation of developmental and physiological processes like growth, differentiation and signal transduction. Here we report the genome-wide analysis of alternative splicing in the multicellular green alga Volvox carteri. The bioinformatic analysis of 132,038 expressed sequence tags (ESTs) identified 580 alternative splicing events in a total of 426 genes. The predominant type of alternative splicing in Volvox is intron retention (46.5%) followed by alternative 5′ (17.9%) and 3′ (21.9%) splice sites and exon skipping (9.5%). Our analysis shows that in Volvox at least ~2.9% of the intron-containing genes are subject to alternative splicing. Considering the total number of sequenced ESTs, the Volvox genome seems to provide more favorable conditions (e.g., regarding length and GC content of introns) for the occurrence of alternative splicing than the genome of its close unicellular relative Chlamydomonas. Moreover, many randomly chosen alternatively spliced genes of Volvox do not show alternative splicing in Chlamydomonas. Since the Volvox genome contains about the same number of protein-coding genes as the Chlamydomonas genome (~14,500 protein-coding genes), we assumed that alternative splicing may play a key role in generation of genomic diversity, which is required to evolve from a simple one-cell ancestor to a multicellular organism with differentiated cell types (Mol Biol Evol 31:1402-1413, 2014). To confirm the alternative splicing events identified by bioinformatic analysis, several genes with different types of alternatively splicing have been selected followed by experimental verification of the predicted splice variants by RT-PCR. The results show that our approach for prediction of alternative splicing events in Volvox was accurate and reliable. Moreover, quantitative real-time RT-PCR appears to be useful in Volvox for analyses of relationships between the appearance of specific alternative splicing variants and different kinds of physiological, metabolic and developmental processes as well as responses to environmental changes.
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validation of reference genes for quantitative gene expression studies in Volvox carteri using real time rt pcr
Molecular Biology Reports, 2013Co-Authors: Arash Kianianmomeni, Armin HallmannAbstract:Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) is a sensitive technique for analysis of gene expression under a wide diversity of biological conditions. However, the identification of suitable reference genes is a critical factor for analysis of gene expression data. To determine potential reference genes for normalization of qRT-PCR data in the green alga Volvox carteri, the transcript levels of ten candidate reference genes were measured by qRT-PCR in three experimental sample pools containing different developmental stages, cell types and stress treatments. The expression stability of the candidate reference genes was then calculated using the algorithms geNorm, NormFinder and BestKeeper. The genes for 18S ribosomal RNA (18S) and eukaryotic translation elongation factor 1α2 (eef1) turned out to have the most stable expression levels among the samples both from different developmental stages and different stress treatments. The genes for the ribosomal protein L23 (rpl23) and the TATA-box binding protein (tbpA) showed equivalent transcript levels in the comparison of different cell types, and therefore, can be used as reference genes for cell-type specific gene expression analysis. Our results indicate that more than one reference gene is required for accurate normalization of qRT-PCRs in V. carteri. The reference genes in our study show a much better performance than the housekeeping genes used as a reference in previous studies.
Arash Kianianmomeni - One of the best experts on this subject based on the ideXlab platform.
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different regulations of cell type transcription by uv b in multicellular green alga Volvox carteri
Plant Signaling & Behavior, 2019Co-Authors: S Ekhtari, Jafar Razeghi, Karim Hasanpur, Arash KianianmomeniAbstract:There is a scarcity of research reports on the effect of ultraviolet (UV)-B radiation on genome-wide transcriptional regulation in the multicellular green microalga including Volvox carteri (V. carteri). This microalga possesses only two cell types including mortal and motile somatic cells, as well as immortal and immotile reproductive cells. Therefore, the present study evaluated the effect of low-dose UV-B radiation on the cell-type-specific gene expression pattern of reproductive and somatic cells in an asexual life cycle of V. carteri using RNA sequence method. To this end, the separated reproductive and somatic cells were treated for 1 hour at an intensity of 0.056 mW/cm-2 UV-B radiation. Then, a transcriptome analysis was conducted between the UV-B and white light treated groups in either of the cell types. Based on differential gene expression analyses, no differentially expressed genes were found in reproductive cells under the treatment as compared to the control group. This type of cell maintained its steady state. However, treating the somatic cells with UV-B radiation led to at least 126 differentially expressed genes compared to the untreated control group. In addition, the results of a direct comparison demonstrated a restricted and wide response to UV-B radiation in somatic cells as compared to reproductive cells. Based on the results, UV-B radiation could be involved in cell-type-specific regulation of biological pathways.
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UV-B response is modulated by cell-type specific signaling pathway in multicellular green algae Volvox carteri
Plant Growth Regulation, 2019Co-Authors: Jafar Razeghi, Arash KianianmomeniAbstract:A fundamental question in biology is how multicellular organisms regulate cellular and physiological processes in response to environmental signals in a tissue/cell type-specific manner. Light is one such cue but little is known about its effect on molecular mechanisms underlying cell-type specific signaling. The Volvox genus presents a Germ-Soma differentiation that can be used to understand the genetic mechanisms of evolutionary transition from single-cell to multicellular organisms. Here we report the transcriptional analysis throughout both asexual and sexual life cycles of Volvox carteri in two different cell types under UV-B light irradiation. Our data show that VcUVR8-V1 , the main splice variant of the VcUVR8 transcript, accumulates during initiation of cleavage division. Moreover, the transcript level of VcUVR8-V1 increases in response to the sex inducer. VcUVR8 expression seems to remain the same in both cell types, while VcCOP1 , the interacting partner of VcUVR8 , is expressed in a cell-type specific manner. Interestingly, illumination with low doses of UV-B leads to an increase of VcCOP1 transcript levels only in the somatic cells. Our results indicate that UV-B signaling pathway is differentially regulated between two cell types and environmental UV-B could be involved in cell-type specific regulation of developmental and physiological processes.
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cell type specific photoreceptors and light signaling pathways in the multicellular green alga Volvox carteri and their potential role in cellular differentiation
Plant Signaling & Behavior, 2015Co-Authors: Arash KianianmomeniAbstract:The formation of multicellular organisms requires genetically predefined signaling pathways in various cell types. Besides differences in size, energy balance and life time, cell types should be enable to modulate appropriate developmental and adaptive responses in ever-changing surrounding environment. One of the most important environmental cues is light which regulates a variety of physiological and cellular processes. During evolution, diverse light-sensitive proteins, so-called photoreceptors, and corresponding signaling pathways have evolved, in almost all kingdoms of life, to monitor light continuously and adjust their growth and development accordingly. However, considering the fact that different cell types should be enable to trigger distinct light signaling pathways according to their needs, cell-type specific light signaling pathways are required to guarantee cell type-matched modulation of cellular and developmental processes in response to different light signals. The multicellular green alga Volvox carteri, which has only 2 cell types with clear division of labor, possesses cell-type specific photoreceptors and light signaling pathways which allow differential regulation of genes involved in various cellular and metabolic pathways in response to environmental light. The existence of cell-type specific light signaling pathways in muticellular organism like Volvox reflects an early development of cell-type specific signaling mechanisms during evolution to ensure maintenance of differentiation.
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genome wide analysis of alternative splicing in Volvox carteri
BMC Genomics, 2014Co-Authors: Arash Kianianmomeni, Cheng Soon Ong, Gunnar Ratsch, Armin HallmannAbstract:Alternative splicing is an essential mechanism for increasing transcriptome and proteome diversity in eukaryotes. Particularly in multicellular eukaryotes, this mechanism is involved in the regulation of developmental and physiological processes like growth, differentiation and signal transduction. Here we report the genome-wide analysis of alternative splicing in the multicellular green alga Volvox carteri. The bioinformatic analysis of 132,038 expressed sequence tags (ESTs) identified 580 alternative splicing events in a total of 426 genes. The predominant type of alternative splicing in Volvox is intron retention (46.5%) followed by alternative 5′ (17.9%) and 3′ (21.9%) splice sites and exon skipping (9.5%). Our analysis shows that in Volvox at least ~2.9% of the intron-containing genes are subject to alternative splicing. Considering the total number of sequenced ESTs, the Volvox genome seems to provide more favorable conditions (e.g., regarding length and GC content of introns) for the occurrence of alternative splicing than the genome of its close unicellular relative Chlamydomonas. Moreover, many randomly chosen alternatively spliced genes of Volvox do not show alternative splicing in Chlamydomonas. Since the Volvox genome contains about the same number of protein-coding genes as the Chlamydomonas genome (~14,500 protein-coding genes), we assumed that alternative splicing may play a key role in generation of genomic diversity, which is required to evolve from a simple one-cell ancestor to a multicellular organism with differentiated cell types (Mol Biol Evol 31:1402-1413, 2014). To confirm the alternative splicing events identified by bioinformatic analysis, several genes with different types of alternatively splicing have been selected followed by experimental verification of the predicted splice variants by RT-PCR. The results show that our approach for prediction of alternative splicing events in Volvox was accurate and reliable. Moreover, quantitative real-time RT-PCR appears to be useful in Volvox for analyses of relationships between the appearance of specific alternative splicing variants and different kinds of physiological, metabolic and developmental processes as well as responses to environmental changes.
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cell type specific light mediated transcript regulation in the multicellular alga Volvox carteri
BMC Genomics, 2014Co-Authors: Arash KianianmomeniAbstract:Background: The multicellular green alga Volvox carteri makes use of none less than 13 photoreceptors, which are mostly expressed in a cell-type specific manner. This gives reason to believe that trasncriptome pattern of each cell type could change differentially in response to environmental light. Here, the cell-type specific changes of various transcripts from different pathways in response to blue, red and far-red light were analyzed. Results: In response to different light qualities, distinct changes in transcript accumulation of genes encoding proteins involved in chlorophyll and carotenoid biosynthesis, light-harvesting complexes, circadian clock and cell cycle control were observed. Namely, blue light tends to be effective to accumulate transcripts in the somatic cells; while red light leads to accumulate transcripts predominantly in the reproductive cells. Blue light also induced marked accumulation of two components of circadian rhythms only in the somatic cells, indicating that these clock-relevant components are affected by blue light in a cell-type specific manner. Further, we show that photosynthetic associated genes are regulated distinctly among cell types by different light qualities. Conclusion: Our results suggest that Volvox uses different sophisticated cell-type specific light signaling pathways to modulate expression of genes involved in various cellular and metabolic pathways including circadian rhythms and photosynthesis in response to environmental light.
Rüdiger Schmitt - One of the best experts on this subject based on the ideXlab platform.
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translational control of rega a key gene controlling cell differentiation in Volvox carteri
Development, 2006Co-Authors: Karin Babinger, Armin Hallmann, Rüdiger SchmittAbstract:The complete division of labour between the reproductive and somatic cells of the green alga Volvox carteri is controlled by three types of genes. One of these is the regA gene, which controls terminal differentiation of the somatic cells. Here, we examined translational control elements located in the 5′ UTR of regA , particularly the eight upstream start codons (AUGs) that have to be bypassed by the translation machinery before regA can be translated. The results of our systematic mutational, structural and functional analysis of the 5′ UTR led us to conclude that a ribosome-shunting mechanism - rather than leaky scanning, ribosomal reinitiation, or internal ribosome entry site (IRES)-mediated initiation - controls the translation of regA mRNA. This mechanism, which involves dissociation of the 40S initiation complex from the message, followed by reattachment downstream, in order to bypass a secondary structure block in the mRNA, was validated by deleting the predicted `landing site9 (which prevented regA expression) and inserting a stable 64 nucleotide hairpin just upstream of this site (which did not prevent regA expression). We believe that this is the first report suggesting that translation of an mRNA in a green eukaryote is controlled by ribosome shunting.
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The Bacterial Paromomycin Resistance Gene, aphH, as a Dominant Selectable Marker in Volvox carteri
Protist, 2004Co-Authors: Thomas Jakobiak, Wolfgang Mages, Birgit E. Scharf, Patrick Babinger, Klaus Stark, Rüdiger SchmittAbstract:Summary The aminoglycoside antibiotic paromomycin that is highly toxic to the green alga Volvox carteri is efficiently inactivated by aminoglycoside 3′-phosphotransferase from Streptomyces rimosus . Therefore, we made constructs in which the bacterial aphH gene encoding this enzyme was combined with Volvox cis -regulatory elements in an attempt to develop a new dominant selectable marker – paromomycin resistance (Pm R ) – for use in Volvox nuclear transformation. The construct that provided the most efficient transformation was one in which aphH was placed between a chimeric promoter that was generated by fusing the Volvox hsp70 and rbcS3 promoters and the 3′ UTR of the Volvox rbcS3 gene. When this plasmid was used in combination with a high-impact biolistic device, the frequency of stable Pm R transformants ranged about 15 per 10 6 target cells. Due to rapid and sharp selection, Pm R transformants were readily isolated after six days, which is half the time required for previously used markers. Co-transformation of an unselected marker ranged about 30%. The chimeric aphH gene was stably integrated into the Volvox genome, frequently as tandem multiple copies, and was expressed at a level that made selection of Pm R transformants simple and unambiguous. This makes the engineered bacterial aphH gene an efficient dominant selection marker for the transformation and co-transformation of a broad range of V. carteri strains without the recurring need for using auxotrophic recipient strains.
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differentiation of germinal and somatic cells in Volvox carteri
Current Opinion in Microbiology, 2003Co-Authors: Rüdiger SchmittAbstract:Abstract Volvox carteri is a spherical alga with a complete division of labor between around 2000 biflagellate somatic cells and 16 asexual reproductive cells (gonidia). It provides an attractive system for studying how a molecular genetic program for cell-autonomous differentiation is encoded within the genome. Three types of genes have been identified as key players in germ–soma differentiation: a set of gls genes that act in the embryo to shift cell-division planes, resulting in asymmetric divisions that set apart the large–small sister-cell pairs; a set of lag genes that act in the large gonidial initials to prevent somatic differentiation; and the regA gene, which acts in the small somatic initials to prevent reproductive development. Somatic-cell-specific expression of regA is controlled by intronic enhancer and silencer elements.
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a link between dna methylation and epigenetic silencing in transgenic Volvox carteri
Nucleic Acids Research, 2001Co-Authors: Patrick Babinger, Wolfgang Mages, Iris Kobl, Rüdiger SchmittAbstract:Epigenetic silencing of foreign genes introduced into plants poses an unsolved problem for transgenic technology. Here we have used the simple multicellular green alga Volvox carteri as a model to analyse the relation of DNA methylation to transgenic silencing. Volvox DNA contains on average 1.1% 5-methylcytosine and 0.3% N6-methyladenine, as revealed by electrospray mass spectrometry and phosphoimaging of chromatographically separated 32P-labelled nucleotides. In two nuclear transformants of V.carteri, produced in 1993 by biolistic bombardment with a foreign arylsulphatase gene (C-ars), the transgene is still expressed in one (Hill 181), but not in the other (Hill 183), after an estimated 500–1000 generations. Each transformant clone contains multiple intact copies of C-ars, most of them integrated into the genome as tandem repeats. When the bisulphite genomic sequencing protocol was applied to examine two select regions of transgenic C-ars, we found that the inactivated copies (Hill 183) exhibited a high-level methylation (40%) of CpG dinucleotides, whereas the active copies (Hill 181) displayed low-level (7%) CpG methylation. These are average values from 40 PCR clones sequenced from each DNA strand in the two portions of C-ars. The observed correlation of CpG methylation and transgene inactivation in a green alga will be discussed in the light of transcriptional silencing.
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quantitative pcr data falsify the chromosomal endoreduplication hypothesis for Volvox carteri volvocales chlorophyta
Journal of Phycology, 1998Co-Authors: Iris Kobl, David L. Kirk, Rüdiger SchmittAbstract:Two conflicting hypotheses for chromosome replication in the Volvocaceae, one postulating multiple rounds of replication prior to cell division (endoreduplication) and the other claiming a canonical sequence of one round of nuclear DNA replication preceding each cell division, have been tested experimentally. Competitive PCR of the single-copy actin gene (target) of Volvox carteri f. nagariensis Iyengar and a shortened gene version (competitor) containing the same primer binding sites were used to assess the genome equivalents present in a given number of cells. Determining the molar ratio of the PCR products generated from target DNA (extracted from a known number of cells) and defined numbers of competitor molecules revealed that Volvox embryos between the one- and 16-cell stages possess an average of between one and two—but never more than two—copies of the actin gene. This led us to conclude that the number of genome equivalents per nucleus in dividing Volvox embryos varies only between one and two and that, unlike the case predicted by endoreduplication, the nuclear genome undergoes only one round of replication prior to each cell division.
David L. Kirk - One of the best experts on this subject based on the ideXlab platform.
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RAPID COMMUNICATIONS A Revision of the Cell Lineages Recently Reported for Volvox carteri Embryos
2013Co-Authors: Kathleen J. Green, David L. KirkAbstract:Volvox offers a unique opportunity to study the segregation of reproductive potential during development of a multicellular organism. At the sixth cleavage division of an asexual embryo of Volvox carteri, strain HK 10, one half of the 32 cells typically cleave unequally to yield 16 large gonidial (reproductive) initials and 16 smaller somatic initials, while the remaining cells divide equally to generate additional somatic initials (6, 7). Different patterns of unequal cleavage, yielding different numbers and locations of reproductive cells, are observed in sexually induced male and female individuals and in germinating zygotes (6, 7). "Pattern mutants, " in which single Mendelian mutations result in modified numbers and/or locations of reproductive cells in asexual or sexual individuals (2, 5), indicate that the process of unequal cleavage is under genetic control; but so far these mutants have not yielded any insigh
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orthologs and paralogs of rega a master cell type regulatory gene in Volvox carteri
Current Genetics, 2006Co-Authors: Leonard R Duncan, David L. Kirk, Ichiro Nishii, Alicia Howard, Stephen M. MillerAbstract:The multicellular green alga Volvox carteri forma nagariensis has only two cell types: terminally differentiated somatic cells and reproductive cells. The regA gene maintains the terminally differentiated state of the somatic cells, apparently by repressing transcription of genes required for chloroplast biogenesis and thereby preventing cell growth. Because the RegA protein sequence bore no obvious motifs, we are attempting to identify regions of functional importance by searching for strongly conserved domains in RegA orthologs. Here we report the cloning and characterization of regA from the most closely related known taxon, V. carteri f. kawasakiensis. Given the closeness of the relationship between these two formas, their regA genes are surprisingly different: they differ in the number of introns and by several lengthy indels, and they encode proteins that are only 80% identical. We also serendipitously discovered a paralogous gene immediately upstream of each regA locus. The two regA genes, both upstream paralogs and several genes in Chlamydomonas (the closest unicellular relative of Volvox) encode a conserved region (the VARL domain) that contains what appears to be a DNA-binding SAND domain. This discovery has opened up a new avenue for exploring how regA and the terminally differentiated state that it controls evolved.
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kangaroo a mobile element from Volvox carteri is a member of a newly recognized third class of retrotransposons
Genetics, 2002Co-Authors: Leonard Duncan, Kristine Bouckaert, Fay Yeh, David L. KirkAbstract:Retrotransposons play an important role in the evolution of genomic structure and function. Here we report on the characterization of a novel retrotransposon called kangaroo from the multicellular green alga, Volvox carteri. kangaroo elements are highly mobile and their expression is developmentally regulated. They probably integrate via double-stranded, closed-circle DNA intermediates through the action of an encoded recombinase related to the λ-site-specific integrase. Phylogenetic analysis indicates that kangaroo elements are closely related to other unorthodox retrotransposons including PAT (from a nematode), DIRS-1 (from Dictyostelium), and DrDIRS1 (from zebrafish). PAT and kangaroo both contain split direct repeat (SDR) termini, and here we show that DIRS-1 and DrDIRS1 elements contain terminal features structurally related to SDRs. Thus , these mobile elements appear to define a third class of retrotransposons (the DIRS1 group) that are unified by common structural features, genes, and integration mechanisms, all of which differ from those of LTR and conventional non-LTR retrotransposons.
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Volvox carteri as a model for studying the genetic and cytological control of morphogenesis
Development Growth & Differentiation, 2001Co-Authors: David L. Kirk, Ichiro NishiiAbstract:The green alga Volvox carteri has a very simple and regular adult form that arises through a short sequence of well-defined morphogenetic steps. A mature gonidium (asexual reproductive cell) initiates a stereotyped sequence of rapid cleavage divisions that will produce all of the cells found later in an adult. A predictable subset of these divisions are asymmetric and result in production of a small set of germ cells in a precise spatial pattern. Throughout cleavage, all intracellular components are held in predictable spatial relationships by a cytoskeleton of unusually regular structure, while neighboring cells are also held in fixed spatial relationships by an extensive network of cytoplasmic bridges that form as a result of incomplete cytokinesis. As a result of these two orienting mechanisms combined, dividing cells are arranged around the anterior-posterior axis of the embryo with precise rotational symmetry. These relationships are maintained by the cytoplasmic bridge system when the embryo that was inside out at the end of cleavage turns right-side out in the gastrulation-like process of inversion. Inversion is driven by a cytoskeleton-mediated sequence of cell shape changes, cellular movements and coordinated contraction. Then, by the time the cytoplasmic bridges begin to break down shortly after inversion, a preliminary framework of extracellular matrix (ECM) has been formed. The ECM traps the cells and holds them in the rotational relationships that were established during cleavage, and that must be maintained in order for the adult to be able to swim. Transposon tagging is now being used to clone and characterize the genes regulating these morphogenetic processes.
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quantitative pcr data falsify the chromosomal endoreduplication hypothesis for Volvox carteri volvocales chlorophyta
Journal of Phycology, 1998Co-Authors: Iris Kobl, David L. Kirk, Rüdiger SchmittAbstract:Two conflicting hypotheses for chromosome replication in the Volvocaceae, one postulating multiple rounds of replication prior to cell division (endoreduplication) and the other claiming a canonical sequence of one round of nuclear DNA replication preceding each cell division, have been tested experimentally. Competitive PCR of the single-copy actin gene (target) of Volvox carteri f. nagariensis Iyengar and a shortened gene version (competitor) containing the same primer binding sites were used to assess the genome equivalents present in a given number of cells. Determining the molar ratio of the PCR products generated from target DNA (extracted from a known number of cells) and defined numbers of competitor molecules revealed that Volvox embryos between the one- and 16-cell stages possess an average of between one and two—but never more than two—copies of the actin gene. This led us to conclude that the number of genome equivalents per nucleus in dividing Volvox embryos varies only between one and two and that, unlike the case predicted by endoreduplication, the nuclear genome undergoes only one round of replication prior to each cell division.
Hideaki Shiraishi - One of the best experts on this subject based on the ideXlab platform.
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a posttranslationally regulated protease vhea is involved in the liberation of juveniles from parental spheroids in Volvox carteri
The Plant Cell, 2006Co-Authors: Kazutake Fukada, Tan Inoue, Hideaki ShiraishiAbstract:The lineage of volvocine algae includes unicellular Chlamydomonas and multicellular Volvox in addition to their colonial relatives intermediate in size and cell number. In an asexual life cycle, daughter cells of Chlamydomonas hatch from parental cell walls soon after cell division, while Volvox juveniles are released from parental spheroids after the completion of various developmental events required for the survival of multicellular juveniles. Thus, heterochronic change in the timing of hatching is considered to have played an important role in the evolution of multicellularity in volvocine algae. To study the hatching process in Volvox carteri, we purified a 125-kD Volvox hatching enzyme (VheA) from a culture medium with enzymatic activity to degrade the parental spheroids. The coding region of vheA contains a prodomain with a transmembrane segment, a subtilisin-like Ser protease domain, and a functionally unknown domain, although purified 125-kD VheA does not contain a prodomain. While 143-kD VheA with a prodomain is synthesized long before the hatching stage, 125-kD VheA is released into the culture medium during hatching due to cleavage processing at the site between the prodomain and the subtilisin-like Ser protease domain, indicating that posttranslational regulation is involved in the determination of the timing of hatching.
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Genes Specifically Expressed in Sexually Differentiated Female Spheroids of Volvox carteri
Journal of Biochemistry, 2005Co-Authors: Naoki Aono, Tan Inoue, Hideaki ShiraishiAbstract:Volvox carteri is a multicellular green alga with only two cell types, somatic cells and reproductive cells. Phylogenetic analysis suggests that this organism has evolved from a Chlamydomonas-like unicellular ancestor along with multicellularity, cellular differentiation, and a change in the mode of sexual reproduction from isogamy to oogamy. To examine the mechanism of sexual differentiation and the evolution of oogamy, we isolated 6 different cDNA sequences specifically expressed in sexually differentiated female spheroids. The genes for the cDNAs were designated SEF1 to SEF6. The time course of accumulation of each mRNA was shown to be distinct. The expression of some of these genes was not significantly affected when the sexual inducer was removed after the induction of sexual development. Sequence analysis indicates that SEF5 and SEF6 encode pherophorin-related proteins. Of these, SEF5 has the unique structural feature of a polyproline stretch in the C-terminal domain in addition to the one found in the central region.
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doi:10.1093/jb/mvi139 Genes Specifically Expressed in Sexually Differentiated Female Spheroids of Volvox carteri
2005Co-Authors: Naoki Aono, Tan Inoue, Hideaki ShiraishiAbstract:Volvox carteri is a multicellular green alga with only two cell types, somatic cells and reproductive cells. Phylogenetic analysis suggests that this organismhas evolved froma Chlamydomonas-like unicellular ancestor alongwithmulticellularity, cellular differen-tiation, and a change in the mode of sexual reproduction from isogamy to oogamy. To examine the mechanism of sexual differentiation and the evolution of oogamy, we iso-lated6different cDNAsequences specifically expressed in sexuallydifferentiated female spheroids. The genes for the cDNAs were designated SEF1 to SEF6. The time course of accumulation of each mRNA was shown to be distinct. The expression of some of these genes was not significantly affected when the sexual inducer was removed after the induction of sexual development. Sequence analysis indicates that SEF5 and SEF6 encode pherophorin-related proteins. Of these, SEF5 has the unique structural feature of a polyproline stretch in the C-terminal domain in addition to the one found in the central region. Key words: extracellular matrix, oogamy, pherophorin, sexual differentiation, Volvox
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cloning and characterization of novel extensin like cdnas that are expressed during late somatic cell phase in the green alga Volvox carteri
Gene, 2002Co-Authors: Toshinobu Shimizu, Tan Inoue, Hideaki ShiraishiAbstract:Asexual individuals of the green alga Volvox carteri consist of two cell types, somatic and reproductive cells. The somatic cells are terminally differentiated post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To understand the gene expression programs associated with senescence of somatic cells, we cloned two cDNAs, LSG1 and LSG2, that are preferentially expressed during this late developmental stage. These two cDNAs were deduced to encode Pro-rich motifs characteristic of extensin proteins that are components of the extracellular matrix. LSG1 also resembled genes encoding plant pathogenesis-related protein 1 (PR-1), while LSG2 showed similarities with genes encoding matrix metalloproteinases, including a gamete lytic enzyme of Chlamydomonas. We also found that S9, one of the late somatic cDNAs previously cloned by Tam and Kirk (Dev. Biol. 145 (1991) 51), was deduced to encode a protein with a composition similar to LSG2. The expression of PR-1 and a matrix-metalloproteinase-encoding gene has been shown to be induced during senescence in higher plants. These results indicate that some of the late somatic genes in V. carteri are related to the senescence-associated genes in higher plants.
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a senescence associated s like rnase in the multicellular green alga Volvox carteri
Gene, 2001Co-Authors: Toshinobu Shimizu, Tan Inoue, Hideaki ShiraishiAbstract:Asexual individuals of the green alga Volvox carteri consist of only two cell types: somatic and reproductive cells. The somatic cells are terminally differentiated, post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To elucidate the self-degrading process of macromolecules associated with senescence, we attempted to clone an RNase whose mRNA accumulation is increased during senescence. The corresponding cDNA clone VRN1, encoding an S-like RNase of V. carteri, is the first T(2)/S-like RNase to be cloned from green algae. Semi-quantitative RT-PCR analysis revealed that a relative amount of VRN1 mRNA is more than three-fold higher in the senescent somatic cells than in young somatic cells when the mRNA of ribosomal protein S18 is used as an internal standard. VRN1 mRNA is not induced by phosphate starvation, indicating that its accumulation during senescence is not due to a self-induced defect in utilizing phosphates. Similar regulation has been reported for RNS3, which encodes the S-like RNase that is induced in senescent leaves of Arabidopsis thaliana. These observations imply that VRN1 may promote RNA degradation during senescence of somatic cells in V. carteri, and that its regulation has similarity with that of certain senescence-associated RNases in higher plants.
