Armin Hallmann | Bielefeld University (original) (raw)

Papers by Armin Hallmann

Proceedings of the National Academy of Sciences of the United States of America, Nov 22, 1994

The multicellular alga Volvox is an attractive model for the study of developmental processes. Wi... more The multicellular alga Volvox is an attractive model for the study of developmental processes. With the

Plant Journal, 1999

The green alga Volvox represents the simplest multicellular organism: Volvax is composed of only ... more The green alga Volvox represents the simplest multicellular organism: Volvax is composed of only two cell types, somatic and reproductive. Volvox, therefore, is an attractive model system for studying various aspects of multicellularity. With the biolistic nuclear transformation of Volvox carteri, the powerful molecular genetic manipulation of this organism has been established, but applications have been restricted to an auxotrophic mutant serving as the DNA recipient. Therefore, a dominant selectable marker working in all strains and mutants of this organism is required. Among several gene constructs tested, the most advantageous results were obtained with a chimeric gene composed of the coding sequence of the bacterial ble gene, conferring resistance to the antibiotic zeocin, modified with insertions of two endogenous introns from the Volvox arylsulfatase gene and fused to 5' and 3' untranslated regions from the Volvox beta 2-tubulin gene. In the most suitable plasmid used, the gene dosage was increased 16-fold by a technique that allows exponential multiplication of a DNA fragment. Co-transformation of this plasmid and a non-selectable plasmid allowed the identification of zeocin resistant transformants with nuclear integration of both selectable and non-selectable plasmids. Stable expression of the ble gene and of genes from several non-selectable plasmids is demonstrated. The modified ble gene provides the first dominant marker for transformation of both wild-type and mutant strains of Volvox.

Proceedings of the National Academy of Sciences of the United States of America, Jul 8, 1997

With only two different cell types, the haploid green alga Volvox represents the simplest multice... more With only two different cell types, the haploid green alga Volvox represents the simplest multicellular model system. To facilitate genetic investigations in this organism, the occurrence of homologous recombination events was investigated with the intent of developing methods for gene replacement and gene disruption. First, homologous recombination between two plasmids was demonstrated by using overlapping nonfunctional fragments of a recombinant arylsulfatase gene (tubulin promoter͞arylsulfatase gene). After bombardment of Volvox reproductive cells with DNA-coated gold microprojectiles, transformants expressing arylsulfatase constitutively were recovered, indicating the presence of the machinery for homologous recombination in Volvox. Second, a well characterized loss-of-function mutation in the nuclear nitrate reductase gene (nitA) with a single G 3 A nucleotide exchange in a 5-splice site was chosen as a target for gene replacement. Gene replacement by homologous recombination was observed with a reasonably high frequency only if the replacement vector containing parts of the functional nitrate reductase gene contained only a few nucleotide exchanges. The ratio of homologous to random integration events ranged between 1:10 and 1:50, i.e., homologous recombination occurs frequently enough in Volvox to apply the powerful tool of gene disruption for functional studies of novel genes. Green algae of the order Volvocales range in complexity from unicellular Chlamydomonas through colonial genera to multicellular organism in the genus Volvox. The unicellular members of this order have proven to be excellent model systems for the biochemical and genetic analysis of cellular processes like photosynthesis, phototaxis and motility, and cell wall biogenesis. The more advanced members of this group, like Volvox have developed a multicellular form of organization with a complete division of labor between somatic and reproductive cells; in Volvox carteri, about 2,000 cells are somatic and only 16 cells are reproductive. Therefore, the Volvocales represent an ideal model system to study the prerequisite for the transition from unicellularity to multicellularity. Recently, the development of nuclear transformation (1, 2) and the introduction of reporter genes (3, 4) for the unicellular as well as the multicellular members of the Volvocales have made it possible to apply the powerful techniques of molecular genetics. However, the important genetic technique of gene replacement and gene disruption by homologous recombination has not yet been established in Volvox. Only a few successful reports on homologous recombination events exist for Chlamydomonas reinhardtii (5-7). Gene targeting by homologous recombination is a genetic tool that permits modification of cellular genes in a precise and predetermined fashion. This technique was initially used as a tool by yeast genetics because site-specific rather than random MATERIALS AND METHODS Recipient Strain. The Volvox strain 153-48, obtained from D. L. Kirk (Washington University, St. Louis), was used as the DNA recipient. Strain 153-48 is an F 1-female progeny of HB11A, a female strain of V. carteri f. nagariensis that has been described (17). This strain with wild-type morphology inherited from HB11A an allele that carries a loss-of-function mutation of nitA, the structural gene encoding nitrate reductase (18, 19). The spontaneous reversion rate of this allele is less than 3 ϫ 10 Ϫ9 per reproductive cell (D. L. Kirk, personal communication). Culture Conditions. Synchronous Volvox recipients were grown in Volvox medium (20) at 28°C in an 8-h dark͞16-h light (10,000 lx) cycle (21). The nonselective medium used was Volvox medium, supplemented with 1 mM NH 4 Cl; the selective medium was Volvox medium lacking NH 4 Cl and containing only nitrate as a nitrogen source. Construction of the Chimeric ␤-Tubulin͞Arylsulfatase Gene. The Volvox arylsulfatase gene was placed under the control of the Volvox ␤-tubulin promoter in Volvox by using genomic clones of Volvox ␤-tubulin (22) and Volvox arylsulfatase (23). Additional restriction sites were introduced by PCR to facilitate ligation of the parent DNAs. An EcoRV site was The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.

European journal of biochemistry, Apr 1, 1994

MATERIALS AND METHODS Culture conditions V carteri forma nagariensis strain HKlO (female) was obt... more MATERIALS AND METHODS Culture conditions V carteri forma nagariensis strain HKlO (female) was obtained from the Culture Collection of Algae at the University of Texas (Dr R. C. Starr). Synchronous cultures were grown in Volvox medium (Provasoli and Pintner, 1959) at 28°C in an 8-h darWl6-h light (10000Ix) cycle (Starr and Jaenicke, 1974). In Volvox medium lacking sulfate, MgSO, was replaced by MgC1,. Assay of arylsulfatase activity Arylsulfatase activity was measured using either 4-nitrocatechol sulfate or 5-bromo-4-chloro-3-indolyl sulfate. With 4-nitrocatechol sulfate, the assay contained 5 mM substrate, 50 mM TrisMCl, pH 8.0, and enzyme in a final volume of CI carteri (23.57) C. reinhardtii: I (z 4-s~) C. reinhardtii: I1 (frame shift) CI carleri (58-92) C. reinhardtii: I (59-93) C. reinhardfii: I1 (frame Shifi) CI carteri (93-127) C. reinhardtii: I (94.128) C. reinhardtii: I1 (frame shift) carteri (128-162) C. reinhardtii: I (129-162) C. reinhardtii: I1 (frame shift) CI carteri (I 63-197) C. reinhardtii: I (163-196) C. reinhardtii: I1 (frame shift)

International review of cytology, 1998

The volvocine algae range in complexity from unicellular Chlamydomonas to multicellular organisms... more The volvocine algae range in complexity from unicellular Chlamydomonas to multicellular organisms in the genus Volvox. The transition from unicellularity to multicellularity in the Volvocales is a recent event in evolution. Thus, these organisms provide a unique opportunity for exploring the development of a complex extracellular matrix (ECM) from the cell wall of a unicellular ancestor. The ECM of Volvox is divided into four main zones: The flagellar, boundary, cellular, and deep zones. Each zone is defined by ultrastructure and by characteristic ECM glycoproteins. Volvox ECM is modified under developmental control or in response to external stimuli, like the sex-inducing pheromone or stress factors. The structures of more than 10 ECM glycoproteins from a single species of Volvox are now known in molecular detail and are compared to other algal and plant cell wall/ECM glycoproteins. Although usually classified as hydroxyproline-rich glycoproteins, the striking feature of all algal ECM glycoproteins is a modular composition. Rod-shaped hydroxyproline-rich modules are combined with hydroxyproline-free domains that meet the multiple functional requirements of a complex ECM. The algal ECM provides another example of the combinatorial advantage of shuffling modules that is so evident in the evolution of the metazoan ECMs.

Molecular Genetics and Genomics, Nov 20, 2015

information on the Family-1 Ugts in maize, and will facilitate their further characterization to ... more information on the Family-1 Ugts in maize, and will facilitate their further characterization to better understand their functions. Keywords expression profile • gene family • glycosylation • Maize (Zea mays) • Phylogenetic analysis Abbreviations Iaa Indole-3-acetic acid OrF Open reading frame PSPg Plant secondary product glycosyltransferase qrt-Pcr Quantitative real-time polymerase chain reaction UDP Uridine diphosphate Ugt Uridine diphosphate glycosyltransferase ZOg Cis-zeatin O-glucosyltransferase

BMC Genomics, 2014

Background: Alternative splicing is an essential mechanism for increasing transcriptome and prote... more Background: 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. Results: 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. Conclusions: 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.

The algae of the volvocine lineage. (PDF 3075 kb)

Functional enrichment analysis of the most overexpressed genes of both cell types. (PDF 54 kb)

Figure S2. Alignment of Cr2c-Cylcop1 and Vc2c-Cyclop1. Cr2c-Cylcop1 (Cre11.g467678) and Vc2c-Cycl... more Figure S2. Alignment of Cr2c-Cylcop1 and Vc2c-Cyclop1. Cr2c-Cylcop1 (Cre11.g467678) and Vc2c-Cyclop1 (Vocar.0009 s0380.1) were aligned using Clustal Omega 1.2.2. Four main domains are labeled, including opsin domain, histidine kinase (comprises DHp and CA domains), response regulator, and guanylyl cyclase. Key residues are marked in red. Yellow color backgrounded sequences in the middle and C-terminus indicate the sequences deleted for Xenopus oocyte characterization. See Additional file 5: Figure S5. (PDF 85 kb)

Methods in molecular biology, 2016

The light absorption system in eukaryotic (micro)algae includes highly sensitive photoreceptors, ... more The light absorption system in eukaryotic (micro)algae includes highly sensitive photoreceptors, which change their conformation in response to different light qualities on a subsecond time scale and induce physiological and behavioral responses. Some of the light sensitive modules are already in use to engineer and design photoswitchable tools for control of cellular and physiological activities in living organisms with various degrees of complexity. Thus, identification of new light sensitive modules will not only extend the source material for the generation of optogenetic tools but also foster the development of new light-based strategies in cell signaling research. Apart from searching for new proteins with suitable light-sensitive modules, smaller variants of existing light-sensitive modules would be helpful to simplify the construction of hybrid genes and facilitate the generation of mutated and chimerized modules. Advances in genome and transcriptome sequencing as well as fu...

Pdn Biologie, 2012

Hallmann A. Fortbewegung bei Mikroorganismen und Keimzellen. PdN Biologie. 2012;61:7-13

Bioforum Europe 6, 2003

Hallmann A. Experienced developers of multicellularity - the Volvocales. Bioforum Europe. 2003;6:... more Hallmann A. Experienced developers of multicellularity - the Volvocales. Bioforum Europe. 2003;6:326-328

Praxis Der Naturwissenschaften Biologie in Der Schule, 2011

Hallmann A. Lumineszenz - Coole Leuchterscheinungen in der Biologie und anderswo. Praxis der Natu... more Hallmann A. Lumineszenz - Coole Leuchterscheinungen in der Biologie und anderswo. Praxis der Naturwissenschaften - Biologie in der Schule. 2011;60:4-11

Science, 2007

Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants ove... more Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the ∼120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella.

Current Biotechnology, 2016

Recent years have witnessed fast growing developments in algae biotechnology. Algae are already u... more Recent years have witnessed fast growing developments in algae biotechnology. Algae are already used as bioreactors for producing bioproducts such as pharmaceuticals, nutraceuticals, cosmetics, pigments and other useful chemicals, value-add products, algalbased biomaterials, feed, aquaculture and more. In addition, many efforts are currently being undertaken to make algae competitive for production of bioenergy and biofuels. Some algalbased strategies also meet the requirements for use in biodegradation, bioconversion, bioremediation or other pollution solutions. A powerful driving force in algae biotechnology is the enticing option to use genetically improved organisms. Selectable marker genes, reporter genes, constitutive and switchable promoters, transformation techniques, and other genetic tools and methods are already available for quite a few algae species and this molecular toolbox is becoming increasingly powerful. Moreover, omic' technologies have been established in some algae species and several genome sequencing projects are completed, in progress or planned. Genetically engineered algae promise a much broader field of application than unmodified organisms or breeds, e.g., through additionally acquired physiological capabilities and new biochemical reactions or even pathways. For some time, light-sensitive proteins from algae are even being used in brain science and they represent a cornerstone in the emerging field of optogenetics: in transgenic animals, these algal ion channels are able to turn individual neurons on and off instantly in a lightdependent manner. In contrast to basic research approaches, applied research frequently takes advantage of massculture strategies for algae. Large scale industrial production of bioproducts from genetically engineered, bred or unmodified algae requires state-of-the-art bioprocess engineering, fermentation, harvesting and downstream processing.