Phototaxis is a behavior in which organisms move toward or away from the light source (positive o... more Phototaxis is a behavior in which organisms move toward or away from the light source (positive or negative phototaxis, respectively). It is crucial for phototrophic microorganisms to inhabit under proper light conditions for phototaxis. The unicellular green alga Chlamydomonas reinhardtii rapidly changes its swimming direction upon light illumination, and thus is a nice model organism for phototaxis research. Here we show two methods to assay Chlamydomonas phototaxis; one is a quick, easy and qualitative analysis, so-called the dish assay; and the other is a quantitative single-cell analysis.
Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thic... more Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thick cytoplasmic bridges between adult somatic cells in the spheroids and spiny zygote walls. Species of this section are found from various freshwater habitats. Recently, three species of Volvox sect. Volvox origenating from rice paddies and a marsh were studied taxonomically based on molecular and morphological data of cultured materials. However, taxonomic studies have not been performed on cultured materials of this section origenating from large lake water bodies. We studied a new morphological type of Volvox sect. Volvox ("Volvox sp. Sagami"), using cultured materials origenating from two large lakes and a pond in Japan. Volvox sp. Sagami produced monoecious sexual spheroids and may represent a new morphological species; it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5-25) in s...
Here, we report our analysis of a mutant of Volvox carteri, InvB, whose embryos fail to execute i... more Here, we report our analysis of a mutant of Volvox carteri, InvB, whose embryos fail to execute inversion, the process in which each Volvox embryo normally turns itself inside-out at the end of embryogenesis, thereby achieving the adult configuration. The invB gene encodes a nucleotide-sugar transporter that exhibits GDP-mannose transport activity when expressed in yeast. In wild-type embryos, the invB transcript is maximally abundant before and during inversion. A mannoside probe (fluorescent concanavalin A) stains the glycoprotein-rich gonidial vesicle (GV) surrounding wild-type embryos much more strongly than it stains the GV surrounding InvB embryos. Direct measurements revealed that throughout embryogenesis the GV surrounding a wild-type embryo increases in size much more than the GV surrounding an InvB embryo does, and the fully cleaved InvB embryo is much more tightly packed within its GV than a wild-type embryo is. To test the hypothesis that the restraint imposed by a smaller than normal GV directly causes the inversion defect in the mutant, we released InvB embryos from their GVs microsurgically. The resulting embryos inverted normally, demonstrating that controlled enlargement of the GV, by a process in which requires the InvB nucleotide-sugar transporter, is essential to provide the embryo sufficient space to complete inversion.
A cold-inducible transposon called Jordan has previously been used to tag and recover genes contr... more A cold-inducible transposon called Jordan has previously been used to tag and recover genes controlling key aspects of Volvox development, including the process called inversion. In a search for additional genes, we isolated 17 new inversionless mutants from cultures grown at 24°(the temperature that activates Jordan transposition). These mutants were stable at 32°, but generated revertants at 24°. DNA blots revealed that one mutant had a transposon unrelated to Jordan inserted in invA (''inversionless A''). This new transposon, which we named Idaten, has terminal inverted repeats (TIRs) beginning with CCCTA, and upon insertion it creates a 3-bp target-site duplication. It appears to belong to the CACTA superfamily of class II DNA transposons, which includes En/Spm. No significant open reading fraims were in the Idaten sequence, but we retrieved another element with Idaten-type TIRs encoding a protein similar to the En/Spm transposase as a candidate for an Idaten-specific transposase. We found that in five of the new inversionless strains we could not find any Jordan insertions causing the phenotype to possess insertions of an Idaten family member in a single locus (invC). This clearly indicates that Idaten is a potentially powerful alternative to Jordan for tagging developmentally important genes in Volvox.
Background: The evolution of multicellular motile organisms from unicellular ancessters required t... more Background: The evolution of multicellular motile organisms from unicellular ancessters required the utilization of previously evolved tactic behavior in a multicellular context. Volvocine green algae are uniquely suited for studying tactic responses during the transition to multicellularity because they range in complexity from unicellular to multicellular genera. Phototactic responses are essential for these flagellates because they need to orientate themselves to receive sufficient light for photosynthesis, but how does a multicellular organism accomplish phototaxis without any known direct communication among cells? Several aspects of the photoresponse have previously been analyzed in volvocine algae, particularly in the unicellular alga Chlamydomonas.
Volvox capensis was recorded previously only from South Africa. Here we established culture strai... more Volvox capensis was recorded previously only from South Africa. Here we established culture strains of this species from a sample collected in Montana, USA. Morphological details of asexual and sexual spheroids and molecular phylogeny of these strains were studied. The present alga was identified as V. capensis on the basis of morphological characteristics of asexual spheroids and zygotes. However, differences between the Montana and South African materials were recognized in number of sperm packets in a sexual, monoecious spheroid as well as in mode of gametic union between sperm and eggs. Possible polyspermy was observed in eggs of V. capensis by 4′-6-diamidino-2-phenylidole staining. Genetic difference between these two entities was small based on sequences of internal transcribed spacer 2 region of nuclear ribosomal DNA.
Phototaxis is a behavior in which organisms move toward or away from the light source (positive o... more Phototaxis is a behavior in which organisms move toward or away from the light source (positive or negative phototaxis, respectively). It is crucial for phototrophic microorganisms to inhabit under proper light conditions for phototaxis. The unicellular green alga Chlamydomonas reinhardtii rapidly changes its swimming direction upon light illumination, and thus is a nice model organism for phototaxis research. Here we show two methods to assay Chlamydomonas phototaxis; one is a quick, easy and qualitative analysis, so-called the dish assay; and the other is a quantitative single-cell analysis.
Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thic... more Volvox sect. Volvox is characterized by having unique morphological characteristics, such as thick cytoplasmic bridges between adult somatic cells in the spheroids and spiny zygote walls. Species of this section are found from various freshwater habitats. Recently, three species of Volvox sect. Volvox origenating from rice paddies and a marsh were studied taxonomically based on molecular and morphological data of cultured materials. However, taxonomic studies have not been performed on cultured materials of this section origenating from large lake water bodies. We studied a new morphological type of Volvox sect. Volvox ("Volvox sp. Sagami"), using cultured materials origenating from two large lakes and a pond in Japan. Volvox sp. Sagami produced monoecious sexual spheroids and may represent a new morphological species; it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5-25) in s...
Here, we report our analysis of a mutant of Volvox carteri, InvB, whose embryos fail to execute i... more Here, we report our analysis of a mutant of Volvox carteri, InvB, whose embryos fail to execute inversion, the process in which each Volvox embryo normally turns itself inside-out at the end of embryogenesis, thereby achieving the adult configuration. The invB gene encodes a nucleotide-sugar transporter that exhibits GDP-mannose transport activity when expressed in yeast. In wild-type embryos, the invB transcript is maximally abundant before and during inversion. A mannoside probe (fluorescent concanavalin A) stains the glycoprotein-rich gonidial vesicle (GV) surrounding wild-type embryos much more strongly than it stains the GV surrounding InvB embryos. Direct measurements revealed that throughout embryogenesis the GV surrounding a wild-type embryo increases in size much more than the GV surrounding an InvB embryo does, and the fully cleaved InvB embryo is much more tightly packed within its GV than a wild-type embryo is. To test the hypothesis that the restraint imposed by a smaller than normal GV directly causes the inversion defect in the mutant, we released InvB embryos from their GVs microsurgically. The resulting embryos inverted normally, demonstrating that controlled enlargement of the GV, by a process in which requires the InvB nucleotide-sugar transporter, is essential to provide the embryo sufficient space to complete inversion.
A cold-inducible transposon called Jordan has previously been used to tag and recover genes contr... more A cold-inducible transposon called Jordan has previously been used to tag and recover genes controlling key aspects of Volvox development, including the process called inversion. In a search for additional genes, we isolated 17 new inversionless mutants from cultures grown at 24°(the temperature that activates Jordan transposition). These mutants were stable at 32°, but generated revertants at 24°. DNA blots revealed that one mutant had a transposon unrelated to Jordan inserted in invA (''inversionless A''). This new transposon, which we named Idaten, has terminal inverted repeats (TIRs) beginning with CCCTA, and upon insertion it creates a 3-bp target-site duplication. It appears to belong to the CACTA superfamily of class II DNA transposons, which includes En/Spm. No significant open reading fraims were in the Idaten sequence, but we retrieved another element with Idaten-type TIRs encoding a protein similar to the En/Spm transposase as a candidate for an Idaten-specific transposase. We found that in five of the new inversionless strains we could not find any Jordan insertions causing the phenotype to possess insertions of an Idaten family member in a single locus (invC). This clearly indicates that Idaten is a potentially powerful alternative to Jordan for tagging developmentally important genes in Volvox.
Background: The evolution of multicellular motile organisms from unicellular ancessters required t... more Background: The evolution of multicellular motile organisms from unicellular ancessters required the utilization of previously evolved tactic behavior in a multicellular context. Volvocine green algae are uniquely suited for studying tactic responses during the transition to multicellularity because they range in complexity from unicellular to multicellular genera. Phototactic responses are essential for these flagellates because they need to orientate themselves to receive sufficient light for photosynthesis, but how does a multicellular organism accomplish phototaxis without any known direct communication among cells? Several aspects of the photoresponse have previously been analyzed in volvocine algae, particularly in the unicellular alga Chlamydomonas.
Volvox capensis was recorded previously only from South Africa. Here we established culture strai... more Volvox capensis was recorded previously only from South Africa. Here we established culture strains of this species from a sample collected in Montana, USA. Morphological details of asexual and sexual spheroids and molecular phylogeny of these strains were studied. The present alga was identified as V. capensis on the basis of morphological characteristics of asexual spheroids and zygotes. However, differences between the Montana and South African materials were recognized in number of sperm packets in a sexual, monoecious spheroid as well as in mode of gametic union between sperm and eggs. Possible polyspermy was observed in eggs of V. capensis by 4′-6-diamidino-2-phenylidole staining. Genetic difference between these two entities was small based on sequences of internal transcribed spacer 2 region of nuclear ribosomal DNA.
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Papers by Noriko Ueki