Stratmann J, Paputsoglu G, Oertel W
Differentiation
of Ulva mutabilis (Chlorophyta) gametangia and gamete release are controlled by
extracellular inhibitors
J PHYCOL 32 (6): 1009-1021 DEC 1996
Abstract:
Blade cells of Ulva mutabilis Foyn (Chlorophyta) excrete regulatory factors
into their cell walls and into the environment. These factors are essential for
the maintenance of the vegetative state. ''Sporulation inhibitor-1a'' (SI-1a)
is a glycoprotein that was isolated from the culture medium of axenic Ulva
growing as an undifferentiated callus. This protein was unusually stable to
denaturing treatments and showed an extremely high apparent molecular mass
(M(r)) of 1-4 X 10(7) daltons estimated by size exclusion chromatography. The
glycosylation was not essential for activity. SI-1a suppressed gametogenesis
completely at concentrations lower than 10(-14) M. When Ulva developed normally
in the presence of their symbiotic bacteria, smaller forms of SI-1 accumulated
in the medium (10(4) - 10(6) daltons). Sporulation inhibitors of the same size
spectrum and with similar properties were also extracted from crude cell walls
of nonaxenic Ulva. A class of different nonprotein sporulation inhibitors
(SI-2) of very low M(r) and yet unknown structure was isolated from the inner
space between the two blade cell layers. Excretion of all SI-1 forms decreased
with maturation of the thallus, whereas the overally concentration of SI-2 in
the thallus stayed constant throughout the life cycle. The SI-2 affected
different Ulva species whereas SI-1 was species-specific. Gametogenesis was
induced upon removal of both sporulation inhibitors from small single-layered
fragments of mature blades. After a ''determination phase'' of 23-46 h,
dependent on the time of induction within the cell cycle, the cells became
irreversibly committed to differentiation and were no longer susceptible to
SI-1 or SI-2. Subsequently, during a 28-h ''differentiation phase,'' 16
progametes were formed by synchronous genome doublings and cell divisions and
differentiated into mature gametes. These became motile and were released from
the gametangia when the concentration of a ''swarming inhibitor'' of low M(r),
excreted mainly during the ''determination phase,'' declined below a threshold
concentration. The biochemical properties of these regulatory factors and their
effects on gametogenesis and gamete release are described.
Ichimura T
Genome
rearrangement and speciation in freshwater algae
HYDROBIOLOGIA 336 (1-3): 1-17
Abstract:
Speciation problems are reviewed in the context of biogeography of fresh-water
algae. Currently accepted species concept in phycology is based on
morphological characters, and according to this concept, most freshwater algal
species are considered cosmopolitan. This implies whether they have a highly
efficient means of dispersal or their morphological characters are very static
through a long evolutionary time. Recent studies of reproductive isolation show
that some biological species of fresh-water algae are not so static or may not
have such a high power of dispersal means, though some are indeed very static
in morphological characters. The life cycle of most freshwater algae is
composed of a vegetative cycle of growth and reproduction and a sexual cycle of
gametic fusion and meiosis in the zygote, which forms a dormant spore-like
structure. Since any freshwater habitat is ephemeral in terms of evolutionary
time scale, each species has a capacity of forming germlings from a dormant
cell in order to recycle its life history. The genome of freshwater algae,
therefore, contains various coadapted gene systems, at least two, for the
vegetative and for the sexual cycle. Homothallism and heterothallism are two
contrasting mating systems that represent two opposing ways of life to
harmonize antagonism between the vegetative stage of growth and reproduction
and the sexual and dormant stage. Geographic and ecological distribution,
polyploidy, and sex determination are discussed in conjunction with sexual and
postzygotic isolating mechanisms.
Nozaki H
Morphology
and evolution of sexual reproduction in the Volvocaceae (Chlorophyta)
J PLANT RES 109 (1095): 353-361 SEP 1996
Abstract:
Morphological features of sexual reproduction in the Volvocaceae are reviewed,
focusing particularly on gametic union and zygote germination. Both of the two
conjugating gametes of the isogamous genera Pandorina, Volvulina and
Yamagishiella bear a tubular mating structure (mating papilla), and plasmogamy
is initiated by union of the papillae tips. On zygote germination, a single
biflagellate gone cell is released from the zygote wall. Although all the
anisogamous and oogamous genera of the Volvocaceae produce ''sperm packets''
during gametogenesis and a single gone cell at zygote germination, some
difference can be recognized in the male gametes. The male gametes of Eudorina
bear a tubular cytoplasmic protuberance (putative mating papilla) near the base
of the flagella, whereas such a structure recognized at the light microscopic
level is not evident in Pleodorina and Volvox, Evolution of the sexual
reproduction characteristics of volvocacean algae is discussed on the basis of
recent cladistic analysis of morphological data as well as of the ribosomal (r)
RNA phylogeny and large subunit of the ribulose-1,5-biphosphate
carboxylase/oxygenase(rbcL) gene trees.
Beyser K, Fabry S
Identification
and characterization of a lower plant Ypt/Rab guanosine dissociation inhibitor
(GDI)
FEBS LETT 396 (2-3): 298-304
Abstract:
The cDNA encoding a Ypt/Rab guanosine dissociation inhibitor (Ypt-GDI) was
isolated from the multicellular green alga Volvox carteri, representing
the first complete plant gdi gene described. The gdiV1 gene occurs as a single
copy in the algal genome, indicating that its product regulates all YptV
proteins from Volvox. The derived GDI protein (GDIV1p) shows high
similarity to animal and fungal GDIs. A specific antibody developed against
GDIV1p detected the protein throughout the whole Volvox life-cycle.
GDIV1p was localized in the cytoplasm and in the algal flagellum. This is in
line with earlier findings of a dual localization of Ypt proteins both in the
cell body and in the motility organelle, and indicates a novel role of the
GDI/Ypt system, possibly in intraflagellar transport.
Choi G, Przybylska M, Straus D
Three
abundant germ line-specific transcripts in Volvox carteri encode photosynthetic proteins
CURR GENET 30 (4): 347-355 SEP 1996
Abstract:
Volvox carteri is a multicellular eukaryotic green alga composed of
about 2000 cells of only two differentiated types: somatic and germ line. To
understand how embryonic cells are assigned either to somatic or germ line
fates, we are investigating the regulation of transcripts that are abundant in
only one cell type. Here we report the identity of three transcripts that are
coordinately expressed at high levels in germ line cells but not in somatic
cells. Surprisingly, all three transcripts encode photosynthetic chloroplast
proteins (light-harvesting complex protein. oxygen-evolving enhancer protein 3,
and ferredoxin-NADP(+) reductase) that are transcribed from nuclear genes. We
discuss why these mRNAs might be required at high levels in germ line cells and
present a hypothesis, suggested by our results, on the evolution of cell
specialization in the Volvocales.
Ortega MA, DiazGuerra M, Sastre L
Actin gene
structure in two Artemia species, A-franciscana and A-parthenogenetica
J MOL EVOL 43 (3): 224-235 SEP 1996
Abstract:
Genomic clones coding for actin have been isolated from two species of the
crustacean Artemia, A. parthenogenetica and A. franciscana. The Act211 isoform
gene was isolated from A. parthenogenetica, and the two other isoform genes,
Act302 and Act403, were isolated from A. franciscana. The comparison of the
nucleotide sequence of genomic and cDNA clones showed an interspecific
divergence of 4% in translated and 6.1% in untranslated regions. However, the
establishment of the partial structure of the Act211 gene in A. franciscana and
of the Act302 gene in A. parthenogenetica suggests their similarity in the two
species. The Act211 gene is divided into four exons, the Act302 gene into six
exons, and the Act403 gene into seven exons. The three genes have introns in
the 5' untranslated region and between codons 41 and 42. The Act211 and 403
genes have one common intron in codon 168. The Act302 and 403 genes have common
introns between codons 121-122, 246-247, and within codon 301. While introns in
the 5' untranslated region and between codons 41-42 and 121-122 are present in
many organisms, the introns in positions 168 and 246-247 had only been found
previously in actin genes from the nematode Onchocerca volvulus and the green
alga Volvox carterii, respectively. The intron in position 301 had not
been reported before. The transcription initiation sites of these three genes
as well as the nucleotide sequences of the promoter regions have been also
determined.
Huber H, Beyser K, Fabry S
Small G
proteins of two green algae are localized to exocytic compartments and to
flagella
PLANT MOL BIOL 31 (2): 279-293 MAY 1996
Abstract:
The Ypt/Rab proteins are small GTPases, which belong to the Ras superfamily and
have been shown to be involved in endo- and exocytosis in mammalian cells and
yeast. Using affinity-purified antibodies specific for four Ypt proteins,
namely Ypt1p, Ypt4p, Ypt5p and Ypt6p, of the multicellular green alga Volvox
carteri (YptVp) and its close unicellular relative Chlamydomonas reinhardtii
(YptCp), we examined the abundance of the corresponding antigens during the
asexual life cycle of Volvox, and their intracellular localization. The
YptV proteins were found in all stages throughout the asexual life cycle and
are tightly associated with intracellular membranes. Indirect
immunofluorescence revealed that YptV4p, YptV5p and YptV6p are present in
perinuclear regions of the cell, indicating an association with the Golgi
region. Golgi localization of YptV4p and YptV6p in Volvox was confirmed
by immunogold electron microscopy. In contrast, we found Ypt1p associated with
the contractile vacuole in both V. carteri and C. reinhardtii. Furthermore, the
YptV proteins were also detected along the entire length of the flagella of
somatic Volvox cells. This flagellar location was substantiated by
western blot analysis of extracts prepared from isolated flagella of both
algae. While localization to exocytic compartments is in agreement with the
established Ypt/Rab function in intracellular vesicle transport of eukaryotic
cells, presence in the algal flagellum is the first hint of a possible role for
small G proteins also in motility organelles.
Ferris PJ, Woessner JP, Goodenough UW
A sex
recognition glycoprotein is encoded by the plus mating-type gene fus1 of
Chlamydomonas reinhardtii
MOL BIOL CELL 7 (8): 1235-1248 AUG 1996
Abstract:
Sexual fusion between plus and minus gametes of the unicellular green alga
Chlamydomonas reinhardtii entails adhesion between plus-specific and
minus-specific ''fringe'' proteins displayed on the plasma membrane of gametic
mating structures. We report the identification of the gene (fus1) encoding the
plus fringe glycoprotein, which resides in a unique domain of the mating-type
plus (mt(+)) locus, and which was identified by transposon insertions in three
fusion-defective mutant strains. Transformation with fus1(+) restores fringe
and fusion competence to these mutants and to the pseudo-plus mutant imp11
mt(-), defective in minus differentiation. The fus1 gene is remarkable in
lacking the codon bias found in all other nuclear genes of C. reinhardtii.
Gruber H, Kirzinger SH, Schmitt R
Expression of
the Volvox gene encoding nitrate
reductase: Mutation-dependent activation of cryptic splice sites and
intron-enhanced gene expression from a cDNA
PLANT MOL BIOL 31 (1): 1-12 APR 1996
Abstract:
Use of the nitrate reductase encoding gene (nitA) as selection marker has
facilitated the successful nuclear transformation of Volvox carteri. The
Volvox nitA gene contains 10 introns. A stable nitA mutation in the Volvox
recipient strain 153-81 resides in a G-to-A transition of the first nucleotide
in the 5' splice site of nitA intron 2. This mutation resulted in at least
three non-functional splice variants, namely: (1) intron 2 was not spliced at
all; (2) a cryptic 5' splice site 60 nt upstream or (3) a cryptic 5' splice
site 16 nt downstream of the mutation were activated and used for splicing.
When we used nitA cDNA (pVcNR13) for transformation of V. carteri 153-81, a low
efficiency of about 5 x 10(-5) transformants per reproductive cell was
observed. Re-integration of either intron 1 (pVcNR15) or introns 9 and 10
(pVcNR16) in the transforming cDNA increased transformation rates to 5 x
10(-4). In parallel, pVcNR15-transformed Volvox exhibited growth rates
that were 100-fold increased over the pVcNR13-transformed alga. This
intron-enhancement of nitA gene expression appears to be associated with
post-transcriptional processing and 'channelling' of the message. These data
suggest an important role of splicing for gene expression in V. carteri.
Agrawal SC, Sharma
Chemical and
biological properties of culture filtrates of Westiellopsis prolifica and
Chaetophora attenuata
ISRAEL J PLANT SCI 44 (1): 43-48 1996
Abstract:
Westiellopsis prolifica Janet and Chaetophora attenunta Hazen cultures released
sugars (glucose, fructose, and sucrose), organic acids (oxaloacetic acid and
oxalic acid), amino acids, and protein. W. prolifica cultures released the
amino acids glycine, serine, cystine, glutamic acid, aspartic acid, and
cc-alanine, while C. attenuata cultures released glycine, serine, aspartic
acid, and cr-alanine. W. prolifica and C. attenuata cultures of all ages
released more extracellular protein than total free amino acids. Cultures of C.
attenuata released more protein than cultures of the same age of W. prolifica.
The filtrates from old cultures of W. prolifica and C. attenunta decreased the
total chlorophyll content of all algae tested, totally suppressed conjugation
in Spirogyra decimina and zoospore formation in C. attenuata, and drastically
decreased spore germination in W. prolifica, thus producing stressful
conditions affecting the growth and reproduction of these and other algae.
Selmer T, Hallmann A, Schmidt B, et al.
The
evolutionary conservation of a novel protein modification, the conversion of
cysteine to serinesemialdehyde in arylsulfatase from Volvox carteri
EUR J BIOCHEM 238 (2): 341-345
Abstract:
A novel post-translational protein modification has recently been described in
two human sulfatases, by which a cysteine is replaced by a serinesemialdehyde
(2-amino-3-oxopropionic acid) residue [Schmidt, B., Selmer, T., Ingendoh, A.
& von Figura, K. (1995) Cell 82, 271-278]. This cysteine is conserved among
all known eukaryotic sulfatases. Here we report the presence of this
modification in arylsulfatase from the green alga Volvox carteri. The
evolutionary conservation of this novel protein modification between sulfatases
of V. carteri and man lends further support to the assumption that this
modification is required for the catalytic activity of sulfatases and may be
present in all sulfatases of eukaryotic origin.
Sugase Y, Hirono M, Kindle KL, et al.
Cloning and
characterization of the actin-encoding gene of Chlamydomonas reinhardtii
GENE 168 (1): 117-121
Abstract:
The genomic and complementary DNA sequences were determined for the unique
actin-encoding gene in Chlamydomonas reinhardtii (Cr). The deduced amino acid
(aa) sequence of this actin was similar to most known actin sequences, with the
highest identity (98.1%) being with that of Volvox carteri actin. The Cr
actin-encoding gene has one intron in the 5'-untranslated region and eight
introns in the coding region. The latter eight introns occur at the same
positions as those in the V. casteri actin-encoding gene. The 5'-upstream
region contains four short stretches of sequence similar to the so-called 'tub
box', a characteristic sequence proposed to be responsible for the regulation
of synthesis of various axonemal proteins upon deflagellation and during the
cell cycle, Southern blot analysis indicated that the Cr genome has only a
single actin-encoding gene. An antibody specific for the 11-aa peptide
corresponding to the N-terminal sequence of this actin was found to react with
a 43-kDa protein associated with flagellar inner-arm dynein. These findings
indicate that a single actin functions in both the cytoplasm and flagella of
this organism.
Fabry S, Beyser K
YptV2p, a
membrane-associated small G protein abundant during embryogenesis in the green
alga Volvox carteri
PROTOPLASMA 190 (1-2): 79-87 1996
Abstract:
The multicellular fresh-water alga Volvox carteri contains at least six
small G protein-encoding genes (ypt genes) whose products are probably involved
in intracellular vesicle transport. Four of them, YptV1, YptV3, YptV4, and
YptV5, have been isolated and characterized previously. Here we report the
cloning of yptV2 cDNA, the production of recombinant His-tagged YptV2p protein
(reYptV2p) in E. coli, and the analysis of its GTPase activity and
intracellular localization. YptV2p is predominantly present in dividing Volvox
embryos. It is a membrane-associated protein which is localized to the cell
periphery (plasma membrane or plasma-membrane-associated vesicles), probably by
a lipid moiety. Purified, E. coli-expressed YptV2p binds GTP specifically, and
has a typically low intrinsic GTPase activity (k(cat) = 0.004/min), which is
enhanced by a GTPase activating protein activity present in Volvox. Our
observations suggest a role of YptV2p in secretion, with a peak during the
rapid cleavages of the Volvox embryo.
Hallmann A, Sumper M
The Chlorella
hexose H+ symporter is a useful selectable marker and biochemical reagent when
expressed in Volvox
P NATL ACAD SCI USA 93 (2): 669-673 JAN 23 1996
Abstract:
The multicellular obligately photoautotrophic alga Volvox is composed of
only two types of cells, somatic and reproductive, Therefore, Volvox
provides the simplest model system for the study of multicellularity. Metabolic
labeling experiments using radioactive precursors are crucial for the detection
of stage- and cell-type-specific proteins, glycoproteins, lipids, and
carbohydrates. However, wild-type Volvox lacks import systems for sugars
or amino acids. To circumvent this problem, the hexose/H+ symporter (HUP1) gene
from the unicellular alga Chlorella was placed under the control of the
constitutive Volvox beta-tubulin promoter. The corresponding transgenic Volvox
strain synthesized the sugar transporter in a functional state and was able to
efficiently incorporate C-14 from labeled glucose or glucosamine. Sensitivity toward
the toxic glucose/mannose analogue 2-deoxyglucose increased by orders of
magnitude in transformants. Thus we report the successful transformation of Volvox
with a gene of heterologous origin. The chimeric gene may be selected for in
either a positive or a negative manner, because transformants exhibit both
prolonged survival in the dark in the presence of glucose and greatly increased
sensitivity to the toxic sugar 2-deoxyglucose. The former trait may make the
gene useful as a dominant selectable marker for use in transformation studies,
whereas the latter trait may make it useful in development of a gene-targeting
system.
Nishii I, Ogihara S
Role of actomyosin
in multicellular deformation: Inversion of Volvox embryos.
MOL BIOL CELL 7: 2219-2219 Suppl. S DEC 1996
Girardin HM, Pelletier JA, Jovanovic L, et al.
Translational
control during the development of Volvox.
MOL BIOL CELL 7: 624-624 Suppl. S DEC 1996