Desnitski AG
Dormant stages of the green flagellate in Volvox
in a natural habitat
RUSSIAN JURNAL OF DEVELOPMENTAL BIOLOGY 33(2): 107-109; 2002 (for pdf click here)
Coleman AW
Comparison of
Eudorina/Pleodorina ITS sequences of isolates from nature with those from
experimental hybrids
AM J BOT 89 (9): 1523-1530 SEP 2002
Abstract:
Internal transcribed spacer (ITS) regions of nuclear ribosomal repeats were
compared among 50 Eudorina and Pleodorina isolates and two Volvox
species known to clade with Eudorina species. Of the six major subclades found,
four containing Eudorina and Pleodorina illinoisensis isolates, one containing
Eudorina and Pleodorina indica, and one containing Volvox gigas and V.
powersii, the basal branching order remains uncertain, but the positioning of
isolates known to mate was always as nearest neighbors on the terminal branches
of the tree. Four hybrid clones from a cross of E. elegans with P.
illinoisensis, known from chromosome counts to be products of the failure of
meiosis at zygote germination, contain both parental ITS repeat regions, as
expected. However, they have in addition both crossover and other variant ITS
cistrons among their many repeats of ITS. Such variation is limited to terminal
regions of helices, as recognized from knowledge of RNA transcript secondary
structure. Proper alignment then utilizes all of the nucleotide positions; the
hybrid variants appear in positions intermediate between their parents in the
tree. In fact, such variants seem to be hallmarks of recent hybridization
events, since they were not found in any of the other 50 isolates.
Duncan L, Bouckaert K, Yeh F, et al.
Kangaroo, a
mobile element from Volvox
carteri, is a member of a newly recognized third class of retrotransposons
GENETICS 162 (4): 1617-1630 DEC 2002
Abstract:
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 front the multicellular green alga, Volvox carteri.
kangaroo elements are highly mobile and their expression is developmentally
regulated. The), probably integrate via double-stranded, closed-circle DNA
intermediates through the action of an encoded recombinase related to the
X-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.
Berthold P, Schmitt R, Mages W
An engineered
Streptomyces hygroscopicus aph 7" gene mediates dominant resistance
against hygromycin B in Chlamydomonas reinhardtii
PROTIST 153 (4): 401-412 DEC 2002
Abstract:
We have developed a positively selectable marker for the green alga
Chlamydomonas reinhardtii using the Streptomyces hygroscopicus aminoglycoside
phosphotransferase gene (aph7"). Its expression is controlled by C.
reinhardtii regulatory elements, namely, the beta2-tubulin gene promoter in
combination with the first intron and the 3' untranslated region of the small
subunit of ribulose bisphosphate carboxylase, rbcS2. C. reinhardtii cell-wall
deficient and wild-type strains were transformed at rates up to 5 x 10(-5) with
two constructs, pHyg3 and pHyg4 (intron-less). Transformants selected on plates
with 10 mug/ml hygromycin B exhibited diverse levels of resistance of up to 200
mug/ml that were stably maintained for at least seven months; they contained
two to five copies of the construct integrated in their genomes. Transcription
of the chimeric aph7" gene, correct splicing of the rbcS2 intron, and
polyadenylation of the transcripts have been verified by sequencing of RT-PCR
products. Average co-transformation rates using pHyg3 and a second selectable
plasmid were about 11%. This advocates the hygromycin-resistance plasmid,
pHyg3, as a new versatile tool for the transformation of a broad range of C.
reinhardtii strains without the sustained need for using auxotrophic mutants as
recipients.
Gradmann D, Ehlenbeck S, Hegemann P
Modeling
light-induced currents in the eye of Chlamydomonas reinhardtii
J MEMBRANE BIOL 189 (2): 93-104
Abstract:
Rhodopsin-mediated electrical events in green algae have been recorded in the
past from the eyes of numerous micro-algae like Haematococcus pluvialis,
Chlamydomonas reinhardtii and Volvox carteri. However, the electrical
data gathered by suction-pipette techniques could be interpreted in qualitative
terms only. Here we present two models that allow a quantitative analysis of
such results: First, an electrical analog circuit for the cell in suction pipette
configuration is established. Applying this model to experimental data from
unilluminated cells of C. reinhardtii yields a membrane conductance of about 3
Sm-2. Furthermore, an analog circuit allows the determination of the
photocurrent fraction that is recorded under experimental conditions. Second, a
reaction scheme of a rhodopsin-type photocycle with an early Ca2+ conductance
and a later H+ conductance is presented. The combination of both models
provides good fits to light-induced currents recorded from C. reinhardtii.
Finally, it allowed the calculation of the impact of each model parameter on
the time courses of observable photocurrent and of inferred transmembrane
voltage. The reduction of the flash-to-peak times at increasing. light
intensities are explained by superposition of two kinetically distinct
rhodopsins and by assuming that the Ca2+-conducting state decays faster at more
positive membrane voltages.
Saliu JK
The diet of
Brycinus nurse (Pisces : Characidae) from Asa Reservoir, Ilorin, Nigeria
REV BIOL TROP 50 (1): 239-243 MAR 2002
Abstract:
From November 1991 to October 1993, 980 specimens of the characid Brycinus
nurse were collected from Asa reservoir to examine its diet. The diet was
analyzed using the frequency of occurrence, numerical and gravimetric methods.
Two hundred and sixty nine (27.45%) of the stomachs examined were empty. The
fish was an omnivore feeding extensively on a wide array of plant and animal
food items. These consisted of 9 families, 10 genera and 10 species. The most
extensively consumed plant food item was aquatic plant parts which occurred in
63.88% of the stomachs, and accounted for 6.06% by number and 12.10% by weight
while the ephemeropteran, Povilla adusta was the most dominant animal food
item, occurring in 50.92% of the stomachs, and accounting for 11.98% by number
and 11.86% by weight. Conversely, the least consumed plant food item was Volvox
occurring in 4.49% of the stomachs and accounting for 0.18% by number and 0.35%
by weight, while the fish Barbus sp. was the least consumed animal food item
occurring in 0.51% of the stomachs, accounting for 0.03% by number and 1.62% by
weight. New food items not previously recorded such as a watermite, Aspatharia
sinuata and Barbus callipterus were found in the stomach contents. The
nonspecific feeding regime of the fish and its ability to utilize different
food items effectively was what accounted for the prominence and wide
distribution of the fish in the lake.
Heitzer M, Hallmann A
An extracellular
matrix-localized metalloproteinase with an exceptional QEXXH metal binding site
prefers copper for catalytic activity
J BIOL CHEM 277 (31): 28280-28286
Abstract:
The extracellular matrix (ECM) of the simple multicellular organism Volvox
contains many region-specific morphological elements and mediates a variety of
developmental and physiological responses by modification of its components.
The fact that >95% of the mature organism is ECM makes Volvox
suitable as a model system for ECM investigations. VMPs are a family of Volvox
genes that are homologous to zinc-dependent matrix metalloproteinases (MMPs).
Here we describe the identification and purification of the first VMP protein,
VMP3. The 470-kDa VMP3 glycoprotein is localized within the ECM, and its
biosynthesis is induced by the sex pheromone. The metal binding motif of VMP3
is QEXXH, not HEXXH as known for 1300 other metalloproteinases. VMP3 shows
proteinase activity and is inhibited by EDTA or the MMP inhibitor GM 6001, but
in contrast to all known proteinases, VMP3 clearly prefers copper for activity
rather than zinc. The exchange from Q to H within the QEXXH motif abolishes its
copper preference. The unique properties of VMP3 suggest a novel type of
metalloproteinase.
Nozaki H, Takahara M, Nakazawa A, et al.
Evolution of
rbcL group IA introns and intron open reading frames within the colonial
Volvocales (Chlorophyceae)
MOL PHYLOGENET EVOL 23 (3): 326-338 JUN 2002
Abstract:
Aono N,
Palindromic
repetitive elements in the mitochondrial genome of Volvox
FEBS LETT 521 (1-3): 95-99
Abstract:
Group I introns were found in the cob and cox I genes of Volvox carteri.
These introns contain tandem arrays of short palindromic sequences that are
related to each other. Inspection of other regions in the mtDNA revealed that
similar palindromic repetitive sequences are dispersed in the non-protein
coding regions of the mitochondrial genome. Analysis of the group I intron in
the cob gene of another member of Volvocaceae, Volvox aureus, has shown
that its sequence is highly homologous to its counterpart in V. carteri with
the exception of a cluster of palindromic sequences not found in V. carteri.
This indicates that the palindromic clusters were inserted into the introns
after divergence of the two species, presumably due to frequent insertions of
the palindromic elements during evolution of the Volvocaceae. Possible
involvement of the palindromic repetitive elements in the molecular evolution
of functional RNAs is discussed. (C) 2002 Published by Elsevier Science B.V. on
behalf of the Federation of European Biochemical Societies.
Ender F, Godl K, Wenzl S, et al.
Evidence for
autocatalytic cross-linking of hydroxyproline-rich glycoproteins during
extracellular matrix assembly in volvox
PLANT CELL 14 (5): 1147-1160 MAY 2002
Abstract:
The alga Volvox carteri is one of the simplest multicellular organisms,
yet it has a surprisingly complex extracellular matrix (ECM), making Volvox
suitable as a model system in which to study ECM self-assembly. Here, we
analyze the primary structures and post-translational modifications of two main
ECM components synthesized in response to sexual induction as well as wounding.
These proteins are members of the pherophorin family with as yet unknown
properties. They contain polyhydroxyproline spacers as long as 500 and 2750
residues. Even the highly purified proteins retain the capacity to
self-assemble and cross-link, producing an insoluble fibrous network in an
apparently autocatalytic reaction. This pherophorin-based network is located
within the deep zone of the ECM. A molecular genetic search for additional
members of the pherophorin family indicates that at least nine different
pherophorin species can be expected to serve as precursors for ECM
substructures. Therefore, the highly diversified members of the pherophorin
family represent region-specific morphological building blocks for ECM assembly
and cross-linking.
Cloning and
characterization of novel extensin-like cDNAs that are expressed during late
somatic cell phase in the green alga Volvox
carteri
GENE 284 (1-2): 179-187 FEB 6 2002
Abstract:
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 in 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. (C) 2002 Elsevier Science B.V.
All rights reserved.
Miller SM
Taming the
fierce roller: an "enhanced" understanding of cellular
differentiation in Volvox
BIOESSAYS 24 (1): 3-7 JAN 2002
Abstract:
Few organisms offer a better opportunity to explore the mechanisms of cellular
differentiation, and their origins, than Volvox. Volvox consists
of just two cell types, germ and soma, and is the most complex member of a
family of green algae that includes unicellular and multicellular relatives. At
the heart of the cell-fate determination program of Volvox carted is the
regA gene, which encodes a putative transcriptional repressor that prevents
somatic cells from expressing reproductive functions. Stark et al.((1)) have
dissected the regA gene to determine how its expression is restricted to
somatic cells. Their results suggest that regrA expression is controlled by
multiple enhancers, the most important of which prevents transcription in
reproductive cells. While these findings shed light on Volvox
development, they also raise a new set of questions about the mechanisms that
control the germ-soma dichotomy in this organism. (C) 2002 John Wiley Sons,
Inc.