Desnitski AG
Development and reproduction of two species of the genus Volvox
in a shallow temporary pool
PROTISTOLOGY 1(4): 195-198; 2000 (for pdf click here)
Kirk DL
Volvox as a model system for studying the ontogeny and phylogeny
of multicellularity and cellular differentiation
J PLANT GROWTH REGUL 19 (3): 265-274 SEP 2000
Abstract:
Volvox carteri, a spherical alga with a complete division of labor
between approximately 2000 biflagellate somatic cells and 16 asexual reproductive
cells called gonidia, provides a very attractive system for analyzing how a
molecular-genetic program for cell-autonomous cellular differentiation may be
encoded within a genome. Then, when considered in combination with a group of
closely related "volvocine algae" that includes unicellular
Chlamydomonas plus a series of colonial forms of increasing cell number and
complexity, it also provides an attractive model system for analyzing how such
a program for multicellularity and cytodifferentiation may have evolved. It is
proposed that the following were some of the key steps in this evolutionary
pathway: (1) The Chlamydomonas cell wall was transformed into an extracellular
matrix (ECM) that joined sister cells into a colonial unit. (2) Larger organisms
with more abundant ECM were favored because of the role the ECM plays in
storing limiting nutrients. (3) In the V. carteri lineage the ancestral
biphasic "first biflagellate and then reproductive" pathway of
development bt came converted to a dichotomous pathway by introduction of two
kinds of cell-type-specific negative regulators: one that blocked growth and
reproduction in presumptive somatic cells and one that blocked somatic
development in presumptive gonidia. Progress has been made in cloning and characterizing
genes that are involved in setting apart the two cell lineages of V. carteri
and in subsequently controlling their dichotomous differentiation. The
strengths and weaknesses of V. carteri and its relatives as a model system for
studying the evolution of multicellularity are discussed.
Hallmann A, Kirk DL
The
developmentally regulated ECM glycoprotein ISG plays an essential role in
organizing the ECM and orienting the cells of Volvox
J CELL SCI 113 (24): 4605-4617 DEC 2000
Abstract:
Volvox is one of the simplest multicellular organisms with only two cell
types, yet it has a surprisingly complex extracellular matrix (ECM) containing
many region-specific morphological components, making Volvox suitable as
a model system for ECM investigations. ECM deposition begins shortly after
inversion, which is the process by which the embryo turns itself right-side-out
at the end of embryogenesis. It was previously shown that the gene encoding an
ECM glycoprotein called ISG is transcribed very transiently during inversion.
Here we show that the developmentally controlled ISG accumulates at the bases
of the flagella right after inversion, before any morphologically recognizable
ECM structures have yet developed. Later, ISG is abundant in the 'flagellar
hillocks' that encircle the basal ends of all flagella, and in the adjacent
'boundary zone' that delimits the spheroid. Transgenic Volvox were
generated which express a truncated form of ISG, These transgenics exhibit a
severely disorganized ECM within which the cells are embedded in a highly
chaotic manner that precludes motility, A synthetic version of the C-terminal
decapeptide of ISG has a similar disorganizing effect, but only when it is
applied during or shortly after inversion. We postulate that ISG plays a
critical role in morphogenesis and acts as a key organizer of ECM architecture;
at the very beginning of ECM formation ISG establishes an essential initial
framework that both holds the somatic cells in an adaptive orientation and acts
as the scaffold upon which the rest of the ECM can be properly assembled,
assuring that somatic cells of post-inversion spheroids are held in
orientations and locations that makes adaptive swimming behavior possible.
Goodwin PH, Li J, Jin SM
Evidence for
sulfate derepression of an arylsulfatase gene of Colletotrichum gloeosporioides
f. sp malvae during infection of round-leaved mallow, Malva pusilla
PHYSIOL MOL PLANT P 57 (4): 169-176 OCT 2000
Abstract:
An arylsulfatase gene, cgars, was cloned from Colletotrichum gloeosporioides f.
sp. malvae (Cgm), a hemibiotrophic plant pathogenic fungus that causes
anthlacnose disease of round-leaved mallow (Malva pusilla). The clone of cgars
showed high amino acid sequence identity to ass-1(+), an arylsulfatase gene of
Neurospora crassa. Arylsulfatase genes have been shown to be good reporter
genes for detecting available sulfur levels in a variety of microorganisms.
Expression of cgars was determined by relative RT-PCR, in which gars expression
levels were compared to those of actA, a constitutively expressed actin gene of
Cgm, following coamplification. In culture, expression of gars was found to be
repressed by methionine as has been demonstrated for ars-1(+). In host leaf
tissue, cgars expression was relatively higher than actA during penetration,
similar to actA during biotrophic growth and then progressively lower than actA
during necrotrophic growth. These results show that the availability of host
sulfur differs depending upon the stage of infection. (C) 2000 Academic Press.
Nozaki H, Misawa K, Kajita T, et al.
Origin and
evolution of the colonial Volvocales (Chlorophyceae) as inferred from multiple,
chloroplast gene sequences
MOL PHYLOGENET EVOL 17 (2): 256-268 NOV 2000
Abstract:
A combined data set of DNA sequences (6021 bp) from five protein-coding genes
of the chloroplast genome (rbcL, atpB, psaA, psaB, and psbC genes) were
analyzed for 42 strains representing 30 species of the colonial Volvocales (Volvox
and its relatives) and 5 related species of green algae to deduce robust
phylogenetic relationships within the colonial green flagellates. The 4-celled
family Tetrabaenaceae was robustly resolved as the most basal group within the
colonial Volvocales. The sequence data also suggested that all five volvocacean
genera with 32 or more cells in a vegetative colony (all four of the
anisogamous/oogamous genera, Eudorina, Platydorina, Pleodorina, and Volvox,
plus the isogamous genus Yamagishiella) constituted a large monophyletic group,
in which 2 Pleodorina species were positioned distally to 3 species of Volvox.
Therefore, most of the evolution of the colonial Volvocales appears to
constitute a gradual progression in colonial complexity and in types of sexual
reproduction, as in the traditional volvocine lineage hypothesis, although
reverse evolution must be considered for the origin of certain species of
Pleodorina. Data presented here also provide robust support for a monophyletic
family Goniaceae consisting of two genera: Gonium and Astrephomene. (C) 2000
Academic Press.
Sekimoto H
Intercellular
communication during sexual reproduction of Closterium (Conjugatophyceae)
J PLANT RES 113 (1111): 343-352 SEP 2000
Abstract:
Processes of intercellular communication during sexual reproduction of
conjugating green algae Closterium were reviewed. In the case of Closterium
peracerosum-strigosum-littorale complex, two sex-specific pheromones and their
receptors were involved in sexual reproduction. These pheromones were
glycoproteins and the expression of corresponding genes was critically
regulated by the sex and environmental conditions. In the case of Closterium
ehrenbergii, chemotactic and sexual cell division-inducing activities for
mating-type plus cells were detected and characterized. Although many processes
remain to be elucidated, the present results will be helpful for understanding
not only the mode of sexual reproduction in Closterium but also the variety of
intercellular communication in the plant kingdom especially during sexual
reproduction.
Kerszberg M
The survival
of slow reproducers
J THEOR BIOL 206 (1): 81-89 SEP 7 2000
Abstract:
Multicellularity, and the attendant segregation of the germ line, entails the
loss of reproductive capacity by the soma: in Volvox carteri, less than
1 cell in 100 contributes to the next generation. However, compensatory
advantages are unlikely to be very large (Koufopanou & Bell, 1993. Proc. R.
Soc. Lond. (B) 254, 107-113). Somewhat similarly, sex implies the generation of
males, hence a dramatic reproductive slowdown (Barton & Charlesworth, 1998.
Science 281, 1986-1990); yet, a compensating (two-fold) advantage of sex has
not been found. Here, I try to evaluate the actual cost of maintaining slow
reproductive cycles, namely cycles that necessitate the production of
"dead end" units such as somatic cells or males. In a quantitative
model for the competition of individuals with different, heritable reproductive
rates, this cost turns out to be unexpectedly small, and may even sometimes
become irrelevant. The bases for this are made fairly clear: thus, when all
enjoy high fecundity (e.g. a long reproductive life) the handicap of a slower
reproduction vanishes; alternatively, a slight separation of ecological niches
may be sufficient for survival of slower but otherwise unchanged reproducers;
and finally, inherent to slow reproduction is a low rate of destabilizing
genetic change. These facts are largely independent of the formal model
details, and are supported by direct computer simulations. They give a
quantitative basis for analysing the evolution and prevalence of slow life
cycles. The implications of these findings for the evolution of
multicellularity are briefly discussed. (C) 2000 Academic Press.
Matveev V, Matveeva L, Jones GJ
Relative
impacts of Daphnia grazing and direct stimulation by fish on phytoplankton
abundance in mesocosm communities
FRESHWATER BIOL 44 (3): 375-385 JUL 2000
Abstract:
1. Planktivorous fish were hypothesised to influence the abundance of algal
biomass in lakes by changing zooplankton grazing, affecting zooplankton
nutrient recycling and by direct recycling of nutrients to phytoplankton. The
relative roles of direct fish effects vs. zooplankton grazing were tested in
mesocosm experiments by adding to natural communities large grazing zooplankton
(Daphnia carinata) and small planktivorous fish (mosquitofish or juveniles of
Australian golden perch).
2. The addition of Daphnia to natural communities reduced the numbers of all phytoplankton less than 30 mu m in size, but did not affect total biomass of phytoplankton as large Volvox colonies predominated.
3. The addition of Daphnia also reduced the abundance of some small (Moina, Bosmina, Keratella) and large (adult Boeckella) zooplankton, suggesting competitive interactions within zooplankton.
4. The addition of mosquitofish to communities containing Daphnia further reduced the abundance of some small zooplankton (Moina, Keratella), but increased the numbers of Daphnia and adult Boeckella. In spite of the likely increase in grazing due to Daphnia, the abundance of total phytoplankton and dominant alga Volvox did not decline in the presence of mosquitofish but was maintained at a significantly higher level than in control.
5. The addition of juveniles of golden perch to communities containing Daphnia reduced the abundance of small zooplankton (Moina), increased the abundance of large zooplankton (adult Boeckella) but had no significant effect on Daphnia and total phytoplankton abundance.
6. The results of the present study suggest that some planktivorous fish can promote the growth of phytoplankton in a direct way, probably by recycling nutrients, and even in the presence of large grazers. However, the manifestation of the direct effect of fish can vary with fish species.
Suzuki L, Woessner JP, Uchida H, et al.
Zygote-specific
protein with hydroxyproline-rich glycoprotein domains and lectin-like domains
involved in the assembly of the cell wall of Chlamydomonas reinhardtii
(Chlorophyta)
J PHYCOL 36 (3): 571-583 JUN 2000
Abstract:
The cell wall of Chlamydomonas reinhardtii zygotes, which forms rapidly after
the fusion of wall-free gametes, provides a tractable system for studying the
properties and assembly of hydroxyproline-rich glycoproteins, the major
proteinaceous components of green algal and plant cell walls. We report the
cloning of the zsp2 gene and the analysis of its ZSP-2 product, a 58.9 kDa
poly-peptide that is synthesized exclusively by zygotes, The protein contains
two (SP), repeats, establishing it as a member of the cell wall
hydroxyproline-rich glycoproteins family. It also contains a 4-fold iteration
of an amino acid sequence centered around cysteine residues, a configuration
found in both plant and animal lectins, Furthermore, we report four
observations on pellicle composition and production, First, cell-free
preparations of the pellicle matrix are rich in hydroxyproline, arabinose, and
galactose and contain bundles of very long fibrils, Second, glutathione blocks
pellicle formation and results in the accumulation of long fibrils in the
growth medium. Third, antibody to ZSP-8 also blocks pellicle formation, Fourth,
ZSP-2 immunolocalizes to the boundary between the outer layers of the wall
proper and the pellicle matrix. These observations are consistent with the
possibility that the Cys-rich (glutathione-sensitive) lectin-like domains of
ZSP-2 may bind to sugar residues on the long fibrils and anchor
Sumper M, Nink J, Wenzl S
Self-assembly
and cross-linking of Volvox
extracellular matrix glycoproteins are specifically inhibited by Ellman's
reagent
EUR J BIOCHEM 267 (8): 2334-2339 APR 2000
Abstract:
A major impediment to the biochemical characterization of extracellular
matrices from algae (as well as higher plants) is the extensive covalent
cross-linking that exists in the matrix, rendering most components insoluble
and resistant to conventional extraction procedures. In the multicellular green
alga Volvox, biogenesis of the extracellular matrix (ECM) is initiated
immediately after the process of embryonic inversion. At this stage of
development, the sulfhydryl reagent 5,5'-dithio-bis(2-nitrobenzoic acid), known
as Ellman's reagent, interferes in a highly specific manner with ECM
biogenesis. Treated post-inversion embryos are no longer able to assemble an
intact ECM and consequently dissociate into a suspension of single cells.
Dissociated cells remain viable and continue to secrete ECM proteins into the
growth medium, as documented by the identification of several members of the
pherophorin family. Cross-linked ECM polymers such as sulfated surface
glycoprotein 185 remain in a soluble state. Thus, treatment with Ellman's
reagent opens a simple approach for the isolation and characterization of otherwise
inaccessible monomeric precursors.
Wittstock U, Fischer M, Svendsen I, et al.
Cloning and
characterization of two, cDNAs encoding sulfatases in the Roman snail, Helix
pomatia
IUBMB LIFE 49 (1): 71-76 JAN 2000
Abstract:
The sulfatase from the snail Helix pomatia is widely used for analytical
applications. We have investigated the content of sulfatases in H, pomatia,
using a biochemical and a molecular approach. A 112-kDa protein from the
intestinal juice of H. pomatia comigrated with sulfatase activity when
chromatographed on Sephacryl S300 and concanavalin A-Sepharose. The N-terminal
amino acid sequence of the protein was similar to one of three sulfatase motifs
defined by sequence alignment of known sulfatases, Degenerate primers designed
from the motifs and the N-terminal amino acid sequence obtained were used to
generate PCR fragments and to isolate both a full-length and a 3'-truncated
cDNA encoding H, pomatia sulfatases, designated SULF1 and SULF2, SULF1 consists
of 503 amino acids and shows 53-55% identity to the mammalian arylsulfatase B,
The amino acid sequence deduced from the 878-bp SULF2 cDNA fragment is 55%
identical with SULF1, Both SULF1 and SULF2 contain the cysteine residue
conserved in the active site of many sulfatases, which is known to be
posttranslationally modified into formylglycine in eukaryotic sulfatases,
However, the SULF1 and SULF2 cDNAs do not code for the protein purified. This
indicates the presence of at least three sulfatase genes in H. pomatia.
Kirk DL, Miller SM
Embryonic
polarity, asymmetric division,and cell fate determination in Volvox.
DEV BIOL 222 (1): 24 JUN 1 2000