Schmitt R
Differention of germinal and somatic cells in Volvox carteri
CURRENT OPINION IN MICROBIOLOGY
6 (6): 608-613 DEC 2003
Abstract:
Volvox carteri is a
spherical alga with a complete division of labor between around 2000 biflagellate
somatic cells and 16 asexual reproductive cells (gonidia).
It provides an attractive system for studying how a molecular genetic program
for cell-autonomous differentiation is encoded within the genome. Three types
of genes have been identified as key players in germ-soma differentiation: a
set of gls genes that act in the embryo to shift
cell-division planes, resulting in asymmetric divisions that set apart the
large-small sister-cell pairs; a set of lag genes that act in the large gonidial initials to prevent somatic differentiation; and
the regA gene, which acts in the small somatic
initials to prevent reproductive development. Somatic-cell-specific expression
of regA is controlled by intronic
enhancer and silencer elements.
Nozaki H
Origin and
evolution of the genera Pleodorina and Volvox (Volvocales)
BIOLOGIA 58 (4): 425-431 JUL 2003
Abstract:
The previous molecular phylogenetic study using 6021
base pairs from five chloroplast genes suggested that two species of Pleodorina (P. californica, P.
japonica) might have evolved from a Volvox-like alga
by the decrease in colony cell number and size. However, number of species of
the genus Volvox was very limited especially in the
section Merrillosphaera. In
the present study, 6021 base pairs of the concatenated five chloroplast genes
from 10 strains representing seven taxa of the genus Volvox were added to the previous data matrix. The sequence
data resolved two anisogamous/oogamous clades within a large monophyletic group comprising five
advanced genera of the Volvocaceae (Yamagishiella, Platydorina, Eudorina, Pleodorina and Volvox), one containing Volvox
sect. Volvox and the anisogamous
genus Platydorina (32-celled flattened colony), and
the other (Eudorina group) composed of three other
sections of Volvox, Pleodorina
and Eudorina. The isogamous
genus Yamagishiella (32-celled colony) was positioned
basally to the Eudorina group. Therefore, evolution of
anisogamy with sperm packets from isogamy
might have occurred twice within the Volvocaceae.
Based on the present molecular phylogenetic analysis,
species of Volvox and Pleodorina
within the Eudorina group represented three and two,
respectively, separate lineages. One the three Volvox lineages [composed of V (sect. Merrillosphaera)
carteri, V (sect. Merrillosphaera) obversus, V. (sect. Merrillosphaera) tertius, V. (sect. Merrillosphaera) africanus and V (sect. Copelandosphaera)
dissipatrix] was sister to the monophyletic group
consisting of one of the two Pleodorina lineages (P. californica and P. japonica) and V (sect. Janetosphaera) aureus. In addition, species of Eudorina
were basal to the two lineages of Pleodorina and
three Volvox lineages within the Eudorina
group, representing the ancestral situation of Pleodorina/Volvox
(excluding sect. Volvox). Thus, reverse evolution from a Volvox-like
alga to Pleodorina suggested previously appears
unlikely.
Cheng Q, Fowler R, Tam LW, et al.
The role of GlsA in the evolution of asymmetric cell division in the
green alga Volvox
caiteri
DEV GENES EVOL 213 (7): 328-335 JUL 2003
Abstract:
Volvox carteri, a green
alga in the order Volvocales, contains two completely
differentiated cell types, small motile somatic cells and large reproductive
cells called gonidia, that are set apart from each
other during embryogenesis by a series of visibly asymmetric cell divisions.
Mutational analysis has revealed a class of genes (gonidialess,
gls) that are required specifically for asymmetric
divisions in V. carteri, but that are dispensable for
symmetric divisions. Previously we cloned one of these genes, glsA, and showed that it encodes a chaperone-like protein
(G1sA) that has close orthologs in a diverse set of
eukaryotes, ranging from fungi to vertebrates and higher plants. In the present
study we set out to explore the role of glsA in the
evolution of asymmetric division in the volvocine
algae by cloning and characterizing a glsA ortholog from one of the simplest members of the group, Chlamydomonas reinhardtii, which
does not undergo asymmetric divisions. This ortholog
(which we have named gar1, for glsA related) is
predicted to encode a protein that is 70% identical to G1sA overall, and that
is most closely related to G1sA in the same domains that are most highly
conserved between G1sA and its other known orthologs.
We report that a gar1 transgene fully complements the
glsA mutation in V. carteri,
a result that suggests that asymmetric division probably arose through the
modification of a gene whose product interacts with G1sA, but not through a
modification of glsA itself.
Grewing A, Krings M, Galtier
J, et al.
The oldest fossil endophytic alga and its unusual habitat
SYMBIOSIS 34 (3): 215-230 2003
Abstract:
Lycophyte megaspores from the Lower Carboniferous of France
sometimes contain a colonial (volvocacean) alga as an
endophyte. This peculiar plant-plant association was
briefly described more than 100 years ago and the name Lageniastrum
macrosporae introduced for the alga, but the
biological significance of the discovery was never fully appreciated. Here we
present a reappraisal of the original material, which to date provides the
oldest unequivocal fossil evidence for endophytic
algae and the only example of an alga residing in the interior of spores of
vascular cryptogams.
Nedelcu AM, Michod RE
Sex as a response
to oxidative stress: the effect of antioxidants on sexual induction in a facultatively sexual lineage
P ROY SOC LOND B BIO 270: S136-S139 Suppl. 2
Abstract:
The evolution of sex is one of the long-standing unsolved problems in biology.
Although in many lineages sex is an obligatory part of the life cycle and is
associated with reproduction, in prokaryotes and many lower eukaryotes, sex is
facultative, occurs in response to stress and often involves the formation of a
stress-resistant dormant form. The proximate and ultimate causes of the
connection between stress and sex in facultatively
sexual lineages are unclear. Because most forms of stress result in the
overproduction of cellular reactive oxygen species (ROS), we address the
hypothesis that this connection involves ROS and possibly reflects the
ancestral role of sex as an adaptive response to the damaging effects of
stress-induced ROS (i.e. oxidative stress) . Here, we report that two
antioxidants inhibit sexual induction in a facultatively
sexual species-the multicellular green alga, Volvox carteri.
Furthermore, the nature of the sex response and the effect of an iron chelator on sexual induction are consistent with sex being
a response to the DNA-damaging effects of ROS. In addition, we present
preliminary data to suggest that sex, cell-cycle arrest and apoptosis are
alternative responses to increased levels of oxidative stress.
Rudel D, Sommer RJ
The evolution of
developmental mechanisms
DEV BIOL 264 (1): 15-37 DEC 1 2003
Abstract:
Over the past two to three decades, developmental biology has demonstrated that
all multicellular organisms in the animal kingdom
share many of the same molecular building blocks and many of the same
regulatory genetic pathways. Yet we still do not understand how the various
organisms use these molecules and pathways to assume all the forms we know
today. Evolutionary developmental biology tackles this problem by comparing the
development of one organism to another and comparing the genes involved and
gene functions to understand what makes one organism different from another. In
this review, we revisit a set of seven concepts defined by Lewis Wolpert (fate maps, asymmetric division. induction,
competence, positional information, determination, and lateral inhibition) that
describe the characters of many developmental systems and supplement them with
three additional concepts (developmental genomics, genetic redundancy, and
genetic networks). We will discuss examples of comparative developmental
studies where these concepts have guided observations on the advent of a
developmental novelty. Finally, we identify a set of evolutionary frameworks,
such as developmental constraints, cooption, duplication, parallel and
convergent evolution, and homoplasy, to adequately
describe the evolutionary properties of developmental systems. (C) 2003
Elsevier Inc. All rights reserved.
Kato-Minoura T,
Okumura M, Hirono M, et al.
A novel family of
unconventional actins in volvocalean algae
J MOL EVOL 57 (5): 555-561 NOV 2003
Abstract:
The unicellular green alga Chlamydomonas reinhardtii has two actin genes,
one encoding a conventional actin (90% amino acid
identity with mammalian actin), the other a highly
divergent actin (64% identity) named novel actin-like protein (NAP). To see whether the presence of
conventional and unconventional actins in a single organism is unique to C. reinhardtii, we searched for genomic sequences related to
the NAP sequence in several other species of volvocalean
algae. Here we show that Chlamydomonas moewusii and Volvox carteri also have, in addition to a conventional actin, an unconventional actin
similar to the C. reinhardtii NAP. Analyses of the
deduced protein sequences indicated that the NAP homologues form a distinct
group derived from conventional actin.
Golstein P, Aubry L, Levraud
JP
Cell-death
alternative model organisms: Why and which?
NAT REV MOL CELL BIO 4 (10): 798-807 OCT 2003
Abstract:
Classical model organisms have helped greatly in our understanding of cell
death but, at the same time, night have constrained it. The use of other,
nor-classical model organisms from all biological kingdoms could reveal
undetected molecular pathways and better-defined morphological types of cell
death. Here we discuss what is known and what might be learned from these
alternative model systems.
Ohta H, Suzuki T, Ueno M, et al.
Extrinsic proteins
of photosystem II - An intermediate member of the PsbQ protein family in red algal PSII
EUR J BIOCHEM 270 (20): 4156-4163 OCT 2003
Abstract:
The oxygen-evolving photosystem II (PS II) complex of
red algae contains four extrinsic proteins of 12 kDa,
20 kDa, 33 kDa and cyt c-550, among which the 20 kDa
protein is unique in that it is not found in other organisms. We cloned the gene
for the 20-kDa protein from a red alga Cyanidium
caldarium. The gene consists of a leader sequence which can be divided into two
parts: one for transfer across the plastid envelope and the other for transfer
into thylakoid lumen, indicating that the gene is
encoded by the nuclear genome. The sequence of the mature 20-kDa protein has
low but significant homology with the extrinsic 17-kDa (PsbQ)
protein of PS II from green algae Volvox Carteri and Chlamydomonas reinhardtii, as well as the PsbQ
protein of higher plants and PsbQ-like protein from cyanobacteria. Cross-reconstitution experiments with
combinations of the extrinsic proteins and PS Its from
the red alga Cy. caldarium and green alga
Cole DG, Reedy MV
Algal
morphogenesis: How Volvox
turns itself inside-out
CURR BIOL 13 (19): R770-R772
Abstract:
During its development, the multicellular green alga Volvox undergoes inversion, in which spherical
embryos turn their multicellular sheet completely
inside out. A mutant analysis has revealed that a novel kinesin
motor protein is essential for completing this process.
Voigt J, Frank R
14-3-3 proteins
are constituents of the insoluble glycoprotein framework of the Chlamydomonas cell wall
PLANT CELL 15 (6): 1399-1413 JUN 2003
Abstract:
The cell wall of the unicellular green alga Chlamydomonas
reinhardtii consists predominantly of Hyp-rich glycoproteins, which
also occur in the extracellular matrix of multicellular green algae and higher plants. In addition to
the Hyp-rich polypeptides, the insoluble glycoprotein
framework of the Chlamydomonas cell wall contains
minor amounts of
Michod RE, Nedelcu AM
On the
reorganization of fitness during evolutionary transitions in individuality
INTEGR COMP BIOL 43 (1): 64-73 FEB 2003 (for
pdf click here)
Abstract:
The basic problem in an evolutionary transition is to understand how a group of
individuals becomes a new kind of individual, possessing the property of heritable
variation in fitness at the new level of organization. During an evolutionary
transition, for example, from single cells to multicellular
organisms, the new higher-level evolutionary unit (multicellular
organism) gains its emergent properties by virtue of the interactions among
lower-level units (cells). We see the formation of cooperative interactions
among lower-level units as a necessary step in evolutionary transitions; only
cooperation transfers fitness from lower levels (costs to group members) to
higher levels (benefits to the group). As cooperation creates new levels of
fitness, it creates the opportunity for conflict between levels as deleterious
mutants arise and spread within the group. Fundamental to the emergence of a
new higher-level unit is the mediation of conflict among lower-level units in
favor of the higher-level unit. The acquisition of heritable variation in
fitness at the new level, via conflict mediation, requires the reorganization
of the basic components of fitness (survival and reproduction) and
life-properties (such as immortality and totipotency)
as well as the co-option of lower-level processes for new functions at the
higher level. The way in which the conflicts associated with the transition in
individuality have been mediated, and fitness and general life-traits have been
re-organized, can influence the potential for further evolution (i.e., evolvability) of the newly emerged evolutionary individual.
We use the volvocalean green algal group as a
model-system to understand evolutionary transitions in individuality and to
apply and test the theoretical principles presented above. Lastly, we discuss
how the different notions of individuality stem from the basic properties of
fitness in a multilevel selection context.
Kirk DL
Seeking the
ultimate and proximate causes of Volvox multicellularity and
cellular differentiation
INTEGR COMP BIOL 43 (2): 247-253 APR 2003
Abstract:
Volvox
and its relatives provide an exceptional model for integrative studies of the
evolution of multicellularity and cellular
differentiation. The volvocine algae range in
complexity from unicellular Chlamydomonas through
several colonial genera with a single cell type, to multicellular
Volvox with its germsoma
division of labor. Within the monophyletic family Volvocaceae,
several species of Volvox have evolved
independently in different lineages, the ultimate cause presumably being the
advantage that large size and cellular differentiation provide in competing for
limiting resources such as phosphorous. The proximate causes of this type of
evolutionary transition are being studied in V carteri.
All volvocine algae except Volvox
exhibit biphasic development: cells grow during a motile, biflagellate phase, then they lose motility and divide repeatedly during the
reproductive phase. In V carteri three kinds of genes
transform this ancestral biphasic program into a dichotomous one that generates
non-motile reproductive cells and biflagellate somatic cells with no
reproductive potential: first the gls genes act in
early embryos to cause asymmetric division and production of large-small
sister-cell pairs; then lag genes act in the large cells to repress the biflagellate
half of the ancestral program, while regA acts in the
small cells to repress the reproductive half of the program. Molecular-genetic
analysis of these genes is progressing, as will be illustrated with regA, which encodes a transcription factor that acts in
somatic cells to repress nuclear genes encoding chloroplast proteins.
Repression of chloroplast biogenesis prevents these obligately
photoautotrophic cells from growing, and since they cannot grow, they cannot
reproduce.
Mori T, Kuroiwa
H, Higashiyama T, et al.
Identification of
higher plant GlsA, a putative morphogenesis factor of
gametic cells
BIOCHEM BIOPH RES CO 306 (2): 564-569
Abstract:
GlsA has been identified in an
asexual-reproductive-cell (gonidia)-deficient mutant
of Volvox as a chaperone-like protein
essential for gonidia production. In this study, we
isolated an angiosperm glsA (LlglsA)
gene expressed during Lilium longiflorum
pollen development. Immunoblot analyses showed that
the strong LlGlsA expression occurred in the
generative cell and its pattern during pollen development corresponded to that
of alpha-tubulin. Morphological analyses succeeded in
visualizing the dispersion of the strong LlGlsA
signal in developing generative cells. In addition, multiple-immunofluorescence staining of LIGNA and alpha-tubulin revealed that some of the dot-like LlGlsA signals were co-localized with microtubule
filaments. From those results, we suggest that angiosperm GlsA
functions as a chaperone modifying various structures during male gametic cell formation. (C) 2003 Elsevier Science (
Nishii
I, Ogihara S, Kirk DL
A kinesin, InvA, plays an essential
role in Volvox
morphogenesis
CELL 113 (6): 743-753
Abstract:
In Volvox carted adults, reproductive cells
called gonidia are enclosed within a spherical monolayer
of biflagellate somatic cells. Embryos must "invert" (turn inside
out) to achieve this configuration, however, because at the end of cleavage the
gonidia are on the outside and the flagellar ends of all somatic cells point inward.
Generation of a bend region adequate to turn the embryo inside out involves a
dramatic change in cell shape, plus cell movements. Here, we cloned a gene
called invA that is essential for inversion and found
that it codes for a kinesin localized in the cytoplasmic bridges that link all cells to their neighbors.
In invA null mutants, cells change shape normally,
but are unable to move relative to the cytoplasmic
bridges. A normal bend region cannot be formed and inversion stops. We conclude
that the InvA kinesin
provides the motile force that normally drives inversion to completion.
Bonner JT
On the origin of
differentiation
J BIOSCIENCES 28 (4): 523-528 JUN 2003
Abstract:
Following the origin of multicellularity in many
groups of primitive organisms there evolved more than one cell type. It has
been assumed that this early differentiation is related to size - the larger
the organism the more cell types. Here two very different kinds of organisms
are considered: the volvocine algae that become multicellular by growth, and the
cellular slime moulds that become multicellular by
aggregation. In both cases there are species that have only one cell type and
others that have two. It has been possible to show that there is a perfect
correlation with size: the forms with two cell types are significantly
larger-than those with one. Also in both groups there are forms of intermediate
size that will vary from one to two cell types depending on the size of the
individuals, suggesting a form of quorum sensing. These observations reinforce
the view that size plays a critical role in influencing the degree of
differentiation.
Michod RE, Nedelcu AM, Roze D
Cooperation
and conflict in the evolution of individuality IV. Conflict
mediation and evolvability in Volvox carteri
BIOSYSTEMS 69 (2-3): 95-114 MAY 2003 (for pdf click here)
Abstract:
The continued well being of evolutionary individuals (units of selection and
evolution) depends upon their evolvability, that is
their capacity to generate and evolve adaptations at their level of
organization, as well as their longer term capacity for diversifying into more
complex evolutionary forms. During a transition from a lower- to higher-level
individual, such as the transition between unicellular and multicellular
organisms, the evolvability of the lower-level
(cells) must be restricted, while the evolvability of
the new higher-level unit (multicellular organism)
must be enhanced. For these reasons, understanding the factors leading to an
evolutionary transition should help us to understand the factors underlying the
emergence of evolvability of a new evolutionary unit.
Cooperation among lower-level units is fundamental to the origin of new
functions in the higher-level unit. Cooperation can produce a new more complex
evolutionary unit, with the requisite properties of heritable fitness variations,
because cooperation trades fitness from a lower-level (the costs of
cooperation) to the higher-level (the benefits for the group). For this reason,
the evolution of cooperative interactions helps us to understand the origin of
new and higher-levels of fitness and organization. As cooperation creates a new
level of fitness, it also creates the opportunity for conflict between levels
of selection, as deleterious mutants with differing effects at the two levels
arise and spread. This conflict can interfere with the evolvability
of the higher-level unit, since the lower and higher-levels of selection will
often "disagree" on what adaptations are most beneficial to their
respective interests. Mediation of this conflict is essential to the emergence
of the new evolutionary unit and to its continued evolvability.
As an example, we consider the transition from unicellular to multicellular organisms and study the evolution of an
early-sequestered germ-line in terms of its role in mediating conflict between
the two levels of selection, the cell and the cell group. We apply our
theoretical framework to the evolution of germ/soma differentiation in the
green algal group Volvocales. In the most complex
member of the group, Volvox carteri, the potential conflicts among lower-level cells as
to the "right" to reproduce the higher-level individual (i.e. the
colony) have been mediated by restricting immortality and totipotency
to the germ-line. However, this mediation, and the evolution of an early
segregated germ-line, was achieved by suppressing mitotic and differentiation
capabilities in all post-embryonic cells. By handicapping the soma in this way,
individuality is ensured, but the solution has affected the long-term evolvability of this lineage. We think that although
conflict mediation is pivotal to the emergence of individuality at the
higher-level, the way in which the mediation is achieved can greatly affect the
longer-term evolvability of the lineage. (C) 2002
Elsevier Science Ireland Ltd. All rights reserved.
Laflamme M, Lee RW
Mitochondrial
genome conformation among CW-group chlorophycean
algae
J PHYCOL 39 (1): 213-220 FEB 2003
Abstract:
Most green algal taxa have circular-mapping
mitochondrial genomes, whereas some have linear genome- or subgenomic-sized
mitochondrial DNAs (mtDNA).
It is not clear, however, if the circular-mapping genomes represent
genome-sized circular molecules, if such circular molecules and the linear
forms are the predominant in vivo mtDNA structures,
or if the linear forms arose only once or multiple times among extant green
algal lineages. We therefore examined the DNA components detected with
homologous mtDNA probes after pulsed-field gel
electrophoresis of total cellular DNA from the chlorophycean
basal bodies displaced clockwise(CW)-group taxa Chlamydomonas reinhardtii and Chlamydomonas moewusii. For C. reinhardtii ,
the 15.8-kb linear mtDNA was the only DNA component
detected, and there was no evidence of circular or large linear precursors of
this DNA. In the case of C. moewusii , which is known
to have a circular-mapping 22.9-kb mitochondrial genome, three DNA components
were detected; these appeared to be circular (relaxed and supercoiled)
and genome-sized linear DNA molecules, the latter of which likely resulted from
random double-strand breaks in the circular forms during DNA isolation. In
further studies, DNA from additional CW-group taxa
was examined using conventional gel electrophoresis and DNA-filter blot
analysis with C. reinhardtii and C. moewusii mtDNA probes. We
conclude that all taxa from the "Volvox clade" (sensu Nakayama et al. 1996) of the CW-group have genome- or
subgenomic-sized linear mtDNAs
as their predominant mtDNA form and that these arose
from a genome-sized circular form in an ancestor that existed near the base of
this clade.
Hallmann A
Extracellular matrix and sex-inducing pheromone in Volvox
INT REV CYTOL 227: 131-+ 2003
Schmitt R, Sumper M
Developmental
biology - How to turn inside out
NATURE 424 (6948): 499-500
Peculiarities
of the geographical distribution of coenobial volvocine algae (Volvocaceae, Chlorophyta).
Botanical
Journal (
Abstract:
Data on the
geographical distribution of 36 species from 7 genera of the family Volvocaceae sensu Nozaki (Pandorina, Volvulina, Yamagishiella, Eudorina, Platydorina, Pleodorina and Volvox) have been summarized. Both cosmopolitan species and
species with local distribution have been detected. An attempt was made to
trace a correlation of latitudinal distribution of the coenobial
volvocine algae with obligatory differentiated
somatic cells (22 species of the genera Volvox and Pleodorina) with peculiarities of proceeding of the cell
divisions during asexual developmental cycle. In high latitudes of the Northern
Hemisphere (northward of 50-57° north) only 3 species of Volvox
occur, in which the formation of new coenobia (a
series of consecutive gonidial divisions) starts with
the light period (in the morning), the rate of division is slow and the gonidial divisions are temporarily blocked in darkness.