KOUFOPANOU V,
DEVELOPMENTAL
MUTANTS OF VOLVOX - DOES
MUTATION RECREATE THE PATTERNS OF PHYLOGENETIC DIVERSITY
EVOLUTION 45 (8): 1806-1822 DEC 1991
Abstract:
The nature of the variation which is created by mutation can show how the
direction of evolution is constrained by internal biases arising from
development and pre-existing design. We have attempted to quantify these biases
by measuring eight life history characters in developmental mutants of Volvox
carteri. Most of the mutants in our sample were inferior to the wild type, but
deviated by less than tenfold from the wild-type mean. Characters differed in
mutability, suggesting different levels of canalisation. Most correlations
between life history characters among strains were positive, but there was a
significant negative correlation between the size and the number of
reproductive cells, suggesting an upper limit to the total quantity of germ
produced by individuals. The most extreme phenotypes in our sample were very
vigorous, showing that not all mutations of large effect are unconditionally
deleterious. We investigated the effect of developmental constraints on the
course of evolution by comparing the variance and covariance patterns among
mutant strains with those among species in the family Volvocaceae. A close
correspondence between patterns at these two levels would suggest that
pre-existing design has a strong influence on evolution, while little or no
correspondence shows the action of selection. The variance generated by
mutation was equal to that generated by speciation in the family Volvocaceae,
the genus Volvox, or the section Merillosphaera, depending on the
character considered. We found that mutation changes the volume of somatic
tissue independently of the quantity of germ tissue, so that the interspecific
correlation between soma and germ can be attributed to selection. The negative
correlation between size and number of germ cells among mutants of V. carteri
is also seen among the larger members of the family (Volvox spp.), but
not among the smaller members, suggesting a powerful design constraint that may
be responsible for the absence of larger forms in the entire group.
HAAS E, SUMPER M
THE SEXUAL
INDUCER OF VOLVOX-CARTERI - ITS LARGE-SCALE
PRODUCTION AND SECRETION BY SACCHAROMYCES-CEREVISIAE
FEBS LETT 294 (3): 282-284 DEC 9 1991
Abstract:
The DNA sequence coding for the sexual inducer glycoprotein of Volvox
carteri and its N-terminal signal peptide was placed under the control of the
repressible acid phosphatase promoter of the yeast Saccharomyces cerevisiae in
a yeast-E. coli shuttle vector. Yeast transformed by this construct synthesized
and secreted into the culture medium biologically active inducer in amounts two
to three orders of magnitude higher than observed in the Volvox system.
JAENICKE L, VANLEYEN K, SIEGMUND HU
DOLICHYL
PHOSPHATE-DEPENDENT GLYCOSYLTRANSFERASES UTILIZE TRUNCATED COFACTORS
BIOL CHEM H-S 372 (11): 1021-1026 NOV 1991
Abstract:
Synthetic truncated dolichyl phosphates of chain lengths from four to thirteen
isoprene units (Jaenicke L. and Siegmund H.-U., Chem. Phys. Lipids 51 (1989)
159-170) were assayed for their cofactor activity in the enzymatic transfer of
hexoses and hexosamines. The enzymes were microsomal preparations from the
green alga Volvox carteri, baker's yeast, and mammalian liver cells.
Under saturating conditions, the acceptor activities of the truncated dolichyl
phosphates increased from zero to full strength as compared to the mixture of
long-chain dolichyl phosphates from natural sources with growing chain length
from five to nine isoprene units. K(m) determinations confirmed the results. Of
the geometric isomers of dolichyl 7-phosphate (35 carbon atoms), the 14-trans
compound has unchanged acceptor activity; all-trans dolichyl 7-phosphate,
however, was almost inactive. The data suggest that hydrophobicity may be an
important, but not the only criterion for the binding of the isoprene moiety to
the active sites of the transferase enzyme(s) and that the geometry of more
than only one double bond in the dolichols is recognized.
KIRK DL, KAUFMAN MR, KEELING RM, et al.
GENETIC AND
CYTOLOGICAL CONTROL OF THE ASYMMETRIC DIVISIONS THAT PATTERN THE VOLVOX EMBRYO
DEVELOPMENT : 67-82 Suppl. 1 1991
Abstract:
The highly regular pattern in which approximately 2000 small somatic cells and
16 large reproductive cells (or 'gonidia') are arranged in a typical asexual
adult of Volvox carteri can be traced back to a stereotyped program of
embryonic cleavage divisions. After five symmetrical divisions have produced 32
cells of equal size, the anterior 16 cells cleave asymmetrically, to produce
one small somatic cell initial and one larger gonidial initial each. The
gonidial initials then cease dividing before the somatic cell initials do. The
significance of the visibly asymmetric divisions is underscored by genetic and
experimental evidence that differences in size - rather than differences in
cytoplasmic quality - are causally important in activating the programs that
cause small cells to become mortal somatic cells and large cells to
differentiate as reproductive cells. A number of loci, including at least five
mul ('multiple gonidia') loci, appear to be responsible for determining where
and when asymmetric divisions will occur, since mutations at these loci result
in modified temporal and/or spatial patterns of asymmetric division in one or
more portions of the life cycle. But the capacity to divide asymmetrically at
all appears to require a function encoded by the gls (gonidialess) locus, since
gls mutants fail to execute any asymmetric divisions. Second-site suppressors
of gls that have been identified may encode other functions required for
asymmetric division. Cytological and immunocytochemical studies of dividing
embryos are being undertaken in an attempt to elucidate the mechanisms by which
cell-division planes are established - and shifted - under the influence of
such pattern-specifying genes. Studies to date clearly indicate a central role
for the basal body apparatus, and particularly its microtubular rootlets, in
establishing the orientation of both the mitotic spindle and the cleavage
furrow; but it remains to be determined how behavior of the division apparatus
becomes modified during asymmetric division.
WAYNE R, KADOTA A, WATANABE M, et al.
PHOTOMOVEMENT
IN DUNALIELLA-SALINA - FLUENCE RATE-RESPONSE CURVES AND ACTION SPECTRA
PLANTA 184 (4): 515-524 1991
Abstract:
We determined the action spectra of the photophobic responses as well as the
phototactic response in Dunaliella salina (Volvocales) using both single cells
and populations. The action spectra of the photophobic responses have maximum
at 510 nm, the spectrum for phototaxis has a maximum at 450-460 nm. These
action spectra are not compatible with the hypothesis that flavoproteins are
the photoreceptor pigments, and we suggest that carotenoproteins or rhodopsins
act as the photoreceptor pigments. We also conclude that the phototactic
response in Dunaliella is an elementary response, quite independent of the
step-up and step-down photophobic responses. We also determined the action
spectra of the photoaccumulation response in populations of cells adapted to
two different salt conditions. Both action spectra have a peak a 490 nm. The
photoaccumulation response may be a complex response composed of the
phototactic and photophobic responses. Blue or blue-green light does not elicit
a photokinetic response in Dunaliella.
TAM LW, KIRK DL
THE PROGRAM
FOR CELLULAR-DIFFERENTIATION IN VOLVOX-CARTERI
AS REVEALED BY MOLECULAR ANALYSIS OF DEVELOPMENT IN A GONIDIALESS SOMATIC
REGENERATOR MUTANT
DEVELOPMENT 112 (2): 571-580 JUN 1991
Abstract:
Development of a 'gonidialess'/'somatic regenerator' double mutant of Volvox
carteri was analyzed with a number of cell-type-specific cDNA probes that had
been identified in a previous study. Whereas in wild-type strains somatic cells
and gonidia (asexual reproductive cells) constitute two distinct cell lineages,
in this mutant all cells first differentiate as somatic cells and then
redifferentiate as gonidia. During the initial period of somatic
differentiation, we found that both gonidial and 'early' somatic transcripts
were accumulated in the mutant, consistent with the idea that it is the regA
gene product (which is defective in this mutant) that normally acts to suppress
gonidial gene expression in somatic cells. Later in development, levels of
early somatic transcripts fell abruptly, levels of the late somatic transcripts
remained extremely low, and levels of gonidial transcripts rose as the cells
redifferentiated. Thus it appears that in the mutant cells the gonidial program
of development takes over and somatic differentiation is aborted before the
stage at which late somatic genes are normally activated. These results provide
molecular genetic support for a model which postulates that three types of
genes (including the two that are defective in the strain studied here) are
crucial for converting the sequential program of differentiation seen in more
primitive volvocalean algae to the dichotomous program of germ-soma
differentiation that occurs in wild-type V. carteri.
ROSATI G, VERNI F
SEXUAL
RECOGNITION IN PROTOZOA - CHEMICAL SIGNALS AND TRANSDUCTION MECHANISMS
ZOOL SCI 8 (3): 415-429 JUN 1991
TAM LW, STAMER KA, KIRK DL
EARLY AND
LATE GENE-EXPRESSION PROGRAMS IN DEVELOPING SOMATIC-CELLS OF VOLVOX-CARTERI
DEV BIOL 145 (1): 67-76 MAY 1991
RANSICK A
REPRODUCTIVE
CELL SPECIFICATION DURING VOLVOX-OBVERSUS
DEVELOPMENT
DEV BIOL 143 (1): 185-198 JAN 1991