Non-flagellate Cells Research Articles

CURRENT KNOWLEDGE OF THE LIFE CYCLES OF PHAEOCYSTIS GLOBOSA AND PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE)(1).

Despite continuous efforts since the 1950s and more recent advances in culturing flagellates and nonflagellate cells of the prymnesiophyte Phaeocystis, a number of different life-cycle models exist today that appear to apply for P. globosa Scherff. and P. antarctica G. Karst., both spherical colony formers. In one such model, this life cycle consists of three different flagellates and one nonmotile cell stage that is embedded in carbohydrate matrix-forming colonies of different sizes and forms. Recently, noncolonial aggregates of diploid nonmotile cells attached to surfaces of diatoms were put forward as a new stage in the sexual life cycle of P. antarctica. However, it can be discussed that these "attached aggregates" (AAs) are an intermediate between motile diploid flagellates, with their well-known tendency to adhere to surfaces, and the young spherical colony with its diploid nonmotile cells, which in nature is commonly found attached to diatoms. A life-cycle model pertaining to both P. globosa and P. antarctica is presented.

Centrin deficiency in Chlamydomonas causes defects in basal body replication, segregation and maturation.

Centrin, a 20 kDa calcium-binding protein, is a constituent of contractile basal body-associated fibers in protists and of various centrosomal structures. A construct inducing centrin RNAi was used to study the effect of centrin deficiency in Chlamydomonas. Transformants contained variable amounts of residual centrin (down to 5% of wild-type) and lacked centrin fibers. They displayed a variable flagellar number phenotype with mostly nonflagellate cells, suggesting that centrin is required for basal body assembly. Furthermore, basal bodies often failed to dock to the plasma membrane and to assemble flagella, and displayed defects in the flagellar root system indicating that centrin deficiency interferes with basal body development. Multiple basal bodies caused the formation of additional microtubular asters, whereas the microtubular cytoskeleton was disordered in most cells without basal bodies. The number of multinucleated cells was increased, indicating that aberrant numbers of basal bodies interfered with the cytokinesis of Chlamydomonas. In contrast to wild-type cells, basal bodies in centrin-RNAi cells were separated from the spindle poles, suggesting a role of centrin in tethering basal bodies to the spindle. To test whether an association with the spindle poles is required for correct basal body segregation, we disrupted centrin fibers in wild-type cells by over-expressing a nonfunctional centrin-GFP. In these cells, basal bodies were disconnected from the spindle but segregation errors were not observed. We propose that basal body segregation in Chlamydomonas depends on an extranuclear array of microtubules independent of the mitotic spindle.

The vitamin B requirement of Phaeocystis globosa (Prymnesiophyceae)

In batch cultures of flagellates and non-flagellate cells of Phaeocystis globosa, the biomass yield was significantly enhanced by the addition of a mixture of the vitamins thiamine (B1), cyanocobalamin (B12) and biotin (H). A bioassay with B1 and B12 using the non-flagellate cells of P.globosa showed that this prymnesiophyte is a B1 auxotroph. The bioassay also indicated a significant difference in growth rate between culture medium with 10 nmol l(-1) B1 (mu = 0.80 day(-1)) and culture medium with 10 nmol l(-1) 1312 (mu = 0.52 day(-1)). These findings are discussed in relation to the hypothesis that centric diatoms, through vitamin B1 excretion or B12 depletion, initiate Phaeocystis blooms. It is concluded, however, that an alternative hypothesis, that diatoms provide a solid substrate for colony initiation, has more experimental support.

Growth and mortality of flagellates and non-flagellate cells of Phaeocystis globosa (Prymnesiophyceae)

Two cell types of the same clone of Phaeocystis globosa, solitary non-flagellate cells and flagellates, were grown in batch cultures under identical conditions. The non-flagellate cells had a shorter lag phase (1.4 versus 2.8 days) and a higher growth rate (0.72 versus 0.65 day -1 ) than flagel- late cells. The flagellates had a longer stationary phase (15.6 versus 9.5 days) and a lower death rate (0.07 versus 0.52 day -1 ) than non-flagellate cells. All differences were statistically significant. Biomass yield did not differ between the two cell types. The short lag phase and high growth rate of non- flagellate cells corresponds to field observations of rapidly developing non-flagellate Phaeocystis blooms that are typically observed in nutrient-rich environments such as temperate seas in spring. The flagellate cell type, with its longer stationary phase and lower death rate than non-flagellate cells, is better equipped for survival in oligotrophic environments. This explains why the flagellates of Phaeocystis are abundant after the spring phytoplankton bloom in temperate seas and in other nutrient-poor environments such as the open ocean.

Deletion analysis of the FliM flagellar switch protein of Salmonella typhimurium.

The flagellar switch of Salmonella typhimurium and Escherichia coli is composed of three proteins, FliG, FliM, and FliN. The switch complex modulates the direction of flagellar motor rotation in response to information about the environment received through the chemotaxis signal transduction pathway. In particular, chemotaxis protein CheY is believed to bind to switch protein FliM, inducing clockwise filament rotation and tumbling. To investigate the function of FliM and its interactions with FliG and FliN, we engineered a series of 34 FliM deletion mutant proteins, each lacking a different 10-amino-acid segment. We have determined the phenotype associated with each mutant protein, the ability of each mutant protein to interfere with the motility of wild-type cells, and the effect of additional FliG and FliN on the function of selected FliM mutant proteins. Overall, deletions at the N terminus produced a counterclockwise switch bias, deletions in the central region of the protein produced poorly motile or nonflagellate cells, and deletions near the C terminus produced only nonflagellate cells. On the basis of this evidence and the results of a previous study of spontaneous FliM mutants (H. Sockett, S. Yamaguchi, M. Kihara, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 174:793-806, 1992), we propose a division of the FliM protein into four functional regions: an N-terminal region primarily involved in switching, an extended N-terminal region involved in switching and assembly, a middle region involved in switching and motor rotation, and a C-terminal region primarily involved in flagellar assembly.

GLOEOCOCCUS TETIMSPORUS SP. NOV. (TETRASPORALES, PALM ELL ACEAE), FROM COLORADO MOUNTAIN LAKES1

ABSTRACTA new species, Gloeococcus tetrasporus sp. nov., collected from mountain lakes, is described from unialgal culture. Vegetative cells are ellipsoid and Chlamydomo nas–like, occur in tetrad complexes within the general colonial matrix, and exhibit slow, limited motility within the confines of the individual gelatinous matrices. The colonial matrix is amorphous and structureless, without a definite bounding layer. Colonies may reach several centimeters in size. Vegetative cells have a parietal cup–shaped chloroplast with a central–basal pyrenoid and a small, linear stigma, two contractile vacuoles, and two short flagella. Cell division is by eleutheroschisis in nonflagellate cells. After two divisions, four daughter cells arc formed within the expanded parent wall that will become incorporated into the colonial matrix. Zoospores are formed either from transformed vegetative cells or after cytokinesis. Zoospore flagella are two to three times the length of vegetative cell flagella. Rapid flagellar movement ruptures the sheath and liberates the zoospores. When zoospores settle, they secrete new sheaths, and divide twice to initiate new colonies. Sexual reproduction and formation of resistant spores were not observed.

Effect of medroxyprogesterone acetate of 3 alpha-hydroxysteroid oxidoreductase of testicular germ cells and prostate of the rat.

On incubation with testosterone (T), nonflagellate germ cells of rat testis produced dihydrotestosterone (DHT) and 5a-androstane-3cs, I 7�I-diol (3o-diol). When the concentration of T was adjusted to 0.1 �zM (its level in rete testis fluid), 4-androstene-3, 17-dione (A) and DHT accumulated during the first 30 mm; during the subsequent 90 mm, A declined and 3&-diol accumulated, DHT remaining at almost constant level. Medroxyprogesterone acetate (MPA, 5 pM) abolished 3s-diol production, but allowed DHT to accumulate at linear rates. Separation of nonflagellate germ cells by velocity gradient sedimentation yielded spermatocytes and spermatids as major fractions. On incubation with 0.1 pM T, the spermatocytes produced A and DHT; the spermatids, although metabolizing T at lower rates, produced relatively large amounts of 3cs-diol. In the presence of T in physiological concentration, MPA did not inhibit Scs-reductase or 1 713-hydroxysteroid oxidoreductase of germ cells. It abolished 3o-diol formation in the spermatids, allowing DHT to accumulate in equivalent amounts. The action of MPA as a specific inhibitor of 3o-hydroxysteroid oxidoreductase without effect on Scs-reductase was also observed in rat prostate extracts when

Progesterone and androgen receptors in non-flagellate germ cells of the rat testis.

SUMMARY In continuation of a previously reported study which showed that isolated non-flagellate germ cells of the rat testis metabolize progesterone to androgens, a search was made for the presence in these cells of specific progesterone and androgen receptors. Intact germ cells and their cytosol and nuclear fractions were incubated with 3H-labelled steroids; established analytical techniques were used to distinguish specific from non-specific binding. The steroid-protein complexes of progesterone, testosterone and dihydrotestosterone were partially purified by Sephadex column chromatography, acrylamide gel electrophoresis and sucrose density gradient analysis. The association constants of the three protein–steroid complexes were about 2 × 109 l/mol. The non-flagellate germ cells of the testis were found to have a higher binding capacity for progesterone than for testosterone and dihydrotestosterone. Epididymal spermatozoa did not bind progesterone specifically, but bound dihydrotestosterone to about the same extent as nuclei of non-flagellate cells. In extracts of seminal vesicles and prostate glands androgen binding was dominant, with negligible binding of progesterone. Synthetic progestogens (anti-androgens) competed effectively for the progesterone binding sites of the non-flagellate cells. In view of the finding that non-flagellate germ cells bind progesterone specifically and convert it to androgens, it is suggested that the metabolism of progesterone within the seminiferous epithelium of the testis may serve the purpose of maintaining an intratubular level of androgen for the support of spermatogenesis, independent of the extratubular secretion of androgen by the Leydig cells.