Two G12 family G proteins, G alpha12 and G alpha13, show different subcellular localization

The G alpha subunits of the G12 family of heterotrimeric G proteins, G alpha12 and G alpha13, are closely related in sequences and some effectors, but they often act through different pathways or bind to different proteins. We have examined subcellular distribution of these two G proteins and found that endogenous G alpha12 and G alpha13 localize in membrane and cytoplasmic fractions, respectively. Exogenously expressed G alpha12 and G alpha13 also localize in membrane and cytoplasmic fractions, respectively, in COS-7 cells. Stimulation of lysophosphatidic acid receptor coupled to G alpha13 markedly promotes the translocation of G alpha13 from cytoplasm to membrane. This different localization of G alpha12 and G alpha13 may explain some of the nonoverlapping actions of G alpha12 and G alpha13.     

A new method to discriminate G1, S, G2, M, and G1 postmitotic cells

A new flow cytometric method combining light scattering measurements, detection of bromodeoxyuridine (BrdU) incorporation via fluorescent antibody, and quantitation of cellular DNA content by propidium iodide (PI) allows identification of additional compartments in the cell cycle. Thus, while cell staining with BrdU-antibodies and PI reveals the G1, S, and G2 + M phases of the cell cycle, differences in light scattering allow separation of G2 phase cells from M phase cells and subdivision of G1 phase into two compartments, i.e., G1A representing postmitotic cells which mature to G1B cells ready to initiate DNA synthesis. The method involves fixation of cells in 70% ethanol, extraction of histones with HC1, and thermal denaturation of DNA. This treatment appears to enhance the differences in chromatin structure of cells in the various phases of the cell cycle to the extent that cells could be separated on the basis of the 90 degrees scatter. Mitotic cells show much lower scatter than G2 phase cells, and G1 postmitotic cells (G1A) show lower scatter than G1 cells about to enter the S phase (G1B). Light scattering is correlated with chromatin condensation, as judged by microscopic evaluation of cells sorted on the basis of light scatter. The method has the advantage over the parental BrdU/DNA bivariate analysis in allowing the G2 and M phases of the cell cycle to be separated and the G1 phase to be analyzed in more detail. The method may also allow separation of unlabeled S phase cells from mitotic cells and distinguish between labeled and unlabeled mitotic cells.     

Big G,little G: G proteins and actin cytoskeletal reorganization

It has been known for some time that stimulation of heterotrimeric G protein-coupled receptors can cause cytoskeletal reorganization. A recent report in Developmental Cell demonstrates that the activation of a tyrosine kinase, C-terminal Src kinase, by heterotrimeric G protein subunits provides the trigger for Rho-dependent actin stress fiber formation.     

Micropropagation of four Gentiana species (G. lutea, G. cruciata, G. purpurea and G. acaulis)

The growth of axillary shoots was initiated on nodal stem segments, excised from aseptically grown seedlings of Gentiana acaulis L., G. cruciata L., G. lutea L. and G. purpurea L. In later subcultures, a basal callus tissue developed on the shoots, giving rise to de novo formed buds. Optimum benzyladenine and indoleacetic acid combinations for shoot development were established. They were slightly different in the four species. From 35-70% of shoots rooted spontaneously, except in G. lutea, in which adventitious roots were induced by applying naphthaleneacetic acid. It was conduded that the four Gentiana species were amenable to propagation in vitro. This revised version was published online in June 2006 with corrections to the Cover Date.     

Pollination in Geonoma macrostachys and Three Congeners,G. acaulis,G. gracilis,and G. interrupta

A continuous 15 month study of the floral ecology of four syntopic understorey palm species of Genoma was conducted in Amazonian Peru lowland rainforest. The spicate inflorescences of G. macrostachys, G. acaulis and G. gracilis are strictly protandrous and the plants are functionally dioecious. Data suggest that in G. macrostachys and G. acaulis pollination is based on a mimicry system, the pistillate flowers mimicking the staminate ones in colour, shape and scent. Pollen-collecting meliponine bees (Hymenoptera, Apidae, Meliponinae) and pollen-feeding syrphid flies (Diptera, Syrphidae) which visit inflorescences during both sexual stages are the pollinators of G. macrostachys. Geonoma acaulis is pollinated by small pollen-feeding weevils (Coleoptera, Curculionidae, Derelomini) that visit male and female spikes. Additionally, in G. macrostachys another pollinator type, viz. euglossine bees (Hymenoptera, Apidae, Euglossinae), which are attracted and rewarded by both types of flowers may account for long-distance pollination. The palm G. gracilis shows a very distinct pollination system. Although opportunistic insect visitors are attracted to the inflorescences of this species it seems to be mainly anemophilous because pollen becomes powdery during an thesis. The branched inflorescences of G. interrupta are also protandrous, but unlike the other species of Geonoma observed, staminate and pistillate anthesis of individual flowers are, for the most, overlapping. A broad spectrum of visitors is attracted (bees, wasps, flies, and beetles), which all may act as pollinators. Outcrossing is especially encouraged during the purely female phase at the end of the flowering cycle when there are no more staminate flowers in the inflorescence. Effects on the reproductive biology and population structure of different pollination systems and breeding system are discussed.     

The comparative leaf anatomy of Goniothamus andersonii, G. macrophyllus, G. malayanus and G. velutinus

The leaf anatomy of Goniothalamus andersonii, G. macrophyllus, G. malayanus and G. velutinus from the peat swamps of Sarawak is compared. Sufficient anatomical differences exist to differentiate the four species. G. velutinus has many points of difference from the other three species and G. macrophyllus is readily identified by the presence of fibre-sclereids in the lamina mesophyll. G. andersonii and G. malayanus are similar to each other, but G. andersonii can be distinguished, in particular by the more pronounced multiple projections of the outer periclinal walls of the epidermal cells and the presence of thick and cutinised outer ends of the anticlinal walls of the epidermal cells.     

G12/G13 family G proteins regulate marginal zone B cell maturation, migration, and polarization

G protein-coupled receptors play an important role in the regulation of lymphocyte functions such as migration, adhesion, proliferation, and differentiation. Although the role of G(i) family G proteins has been intensively studied, no in vivo data exist with respect to G12/G13 family G proteins. We show in this study that mice that lack the G protein alpha-subunits G alpha12 and G alpha13 selectively in B cells show significantly reduced numbers of splenic marginal zone B (MZB) cells, resulting in a delay of Ab production in response to thymus-independent Ags. Basal and chemokine-induced adhesion to ICAM-1 and VCAM-1, two adhesion molecules critically involved in MZB localization, is normal in mutant B cells, and the same is true for chemokine-induced migration. However, migration in response to serum and sphingosine 1-phosphate is strongly increased in mutant MZB cells, but not in mutant follicular B cells. Live-cell imaging studies revealed that G alpha12/G alpha13-deficient MZB cells assumed more frequently an ameboid form than wild-type cells, and pseudopod formation was enhanced. In addition to their regulatory role in serum- and sphingosine 1-phosphate-induced migration, G12/G13 family G proteins seem to be involved in peripheral MZB cell maturation, because also splenic MZB cell precursors are reduced in mutant mice, although less prominently than mature MZB cells. These data suggest that G12/G13 family G proteins contribute to the formation of the mature MZB cell compartment both by controlling MZB cell migration and by regulating MZB cell precursor maturation.