Targeted gene expression as a means of altering cell fates and generating dominant phenotypes

We have designed a system for targeted gene expression that allows the selective activation of any cloned gene in a wide variety of tissue- and cell-specific patterns. The gene encoding the yeast transcriptional activator GAL4 is inserted randomly into the Drosophila genome to drive GAL4 expression from one of a diverse array of genomic enhancers. It is then possible to introduce a gene containing GAL4 binding sites within its promoter, to activate it in those cells where GAL4 is expressed, and to observe the effect of this directed misexpression on development. We have used GAL4-directed transcription to expand the domain of embryonic expression of the homeobox protein even-skipped. We show that even-skipped represses wingless and transforms cells that would normally secrete naked cuticle into denticle secreting cells. The GAL4 system can thus be used to study regulatory interactions during embryonic development. In adults, targeted expression can be used to generate dominant phenotypes for use in genetic screens. We have directed expression of an activated form of the Dras2 protein, resulting in dominant eye and wing defects that can be used in screens to identify other members of the Dras2 signal transduction pathway.

Multinuclear NMR studies on the energy metabolism of glial and neuronal cells

In this multinuclear NMR study myo-inositol is identified as a glia-specific marker for in vivo NMR studies. The unusually high inositol concentration may participate in the osmoregulatory system in astrocytes. Primary astrocytes also synthesize and export high amounts of hypotaurine, an intermediate of taurine synthesis. Taurine--another osmolyte--is synthesized from cysteine by astrocytes but not by primary neurons. Taurine as well as hypotaurine is accumulated by neurons from the extracellular medium. 13C NMR labelling results with 2-13C pyruvate indicate a considerable contribution of the anaplerotic pathway in primary neurons from rat. The activity is only half of the activity in primary astrocytes. The ratio of pyruvate carboxylase/malic enzyme activity versus pyruvate dehydrogenase activity reflects the degree of maturation. The 13C isotopomer ratio of glutamate and glutamine is different for pure astrocyte cultures. Therefore, the different isotopomer ratios of glutamate to glutamine obtained from intact brain studies alone do not prove TCA cycle compartimentation in the brain. Finally, the PCr/ATP ratio in primary astrocytes is 3 times higher than in primary neurons. This has to be considered in case of recovery from ischemic insults.

Characterization of a "silencer" in yeast: a DNA sequence with properties opposite to those of a transcriptional enhancer

The mating type of yeast is determined by the allele, either a or alpha, at the MAT locus. Two other loci, HML and HMR, contain complete copies of the alpha and a genes, respectively, which are not expressed. The four SIR gene products are required in trans for repression of the silent loci, as are cis-acting sites on either side of HML and HMR, about 1000 bp from the mating-type promoters. We demonstrate that one of these cis-acting sequences, HMRE, is able to switch off at least two nonmating-type promoters. In common with enhancers, it is able to function in either orientation, relatively independently of its position with respect to the regulated promoter, and can act on promoters 2600 bp away. However since HMRE represses, rather than enhances, transcription we have called it a "silencer" sequence.

Beneficial effects of leukocyte depletion of transfused blood on postoperative complications in patients undergoing cardiac surgery: a randomized clinical trial

BACKGROUND

Leukocytes in transfused blood are associated with several posttransfusion immunomodulatory effects. Although leukocytes play an important role in reperfusion injury, the contribution of leukocytes in transfused blood products has not been investigated. To estimate the role and the timing of leukocyte filtration of red cells in cardiac surgery, we performed a randomized study.

METHODS AND RESULTS

Patients scheduled for cardiac surgery were randomly allocated to receive either packed cells without buffy coat (PC, n = 306), fresh-filtered units (FF, n = 305), or stored-filtered units (SF, n = 303) when transfusion was indicated. We evaluated the periods of hospitalization and stay at the intensive care unit, and the occurrences of postoperative complications up to 60 days after surgery. The average hospital stay was 10.7 days, of which 3.2 days were in the intensive care unit, without significant differences between the groups. In the PC trial arm, 23.0% of the patients had infections versus 16.9% and 17.9% of the patients in the leukocyte-depleted trial arms (P=.13). Within 60 days, 45 patients had died, 24 patients in the PC trial arm (7.8%), versus 11 (3.6%) and 10 (3.3%) patients in the FF and SF trial arms, respectively (P=.015).

CONCLUSIONS

In cardiac surgery patients, especially when more than three blood transfusions are required, leukocyte depletion by filtration results in a significant reduction of the postoperative mortality that can only partially be explained by the higher incidence of postoperative infections in the PC group.

Morbidity and mortality in adults with idiopathic thrombocytopenic purpura

To study outcomes of adults with idiopathic thrombocytopenic purpura (ITP), we performed a follow-up study in a cohort of 152 consecutive patients who were treated according to a well-defined algorithm. Long-term outcomes were determined relative to the response 2 years after diagnosis, because most (93%) patients who ultimately attained platelet counts above 30.0 x 10(9)/L (30 000/microL) did so within this time frame. Complete follow-up for mortality could be studied in 99% of patients and for morbidity in 95% of patients, with a mean of 10.5 years. Within 2 years after diagnosis, 4 patients died, 2 were lost to follow-up, and 12 were reclassified as having secondary immune thrombocytopenia. Of the remaining 134 patients, 114 (85%) had obtained platelet counts above 30.0 x 10(9)/L while all therapies had been discontinued. These patients had a long-term mortality risk equal to the general population. Twelve of 134 patients (9%), all with severe thrombocytopenia, had refractory disease and suffered a mortality risk of 4.2 (95% confidence interval, 1.7-10.0). Bleeding and infection equally contributed to the death of these patients. Another 8 patients (6%) had platelet counts above 30.0 x 10(9)/L while on maintenance therapy. Similar to patients with refractory disease, these latter patients had considerably increased ITP-related hospital admissions, but mortality was only slightly higher than in the general population. In conclusion, most adults with ITP have a good outcome with infrequent hospital admissions and no excess mortality. The absence of gross morbidity and mortality in patients with moderate thrombocytopenia supports clinical practice refraining from further treatment.

folded gastrulation, cell shape change and the control of myosin localization

The global cell movements that shape an embryo are driven by intricate changes to the cytoarchitecture of individual cells. In a developing embryo, these changes are controlled by patterning genes that confer cell identity. However, little is known about how patterning genes influence cytoarchitecture to drive changes in cell shape. In this paper, we analyze the function of the folded gastrulation gene (fog), a known target of the patterning gene twist. Our analysis of fog function therefore illuminates a molecular pathway spanning all the way from patterning gene to physical change in cell shape. We show that secretion of Fog protein is apically polarized, making this the earliest polarized component of a pathway that ultimately drives myosin to the apical side of the cell. We demonstrate that fog is both necessary and sufficient to drive apical myosin localization through a mechanism involving activation of myosin contractility with actin. We determine that this contractility driven form of localization involves RhoGEF2 and the downstream effector Rho kinase. This distinguishes apical myosin localization from basal myosin localization, which we find not to require actinomyosin contractility or FOG/RhoGEF2/Rho-kinase signaling. Furthermore, we demonstrate that once localized apically, myosin continues to contract. The force generated by continued myosin contraction is translated into a flattening and constriction of the cell surface through a tethering of the actinomyosin cytoskeleton to the apical adherens junctions. Our analysis of fog function therefore provides a direct link from patterning to cell shape change.

Incidence of clinical mastitis in dairy herds grouped in three categories by bulk milk somatic cell counts

Incidence of clinical mastitis was studied in 274 herds grouped in three categories by bulk milk somatic cell count (SCC). Mean incidence rate of clinical mastitis was 0.278, 0.257, and 0.252 cases per 365 cow-days at risk in herds with low (< or = 150,000), medium (150,000 to 250,000), and high (250,000 to 400,000 cells/ml) bulk milk SCC, respectively. The incidence rate of clinical mastitis was not different among the three categories. Variance in the incidence of clinical mastitis among herds increased as bulk milk SCC decreased. Clinical mastitis caused by Gram-negative pathogens, such as Escherichia coli, Klebsiella spp., or Pseudomonas spp., occurred more often in herds with a low bulk milk SCC. Clinical mastitis caused by Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus agalactiae occurred more often in herds with a high bulk milk SCC. Systemic signs of illness caused by clinical mastitis occurred more often in herds with a low bulk milk SCC. Both overall culling rate and culling rate for clinical mastitis were not different among groups catergorized by bulk milk SCC. In herds with a high bulk milk SCC, however, more cows that produced milk with a high SCC were culled. In herds with a low bulk milk SCC, more cows were culled for teat lesions, milkability, udder shape, fertility, and character than were cows in herds with a high bulk milk SCC. In herds with a low bulk milk SCC, cows were also culled more for export and production reasons.

Randomised controlled trial comparing transfusion of leucocyte-depleted or buffy-coat-depleted blood in surgery for colorectal cancer

In retrospective studies, perioperative blood transfusions were associated with poor prognosis after surgery for cancer and were a major independent risk factor for postoperative bacterial infection. Leucocyte-depleted, in contrast to buffy-coat-depleted, blood has no immunosuppressive effects in transplantation and so might lack detrimental effects on cancer prognosis and postoperative infections. We studied this hypothesis in a controlled trial by randomly allocating patients to receive either leucocyte-depleted red cells or packed cells without buffy coat when blood was needed. Between 1987 and 1990, 871 eligible patients with colorectal cancer, including 697 patients operated upon with curative intent, were randomised in the 16 participating hospitals. Neither the eligible group nor the curative group showed significant differences between the two trial transfusions in survival, disease-free survival, cancer recurrence rates, or overall infection rates after an average follow-up of 36 months. Patients who had a curative resection and who received blood of any sort had a lower 3-year survival than non-transfused patients (69% vs 81%, p = 0.001) and a higher infection rate (39% vs 24%, p < 0.001). Colorectal cancer recurrence rates, however, were not influenced by blood transfusion (30% vs 26%, p = 0.22). These combined observations confirm the association between blood transfusion and poor patient survival but indicate that the relation is not due to promotion of cancer.

Nutrition-responsive glia control exit of neural stem cells from quiescence

The systemic regulation of stem cells ensures that they meet the needs of the organism during growth and in response to injury. A key point of regulation is the decision between quiescence and proliferation. During development, Drosophila neural stem cells (neuroblasts) transit through a period of quiescence separating distinct embryonic and postembryonic phases of proliferation. It is known that neuroblasts exit quiescence via a hitherto unknown pathway in response to a nutrition-dependent signal from the fat body. We have identified a population of glial cells that produce insulin/IGF-like peptides in response to nutrition, and we show that the insulin/IGF receptor pathway is necessary for neuroblasts to exit quiescence. The forced expression of insulin/IGF-like peptides in glia, or activation of PI3K/Akt signaling in neuroblasts, can drive neuroblast growth and proliferation in the absence of dietary protein and thus uncouple neuroblasts from systemic control.

Prospero Acts as a Binary Switch between Self-Renewal and Differentiation in Drosophila Neural Stem Cells

Stem cells have the remarkable ability to give rise to both self-renewing and differentiating daughter cells. Drosophila neural stem cells segregate cell-fate determinants from the self-renewing cell to the differentiating daughter at each division. Here, we show that one such determinant, the homeodomain transcription factor Prospero, regulates the choice between stem cell self-renewal and differentiation. We have identified the in vivo targets of Prospero throughout the entire genome. We show that Prospero represses genes required for self-renewal, such as stem cell fate genes and cell-cycle genes. Surprisingly, Prospero is also required to activate genes for terminal differentiation. We further show that in the absence of Prospero, differentiating daughters revert to a stem cell-like fate: they express markers of self-renewal, exhibit increased proliferation, and fail to differentiate. These results define a blueprint for the transition from stem cell self-renewal to terminal differentiation.

A yeast silencer contains sequences that can promote autonomous plasmid replication and transcriptional activation

Repression of the yeast silent mating type loci requires cis-acting sequences located over 1 kb from the regulated promoters. One of these sites, a "silencer," exhibits enhancer-like distance- and orientation-independence. The silencer demonstrates both autonomous replication sequence (ARS) activity and a centromere-like segregation function, suggesting roles for DNA replication and segregation in transcriptional repression. Here we identify three sequences (A, E, and B) involved both in repression and in either ARS or segregation activity. The sequences are functionally redundant: no one is essential for complete transcriptional control, but mutations in any two inactivate the silencer. Surprisingly, elements E and B can each activate transcription from heterologous promoters, and E shows striking homology to several yeast upstream activation sequences. Therefore, sequences individually involved in replication, segregation, and transcriptional activation can, at the silencer, efficiently repress transcription.

Staufen- and FMRP-containing neuronal RNPs are structurally and functionally related to somatic P bodies

Local control of mRNA translation modulates neuronal development, synaptic plasticity, and memory formation. A poorly understood aspect of this control is the role and composition of ribonucleoprotein (RNP) particles that mediate transport and translation of neuronal RNAs. Here, we show that staufen- and FMRP-containing RNPs in Drosophila neurons contain proteins also present in somatic "P bodies," including the RNA-degradative enzymes Dcp1p and Xrn1p/Pacman and crucial components of miRNA (argonaute), NMD (Upf1p), and general translational repression (Dhh1p/Me31B) pathways. Drosophila Me31B is shown to participate (1) with an FMRP-associated, P body protein (Scd6p/trailer hitch) in FMRP-driven, argonaute-dependent translational repression in developing eye imaginal discs; (2) in dendritic elaboration of larval sensory neurons; and (3) in bantam miRNA-mediated translational repression in wing imaginal discs. These results argue for a conserved mechanism of translational control critical to neuronal function and open up new experimental avenues for understanding the regulation of mRNA function within neurons.

Rotation and asymmetry of the mitotic spindle direct asymmetric cell division in the developing central nervous system

The asymmetric segregation of cell-fate determinants and the generation of daughter cells of different sizes rely on the correct orientation and position of the mitotic spindle. In the Drosophila embryo, the determinant Prospero is localized basally and is segregated equally to daughters of similar cell size during epidermal cell division. In contrast, during neuroblast division Prospero is segregated asymmetrically to the smaller daughter cell. This simple switch between symmetric and asymmetric segregation is achieved by changing the orientation of cell division: neural cells divide in a plane perpendicular to that of epidermoblast division. Here, by labelling mitotic spindles in living Drosophila embryos, we show that neuroblast spindles are initially formed in the same axis as epidermal cells, but rotate before cell division. We find that daughter cells of different sizes arise because the spindle itself becomes asymmetric at anaphase: apical microtubules elongate, basal microtubules shorten, and the midbody moves basally until it is positioned asymmetrically between the two spindle poles. This observation contradicts the widely held hypothesis that the cleavage furrow is always placed midway between the two centrosomes.

Miranda mediates asymmetric protein and RNA localization in the developing nervous system

Neuroblasts undergo asymmetric stem cell divisions to generate a series of ganglion mother cells (GMCs). During these divisions, the cell fate determinant Prospero is asymmetrically partitioned to the GMC by Miranda protein, which tethers it to the basal cortex of the dividing neuroblast. Interestingly, prospero mRNA is similarly segregated by the dsRNA binding protein, Staufen. Here we show that Staufen interacts in vivo with a segment of the prospero 3' UTR. Staufen protein and prospero RNA colocalize to the apical side of the neuroblast at interphase, but move to the basal side during prophase. Both the apical and basal localization of Staufen are abolished by the removal of a conserved domain from the carboxyl terminus of the protein, which interacts in a yeast two-hybrid screen with Miranda protein. Furthermore, Miranda colocalizes with Staufen protein and prospero mRNA during neuroblast divisions, and neither Staufen nor prospero RNA are localized in miranda mutants. Thus Miranda, which localizes Prospero protein, also localizes prospero RNA through its interaction with Staufen protein.

Frizzled regulates localization of cell-fate determinants and mitotic spindle rotation during asymmetric cell division

Cell-fate diversity is generated in part by the unequal segregation of cell-fate determinants during asymmetric cell divisions. In the Drosophila pupa, the pI sense organ precursor cell is polarized along the anterior-posterior axis of the fly and divides asymmetrically to generate a posterior pIIa cell and an anterior pIIb cell. The anterior pIIb cell specifically inherits the determinant Numb and the adaptor protein Partner of Numb (Pon). By labelling both the Pon crescent and the microtubules in living pupae, we show that determinants localize at the anterior cortex before mitotic-spindle formation, and that the spindle forms with random orientation and rotates to line up with the Pon crescent. By imaging living frizzled (fz) mutant pupae we show that Fz regulates the orientation of the polarity axis of pI, the initiation of spindle rotation and the unequal partitioning of determinants. We conclude that Fz participates in establishing the polarity of pI.

An actomyosin-based barrier inhibits cell mixing at compartmental boundaries in Drosophila embryos

Partitioning tissues into compartments that do not intermix is essential for the correct morphogenesis of animal embryos and organs. Several hypotheses have been proposed to explain compartmental cell sorting, mainly differential adhesion, but also regulation of the cytoskeleton or of cell proliferation. Nevertheless, the molecular and cellular mechanisms that keep cells apart at boundaries remain unclear. Here we demonstrate, in early Drosophila melanogaster embryos, that actomyosin-based barriers stop cells from invading neighbouring compartments. Our analysis shows that cells can transiently invade neighbouring compartments, especially when they divide, but are then pushed back into their compartment of origin. Actomyosin cytoskeletal components are enriched at compartmental boundaries, forming cable-like structures when the epidermis is mitotically active. When MyoII (non-muscle myosin II) function is inhibited, including locally at the cable by chromophore-assisted laser inactivation (CALI), in live embryos, dividing cells are no longer pushed back, leading to compartmental cell mixing. We propose that local regulation of actomyosin contractibility, rather than differential adhesion, is the primary mechanism sorting cells at compartmental boundaries.

Ectopic gene expression in Drosophila using GAL4 system

Expressing a gene in cells in which it is not normally active is a powerful way of determining its function. The GAL4 system allows the selective expression of any cloned gene in a wide variety of cell- and tissue-specific patterns in Drosophila. A promoter (or enhancer) directs expression of the yeast transcriptional activator GAL4 in a particular pattern, and GAL4 in turn directs transcription of the GAL4-responsive (UAS) target gene in an identical pattern. The system's key feature is that the GAL4 gene and UAS-target gene are initially separated into two distinct transgenic lines. In the GAL4 line, the activator protein is present, but has no target gene to activate. In the UAS-target gene line, the target gene is silent because the activator is absent. It is only when the GAL4 line is crossed to the UAS-target gene line that the target gene is turned on in the progeny. In this article we describe, in detail, how to generate and characterize GAL4 lines and how to prepare UAS-target gene lines. Vector maps are provided for pGaTB, P[GawB], and pP[UAST]. In addition, we consider the range of UAS-reporters currently available and review several new modifications of the GAL4 system.

In vitro induction of human cytotoxic T lymphocyte responses against peptides of mutant and wild-type p53

The central role of the p53 tumor suppressor gene product in oncogenesis is gradually being clarified. Point mutations in the p53 tumor suppressor gene are common in most human cancers and are often associated with p53 protein overexpression. Overexpressed wild-type or mutant determinants of the p53 protein thus represent an attractive target for immunotherapy of cancer directed against a structure involved in malignant transformation. An important step towards this goal is identification of epitopes of p53 that can be recognized by human cytotoxic T lymphocytes. We identified peptides of (mutant) p53 capable of binding to HLA-A2.1 in an in vitro assay. These HLA-A2.1-binding peptides were utilized for in vitro induction of primary cytotoxic T lymphocyte responses using a human processing-defective cell line (174CEM.T2) as antigen-presenting cell. These cells display "empty" HLA class I surface molecules, that can efficiently be loaded with a single peptide. We obtained CD8+ cytotoxic T lymphocyte clones capable of specifically lysing target cells loaded with wild-type or tumor-specific mutant p53 peptides. This strategy allows the in vitro initiation of human cytotoxic T lymphocyte responses against target molecules of choice.

Imaging into the future: visualizing gene expression and protein interactions with fluorescent proteins

Since its introduction into heterologous organisms as a marker of gene expression, the green fluorescent protein (GFP) has led a dramatic revolution in cell, developmental and neurobiology. By allowing breathtaking visualization of fluorescent fusion proteins as they move within and between cells, GFP has fundamentally transformed the spatial analysis of protein function. Now, new GFP technologies allow far more than simple observations of fusion protein localization. The growing family of fluorescent protein variants is enabling more sophisticated studies of protein function and illuminating wide-ranging processes from gene expression to second-messenger cascades and intercellular signalling. Together with advances in microscopy, new GFP-based experimental approaches are forging a second GFP revolution.

High-dose intravenous immunoglobulin treatment in chronic inflammatory demyelinating polyneuropathy: a double-blind, placebo-controlled, crossover study

We discontinued high-dose intravenous immunoglobulin treatment (IVIg) in 7 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) who seemed to have responded to IVIg. After discontinuation of treatment, all 7 patients deteriorated. We then randomized the patients to IVIg or placebo (albumin) treatment in a double-blind crossover study. The clinical condition of all patients improved after IVIg and did not improve after placebo treatment. The mean time lapse from the end of the trial treatment to the occurrence of deterioration was 6.4 weeks after treatment with IVIg and 1.3 weeks after treatment with placebo. This selected group of patients with CIDP had a beneficial response to IVIg.

Transfusion of red cells is associated with increased incidence of bacterial infection after colorectal surgery: a prospective study

BACKGROUND

Several studies suggest that perioperative blood transfusion is a major independent risk factor for postoperative bacterial infections. Transfusion-induced immunosuppression is thought to mediate this effect.

STUDY DESIGN AND METHODS

In a randomized clinical trial comprising 697 patients with colorectal cancer, the relationship between two types of red cell components (buffy coat-depleted packed red cells and white cell-reduced [filtered] packed red cells) and postoperative bacterial infections was analyzed.

RESULTS

Both types of red cells appeared to be associated with a greater incidence of postoperative infection than was no transfusion (39 vs. 24%, p < 0.01). A dose-response relationship could be demonstrated: the corrected relative risk was 1.6 for 1 to 3 units of red cells and 3.6 for more than 3 units. Multivariate analyses identified the transfusion of red cells and tumor location as the only significant independent risk factors for postoperative bacterial infection.

CONCLUSION

Because allogeneic white cells, plasma, microaggregates, citrate, and platelets could be ruled out as risk factors for transfusion-associated postoperative infections, it is hypothesized that the transfusion of red cells is a potentially detrimental factor that transiently impairs the clearance of bacteria by phagocytic cells.

Regulation of spindle orientation and neural stem cell fate in the Drosophila optic lobe

Background

The choice of a stem cell to divide symmetrically or asymmetrically has profound consequences for development and disease. Unregulated symmetric division promotes tumor formation, whereas inappropriate asymmetric division affects organ morphogenesis. Despite its importance, little is known about how spindle positioning is regulated. In some tissues cell fate appears to dictate the type of cell division, whereas in other tissues it is thought that stochastic variation in spindle position dictates subsequent sibling cell fate.

Results

Here we investigate the relationship between neural progenitor identity and spindle positioning in the Drosophila optic lobe. We use molecular markers and live imaging to show that there are two populations of progenitors in the optic lobe: symmetrically dividing neuroepithelial cells and asymmetrically dividing neuroblasts. We use genetically marked single cell clones to show that neuroepithelial cells give rise to neuroblasts. To determine if a change in spindle orientation can trigger a neuroepithelial to neuroblast transition, we force neuroepithelial cells to divide along their apical/basal axis by misexpressing Inscuteable. We find that this does not induce neuroblasts, nor does it promote premature neuronal differentiation.

Conclusion

We show that symmetrically dividing neuroepithelial cells give rise to asymmetrically dividing neuroblasts in the optic lobe, and that regulation of spindle orientation and division symmetry is a consequence of cell type specification, rather than a mechanism for generating cell type diversity.

Independent regulation of synaptic size and activity by the anaphase-promoting complex

Neuronal plasticity relies on tightly regulated control of protein levels at synapses. One mechanism to control protein abundance is the ubiquitin-proteasome degradation system. Recent studies have implicated ubiquitin-mediated protein degradation in synaptic development, function, and plasticity, but little is known about the regulatory mechanisms controlling ubiquitylation in neurons. In contrast, ubiquitylation has long been studied as a central regulator of the eukaryotic cell cycle. A critical mediator of cell-cycle transitions, the anaphase-promoting complex/cyclosome (APC/C), is an E3 ubiquitin ligase. Although the APC/C has been detected in several differentiated cell types, a functional role for the complex in postmitotic cells has been elusive. We describe a novel postmitotic role for the APC/C at Drosophila neuromuscular synapses: independent regulation of synaptic growth and synaptic transmission. In neurons, the APC/C controls synaptic size via a downstream effector Liprin-alpha; in muscles, the APC/C regulates synaptic transmission, controlling the concentration of a postsynaptic glutamate receptor.

Polar transport in the Drosophila oocyte requires Dynein and Kinesin I cooperation

BACKGROUND

The cytoskeleton and associated motors play an important role in the establishment of intracellular polarity. Microtubule-based transport is required in many cell types for the asymmetric localization of mRNAs and organelles. A striking example is the Drosophila oocyte, where microtubule-dependent processes govern the asymmetric positioning of the nucleus and the localization to distinct cortical domains of mRNAs that function as cytoplasmic determinants. A conserved machinery for mRNA localization and nuclear positioning involving cytoplasmic Dynein has been postulated; however, the precise role of plus- and minus end-directed microtubule-based transport in axis formation is not yet understood.

RESULTS

Here, we show that mRNA localization and nuclear positioning at mid-oogenesis depend on two motor proteins, cytoplasmic Dynein and Kinesin I. Both of these microtubule motors cooperate in the polar transport of bicoid and gurken mRNAs to their respective cortical domains. In contrast, Kinesin I-mediated transport of oskar to the posterior pole appears to be independent of Dynein. Beside their roles in RNA transport, both motors are involved in nuclear positioning and in exocytosis of Gurken protein. Dynein-Dynactin complexes accumulate at two sites within the oocyte: around the nucleus in a microtubule-independent manner and at the posterior pole through Kinesin-mediated transport.

CONCLUSION

The microtubule motors cytoplasmic Dynein and Kinesin I, by driving transport to opposing microtubule ends, function in concert to establish intracellular polarity within the Drosophila oocyte. Furthermore, Kinesin-dependent localization of Dynein suggests that both motors are components of the same complex and therefore might cooperate in recycling each other to the opposite microtubule pole.