Reduced Fitness of Virulent Aphis glycines (Hemiptera: Aphididae) Biotypes May Influence the Longevity of Resistance Genes in Soybean

Sustainable use of insect resistance in crops require insect resistance management plans that may include a refuge to limit the spread of virulence to this resistance. However, without a loss of fitness associated with virulence, a refuge may not prevent virulence from becoming fixed within a population of parthenogenetically reproducing insects like aphids. Aphid-resistance in soybeans (i.e., Rag genes) prevent outbreaks of soybean aphid (Aphis glycines), yet four biotypes defined by their capacity to survive on aphid-resistant soybeans (e.g., biotype-2 survives on Rag1 soybean) are found in North America. Although fitness costs are reported for biotype-3 on aphid susceptible and Rag1 soybean, it is not clear if virulence to aphid resistance in general is associated with a decrease in fitness on aphid susceptible soybeans. In laboratory assays, we measured fitness costs for biotype 2, 3 and 4 on an aphid-susceptible soybean cultivar. In addition, we also observed negative cross-resistance for biotype-2 on Rag3, and biotype-3 on Rag1 soybean. We utilized a simple deterministic, single-locus, four compartment genetic model to account for the impact of these findings on the frequency of virulence alleles. When a refuge of aphid susceptible was included within this model, fitness costs and negative cross-resistance delayed the increase of virulence alleles when virulence was inherited recessively or additively. If virulence were inherited additively, fitness costs decreased the frequency of virulence. Combined, these results suggest that a refuge may prevent virulent A. glycines biotypes from overcoming Rag genes if this aphid-resistance were used commercially in North America.     

Prevention of quorum-sensing-mediated biofilm development and virulence factors production in Vibrio spp. by curcumin

The increasing occurrence of disease outbreaks caused by Vibrio spp. and the emergence of antibiotic resistance has led to a growing interest in finding alternative strategies to prevent vibriosis. Since the pathogenicity of vibrios is controlled in part by quorum-sensing (QS) system, interfering with this mechanism would prevent the pathogenicity of vibrios without developing resistance. Hence, a non-toxic phytochemical curcumin from Curcuma longa was assessed for its potential in reducing the production of QS-dependent virulence factors in Vibrio spp. The obtained results evidenced 88 % reduction in bioluminescence of Vibrio harveyi by curcumin. Further, curcumin exhibited a significant inhibition in alginate, exopolysaccharides, motility, biofilm development and other virulence factors production in Vibrio parahaemolyticus, Vibrio vulnificus and V. harveyi. In in vivo analysis, curcumin enhanced the survival rate of Artemia nauplii up to 67 % against V. harveyi infection by attenuating its QS-mediated virulence.     

Role of genes 46 and 47 in bacteriophage T4 reproduction. II. Formation of gaps on parental DNA of polynucleotide ligase defective mutants

The nature of nucleolytic activity regulated by genes 46 and 47 of bacteriophage T4 was studied by examining the metabolism of parental DNA of phages carrying a mutation in polynucleotide ligase gene (lig) and an additional mutation in one of the following D0 genes (D0 genes are necessary for T4 DNA synthesis): 32, 43 (DNA polymerase  pol), 44 and 45. Polynucleotide ligase and DNA polymerase were used to distinguish nicks (phosphodiester bond interruptions on duplex DNA) from gaps (interruptions with missing nucleotides). In non-permissive hosts, parental DNA of double mutants (lig, D0) accumulated both single- and double-strand breaks. Up to 30% of this DNA eventually became acid-soluble. An additional mutation in gene 46 (or 47) did not prevent accumulation of double- and single-strand breaks but did prevent degradation to the acid-soluble state. The majority of the single-strand breaks on (lig, D0)-DNA were presumed to be gaps since, after extraction from infected host cells, they were repaired by ligase plus DNA polymerase but not by ligase alone. In contrast, the majority of the single-strand breaks on parental DNA of (lig, D0, 46) or (lig, pol, 47) were repaired by ligase alone, suggesting nicks, rather than gaps. These observations suggest that (i) genes 46 and 47 regulate, either directly or indirectly, an exonuelease activity which can attack T4 DNA at nicks to create gaps, and (ii) T4 DNA polymerase, and the products of genes 32, 44 and 45 are necessary to prevent nicks from becoming gaps in vivo. Possible roles for genes 46 and 47 in T4 DNA replication and in recombination are discussed.     

Salmonella Serovars in the Herpetofauna of Indiana County, Pennsylvania

Herpetofaunal Salmonella enterica serovars have not been fully examined in any U.S. region. Thirty-three Salmonella serovars were isolated from 156 samples from 34 species, all within Indiana County, Pennsylvania. Results suggest that herpetofaunas could potentially pose a threat to humans. Further understanding of Salmonella in herpetofaunas may prevent future human cases.     

Cajanolactone A,a stilbenoid from cajanus cajan,prevents ovariectomy-induced obesity and liver steatosis in mice fed a regular diet

BackgroundVisceral obesity and fatty liver are prevalent in postmenopausal women. The stilbene-rich extract of Cajanus cajan (L.) Millsp. has been reported to prevent ovariectomy-induced and diet-induced weight gain in animal models, and stilbenoids from C. cajan are thought to have the potential to prevent postmenopausal obesity and fatty liver.PurposeCajanolactone A (CLA) is the main stilbenoid from C. cajan with osteoblastogenic promoting activity. This study investigated the potential of CLA to prevent postmenopausal obesity and fatty liver. Underlying mechanisms were also investigated.MethodOvariectomized C57BL/6 mice fed a regular diet were used as mimics of postmenopausal women and given 10, 20, or 40 mg/kg/d of CLA, 0.1 mg/kg/d of estradiol valerate (EV, positive control), or vehicle (OVX) orally for 16 weeks. Mice of the same age subjected to a sham operation were used as control (Sham). Body weights were recorded every 2 weeks for 16 weeks. Body compositions were analyzed via micro-CT. Serum levels of lipids, adipocytokines and aminotransferases were measured using the relevant kits. mRNA levels of genes of interest were detected by RT-qPCR. Proteomic study of perigonadal white adipose tissue (pWAT) was performed using tandem-mass-tags-based proteomic technology combined with Parallel-Reaction-Monitoring (PRM) validation.ResultsCLA showed potential equivalent to that of EV to prevent ovariectomy-induced overweight, obesity, dyslipidemia, liver steatosis and liver dysfunction, but did not prevent uterine atrophy. In the liver, CLA significantly inhibited ovariectomy-induced upregulation in expression of lipogenic genes SREBP-1c and ChREBP, and stimulated the mRNA expression of apolipoprotein B gene ApoB. In pWAT, CLA reversed, or partially reversed ovariectomy-induced downregulation in the expression of a number of metabolism- and mitochondrial-function-related proteins, including Ndufa3, Pcx, Pdhb, Acly, Acaca, Aldh2, Aacs and Echs1. In addition, ovariectomy-inhibited mRNA expression of Pdhb, Aacs, Acsm5, Echs1, and Aldh2 genes in pWAT was also reversed.ConclusionCLA was demonstrated to be a potential non-estrogen-like drug candidate for prevention of postmenopausal obesity and fatty liver. The underlying mechanism might involve the inhibition of lipogenesis and promotion of triglycerides output in the liver, and the promotion of metabolism and mitochondrial functions of visceral white adipose tissue.     

Studies on the mechanism of reduction of W-inducible sulAp expression by recF overexpression in Escherichia coli K-12

UV-inducible sulAp expression, an indicator of the SOS response, is reduced by recF ⁺ overexpression in vivo. Different DNA-damaging agents and amounts of RecO and RecR were tested for their effects on this phenotype. It was found that recF ⁺ overexpression reduced sulAp expression after DNA damage by mitomycin C or nalidixic acid. recO ⁺ and recR ⁺ overexpression partially suppressed the reduction of UV-induced sulAp expression caused by recF ⁺ overexpression. The requirement for ATP binding to RecF to produce the phenotype was tested by genetically altering the putative phosphate binding cleft of recF in a way that should prevent the mutant recF protein from binding ATP that should prevent the mutant recF protein from binding ATP. It was found that a change of lysine to glutamine at codon 36 results in a mutant recF protein (RecF4115) that is unable to reduce UV-inducible sulAp expression when overproduced. It is inferred from these results that recF overexpression may reduce UV-inducible sulAp expression by a mechanism that is sensitive to the ability of RecF to bind ATP and to the levels of RecO and RecR (RecOR) in the cell, but not to the type of DNA damage per se. Models are explored that can explain how recF ⁺ overexpression reduces UV induction of sulAp and how RecOR overproduction might suppress this phenotype.     

Nitric Oxide Induces Cell Death by Regulating Anti-Apoptotic BCL-2 Family Members

Nitric oxide (NO) activates the intrinsic apoptotic pathway to induce cell death. However, the mechanism by which this pathway is activated in cells exposed to NO is not known. Here we report that BAX and BAK are activated by NO and that cytochrome c is released from the mitochondria. Cells deficient in Bax and Bak or Caspase-9 are completely protected from NO-induced cell death. The individual loss of the BH3-only proteins, Bim, Bid, Puma, Bad or Noxa, or Bid knockdown in Bim^−/−/Puma^−/− MEFs, does not prevent NO-induced cell death. Our data show that the anti-apoptotic protein MCL-1 undergoes ASK1-JNK1 mediated degradation upon exposure to NO, and that cells deficient in either Ask1 or Jnk1 are protected against NO-induced cell death. NO can inhibit the mitochondrial electron transport chain resulting in an increase in superoxide generation and peroxynitrite formation. However, scavengers of ROS or peroxynitrite do not prevent NO-induced cell death. Collectively, these data indicate that NO degrades MCL-1 through the ASK1-JNK1 axis to induce BAX/BAK-dependent cell death.     

Oral Immunization with OspC Does Not Prevent Tick-Borne Borrelia burgdorferi Infection

Oral vaccination strategies are of interest to prevent transmission of Lyme disease as they can be used to deliver vaccines to humans, pets, and to natural wildlife reservoir hosts of Borrelia burgdorferi. We developed a number of oral vaccines based in E. coli expressing recombinant OspC type K, OspB, BBK32 from B. burgdorferi, and Salp25, Salp15 from Ixodes scapularis. Of the five immunogenic candidates only OspC induced significant levels of antigen-specific IgG and IgA when administered to mice via the oral route. Antibodies to OspC did not prevent dissemination of B. burgdorferi as determined by the presence of spirochetes in ear, heart and bladder tissues four weeks after challenge. Next generation sequencing of genomic DNA from ticks identified multiple phyletic types of B. burgdorferi OspC (A, D, E, F, I, J, K, M, Q, T, X) in nymphs that engorged on vaccinated mice. PCR amplification of OspC types A and K from flat and engorged nymphal ticks, and from heart and bladder tissues collected after challenge confirmed sequencing analysis. Quantification of spirochete growth in a borreliacidal assay shows that both types of spirochetes (A and K) survived in the presence of OspC-K specific serum whereas the spirochetes were killed by OspA specific serum. We show that oral vaccination of C3H-HeN mice with OspC-K induced significant levels of antigen-specific IgG. However, these serologic antibodies did not protect mice from infection with B. burgdorferi expressing homologous or heterologous types of OspC after tick challenge.     

Recombinant probiotic expressing Listeria adhesion protein attenuates Listeria monocytogenes virulence in vitro

Background

Listeria monocytogenes, an intracellular foodborne pathogen, infects immunocompromised hosts. The primary route of transmission is through contaminated food. In the gastrointestinal tract, it traverses the epithelial barrier through intracellular or paracellular routes. Strategies to prevent L. monocytogenes entry can potentially minimize infection in high-risk populations. Listeria adhesion protein (LAP) aids L. monocytogenes in crossing epithelial barriers via the paracellular route. The use of recombinant probiotic bacteria expressing LAP would aid targeted clearance of Listeria from the gut and protect high-risk populations from infection.

Methodology/Principal Findings

The objective was to investigate the ability of probiotic bacteria or LAP-expressing recombinant probiotic Lactobacillus paracasei (Lbp^LAP) to prevent L. monocytogenes adhesion, invasion, and transwell-based transepithelial translocation in a Caco-2 cell culture model. Several wild type probiotic bacteria showed strong adhesion to Caco-2 cells but none effectively prevented L. monocytogenes infection. Pre-exposure to Lbp^LAP for 1, 4, 15, or 24 h significantly (P<0.05) reduced adhesion, invasion, and transepithelial translocation of L. monocytogenes in Caco-2 cells, whereas pre-exposure to parental Lb. paracasei had no significant effect. Similarly, Lbp^LAP pre-exposure reduced L. monocytogenes translocation by as much as 46% after 24 h. Lbp^LAP also prevented L. monocytogenes-mediated cell damage and compromise of tight junction integrity. Furthermore, Lbp^LAP cells reduced L. monocytogenes-mediated cell cytotoxicity by 99.8% after 1 h and 79% after 24 h.

Conclusions/Significance

Wild type probiotic bacteria were unable to prevent L. monocytogenes infection in vitro. In contrast, Lbp^LAP blocked adhesion, invasion, and translocation of L. monocytogenes by interacting with host cell receptor Hsp60, thereby protecting cells from infection. These data show promise for the use of recombinant probiotics in preventing L. monocytogenes infection in high-risk populations.     

Prevention of Clostridium difficile -induced ileocecitis with Bacteriophage

A bacteriophage specific for Clostridium difficile was examined for its ability to prevent ileocecitis in a hamster model. This species- and strain-specific bacteriophage was isolated from a lysogenic strain of C. difficile . Hamsters were maintained in sterile isolation cages to prevent the acquisition of C. difficile from the environment. Bicarbonate neutralization of gastric acidity was necessary for bacteriophage survival in the hamster's gastrointestinal tract. Bacteriophage recovery from the hamster cecum was 2×10⁴plaque forming units/mL of cecal contents 24 h after orogastric challenge with 10⁸plaque forming units/mL of bacteriophage. However, there was no bacteriophage recovery 48 h post challenge, indicating dissipation of bacteriophage from the hamster intestinal tract within this time frame. Twenty-four hours after being challenged with clindamycin, one group of hamsters was challenged with C. difficile followed by a single dose of bacteriophage (10⁸plaque forming units/mL). Two additional groups of hamsters received phage doses immediately after C. difficile challenge and subsequently thereafter every 8 h up to 48 and 72 h, respectively. The gastric acidity was neutralized with bicarbonate buffer preceding every bacteriophage treatment. Control animals that received only clindamycin and C. difficile died within 96 h after challenge while the majority of bacteriophage treated hamsters survived. Two weeks after stopping bacteriophage treatment, the surviving hamsters were re-challenged with clindamycin and C. difficile . All the hamsters died within 96 h indicating susceptibility of the surviving hamsters to C. difficile disease in the absence of bacteriophage treatment.     

Excretions/Secretions from Bacteria-Pretreated Maggot Are More Effective against Pseudomonas aeruginosa Biofilms

Background

Sterile larvae—maggots of the green bottle blowfly Lucilia sericata are employed as a treatment tool for various types of chronic wounds. Previous studies reported that excretions/secretions (ES) of the sterile larvae could prevent and remove the biofilms of various species of bacteria. In the present study we assessed the effect of ES from the larvae pretreated with Pseudomonas aeruginosa on the bacteria biofilms.

Methods and Findings

We investigated the effects of ES from the maggot pretreated with P. aeruginosa on the biofilms using microtitre plate assays and on bactericidal effect using the colony-forming unit (CFU) assay. The results showed that only 30 µg of the ES from the pretreated maggots could prevent and degrade the biofilm of P. aeruginosa. However, the CFU count of P. aeruginosa was not decrease when compared to the ES from non pretreated maggots in this study condition. It is suggested that the ES from the pretreated maggot was more effective against biofilm of P. aeruginosa than sterile maggot ES.

Conclusions

Our results showed that the maggot ES, especially the bacteria-pretreated larva ES may provide a new insight into the treatment tool of the bacterial biofilms.     

Mutants of the Yeast Yarrowia lipolytica Defective in Protein Exit from the Endoplasmic Reticulum Are Also Defective in Peroxisome Biogenesis

Mutations in the SEC238 and SRP54 genes of the yeast Yarrowia lipolytica not only cause temperature-sensitive defects in the exit of the precursor form of alkaline extracellular protease and of other secretory proteins from the endoplasmic reticulum and in protein secretion but also lead to temperature-sensitive growth in oleic acid-containing medium, the metabolism of which requires the assembly of functionally intact peroxisomes. The sec238A and srp54KO mutations at the restrictive temperature significantly reduce the size and number of peroxisomes, affect the import of peroxisomal matrix and membrane proteins into the organelle, and significantly delay, but do not prevent, the exit of two peroxisomal membrane proteins, Pex2p and Pex16p, from the endoplasmic reticulum en route to the peroxisomal membrane. Mutations in the PEX1 and PEX6 genes, which encode members of the AAA family of N-ethylmaleimide-sensitive fusion protein-like ATPases, not only affect the exit of precursor forms of secretory proteins from the endoplasmic reticulum but also prevent the exit of the peroxisomal membrane proteins Pex2p and Pex16p from the endoplasmic reticulum and cause the accumulation of an extensive network of endoplasmic reticulum membranes. None of the peroxisomal matrix proteins tested associated with the endoplasmic reticulum in sec238A, srp54KO, pex1-1, and pex6KO mutant cells. Our data provide evidence that the endoplasmic reticulum is required for peroxisome biogenesis and suggest that in Y. lipolytica, the trafficking of some membrane proteins, but not matrix proteins, to the peroxisome occurs via the endoplasmic reticulum, results in their glycosylation within the lumen of the endoplasmic reticulum, does not involve transport through the Golgi, and requires the products encoded by the SEC238, SRP54, PEX1, and PEX6 genes.     

An Adenoviral Vector Based Vaccine for Rhodococcus equi

Rhodococcus equi is a respiratory pathogen which primarily infects foals and is endemic on farms around the world with 50% mortality and 80% morbidity in affected foals. Unless detected early and treated appropriately the disease can be fatal. Currently, there is no vaccine available to prevent this disease. For decades researchers have endeavoured to develop an effective vaccine to no avail. In this study a novel human adenoviral vector vaccine for R. equi was developed and tested in the mouse model. This vaccine generated a strong antibody and cytokine response and clearance of R. equi was demonstrated following challenge. These results show that this vaccine could potentially be developed further for use as a vaccine to prevent R. equi disease in foals.     

Austropotamobius pallipes reduction vs. Procambarus clarkii spreading: Management implications

One of the main threats to native European crayfish is the spread of alien crayfish species that are immune carriers of the detrimental crayfish plague Aphanomyces astaci. In this study we analyzed both at a regional and at a local scale factors determining native and alien crayfish distribution in an area where the species Procambarus clarkii is currently spreading. We aim to understand which management strategies could prevent the extinction of native populations. We sampled 81 waterbodies in Lombardy (NW Italy) to assess the Austropotamobius pallipes complex and alien crayfish occurrence; we also monitored the only first order stream in our study area that we found to be currently inhabited by A. pallipes upstream and by P. clarkii downstream. A. pallipes generally occurred in small brooks, near the spring, and was linked to low periphyton abundance, while P. clarkii occurred in sites at lower altitudes, far from the spring area, mainly in lentic waterbodies with large widths; this allochthonous species was positively related to periphyton abundance. Our monitoring showed that physical barriers such as dams may prevent P. clarkii dispersal upstream. Our results confirm that A. pallipes and P. clarkii have different ecological requirements and show that, at least during the first years of invasion, P. clarkii spreading involves lowland or downstream altered sites. We suggest the need for management strategies maximizing connectivity among native populations, to avoid isolation, and promoting the separation of native populations from those of P. clarkii.     

Lipid-protein interactions in mitochondria. The effect of protein interaction on susceptibility of phospholipids to phospholipase A2 and C hydrolysis.

Phospholipase A₂ (Naja naja) and phospholipase C (from either Clostridium welchii or Bacillus cereus) have been tested on phospholipid dispersions and natural or reconstituted membranes; notwithstanding the different substrate specificities, the different enzymes gave comparable behaviors, suggesting that the results were the expression of sterical features in the lipid bilayers, i.e., availability of the phospholipids to enzymatic attack. The hydrolysis of phospholipids (Asolectin) in sonic protein-free vesicles is hindered by ionic interaction with basic proteins (cytochrome c or lysozyme). On the other hand binding of Asolectin to lipid-depleted mitochondria to obtain reconstituted mitochondria does not prevent phospholipase action on the phospholipids; similarly, phospholipids are hydrolyzed at maximal rates in natural membranes (mitochondria or submitochondrial particles). Surprisingly, ionic interaction of RM or natural membranes with basic proteins does not prevent phospholipase hydrolysis of the membrane phospholipids. The interpretation of this phenomenon may be related to the heterogeneity of phospholipid distribution in protein-containing membranes.     

Cucurbitacin E and I in Iberis amara: Feeding inhibitors for Phyllotreta nemorum

Cucurbitacin E and cucurbitacin I have been isolated from green parts of Iberis amara and identified by TLC, UV and MS. It is shown that cucurbitacins act as feeding inhibitors for the flea beetle Phyllotreta nemorum. The most potent feeding inhibitors in green parts of I. amara towards P. nemorum are cucurbitacin E and I, and the concentrations of these compounds in the plant are found to be high enough to prevent feeding of the flea beetle.     

LMNA cardiomyopathy: cell biology and genetics meet clinical medicine

Mutations in the LMNA gene, which encodes A-type nuclear lamins (intermediate filament proteins expressed in most differentiated somatic cells), cause a diverse range of diseases, called laminopathies, that selectively affect different tissues and organ systems. The most prevalent laminopathy is cardiomyopathy with or without different types of skeletal muscular dystrophy. LMNA cardiomyopathy has an aggressive clinical course with higher rates of deadly arrhythmias and heart failure than most other heart diseases. As awareness among physicians increases, and advances in DNA sequencing methods make the genetic diagnosis of LMNA cardiomyopathy more common, cardiologists are being faced with difficult questions regarding patient management. These questions concern the optimal use of intracardiac cardioverter defibrillators to prevent sudden death from arrhythmias, and medical interventions to prevent heart damage and ameliorate heart failure symptoms. Data from a mouse model of LMNA cardiomyopathy suggest that inhibitors of mitogen-activated protein kinase (MAPK) signaling pathways are beneficial in preventing and treating cardiac dysfunction; this basic research discovery needs to be translated to human patients.     

Thioesterase II of Escherichia coli Plays an Important Role in 3-Hydroxydecanoic Acid Production

3-Hydroxydecanoic acid (3HD) was produced in Escherichia coli by mobilizing (R)-3-hydroxydecanoyl-acyl carrier protein-coenzyme A transacylase (PhaG, encoded by the phaG gene). By employing an isogenic tesB (encoding thioesterase II)-negative knockout E. coli strain, CH01, it was found that the expressions of tesB and phaG can up-regulate each other. In addition, 3HD was synthesized from glucose or fructose by recombinant E. coli harboring phaG and tesB. This study supports the hypothesis that the physiological role of thioesterase II in E. coli is to prevent the abnormal accumulation of intracellular acyl-coenzyme A.     

Continued DNA Synthesis in Replication Checkpoint Mutants Leads to Fork Collapse

Hydroxyurea (HU) treatment activates the intra-S phase checkpoint proteins Cds1 and Mrc1 to prevent replication fork collapse. We found that prolonged DNA synthesis occurs in cds1Δ and mrc1Δ checkpoint mutants in the presence of HU and continues after release. This is coincident with increased DNA damage measured by phosphorylated histone H2A in whole cells during release. High-resolution live-cell imaging shows that mutants first accumulate extensive replication protein A (RPA) foci, followed by increased Rad52. Both DNA synthesis and RPA accumulation require the MCM helicase. We propose that a replication fork “collapse point” in HU-treated cells describes the point at which accumulated DNA damage and instability at individual forks prevent further replication. After this point, cds1Δ and mrc1Δ forks cannot complete genome replication. These observations establish replication fork collapse as a dynamic process that continues after release from HU block.     

The PAM-1 aminopeptidase regulates centrosome positioning to ensure anterior-posterior axis specification in one-cell C. elegans embryos

In the one-cell Caenorhabditis elegans embryo, the anterior-posterior (A-P) axis is established when the sperm donated centrosome contacts the posterior cortex. While this contact appears to be essential for axis polarization, little is known about the mechanisms governing centrosome positioning during this process. pam-1 encodes a puromycin sensitive aminopeptidase that regulates centrosome positioning in the early embryo. Previously we showed that pam-1 mutants fail to polarize the A-P axis. Here we show that PAM-1 can be found in mature sperm and in cytoplasm throughout early embryogenesis where it concentrates around mitotic centrosomes and chromosomes. We provide further evidence that PAM-1 acts early in the polarization process by showing that PAR-1 and PAR-6 do not localize appropriately in pam-1 mutants. Additionally, we tested the hypothesis that PAM-1's role in polarity establishment is to ensure centrosome contact with the posterior cortex. We inactivated the microtubule motor dynein, DHC-1, in pam-1 mutants, in an attempt to prevent centrosome movement from the cortex and restore anterior-posterior polarity. When this was done, the aberrant centrosome movements of pam-1 mutants were not observed and anterior-posterior polarity was properly established, with proper localization of cortical and cytoplasmic determinants. We conclude that PAM-1's role in axis polarization is to prevent premature movement of the centrosome from the posterior cortex, ensuring proper axis establishment in the embryo.