Forty-nine metagenomic-assembled genomes from an aquatic virome expand Caudoviricetes by 45 potential new families and the newly uncovered Gossevirus of Bamfordvirae.

Twenty complete genomes (29-63 kb) and 29 genomes with an estimated completeness of over 90 % (30-90 kb) were identified for novel dsDNA viruses in the Yangshan Harbor metavirome. These newly discovered viruses contribute to the expansion of viral taxonomy by introducing 46 potential new families. Except for one virus, all others belong to the class Caudoviricetes. The exception is a novel member of the recently characterized viral group known as Gossevirus. Fifteen viruses were predicted to be temperate. The predicted hosts for the viruses appear to be involved in various aspects of the nitrogen cycle, including nitrogen fixation, oxidation and denitrification. Two viruses were identified to have a host of Flavobacterium and Tepidimonas fonticaldi, respectively, by matching CRISPR spacers with viral protospacers. Our findings provide an overview for characterizing and identifying specific viruses from Yangshan Harbor. The Gossevirus-like virus uncovered emphasizes the need for further comprehensive isolation and investigation of polinton-like viruses.

Restriction of subapical proteins during cellularization depends on the onset of zygotic transcription and the formin Dia.

Cortical domains are characterized by spatially restricted polarity proteins. The pattern of cortical domains is dynamic and changes during cell differentiation and development. Although there is a good understanding for how the cortical pattern is maintained, e. g. by mutual antagonism, less is known about how the initial pattern is established, and its dynamics coordinated with developmental progression. Here we investigate the initial restriction of subapical marker proteins during the syncytial-cellular transition in Drosophila embryos. The subapical markers Canoe/Afadin, the complex ELMO-Sponge, Baz and Arm become initially restricted between apical and lateral domains during cellularization. We define the role of zygotic genome activation as a timer for subapical domain formation. Subapical markers remained widely spread in embryos treated with α-amanitin and became precociously restricted in mutant embryos with premature zygotic transcription. In contrast, remodeling of the nuclear division cycle without cytokinesis to a full cell cycle is not a prerequisite for subapical domain formation, since we observed timely subapical restriction in embryos undergoing an extra nuclear cycle. We provide evidence that earliest subapical markers ELMO-Sponge and Canoe are required for subapical accumulation of Baz. Supporting an important role of cortical F-actin in subapical restriction, we found that the formin Dia was required for Baz restriction, and its distribution depended on the onset of zygotic gene expression. In summary, we define zygotic transcription as a timer, to which subapical markers respond in a dia-dependent mechanism.

Dia- and Rok-dependent enrichment of capping proteins in a cortical region.

Rho signaling with its major targets the formin Dia, Rho kinase (Rok) and non-muscle myosin II (MyoII, encoded by zip in flies) control turnover, amount and contractility of actomyosin. Much less investigated has been a potential function for the distribution of F-actin plus and minus ends. In syncytial Drosophila embryos, Rho1 signaling is high between actin caps, i.e. the cortical intercap region. Capping protein binds to free plus ends of F-actin to prevent elongation of the filament. Capping protein has served as a marker to visualize the distribution of F-actin plus ends in cells and in vitro. In the present study, we probed the distribution of plus ends with capping protein in syncytial Drosophila embryos. We found that capping proteins are specifically enriched in the intercap region similar to Dia and MyoII but distinct from overall F-actin. The intercap enrichment of Capping protein was impaired in dia mutants and embryos, in which Rok and MyoII activation was inhibited. Our observations reveal that Dia and Rok-MyoII control Capping protein enrichment and support a model that Dia and Rok-MyoII control the organization of cortical actin cytoskeleton downstream of Rho1 signaling. This article has an associated First Person interview with the first authors of the paper.

Diverse viruses of marine archaea discovered using metagenomics.

During the past decade, metagenomics became a method of choice for the discovery of novel viruses. However, host assignment for uncultured viruses remains challenging, especially for archaeal viruses, which are grossly undersampled compared to viruses of bacteria and eukaryotes. Here, we assessed the utility of CRISPR spacer targeting, tRNA gene matching and homology searches for viral signature proteins, such as major capsid proteins, for the assignment of archaeal hosts and validated these approaches on metaviromes from Yangshan Harbor (YSH). We report 35 new genomes of viruses which could be confidently assigned to hosts representing diverse lineages of marine archaea. We show that the archaeal YSH virome is highly diverse, with some viruses enriching the previously described virus groups, such as magroviruses of Marine Group II Archaea (Poseidoniales), and others representing novel groups of marine archaeal viruses. Metagenomic recruitment of Tara Oceans datasets on the YSH viral genomes demonstrated the presence of YSH Poseidoniales and Nitrososphaeria viruses in the global oceans, but also revealed the endemic YSH-specific viral lineages. Furthermore, our results highlight the relationship between the soil and marine thaumarchaeal viruses. We propose three new families within the class Caudoviricetes for the classification of the five complete viral genomes predicted to replicate in marine Poseidoniales and Nitrososphaeria, two ecologically important and widespread archaeal groups. This study illustrates the utility of viral metagenomics in exploring the archaeal virome and provides new insights into the diversity, distribution and evolution of marine archaeal viruses.

Efficacy and safety of tafolecimab in Chinese patients with heterozygous familial hypercholesterolemia: a randomized, double-blind, placebo-controlled phase 3 trial (CREDIT-2).

BACKGROUND: Heterozygous familial hypercholesterolemia (HeFH) is largely underdiagnosed and undertreated in China where few patients achieved recommended target levels of low density lipoprotein cholesterol (LDL-C). We conducted the first randomized, placebo-controlled clinical trial in Chinese patients with HeFH to assess the efficacy and safety of tafolecimab, a novel fully human proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibody. METHODS: Patients diagnosed with HeFH by Simon Broome criteria and on a stable lipid-lowering therapy for at least 4 weeks were randomized 2:2:1:1 to receive subcutaneous tafolecimab 150 mg every 2 weeks (Q2W), tafolecimab 450 mg every 4 weeks (Q4W), placebo Q2W or placebo Q4W in the 12-week double-blind treatment period. After that, participants received open-label tafolecimab 150 mg Q2W or 450 mg Q4W for 12 weeks. The primary endpoint was the percent change from baseline to week 12 in LDL-C levels. Secondary endpoints included proportion of participants achieving ≥50% LDL-C reductions and proportion of participants with LDL-C <1.8 mmol/L at week 12 and 24, the change from baseline to week 12 in non-high density lipoprotein cholesterol (non-HDL-C), apolipoprotein B and lipoprotein(a) levels, as well as the change from baseline to week 24 in lipid levels. RESULTS: In total, 149 participants were randomized and 148 received at least one dose of the study treatment. At week 12, tafolecimab treatment induced significant reductions in LDL-C levels (treatment difference versus placebo [on-treatment estimand]: -57.4% [97.5% CI, -69.2 to -45.5] for 150 mg Q2W; -61.9% [-73.4 to -50.4] for 450 mg Q4W; both P <0.0001). At both dose regimens, significantly more participants treated with tafolecimab achieved ≥50% LDL-C reductions or LDL-C <1.8 mmol/L at week 12 as compared with corresponding placebo groups (all P <0.0001). Meanwhile, non-HDL-C, apolipoprotein B and lipoprotein(a) levels were significantly reduced in the tafolecimab groups at week 12. The lipid-lowering effects of tafolecimab were maintained till week 24. During the double-blind treatment period, the most commonly-reported adverse events in the tafolecimab groups included upper respiratory tract infection, increased blood creatine phosphokinase, increased alanine aminotransferase, increased aspartate aminotransferase and hypertension. CONCLUSIONS: Tafolecimab administered either 150 mg Q2W or 450 mg Q4W yielded significant and persistent reductions in LDL-C levels and showed a favorable safety profile in Chinese patients with HeFH. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04179669.

Novel Cell-Virus-Virophage Tripartite Infection Systems Discovered in the Freshwater Lake Dishui Lake in Shanghai, China.

Virophages are small parasitic double-stranded DNA (dsDNA) viruses of giant dsDNA viruses infecting unicellular eukaryotes. Except for a few isolated virophages characterized by parasitization mechanisms, features of virophages discovered in metagenomic data sets remain largely unknown. Here, the complete genomes of seven virophages (26.6 to 31.5 kbp) and four large DNA viruses (190.4 to 392.5 kbp) that coexist in the freshwater lake Dishui Lake, Shanghai, China, have been identified based on environmental metagenomic investigation. Both genomic and phylogenetic analyses indicate that Dishui Lake virophages (DSLVs) are closely related to each other and to other lake virophages, and Dishui Lake large DNA viruses are affiliated with the micro-green alga-infecting Prasinovirus of the Phycodnaviridae (named Dishui Lake phycodnaviruses [DSLPVs]) and protist (protozoan and alga)-infecting Mimiviridae (named Dishui Lake large alga virus [DSLLAV]). The DSLVs possess more genes with closer homology to that of large alga viruses than to that of giant protozoan viruses. Furthermore, the DSLVs are strongly associated with large green alga viruses, including DSLPV4 and DSLLAV1, based on codon usage as well as oligonucleotide frequency and correlation analyses. Surprisingly, a nonhomologous CRISPR-Cas like system is found in DSLLAV1, which appears to protect DSLLAV1 from the parasitization of DSLV5 and DSLV8. These results suggest that novel cell-virus-virophage (CVv) tripartite infection systems of green algae, large green alga virus (Phycodnaviridae- and Mimiviridae-related), and virophage exist in Dishui Lake, which will contribute to further deep investigations of the evolutionary interaction of virophages and large alga viruses as well as of the essential roles that the CVv plays in the ecology of algae.IMPORTANCE Virophages are small parasitizing viruses of large/giant viruses. To our knowledge, the few isolated virophages all parasitize giant protozoan viruses (Mimiviridae) for propagation and form a tripartite infection system with hosts, here named the cell-virus-virophage (CVv) system. However, the CVv system remains largely unknown in environmental metagenomic data sets. In this study, we systematically investigated the metagenomic data set from the freshwater lake Dishui Lake, Shanghai, China. Consequently, four novel large alga viruses and seven virophages were discovered to coexist in Dishui Lake. Surprisingly, a novel CVv tripartite infection system comprising green algae, large green alga viruses (Phycodnaviridae- and Mimiviridae-related), and virophages was identified based on genetic link, genomic signature, and CRISPR system analyses. Meanwhile, a nonhomologous CRISPR-like system was found in Dishui Lake large alga viruses, which appears to protect the virus host from the infection of Dishui Lake virophages (DSLVs). These findings are critical to give insight into the potential significance of CVv in global evolution and ecology.

Diverse and unique viruses discovered in the surface water of the East China Sea.

BACKGROUND: Viruses are the most abundant biological entities on earth and play import roles in marine biogeochemical cycles. Here, viral communities in the surface water of the East China Sea (ECS) were collected from three representative regions of Yangshan Harbor (YSH), Gouqi Island (GQI), and the Yangtze River Estuary (YRE) and explored primarily through epifluorescence microscopy (EM), transmission electron microscopy (TEM), and metagenomics analysis. RESULTS: The virus-like particles (VLPs) in the surface water of the ECS were measured to be 106 to 107 VLPs/ml. Most of the isolated viral particles possessed a head-and-tail structure, but VLPs with unique morphotypes that had never before been observed in the realm of viruses were also found. The sequences related to known viruses in GenBank accounted for 21.1-22.8% of the viromic datasets from YSH, GQI, and YRE. In total, 1029 viral species were identified in the surface waters of the ECS. Among them, tailed phages turn out to make up the majority of viral communities, however a small number of Phycodnaviridae or Mimiviridae related sequences were also detected. The diversity of viruses did not appear to be a big difference among these three aquatic environments but their relative abundance was geographically variable. For example, the Pelagibacter phage HTVC010P accounted for 50.4% of the identified viral species in GQI, but only 9.1% in YSH and 11.7% in YRE. Sequences, almost identical to those of uncultured marine thaumarchaeal dsDNA viruses and magroviruses that infect Marine Group II Euryarchaeota, were confidently detected in the ECS viromes. The predominant classes of virome ORFs with functional annotations that were found were those involved in viral biogenesis. Virus-host connections, inferred from CRISPR spacer-protospacer mapping, implied newly discovered infection relationships in response to arms race between them. CONCLUSIONS: Together, both identified viruses and unknown viral assemblages observed in this study were indicative of the complex viral community composition found in the ECS. This finding fills a major gap in the dark world of oceanic viruses of China and additionally contributes to the better understanding of global marine viral diversity, composition, and distribution.

Slam protein dictates subcellular localization and translation of its own mRNA.

Many mRNAs specifically localize within the cytoplasm and are present in RNA-protein complexes. It is generally assumed that localization and complex formation of these RNAs are controlled by trans-acting proteins encoded by genes different than the RNAs themselves. Here, we analyze slow as molasses (slam) mRNA that prominently colocalizes with its encoded protein at the basal cortical compartment during cellularization. The functional implications of this striking colocalization have been unknown. Here, we show that slam mRNA translation is spatiotemporally controlled. We found that translation was largely restricted to the onset of cellularization when Slam protein levels at the basal domain sharply increase. slam mRNA was translated locally, at least partially, as not yet translated mRNA transiently accumulated at the basal region. Slam RNA accumulated at the basal domain only if Slam protein was present. Furthermore, a slam RNA with impaired localization but full coding capacity was only weakly translated. We detected a biochemical interaction of slam mRNA and protein as demonstrated by specific co-immunoprecipitation from embryonic lysate. The intimate relationship of slam mRNA and protein may constitute a positive feedback loop that facilitates and controls timely and rapid accumulation of Slam protein at the prospective basal region.

Correction to: Complete genome sequence analysis of the Vibrio owensii strain SH­14 isolated from shrimp with acute hepatopancreatic necrosis disease.

In the original article, the funding information was incorrectly published.

Complete genome sequence analysis of the Vibrio owensii strain SH-14 isolated from shrimp with acute hepatopancreatic necrosis disease.

Vibrios are a group of very important bacterial pathogens in marine aquaculture industry and cause serious aquatic animal diseases, such as shrimp acute hepatopancreatic necrosis disease (AHPND). A new AHPND pathogen, the Vibrio owensii strain SH-14, was isolated from diseased shrimp in Shanghai, China. In this study, to better understand the pathogenesis of AHPND at the genomic level, the genome of the strain SH-14 was completely sequenced and analyzed. The SH-14 consists of two circular chromosomes of 3,689,702 bp and 2,430,445 bp, and of two plasmids named as pVHvo (69,148 bp) and pVHvo-R (78,918 bp), respectively. The pVHvo encodes the bi-toxic genes of pirAB, responsible for shrimp AHPND. The whole genomes contain a total of 5703 predicted open reading frames (ORFs), 129 tRNA genes and 37 rRNA genes. The average nucleotide identities (ANIs) between the SH-14 and the other V. owensii strains are all greater than 95%, confirming a new V. owensii strain of the SH-14. The taxonomic affiliation of the SH-14 is also supported by whole-genome alignment and nucleotide identity dotplot analyses. These results pave the way for further study of spread and epidemic of shrimp AHPND.

The genome of a prasinoviruses-related freshwater virus reveals unusual diversity of phycodnaviruses.

BACKGROUND: Phycodnaviruses are widespread algae-infecting large dsDNA viruses and presently contain six genera: Chlorovirus, Prasinovirus, Prymnesiovirus, Phaeovirus, Coccolithovirus and Raphidovirus. The members in Prasinovirus are identified as marine viruses due to their marine algal hosts, while prasinovirus freshwater relatives remain rarely reported. RESULTS: Here we present the complete genomic sequence of a novel phycodnavirus, Dishui Lake Phycodnavirus 1 (DSLPV1), which was assembled from Dishui Lake metagenomic datasets. DSLPV1 harbors a linear genome of 181,035 bp in length (G + C content: 52.7%), with 227 predicted genes and 2 tRNA encoding regions. Both comparative genomic and phylogenetic analyses indicate that the freshwater algal virus DSLPV1 is closely related to the members in Prasinovirus, a group of marine algae infecting viruses. In addition, a complete eukaryotic histone H3 variant was identified in the genome of DSLPV1, which is firstly detected in phycodnaviruses and contributes to understand the interaction between algal virus and its eukaryotic hosts. CONCLUSION: It is in a freshwater ecosystem that a novel Prasinovirus-related viral complete genomic sequence is discovered, which sheds new light on the evolution and diversity of the algae infecting Phycodnaviridae.

Design and evaluation of nested PCR primers for specific detection of genogroup I noroviruses in oysters.

A pair of nested PCR universal primers (NGIOF and NGIOR) specific for genogroup I (GI) noroviruses was designed based on all GI sequences available in public databases. The primers were evaluated for their specificity, sensitivity and coverage, which demonstrate their reliable performance upon detection of GI noroviruses in oysters.

Hepatocellular carcinoma-associated single-nucleotide variants and deletions identified by the use of genome-wide high-throughput analysis of hepatitis B virus.

This study investigated hepatitis B virus (HBV) single-nucleotide variants (SNVs) and deletion mutations linked with hepatocellular carcinoma (HCC). Ninety-three HCC patients and 108 non-HCC patients were enrolled for HBV genome-wide next-generation sequencing (NGS) analysis. A systematic literature review and a meta-analysis were performed to validate NGS-defined HCC-associated SNVs and deletions. The experimental results identified 60 NGS-defined HCC-associated SNVs, including 41 novel SNVs, and their pathogenic frequencies. Each SNV was specific for either genotype B (n = 24) or genotype C (n = 34), except for nt53C, which was present in both genotypes. The pathogenic frequencies of these HCC-associated SNVs showed a distinct U-shaped distribution pattern. According to the meta-analysis and literature review, 167 HBV variants from 109 publications were categorized into four levels (A-D) of supporting evidence that they are associated with HCC. The proportion of NGS-defined HCC-associated SNVs among these HBV variants declined significantly from 75% of 12 HCC-associated variants by meta-analysis (Level A) to 0% of 10 HCC-unassociated variants by meta-analysis (Level D) (P < 0.0001). PreS deletions were significantly associated with HCC, in terms of deletion index, for both genotypes B (P = 0.030) and C (P = 0.049). For genotype C, preS deletions involving a specific fragment (nt2977-3013) were significantly associated with HCC (HCC versus non-HCC, 6/34 versus 0/32, P = 0.025). Meta-analysis of preS deletions showed significant association with HCC (summary odds ratio 3.0; 95% confidence interval 2.3-3.9). Transfection of Huh7 cells showed that all of the five novel NGS-defined HCC-associated SNVs in the small surface region influenced hepatocarcinogenesis pathways, including endoplasmic reticulum-stress and DNA repair systems, as shown by microarray, real-time polymerase chain reaction and western blot analysis. Their carcinogenic mechanisms are worthy of further research. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A Vibrio owensii strain as the causative agent of AHPND in cultured shrimp, Litopenaeus vannamei.

The causative agent of shrimp AHPND was identified as specific Vibrio parahaemolyticus strains, which harbor a virulent plasmid that contains the toxic genes pirA and B (pirAB). Herein, a Vibrio bacterium was isolated from shrimp in Shanghai. This bacterium was identified as Vibrio owensii using 16S rRNA gene phylogeny, whole genome sequencing and comparative analysis. The V. owensii cells are rod-shape (1.86 ±â€¯0.15 µm) with a single polar flagellum (4 µm). In addition, V. owensii form mauve colonies with jagged edges on CHROMagar plates. The pirAB genes on the plasmid revealed 100% sequence similarity to that of AHPND V. parahaemolyticus, and the encoded proteins were detected in the culture media. Subculture of V. owensii showed that the pirAB genes are unstable, and their loss rate is approximately 22% and reaches a dynamic equilibrium after the fifth generation. Upon immersion bioassay, the cumulative mortality of V. owensii (pirAB+)-infected shrimp was up to 100% within 4 days, and typical AHPND clinical signs were observed. Approximately 105 CFU/hepatopancreas of V. owensii cells were observed in the pirAB+-infected shrimp based on both culture-dependent and -independent assay. Our results indicate that the expression of pirAB in the V. owensii strain is responsible for AHPND.

Rapid diagnosis of Vibrio owensii responsible for shrimp acute hepatopancreatic necrosis disease with isothermal recombinase polymerase amplification assay.

A rapid and sensitive AHPND-RPA assay was developed for the specific detection of the AHPND-causing Vibrio owensii. The AHPND-RPA detected as few as 2 copies per reaction in 9.02 ± 0.66 min at 39 °C, and showed 100% positive predictive value and negative predictive value for AHPND diagnosis.

Cloning, sequencing and characterization of the genome of a recombinant norovirus of the rare genotype GII.P7/GII.6 in China.

The genome sequence of a rare recombinant norovirus (NoV) genotype obtained from clinical samples in China was determined using one-step reverse transcription PCR. It was identified as the GII.P7/GII.6 genotype using both phylogenetic and SimPlot analyses. A high degree of variability was observed in the P2 subdomain, especially in the B-loop structure. The recombination breakpoints of all available GII.P7/GII.6 strains were mapped to two different positions within the RdRp region, both of which were at least 40 nt upstream of the overlap of ORF1 and 2. The GII.P7/GII.6 genotype appears to have been circulating in Asia for at least 10 years.

Prevalence and genomic analysis of infectious hypodermal and hematopoietic necrosis virus (IHHNV) in Litopenaeus vannamei shrimp farmed in Shanghai, China.

Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is prevalent among farmed shrimp and results in significant reductions in shrimp production. In order to gain a better understanding of the prevalence of IHHNV in the Litopenaeus vannamei shrimp population of Shanghai, China, samples were collected during two cultivation seasons and subjected to diagnostic PCR. The results of this study showed that 167 out of 200 shrimp were positive for IHHNV, indicating a high viral prevalence (83.5 %) in farmed shrimp populations. Our results also indicated that there was a moderate correlation between IHHNV prevalence and water temperature, salinity and pH and only a slight correlation with the concentration of dissolved oxygen (DO). A mathematical model was developed in order to predict the relationship between these four characteristics of water quality and IHHNV prevalence, ultimately resulting in an estimate of the best water quality criteria (IHHNV prevalence = 0) where T = 30 °C pH = 8.0, DO = 18.3 mg/L, and salinity = 1.5 ‰. Additionally, two IHHNV genotypes were identified, the sequencing of which revealed a high similarity to the known IHHNV genotypes based on a comparison of their nucleotide and amino acid sequences. Two types of repetitive sequences were detected at both the 5' and 3' ends of the non-coding regions, which are commonly found in other IHHNV genomic sequences. Phylogenetic analysis indicated that the IHHNV Shanghai genotypes were closely related to strains from Ganyu and Sheyang, but not to strains originating from Fujian, China. This finding suggests that IHHNVs have emerged independently several times in China.

Function and dynamics of slam in furrow formation in early Drosophila embryo.

The Drosophila embryo undergoes a developmental transition in the blastoderm stage switching from syncytial to cellular development. The cleavage furrow, which encloses nuclei into cells, is a prominent morphological feature of this transition. It is not clear how the pattern of the furrow array is defined and how zygotic genes trigger the formation and invagination of interphase furrows. A key to these questions is provided by the gene slam, which has been previously implicated in controlling furrow invagination. Here we investigate the null phenotype of slam, the dynamics of Slam protein, and its control by the recycling endosome. We find that slam is essential for furrow invagination during cellularisation and together with nullo, for specification of the furrow. During cellularisation, Slam marks first the furrow, which is derived from the metaphase furrow of the previous mitosis. Slightly later, Slam accumulates at new furrows between daughter cells early in interphase. Slam is stably associated with the furrow canal except for the onset of cellularisation as revealed by FRAP experiments. Restriction of Slam to the furrow canal and Slam mobility during cellularisation is controlled by the recycling endosome and centrosomes. We propose a three step model. The retracting metaphase furrow leaves an initial mark. This mark and the border between corresponding daughter nuclei are refined by vesicular transport away from pericentrosomal recycling endosome towards the margins of the somatic buds. Following the onset of zygotic gene expression, Slam and Nullo together stabilise this mark and Slam triggers invagination of the cleavage furrow.

The F-BAR protein Cip4/Toca-1 antagonizes the formin Diaphanous in membrane stabilization and compartmentalization.

During Drosophila embryogenesis, the first epithelium with defined cortical compartments is established during cellularization. Actin polymerization is required for the separation of lateral and basal domains as well as suppression of tubular extensions in the basal domain. The actin nucleator mediating this function is unknown. We found that the formin Diaphanous (Dia) is required for establishing and maintaining distinct lateral and basal domains during cellularization. In dia mutant embryos lateral marker proteins, such as Discs-large and Armadillo/ß-Catenin spread into the basal compartment. Furthermore, high-resolution and live-imaging analysis of dia mutant embryos revealed an increased number of membrane extensions and endocytic activity at the basal domain, indicating a suppressing function of dia on membrane invaginations. Dia function might be based on an antagonistic interaction with the F-BAR protein Cip4/Toca-1, a known activator of the WASP/WAVE-Arp2/3 pathway. Dia and Cip4 physically and functionally interact and overexpression of Cip4 phenocopies dia loss-of-function. In vitro, Cip4 inhibits mainly actin nucleation by Dia. Thus, our data support a model in which linear actin filaments induced by Dia stabilize cortical compartmentalization by antagonizing membrane turnover induced by WASP/WAVE-Arp2/3.