Slight Variations in the Sequence Downstream of the Polyadenylation Signal Significantly Increase Transgene Expression in HEK293T and CHO Cells.

Compared to transcription initiation, much less is known about transcription termination. In particular, large-scale mutagenesis studies have, so far, primarily concentrated on promoter and enhancer, but not terminator sequences. Here, we used a massively parallel reporter assay (MPRA) to systematically analyze the influence of short (8 bp) sequence variants (mutations) located downstream of the polyadenylation signal (PAS) on the steady-state mRNA level of the upstream gene, employing an eGFP reporter and human HEK293T cells as a model system. In total, we evaluated 227,755 mutations located at different overlapping positions within +17..+56 bp downstream of the PAS for their ability to regulate the reporter gene expression. We found that the positions +17..+44 bp downstream of the PAS are more essential for gene upregulation than those located more distal to the PAS, and that the mutation sequences ensuring high levels of eGFP mRNA expression are extremely T-rich. Next, we validated the positive effect of a couple of mutations identified in the MPRA screening on the eGFP and luciferase protein expression. The most promising mutation increased the expression of the reporter proteins 13-fold and sevenfold on average in HEK293T and CHO cells, respectively. Overall, these findings might be useful for further improving the efficiency of production of therapeutic products, e.g., recombinant antibodies.

Genetic Control of Kinetochore-Driven Microtubule Growth in Drosophila Mitosis.

Centrosome-containing cells assemble their spindles exploiting three main classes of microtubules (MTs): MTs nucleated by the centrosomes, MTs generated near the chromosomes/kinetochores, and MTs nucleated within the spindle by the augmin-dependent pathway. Mammalian and Drosophila cells lacking the centrosomes generate MTs at kinetochores and eventually form functional bipolar spindles. However, the mechanisms underlying kinetochore-driven MT formation are poorly understood. One of the ways to elucidate these mechanisms is the analysis of spindle reassembly following MT depolymerization. Here, we used an RNA interference (RNAi)-based reverse genetics approach to dissect the process of kinetochore-driven MT regrowth (KDMTR) after colcemid-induced MT depolymerization. This MT depolymerization procedure allows a clear assessment of KDMTR, as colcemid disrupts centrosome-driven MT regrowth but not KDMTR. We examined KDMTR in normal Drosophila S2 cells and in S2 cells subjected to RNAi against conserved genes involved in mitotic spindle assembly: mast/orbit/chb (CLASP1), mei-38 (TPX2), mars (HURP), dgt6 (HAUS6), Eb1 (MAPRE1/EB1), Patronin (CAMSAP2), asp (ASPM), and Klp10A (KIF2A). RNAi-mediated depletion of Mast/Orbit, Mei-38, Mars, Dgt6, and Eb1 caused a significant delay in KDMTR, while loss of Patronin had a milder negative effect on this process. In contrast, Asp or Klp10A deficiency increased the rate of KDMTR. These results coupled with the analysis of GFP-tagged proteins (Mast/Orbit, Mei-38, Mars, Eb1, Patronin, and Asp) localization during KDMTR suggested a model for kinetochore-dependent spindle reassembly. We propose that kinetochores capture the plus ends of MTs nucleated in their vicinity and that these MTs elongate at kinetochores through the action of Mast/Orbit. The Asp protein binds the MT minus ends since the beginning of KDMTR, preventing excessive and disorganized MT regrowth. Mei-38, Mars, Dgt6, Eb1, and Patronin positively regulate polymerization, bundling, and stabilization of regrowing MTs until a bipolar spindle is reformed.

Fine gene expression regulation by minor sequence variations downstream of the polyadenylation signal.

The termination of transcription is a complex process that substantially contributes to gene regulation in eukaryotes. Previously, it was noted that a single cytosine deletion at the position + 32 bp relative to the single polyadenylation signal AAUAAA (hereafter the dC mutation) causes a 2-fold increase in the transcription level of the upstream eGFP reporter in mouse embryonic stem cells. Here, we analyzed the conservation of this phenomenon in immortalized mouse, human and drosophila cell lines and the influence of the dC mutation on the choice of the pre-mRNA cleavage sites. We have constructed dual-reporter plasmids to accurately measure the effect of the dC and other nearby located mutations on eGFP mRNA level by RT-qPCR. In this way, we found that the dC mutation leads to a 2-fold increase in the expression level of the upstream eGFP reporter gene in cultured mouse and human, but not in drosophila cells. In addition, 3' RACE analysis demonstrated that eGFP pre-mRNAs are cut at multiple positions between + 14 to + 31, and that the most proximal cleavage site becomes almost exclusively utilized in the presence of the dC mutation. We also identified new short sequence variations located within positions + 25.. + 40 and + 33.. + 48 that increase eGFP expression up to ~2-4-fold. Altogether, the positive effect of the dC mutation seems to be conserved in mouse embryonic stem cells, mouse embryonic 3T3 fibroblasts and human HEK293T cells. In the latter cells, the dC mutation appears to be involved in regulating pre-mRNA cleavage site selection. Finally, a multiplexed approach is proposed to identify motifs located downstream of cleavage site(s) that are essential for transcription termination.

GAGA Regulates Border Cell Migration in Drosophila.

Collective cell migration is a complex process that happens during normal development of many multicellular organisms, as well as during oncological transformations. In Drosophila oogenesis, a small set of follicle cells originally located at the anterior tip of each egg chamber become motile and migrate as a cluster through nurse cells toward the oocyte. These specialized cells are referred to as border cells (BCs) and provide a simple and convenient model system to study collective cell migration. The process is known to be complexly regulated at different levels and the product of the slow border cells (slbo) gene, the C/EBP transcription factor, is one of the key elements in this process. However, little is known about the regulation of slbo expression. On the other hand, the ubiquitously expressed transcription factor GAGA, which is encoded by the Trithorax-like (Trl) gene was previously demonstrated to be important for Drosophila oogenesis. Here, we found that Trl mutations cause substantial defects in BC migration. Partially, these defects are explained by the reduced level of slbo expression in BCs. Additionally, a strong genetic interaction between Trl and slbo mutants, along with the presence of putative GAGA binding sites within the slbo promoter and enhancer, suggests the direct regulation of this gene by GAGA. This idea is supported by the reduction in the slbo-Gal4-driven GFP expression within BC clusters in Trl mutant background. However, the inability of slbo overexpression to compensate defects in BC migration caused by Trl mutations suggests that there are other GAGA target genes contributing to this process. Taken together, the results define GAGA as another important regulator of BC migration in Drosophila oogenesis.

RNAi-mediated depletion of the NSL complex subunits leads to abnormal chromosome segregation and defective centrosome duplication in Drosophila mitosis.

The Drosophila Nonspecific Lethal (NSL) complex is a major transcriptional regulator of housekeeping genes. It contains at least seven subunits that are conserved in the human KANSL complex: Nsl1/Wah (KANSL1), Dgt1/Nsl2 (KANSL2), Rcd1/Nsl3 (KANSL3), Rcd5 (MCRS1), MBD-R2 (PHF20), Wds (WDR5) and Mof (MOF/KAT8). Previous studies have shown that Dgt1, Rcd1 and Rcd5 are implicated in centrosome maintenance. Here, we analyzed the mitotic phenotypes caused by RNAi-mediated depletion of Rcd1, Rcd5, MBD-R2 or Wds in greater detail. Depletion of any of these proteins in Drosophila S2 cells led to defects in chromosome segregation. Consistent with these findings, Rcd1, Rcd5 and MBD-R2 RNAi cells showed reduced levels of both Cid/CENP-A and the kinetochore component Ndc80. In addition, RNAi against any of the four genes negatively affected centriole duplication. In Wds-depleted cells, the mitotic phenotypes were similar but milder than those observed in Rcd1-, Rcd5- or MBD-R2-deficient cells. RT-qPCR experiments and interrogation of published datasets revealed that transcription of many genes encoding centromere/kinetochore proteins (e.g., cid, Mis12 and Nnf1b), or involved in centriole duplication (e.g., Sas-6, Sas-4 and asl) is substantially reduced in Rcd1, Rcd5 and MBD-R2 RNAi cells, and to a lesser extent in wds RNAi cells. During mitosis, both Rcd1-GFP and Rcd5-GFP accumulate at the centrosomes and the telophase midbody, MBD-R2-GFP is enriched only at the chromosomes, while Wds-GFP accumulates at the centrosomes, the kinetochores, the midbody, and on a specific chromosome region. Collectively, our results suggest that the mitotic phenotypes caused by Rcd1, Rcd5, MBD-R2 or Wds depletion are primarily due to reduced transcription of genes involved in kinetochore assembly and centriole duplication. The differences in the subcellular localizations of the NSL components may reflect direct mitotic functions that are difficult to detect at the phenotypic level, because they are masked by the transcription-dependent deficiency of kinetochore and centriolar proteins.

Publisher Correction: The role of Patronin in Drosophila mitosis.

During production of the original article [1], there was a technical error that resulted in author corrections not being rendered in the PDF version of the article.

The role of Patronin in Drosophila mitosis.

BACKGROUND: The calmodulin-regulated spectrin-associated proteins (CAMSAPs) belong to a conserved protein family, which includes members that bind the polymerizing mcrotubule (MT) minus ends and remain associated with the MT lattice formed by minus end polymerization. Only one of the three mammalian CAMSAPs, CAMSAP1, localizes to the mitotic spindle but its function is unclear. In Drosophila, there is only one CAMSAP, named Patronin. Previous work has shown that Patronin stabilizes the minus ends of non-mitotic MTs and is required for proper spindle elongation. However, the precise role of Patronin in mitotic spindle assembly is poorly understood. RESULTS: Here we have explored the role of Patronin in Drosophila mitosis using S2 tissue culture cells as a model system. We show that Patronin associates with different types of MT bundles within the Drosophila mitotic spindle, and that it is required for their stability. Imaging of living cells expressing Patronin-GFP showed that Patronin displays a dynamic behavior. In prometaphase cells, Patronin accumulates on short segments of MT bundles located near the chromosomes. These Patronin "seeds" extend towards the cell poles and stop growing just before reaching the poles. Our data also suggest that Patronin localization is largely independent of proteins acting at the MT minus ends such as Asp and Klp10A. CONCLUSION: Our results suggest a working hypothesis about the mitotic role of Patronin. We propose that Patronin binds the minus ends within MT bundles, including those generated from the walls of preexisting MTs via the augmin-mediated pathway. This would help maintaining MT association within the mitotic bundles, thereby stabilizing the spindle structure. Our data also raise the intriguing possibility that the minus ends of bundled MTs can undergo a limited polymerization.

New slbo-Gal4 driver lines for the analysis of border cell migration during Drosophila oogenesis.

Border cell (BC) migration during Drosophila oogenesis is an excellent model for the analysis of the migratory and invasive cell behavior. Most studies on BC migration have exploited a slbo-Gal4 driver to regulate gene expression in these cells or to mark them. Here, we report that the slbo-Gal4 transgene present in the line #6458 from the Bloomington Stock Center is inserted within chickadee (chic), a gene encoding the actin-binding protein Profilin, which promotes actin polymerization and is known to be involved in cell migration. The chic6458 mutation caused by the transgene insertion behaves as a null chic allele and is homozygous lethal. To evaluate possible effects of chic6458 on the assessment of BC behavior, we generated new lines bearing the slbo-Gal4 transgene inserted into different second chromosome loci that do not appear to be involved in cell migration. Using these new lines and the slbo-Gal4-chic6458 line, we defined the functional relationships between the twinfilin (twf) and chic in BC migration. Migration of BCs is substantially reduced by mutations in twf, which encodes an actin-binding protein that inhibits actin filament assembly. The defects caused by twf mutations are significantly suppressed when the slbo-Gal4-chic6458, but not the new slbo-Gal4 drivers were used. These findings indicate twf and chic interact and function antagonistically during BC migration in Drosophila oogenesis.

Regulatory functions and chromatin loading dynamics of linker histone H1 during endoreplication in Drosophila.

Eukaryotic DNA replicates asynchronously, with discrete genomic loci replicating during different stages of S phase. Drosophila larval tissues undergo endoreplication without cell division, and the latest replicating regions occasionally fail to complete endoreplication, resulting in underreplicated domains of polytene chromosomes. Here we show that linker histone H1 is required for the underreplication (UR) phenomenon in Drosophila salivary glands. H1 directly interacts with the Suppressor of UR (SUUR) protein and is required for SUUR binding to chromatin in vivo. These observations implicate H1 as a critical factor in the formation of underreplicated regions and an upstream effector of SUUR. We also demonstrate that the localization of H1 in chromatin changes profoundly during the endocycle. At the onset of endocycle S (endo-S) phase, H1 is heavily and specifically loaded into late replicating genomic regions and is then redistributed during the course of endoreplication. Our data suggest that cell cycle-dependent chromosome occupancy of H1 is governed by several independent processes. In addition to the ubiquitous replication-related disassembly and reassembly of chromatin, H1 is deposited into chromatin through a novel pathway that is replication-independent, rapid, and locus-specific. This cell cycle-directed dynamic localization of H1 in chromatin may play an important role in the regulation of DNA replication timing.

Synthesis and structure-activity relationship of novel 1,4-diazabicyclo[2.2.2]octane derivatives as potent antimicrobial agents.

A series of new quaternary 1,4-diazabicyclo[2.2.2]octane derivatives was synthesized and evaluated for activity against several strains of both Gram positive and Gram negative bacteria and one strain of fungus under different inoculum size. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against six species of microorganisms were tested. Results show a clear structure-activity relationship between alkyl chain length of substitutions of 1,4-diazabicyclo[2.2.2]octane tertiary amine sites and antimicrobial activity. In the case of compounds 4a-4k, MIC was found to decrease with the increase of the alkyl chain length from ethyl to dodecyl and then to increase at higher chain length (n > 14). The MIC values were found to be low for the compounds 4f and 4g with alkyl chains ranging from 10 to 12 carbons in length (1.6 µg/ml) and were comparable to the reference drug Ciprofloxacin. Also, time-kill assay was performed to examine the bactericidal kinetics. Results indicated that 4f and 4g had rapid killing effects against Staphylococcus aureus, and eliminated 100% of the initial inoculum of bacteria in 2.5 h at the concentration of 10 µg/ml. In addition, compound 4g eliminate more than 99.9% of the initial inoculum of Ps. aeruginosa after 2.5 h of interaction but the activity of compound 4f against this species seems to be weak. Thus, 4g had strong bactericidal activity and could rapidly kill Gram positive S. aureus, as well as Gram negative Ps. aeruginosa at low and high inoculum size.